Rogueus belgodereae, a new raninoid crab (Crustacea: Brachyura: Raninoidea) from the Upper Palaeocene (Thanetian) of Southern France, with comments on early palaeocene decapod crustacean faunules

Abstract: Palaeocene crabs are rare globally; crab faunules of this period are mostly described from reefal environments, and little is reported about non-reefal environments. A new raninoid crab is described and formally named from Thanetian (upper Palaeocene) non-reefal deeper water deposits of Boussens, southern France. The new species is assigned to the genus Rogueus, from which only two species were previously known, and this new record suggests the genus was widespread in the European Palaeocene. A rich Palaeocene brachyuran assemblage of this locality is preliminarily presented and briefly discussed. It appears that eubrachyuran crabs dominated this palaeoenvironment. Based on the global fossil record, it appears that brachyuran crabs quickly recovered after the K/Pg extinction event and were able to restock both reefal and non-reefal environments, prior to the explosive diversification of decapods during the Early Eocene Climatic Optimum.

decapoda gymnopleura lyreididae palaeocene france


Trophic relationships in the Early Miocene Upper Marine Molasse of Baden-Württemberg, Southwest Germany, with special emphasis on the elasmobranch fauna

Abstract: The Early Miocene Upper Marine Molasse (OMM) in south-western Germany contains a diverse fossil ecosystem in which elasmobranch teeth are especially abundant. However, the scarcity of outcrops and sometimes poor preservation of fossils resulted in scant recent literature about the OMM. Here, we focus on the elasmobranch fauna to determine the trophic relationships within the OMM, using fossil teeth as proxies for diet and trophic levels based on functional morphology and an actualistic species- or genus-level approach. Herein we present a fresh and comprehensive palaeoecological reconstruction of the OMM ecosystem in Baden-Württemberg. All five outcrop areas available for the present analysis (Baltringen, Meßkirch-Rengetsweiler, Meßkirch-Walbertsweiler, Ulm-Ermingen, and Ursendorf) exhibit a similar faunal composition, with the apex predator being Otodus (Megaselachus) sp. Among the other elasmobranchs, there are mostly piscivorous and malacophagous species; taxa that feed on a variety of other invertebrates or amniotes (including marine mammals) are also present. The OMM sediments deposited in shallow-water settings, but there are fossils of more oceanic species that might, at times, have approached the shore. With a soft bottom, partly covered by sea grass, the OMM environment would have been like the present-day warm-waters settings of the Mediterranean.

dental morphology
elasmobranchii
obere meeresmolasse
omm
palaeoecology
palaeoenvironment


Wear-dependent molar morphology in hypsodont rodents: The case of the spalacine Pliospalax

Abstract: Studying the dental pattern of micromammals has proven to be a valuable tool in classifying and identifying extinct species, but problems may arise when dental morphology changes with wear. This holds particularly true for the high-crowned rodents, such as the Spalacinae. X-ray microtomography provides new opportunities to document the changes in dental morphology of the species with wear. Combining this technology with visualization and analysis software enables the examination of virtual occlusal surfaces of the molars mimicking the various wear stages. In this paper, we apply this technology on Pliospalax macoveii from the locality of Çalta in Turkey, P. tourkobouniensis and P. sotirisi from the Greek localities of Tourkobounia-1 and Maritsa, and the recent species Spalax microphthalmus from Hungary and Romania. This method enables the effective comparison between the spalacine species. As a result, we consider P. sotirisi as a junior synonym of P. macoveii.

variation
rodentia
microtomography
wear stage
pliocene


Dental ecomorphology and macroevolutionary patterns of North American Late Cretaceous metatherians

Abstract: Metatherian mammals were taxonomically rich and abundant in Late Cretaceous faunas of North America. Although much attention has been paid to metatherian taxonomy, a comprehensive, quantitative study on the ecomorphology of this clade is lacking. Here, we predict the diets of a large sample of metatherians using three-dimensional dental topographic analysis, with the aim to better understand macroevolutionary patterns in dental morphology and dietary diversity. Contrary to their taxonomic diversity patterns, our results show that dental disparity and dietary diversity did not significantly change throughout the Late Cretaceous and that most metatherians were invertivorous (diets of insects and soft-bodied invertebrates). Nevertheless, we also found that metatherians occupied a wide range of dietary niches and were arguably the most dietarily diverse of any mammalian clade of the Late Cretaceous. Regarding the timing of metatherian ecomorphological diversification, our results indicate that it began by the mid-Cretaceous in-step with the Cretaceous Terrestrial Revolution and the taxonomic diversification of angiosperms, prior to the ecological diversifications of multituberculates and eutherians that began in the latest Cretaceous and Paleocene.

metatheria
cretaceous
ecomorphology
dental topographic analysis


First report of rodents from the Miocene Siwalik locality of Dunera, Pathankot District, Punjab, India

Abstract: Although there have been a few reports of macromammals from the Siwalik site of Dunera, no micromammals have yet been described. Recently, a diverse micromammal fossil assemblage represented by isolated teeth has been recovered from Dunera. The specimens are identified as a murine similar to Progonomys hussaini (Progonomys cf. hussaini , the ctenodactylid Sayimys sivalensis, the cricetid Democricetodon fejfari, and a sciurid, cf. Tamias urialis. These rodents are documented for the first time from this region of the Indian Siwaliks. Based on the biostratigraphic ranges of these rodents from well-dated localities in the Siwaliks of Pakistan along with previously collected magnetostratigraphic data, Dunera locality best correlates to between ~11-10 Ma (early Late Miocene), approximately equivalent to the lower half of the Nagri Formation. Previous magneto-stratigraphic data suggests that an age closer to ~11 Ma is more likely, perhaps sampling a temporal gap in the known Siwaliks micromammal record and extending the age ranges of P. hussaini and T. urialis by a few hundred thousand years.

dunera (punjab, india)
micromammals
middle siwalik
miocene
nagri formation


An Early Cretaceous Sphenophyllum or a hatchling turtle?

Abstract: Correctly identifying fossil specimens from parautochtonous deposits where marine and terrestrial organisms co-occur can be challenging due to the abundance of rare and obscure specimens with unclear morphologies. In this study, we reviewed fossils from the Lower Cretaceous La Paja Formation (Ricaurte Alto, Villa de Leyva, Colombia) that were originally described as the plant “Sphenophyllum colombianum” based on an apparent resemblance to the upper Paleozoic genus. We determined that the type specimen corresponds to the carapace of a hatchling turtle. In addition, a second specimen of “S. colombianum” although less well-preserved, also exhibits similar features of a hatchling turtle. The two fossil specimens are significant as they represent the first report of hatchling marine turtles from the Aptian of northwestern South America and provide evidence of the exceptional preservation of the Marine Reptile Lagerstätte of Ricaurte Alto.

aptian
testudines
pan-chelonioidea
south america
colombia


Morphospace dynamics and intraspecies variety of Sorex araneus and S. tundrensis according to recent and fossil data

Abstract: Several patterns were revealed in a temporal study on morphological variety of Sorex araneus and S. tundrensis (Soricidae, Mammalia). We examined samples from 18 modern and three fossil Early-Late Holocene Uralian localities. We analyzed shape variation of the first lower molar and hemimandible using two-dimensional geometrical landmarks; size differences were estimated by means of three linear measures. A separate purpose was estimation of the measurement error that arose during the data acquisition. We found that the modern samples of both species share underestimated similarity in both size and shape of morphological structures. Regression analysis revealed different phenotypic traits of the mandibular proportion in the large and small shrews regardless of species attribution. A size decrease of S. araneus and conversely a size increase of S. tundrensis both drive the mandibular shape toward phenotypic convergence. This pattern, however, is violated in the fossil samples, where the largest S. tundrensis from a Late Holocene Sim III locality (South Ural) showed a well-distinguishable mandibular shape located in a separate part of the morphospace. In this work, we found that the m1 shape has only weak resolving power as compared to the mandibular or especially skull shape. Nonetheless, even the moderate resolving power of the mandibular shape allowed us to uncover phenotypic changes during the Holocene that have not been noticed by previous researchers at Uralian late Quaternary localities.

soricidae
sorex
paleocommunity
morphospace dynamics
holocene
geometric morphometrics


An intriguing new species of dabbling duck (Aves: Anseriformes) from the middle Miocene of Austria

Abstract: Several dozen species of Miocene anatids are known worldwide, but few are known from abundant finds and even fewer from nearly complete specimens. Most fossil ducks have been described from very scant fragmentary remains, making it very difficult or impossible to compare them with one another. In Austria, only a few heavily damaged remains of Miocene anatids have been found so far. Here, we describe a new genus and species of a nearly complete medium-sized duck preserved on four slabs from the middle Miocene of Lavanttal, southern Austria. A number of features on various parts of the skeleton including the coracoid, humerus and pelvis indicate that it was a dabbling duck in an ecological sense, and exclude the option of it being a diving duck. The new species shows a unique mosaic of features typical of different groups of ducks and some features specific to it. Its more precise systematic position is uncertain, pending future finding of more fossil specimens.

new species
new genus
miocene
fossil dabbling duck
anseriformes
lavanttal, austria


Diversification events of the shield morphology in shore crabs and their relatives through development and time

Abstract: The group of shore crabs and their relatives, Carcinidae, are first known from the Eocene (56–33.9 mya). Since the group’s first appearance, its representatives have evolved a variety of lifestyles and morphologies. The exact evolutionary steps resulting in these morphologies are still a matter of debate. Here, we analyse the changes of morphology within Carcinidae over time. We also investigate the change of morphology through ontogeny to see how it relates to the evolutionary changes. We focus on the outline of the shield as a proxy for morphology, as it has a strong effect on the appearance of the crab and yields the largest sample size of all body parts. Using an elliptic Fourier transformation of the shield outline and a principal component analysis, we create a morphospace for the shields of Carcinidae. Using the morphospace as input data and a new phylogenetic tree based on a molecular and a morphological character matrix from literature, we reconstruct ancestral states for the shield. Combining data of fossil and extant specimens and reconstructed ancestral states, we analyse changes of the shield shape through time. From the morphospace, we find that the morphological diversity of the shield is strongly influenced by ontogeny, but not so much by ecology. Yet, the shields of the adults show a large diversity, corresponding to adaptations to different lifestyles. The reconstruction of ancestral states showed that the earliest representatives of Carcinidae had quasi-hexagonal shields, which could correspond to an epibenthic lifestyle. From these forms, different shapes evolved, significantly during the Oligocene (ca. 33 mya) and Pliocene (ca. 5 mya).

ancestral state reconstruction
brachyura
carcinidae
elliptic fourier transformation
geometric morphometrics
quantitative morphology


Achieving kinematic identity across shape diversity in musculoskeletal modeling

Abstract: Musculoskeletal modeling is emerging as a powerful approach to investigate the locomotor biomechanics of extinct taxa. These models rely on bony morphology to define joint locations and muscle geometry. Using different motion profiles to drive models of extinct and extant taxa complicates comparisons because results reflect both morphological and kinematic differences. Here we report on an approach that permits changes in shape while maintaining model kinematics. Using a human musculoskeletal model, we carried out walking simulations of ten humans. Next, we morphed the model pelvis and proximal femur to match a reconstructed australopithecine pelvis and proximal femur. Using the kinematic results from the human walking simulations, we created new motion files based on the positions of joint centers and tracked anatomical locations. These files were used to drive simulations of the same walking trials with the australopithecine model. Joint centers and axes of the human and australopithecine models were compared for each walking trial simulation. We found that joint centers in the australopithecine simulations were typically within ~1µm of their locations in human simulations, and joint axes differed by less than 0.005 degrees. Such small differences have negligible effects on external joint moments calculated during inverse dynamics analyses. This conservative comparison will serve as a baseline for more complex simulations. Although this work focuses on one taxon, the approach outlined is applicable to a wide variety of extinct animals.

hominin biomechanics locomotion hip pelvis


Fossil snakes of the Penny Creek Local Fauna from Webster County, Nebraska, USA, and the first record of snakes from the Early Clarendonian (12.5-12 Ma) of North America

Abstract: The Penny Creek Local Fauna in southern Webster County, Nebraska, is an early Clarendonian fossil locality within the Ash Hollow Formation. Undescribed fossils from previously collected Penny Creek material represent the first record of snakes from this time interval and confirm the presence of multiple taxa immediately following the Mid-Miocene Climatic Optimum. We identified eight taxa from the locality, including one booid (Charina), three colubrines (Pantherophis, Lampropeltis, and Salvadora), a dipsadid (Heterodon/Paleoheterodon), and several natricids (Neonatrix elongata, Neonatrix magna, and Nerodia). Of these snakes, only Neonatrix is an extinct genus, Charina and Salvadora are presently extirpated from the area, and all other genera are represented in the Central Great Plains today. Habitats occupied by extant members of genera represented in the Penny Creek snake assemblage suggest a relatively open environment with loose substrates and plentiful ground cover near a permanent water source. This further corroborates previous geological and mammalian paleoecological assessments of the Penny Creek area as a somewhat open, woodland-prairie ecotone environment near a permanent, high-energy fluvial water source. Finally, the snakes of Penny Creek help contribute to our understanding of the modernization of North American snake assemblages in the Central Great Plains by providing data for a poorly understood time within the evolution of North American snakes.

neogene
miocene
clarendonian
snakes
central great plains
nebraska
climate envelope models


Miocene and Pliocene amphibians from Hambach (Germany): new evidence for a late Neogene refuge in northwestern Europe

Abstract: The Hambach lignite mine in northwestern Germany is a renowned fossil locality, which has yielded remains of several vertebrates dated back to the Middle Miocene and the Late Pliocene. Among these is a recently-described and peculiar proteid urodele, Euronecturus grogu, currently known only from the Middle Miocene level in Hambach. Here, we provide detailed descriptions and identifications of the remaining fossil amphibians (both urodeles and anurans) from the Hambach mine, in total identifying at least 12 Middle Miocene taxa (Cryptobranchidae indet., Palaeoproteus cf. miocenicus, E. grogu, Chelotriton sp., Lissotriton sp., Triturus sp., Latonia sp., ?Palaeobatrachidae indet., Pelobatidae indet., Hyla sp., Pelophylax sp., Rana sp.) and at least nine Late Pliocene ones (Palaeoproteus cf. miocenicus, Mioproteus cf. wezei, Lissotriton sp., Latonia sp., Palaeobatrachus eurydices, cf. Eopelobates sp., Hyla sp., Bufo gr. bufo, Ranidae indet.). The high diversity of amphibians in both Miocene and Pliocene levels at Hambach supports a very humid climate persisting in the area for most of the Neogene, possibly originating a refugium for these animals in northwestern Europe that persisted until the Late Pliocene (and possibly even the Early Pleistocene). Urodeles such as Palaeoproteus and Mioproteus and anurans such as Latonia, the palaeobatrachids, and possibly Eopelobates are all significant occurrences in such a northern latitude at the end of the Pliocene, a period when southward withdrawal of thermophilic animals as well as the first effects of a deteriorizing climate ultimately leading to the Quaternary glaciation had already started in the European continent.

urodela
anura
middle miocene
late pliocene
lower rhine embayment
rhine-meuse system


Late Oligocene decapod crustaceans from the Trbovlje Formation of Slovenia, with a description of two new species of hymenosomatid crabs

Abstract: From the Oligocene (Chattian) marls of the Trbovlje Formation, exposed at the Neža locality, Slovenia, a brachyuran crab (Malacostraca: Brachyura) association consisting of three taxa is described. The material presented here includes as many as 15 near-complete crab specimens from the Upper Oligocene of Slovenia does not only allow direct comparison with extant hymenosomatids, but the identification of important diagnostic characters permit classification of the fossils in question within extant genera, i.e., Halicarcinus White, 1846, and Lucascinus Poore, Guinot, Komai, and Naruse, 2016. The newly erected species, Halicarcinus popeius sp. nov. and Lucascinus trifailensis sp. nov., are considered herein the first reliable occurrences of the family Hymenosomatidae MacLeay, 1838, in the fossil record. Previously reported occurrence of hymenosomatid crabs from the Cretaceous of Brazil is disputed herein. The hymenosomatid association from the Neža locality is accompanied with the portunid crab, Necronectes cf. michelini A. Milne-Edwards, 1860, documented by an incomplete claw.

chattian
malacostraca
brachyura
hymenosomatidae
portunidae palaeoecology


Limited convergence in the postcranium of aquatic Crocodylomorpha

Abstract: Thalattosuchia (Early Jurassic to Early Cretaceous) and Dyrosauridea (Late Cretaceous to Early Eocene) are crocodylomorph archosaurs which diversified in fluvial and marine environments and endured extinction events (i.e. Jurassic–Cretaceous boundary for Thalattosuchia; Cretaceous–Palaeogene for Dyrosauridea). Their postcrania remain globally undervalued in anatomical descriptions and diagnoses, shrouding the locomotive adaptations that possibly underpinned their radiations and longevity. We thoroughly surveyed the postcranial morphology of Dyrosauridea and Thalattosuchia, recreated their girdles in three-dimensions using tens of high-precisions 3D scans, and analysed their shape using geometric morphometrics. Dyrosauridea and Thalattosuchia have clearly distinct postcrania, even when found within similar environments, suggesting the existence of clade-specific features limiting the strength of evolutionary convergence. Moreover, the range of postcranial morphologies evolved by dyrosaurids and thalattosuchians is large compared to extant crocodylians, making the latter unsatisfactory functional analogues for every group of extinct crocodylomorphs. Our work reveals the previously unsuspected potential of postcranial anatomy as an abundant source of phylogenetic and taxonomic characters to assess the relationships within Crocodylomorpha. Incorporation of postcranial anatomy therefore appears crucial to fully assess the ecology, disparity, and relationships of crocodylomorphs.

archosauria
postcranium
phylogenetic signal
thalattosuchia
dyrosauroidea
appendicular morphology


Putting the F into FBD analysis: tree constraints or morphological data?

Abstract: The fossilized birth–death (FBD) process provides an ideal model for inferring phylogenies from both extant and fossil taxa. Using this approach, fossils are directly integrated into the tree, leading to a statistically coherent prior on divergence times. Since fossils are typically not associated with molecular sequences, additional information is required to place fossils in the tree. We use simulations to evaluate two different approaches to handling fossil placement in FBD analyses: using topological constraints, where the user specifies monophyletic clades based on established taxonomy, or using total-evidence analyses, which use a morphological data matrix in addition to the molecular alignment. We also explore how rate variation in fossil recovery or diversification rates impacts these approaches. We find that the extant topology is well recovered under all methods of fossil placement. Divergence times are similarly well recovered across all methods, with the exception of constraints which contain errors. We see similar patterns in datasets which include rate variation, however, relative errors in extant divergence times increase when more variation is included in the dataset, for all approaches using topological constraints, and particularly for constraints with errors. Finally, we show that trees recovered under the FBD model are more accurate than those estimated using non-time calibrated inference. Overall, we show that both fossil placement approaches are reliable even when including uncertainty. Our results underscore the importance of core taxonomic research, including morphological data collection and species descriptions, irrespective of the approach to handling phylogenetic uncertainty using the FBD process.

fossilized birth–death
total-evidence
taxonomy
morphological data
topological constraints
phylo-genetic inference


Dental microwear texture analysis reveals a likely dietary shift within Late Cretaceous ornithopod dinosaurs

Abstract: Dinosaurs were the dominant megaherbivores during the Cretaceous when angiosperms, the flowering plants, emerged and diversified. How herbivorous dinosaurs responded to the increasing diversity of angiosperms is largely unknown due to the lack of methods that can reconstruct diet directly from body fossils. We applied dental microwear texture analysis (DMTA), an approach that quantifies microtopography of diet-induced wear marks on tooth surfaces, to ornithopods, the dinosaur clade that includes taxa with the most sophisticated masticatory system. We found that Late Cretaceous ornithopods have significantly rougher dental microwear texture (DMT) compared to pre-Late Cretaceous ornithopods, and DMT variation increased in hadrosaurids, a derived Late Cretaceous ornithopod clade. These changes indicate a likely temporal dietary shift towards more abrasive foodstuffs within ornithopods, probably due to the increased ingestion of phytoliths (amorphous silica bodies in plants). Phytoliths are a main source of rough DMT in modern herbivores, along with exogenous dust and grit, and were generally more concentrated in Late Cretaceous angiosperms than in other major plant groups. Our results show that DMTA of the occlusal enamel surface can be used to reconstruct the diets of herbivorous dinosaurs, with a resolution superior to conventional methods.

dental microwear texture analysis
ornithopoddinosaurs
angiosperm
cretaceous
dietary reconstruction


Machine-learning-based morphological analyses of leaf epidermal cells in modern and fossil ginkgo and their implications for palaeoclimate studies

Abstract: Leaf stomata form an essential conduit between plant tissue and the atmosphere, thus presenting a link between plants and their environments. Changes in their properties in fossil leaves have been studied widely to infer palaeo-atmospheric-CO2 in deep time, ranging from the Palaeozoic to the Cenozoic. Epidermal cells of leaves, however, have often been neglected for their usefulness in reconstructing past-environments, as their irregular shape makes the manual analyses of epidermal cells a challenging and error-prone task. Here, we used machine-learning (using the U-Net architecture, which evolved from a fully convolutional network) to segment epidermal cells automatically, to efficiently reduce artificial errors. We furthermore applied minimum bounding rectangles to extract length-to-width ratios (RL/W) from the irregularly shaped cells. We applied this to a dataset including over 21000 stomata and 170000 epidermal cells in 114 Ginkgo leaves from 16 locations spanning three climate zones in China. Our results show negative correlations between the RL/W and specific climatic parameters, suggesting that local temperature and precipitation conditions may have affected the RL/W of epidermal cells. We subsequently tested this methodology and the observations from the modern dataset on 15 fossil ginkgoaleans from the Lower to the Middle Jurassic (China). It suggested that the RL/W values of fossil ginkgo generally had a similar negative response to warmer climatic backgrounds as modern G. biloba. The automated analyses of large palaeo-floral datasets provide a new direction for palaeoclimate reconstructions and emphasize the importance of hidden morphological characters of epidermal cells in ginkgoaleans.

ginkgo
epidermal cell
micro-character
machine learning
palaeoclimate parameter


Taxic and morphological diversification during the early radiation of Clupeomorpha (Actinopterygii, Teleostei)

Abstract: Evolutionary radiation is a problematic concept whose definition and classification have recently changed. Radiations can be defined as the pattern of abrupt increase in diversity of a lineage. It is relevant to evaluate the presence and interaction of different types of radiation in extant and fossil organisms to adequately delimitate the radiation types and to know the diversity in the context of Earth's history. Here, we employed the superorder Clupeomorpha at the Early–Late Cretaceous boundary as a study case to investigate radiation types and their interactions, using both taxic and morphological approaches. Clupeomorpha is an extensively studied, diverse and ancient teleostean superorder with wide geographical and ecological distributions. We propose a model for calculating rates of origination in order to analyse the taxic diversification and employ geometric morphometrics to analyse the morphological diversification that occurred at the temporal boundary. The results suggest the absence of taxic radiation due to a constant increase in taxon origination. However, the expansion of the phylomorphospace occupation and the disparity increase suggest the presence of a ‘climatic–geographical’ or ‘broad diversification-like’ disparity, according to current classifications. This illustrates the incompatibility of current radiation classifications with this case study.

origin rate
phylomorphospace
disparity
clupeiformes
ellimmichthyiformes
diversification


Quantifying the gastral mass in Early Cretaceous ornithuromorphs (Aves, Ornithothoraces) from the Jehol avifauna

Abstract: Some birds intentionally ingest stones to facilitate digestion of hard foodstuffs, a behaviour inherited from non-avian dinosaurs and present in some of the earliest birds, as evidenced by clusters of gastroliths preserved within the abdominal cavity of a wide range of dinosaurs and Cretaceous birds. For the first time, high-resolution computed laminographic and computed tomographic scans were used to reconstruct the gastral mass in two species of non-neornithine ornithuromorph birds from the Lower Cretaceous Jehol Group. Four specimens of each taxon were analysed. Preservation of the gastral mass in most of these specimens is in situ and regarded as complete or nearly so. The number of gastroliths, their total volume, and their total mass relative to the estimated body mass were calculated for each specimen. The resultant gastral mass to body mass ratios fall within the range observed in extant birds, supporting previous inferences that the digestive system in non-neornithine ornithuromorphs was comparable to that of extant taxa. Compared to available data for non-volant non-avian theropods, the gastral mass is proportionately smaller in birds suggesting that the evolution of flight constrained gastral mass size in the theropod lineage. Currently available data on gastral mass characteristics suggests that Iteravis ate larger food particles compared to Archaeorhynchus but cannot be used to determine diet more precisely. Better understanding of the relationship between gastral mass characteristics and food items across a broader range of extant taxa may provide an indirect but important method through which to infer diet and digestive function in archosaurs.

ornithuromorpha
aves
gastrolith
digestive system
ct reconstruction
diet


Cranial endocast of Anagale gobiensis (Anagalidae) and its implications for early brain evolution in Euarchontoglires

Abstract: Anagalids are an extinct group of primitive mammals from the Asian Palaeogene thought to be possible basal members of Glires. Anagalid material is rare, with only a handful of crania known. Here we describe the first virtual endocast of an anagalid, based on the holotype of Anagale gobiensis (AMNH 26079; late Eocene, China), which allows for comparison with published endocasts from fossil members of modern euarchontogliran lineages (i.e. primates, rodents, lagomorphs). The endocast displays traits often observed in fossorial mammals, such as relatively small petrosal lobules and a low neocortical ratio, which would be consistent with previous inferences about use of subterranean food sources based on heavy dental wear. In fact, Anagale gobiensis has the lowest neocortical ratio yet recorded for a euarchontogliran. This species was olfaction-driven, based on the relatively large olfactory bulbs and laterally expansive palaeocortex. The endocast supports previous inferences that relatively large olfactory bulbs, partial midbrain exposure and low encephalization quotient are ancestral for Euarchontoglires, although the likely fossorial adaptations of Anagale gobiensis may also partly explain these traits. While Anagale gobiensis is a primitive mammal in many aspects, some of its derived endocranial traits point towards a new, different trajectory of brain evolution within Euarchontoglires.

anagalidae
eocene
china
endocast
brain evolution
mammal


Did the Late Ordovician mass extinction event trigger the earliest evolution of ‘strophodontoid’ brachiopods?

Abstract: ‘Strophodontoid’ brachiopods represented the majority of strophomenide brachiopods in the Silurian and Devonian periods. They are characterized by denticles developed along the hinge line. The evolution of denticles correlated with the disappearance of dental plates and teeth and were already present when the clade originated in the Late Ordovician. Specimens of Eostropheodonta parvicostellata from the Kuanyinchiao Bed (early–middle Hirnantian, uppermost Ordovician) in the Hetaoba Section, Meitan, Guizhou Province, South China, display clear fossil population variation, during a process of loss of dental plates and the development of denticles. Three phenotypes of E. parvicostellata are recognized in a single fossil bed, likely heralding a speciation process. Non-metric multidimensional scaling (NMDS) based on five key characters of genera of the Family Leptostrophiidae shows a much wider morphospace for Silurian genera than for those in the Devonian. Phylogenetic analysis of the Family Leptostrophiidae supports the NMDS analysis and mostly tracks their geological history. The fossil population differentiation in E. parvicostellata discovered between the two phases of the Late Ordovician mass extinction event (LOME) linked to a major glaciation, suggests a Hirnantian origination of the ‘strophodontoid’ morphology, and links microevolutionary change to a macroevolutionary event.

brachiopod
late ordovician mass extinction
leptostrophiidae
microevolution
morphospace
speciation


Three-dimensional anatomy of the Tully monster casts doubt on its presumed vertebrate affinities

Abstract: Tullimonstrum gregarium, also known as the Tully monster, is a well-known phylogenetic enigma, fossils of which have been found only in the Mazon Creek Lagerstätte. The affinities of Tullimonstrum have been debated since its discovery in 1966, because its peculiar morphology with stalked eyes and a proboscis cannot easily be compared with any known animal morphotypes. Recently, the possibility that Tullimonstrum was a vertebrate has attracted much attention, and it has been postulated that Tullimonstrum might fill a gap in the fossil record of early vertebrates, providing important insights into vertebrate evolutionary history. With the hope of resolving this debate, we collected 3D surface data from 153 specimens of Tullimonstrum using a high-resolution laser 3D scanner and conducted x-ray micro-computed tomographic (μCT) analysis of stylets in the proboscis. Our investigation of the resulting comprehensive 3D morphological dataset revealed that structures previously regarded as myomeres, tri-lobed brain, tectal cartilages and fin rays are not comparable with those of vertebrates. These results raise further doubts about its vertebrate affinities, and suggest that Tullimonstrum may have been either a non-vertebrate chordate or a protostome.

tully monster
mazon creek
problematica
vertebrate
lagerstätten


Thecate stem medusozoans (Cnidaria) from the early Cambrian Chengjiang biota

Abstract: Cnidarians are phylogenetically located near the base of the ‘tree of animals’, and their early evolution had a profound impact on the rise of bilaterians. However, the early diversity and phylogeny of this ‘lowly’ metazoan clade has hitherto been enigmatic. Fortunately, cnidarian fossils from the early Cambrian could provide key insights into their evolutionary history. Here, based on a scrutiny of the purported hyolith Burithes yunnanensis Hou et al. from the early Cambrian Chengjiang biota in South China, we reveal that this species shows characters distinct from those typical of hyoliths, not least a funnel-shaped gastrovascular system with a single opening, a whorl of tentacles surrounding the mouth, and the lack of an operculum. These characters suggest a great deviation from the original definition of the genus Burithes, and a closer affinity with cnidarians. We therefore reassign the material to a new genus: Palaeoconotuba. Bayesian inference of phylogeny based on new anatomical traits identifies a new clade, including Palaeoconotuba and Cambrorhytium, as a stem group of sessile medusozoan cnidarians that are united by the synapomorphies of developing an organic conical theca and a funnel-like gastrovascular system. This study unveils a stem lineage of medusozoans that evolved a lifelong conical theca in the early Cambrian.

cambrian cnidaria medusozoa burithes palaeoconotuba cambrorhytiu


An early Cambrian polyp reveals a potential anemone-like ancestor for medusozoan cnidarians

Abstract: Cnidarians form a disparate phylum of animals and their diploblastic body plan represents a key step in animal evolution. Cnidarians are split into two main classes; anthozoans (sea anemones, corals) are benthic polyps, while medusozoans (hydroids, jellyfishes) generally have alternating life cycle stages of polyps and medusae. A sessile polyp is present in both groups and is widely regarded as the ancestral form of their last common ancestor. However, the nature and anatomy of the ancestral polyp, particularly of medusozoans, is controversial, owing to the divergent body plans of the extant lineages and the scarcity of medusozoan soft tissues in the fossil record. Here, we redescribe Conicula striata Luo & Hu from the early Cambrian Chengjiang biota, south China, which has previously been interpreted as a polyp, lophophorate or deuterostome. Through re-examination of the holotype and 51 exceptionally preserved specimens, we show that C. striata possessed features of both anthozoans and medusozoan polyps. A conical, annulated organic skeleton (periderm) fully encasing a polyp is found in fossil and living medusozoans, while a tubular pharynx extending from the mouth into a gut partitioned by c. 28 mesenteries, resembling the actinopharynx of anthozoans. Our phylogenetic analyses recover C. striata as a stem-group medusozoan, implying that the wealth of medusozoan diversity derived, ultimately, from an anemone-like ancestor.

cnidaria
medusozoan polyp
evolution
early cambrian
chengjiang biota


Morphological disparity and evolutionary rates of cranial and postcranial characters in sloths (Mammalia, Pilosa, Folivora)

Abstract: Sloth morphological evolution has been widely studied qualitatively, with comparative anatomy and morpho-functional approaches, or through quantitative assessments of morphological variation using morphometrics. Only recently, however, have folivoran morphological disparity and evolutionary rates begun to be evaluated using discrete character data. Nonetheless, patterns of morphological evolution in separate character partitions have not been investigated, neither the relative influence of, on the one hand, phylogeny, and on the other, dietary and locomotory adaptations of sloths. Here we evaluate those patterns using a phylomorphospace approach, quantifying morphological disparity and evolutionary rates, and investigating possible drivers of morphological evolution for cranial and postcranial characters in Folivora. The evolution of the morphology in those partitions is associated with distinct patterns of disparity among clades and ecological groups, even though the two partitions do not differ substantially in overall evolutionary tempo. Historical processes shaped the morphological evolution of sloths more consistently than ecological ones, although changes in postcranial characters also seem to be associated with locomotory adaptations, in which morphological convergences were much more common. We also discuss important methodological trade-offs in investigations of partitioned datasets mostly composed of fossil taxa.

sloth morphology partition phylomorphospace diet locomotion


An efficient method for estimating vein density of Glossopteris and its application

Abstract: Glossopteris-type leaves are the most abundant floristic element from the Gondwanan continent and are recorded throughout the Permian, which was a period of extreme icehouse-to-hothouse climatic global change. Fossil leaf traits can be useful for the reconstruction of palaeoenvironments and identification of climatic changes throughout geological time, but the conservative morphology of Glossopteris leaves has thus far made them difficult to use for this purpose. If the characters of Glossopteris can be better quantified then it should make them useful for tracking environmental changes over a wide geographical area and over a long time interval. Venation density is a highly variable leaf trait that might be useful for this purpose. This trait can be calculated, usually as vein length per centimetre squared, but this can be a time-consuming procedure. In this paper we propose a new rapid method to estimate venation density in a conical sector of Glossopteris leaf lamina using an accurate linear model whose predictors are three linear venation densities, measured as veins per centimetre. In addition to substantially reducing the data collection time, it is less biased and more reproducible than methods applied previously with this leaf type. Using this more robust method, preliminary results significantly distinguish the venation densities of leaves produced in wet and drier ecosystems, matching a pattern similar to modern plants. This is the first survey using a large sample size to reveal that environmental stress controlled the vein architecture of Palaeozoic plants, in a manner similar to plants in modern ecosystems.

gondwana palaeoecology permian palaeobotany glossopteris


Associations between trilobite intraspecific moulting variability and body proportions: Estaingia bilobata from the Cambrian Emu Bay Shale, Australia

Abstract: Abstract Trilobites were notably flexible in the moulting behaviours they employed, producing a variety of moult configurations preserved in the fossil record. Investigations seeking to explain this moulting variability and its potential impacts are few, despite abundant material being available for study. We present the first quantitative study on moulting in a single trilobite species using a dataset of almost 500 moult specimens of Estaingia bilobata from the Cambrian (Series 2, Stage 4) Emu Bay Shale, South Australia. Specimens were categorized by moulting mode (Salter's or Sutural Gape) and their associated configurations, and their body proportions measured from both a museum collection (including a bycatch sample) and a randomly-collected field sample. This enabled analysis of the proportion of E. bilobata specimens displaying the Sutural Gape and Salter's modes of moulting and their different configurations, and tests for association between moulting behaviour and body proportions. The results show a wide range of E. bilobata moulting configurations in all samples, suggesting that configurations represent definable instances in a largely continuous spectrum of variation. Analyses comparing body proportions of specimens showing the two modes of moulting were non-significant, suggesting there is no true association between moulting behaviour and body proportion, except for a single significant result for body length. All results were relatively consistent between the museum and field samples. However, removing accessioned specimens from the museum sample brought results even further in line with the field sample, supporting the need for consideration of museum collection bias in palaeontological analyses.

moulting
emu bay shale
behaviour
trilobite
cambrian
collection bias


Abstract: Abstract Anagalids are an extinct group of primitive mammals from the Asian Palaeogene thought to be possible basal members of Glires. Anagalid material is rare, with only a handful of crania known. Here we describe the first virtual endocast of an anagalid, based on the holotype of Anagale gobiensis (AMNH 26079; late Eocene, China), which allows for comparison with published endocasts from fossil members of modern euarchontogliran lineages (i.e. primates, rodents, lagomorphs). The endocast displays traits often observed in fossorial mammals, such as relatively small petrosal lobules and a low neocortical ratio, which would be consistent with previous inferences about use of subterranean food sources based on heavy dental wear. In fact, Anagale gobiensis has the lowest neocortical ratio yet recorded for a euarchontogliran. This species was olfaction-driven, based on the relatively large olfactory bulbs and laterally expansive palaeocortex. The endocast supports previous inferences that relatively large olfactory bulbs, partial midbrain exposure and low encephalization quotient are ancestral for Euarchontoglires, although the likely fossorial adaptations of Anagale gobiensis may also partly explain these traits. While Anagale gobiensis is a primitive mammal in many aspects, some of its derived endocranial traits point towards a new, different trajectory of brain evolution within Euarchontoglires.


Unique dentition of rhynchosaurs and their two-phase success as herbivores in the Triassic

Abstract: Abstract Rhynchosaurs were key herbivores over much of the world in the Middle and Late Triassic, often dominating their faunas ecologically, and much of their success may relate to their dentition. They show the unique ankylothecodont mode of tooth implantation, with deep roots embedded in the bone of the jaw and low crowns that were rapidly worn down in use. During growth, the main area of oral food processing, located in the middle and posterior portions of the occlusal surfaces of the jaws, moved posteriorly relative to the anterior tips of the jaws, which curved up. As the maxilla and dentary grew by addition of new bone posteriorly, the dental lamina fed in new teeth at the back of the tooth rows. CT scanning of the holotype skull of Bentonyx sidensis from the Middle Triassic of England reveals previously concealed details of the dentition. Together with new dentary material from the same location, this has enabled us to examine the tooth replacement process and elucidate ontogenetic changes in dentition and jaw morphology as the animals aged. There were major changes in rhynchosaur anatomy and function through their evolutionary history, with the early forms of the Middle Triassic dying out before or during the Carnian Pluvial Episode (233–232 Ma), and the subclade Hyperodapedontinae, with broad skulls and adaptations to chop tough vegetation, subsequently diversifying worldwide in a successful ecological expansion until their global extinction 227–225 Ma.

dentition
rhynchosaur
tooth replacement
herbivory
triassic
carnian pluvial episode


Decoding the drivers of deep-time wetland biodiversity: insights from an early Permian tropical lake ecosystem

Abstract: Abstract Wetlands are important to continental evolution, providing both arenas and refugia for emerging and declining biotas. This significance and the high preservation potential make the resulting fossiliferous deposits essential for our understanding of past and future biodiversity. We reconstruct the trophic structure and age of the early Permian Manebach Lake ecosystem, Germany, a thriving wetland at a time when the tropical biosphere faced profound upheaval in the peaking Late Palaeozoic Icehouse. Nine excavations, high-resolution spatiotemporal documentation of fossils and strata, and U–Pb radioisotopic dating of tuffs allow us to distinguish autogenic and allogenic factors shaping the limnic biocoenosis. The Manebach Lake was an exorheic, oxygen-stratified, perennial water body on the 101–102 km2 scale, integrated into the catchment draining much of the European Variscides. Lake formation paralleled an Asselian regional wet climatic interval and benefited from rising base level due to post-Variscan half-graben tectonics. Stromatolite-forming cyanobacteria, bivalves, several crustaceans, amblypterids and xenacanthid sharks formed a differentiated biocoenosis in the lake. Fossil stomach remains and teeth prove the rare presence of acanthodians, branchiosaurs and large amphibians. The results indicate woody-debris-bearing lake littorals devoid of semi-aquatic and aquatic plants as places suitable for stromatolites to grow, underpin the model of declining freshwater-shark diversity in most Permian Variscan basins, demonstrate fish/amphibian ratios in limnic assemblages to measure lake perenniality and reveal taphonomic biases in lake taphocoenoses. Our outcomes call for more knowledge about the diversity, ecology and fossilization pathways of past limnic biotas, particularly microorganisms and actinopterygian fishes, to reconstruct deep-time continental ecosystems.

limnic sedimentology
palaeobotany
permineralization
silica
stromatolite
vertebrate palaeontology


Early Cenozoic increases in mammal diversity cannot be explained solely by expansion into larger body sizes

Abstract: Abstract A prominent hypothesis in the diversification of placental mammals after the Cretaceous–Palaeogene (K/Pg) boundary suggests that the extinction of non-avian dinosaurs resulted in the ecological release of mammals, which were previously constrained to small body sizes and limited species richness. This ‘dinosaur incumbency hypothesis’ may therefore explain increases in mammalian diversity via expansion into larger body size niches, that were previously occupied by dinosaurs, but does not directly predict increases in other body size classes. To evaluate this, we estimate sampling-standardized diversity patterns of terrestrial North American fossil mammals within body size classes, during the Cretaceous and Palaeogene. We find strong evidence for post-extinction diversity increases in all size classes. Increases in the diversity of small-bodied species (less than 100 g, the common body size class of Cretaceous mammals, and much smaller than the smallest non-avialan dinosaurs (c. 400 g)) were similar to those of larger species. We propose that small-bodied mammals had access to greater energetic resources or were able to partition resources more finely after the K/Pg mass extinction. This is likely to be the result of a combination of widespread niche clearing due to the K/Pg mass extinctions, alongside a suite of biotic and abiotic changes that occurred during the Late Cretaceous and across the K/Pg boundary, such as shifting floral composition, and novel key innovations among eutherian mammals.

mammal
diversity
body size
cretaceous–palaeogene mass extinction
adaptive radiation


Exceptions to the temperature–size rule: no Lilliput Effect in end-Permian ostracods (Crustacea) from Aras Valley (northwest Iran)

Abstract: Abstract The body size of marine ectotherms is often negatively correlated with ambient water temperature, as seen in many clades during the hyperthermal crisis of the end-Permian mass extinction (c. 252 Ma). However, in the case of ostracods, size changes during ancient hyperthermal events are rarely quantified. In this study, we evaluate the body size changes of ostracods in the Aras Valley section (northwest Iran) in response to the drastic warming during the end-Permian mass extinction at three taxonomic levels: class, order, species. At the assemblage level, the warming triggers a complete species turnover in the Aras Valley section, with larger, newly emerging species dominating the immediate post-extinction assemblage for a short time. Individual ostracod species and instars do not show dwarfing or a change in body size as an adaptation to the temperature stress during the end-Permian crisis. This may indicate that the ostracods in the Aras Valley section might have been exceptions to the temperature–size rule (TSR), using an adaptation mechanism that does not involve a decrease in body size. This adaptation might be similar to the accelerated development despite constant instar body sizes that can be observed in some recent experimental studies of ostracod responses to thermal stress.

permian–triassic
ostracoda
body size
mass extinction
aras valley section


The evolutionary origin of the durophagous pelagic stingray ecomorph

Abstract: Abstract Studies of the origin of evolutionary novelties (novel traits, feeding modes, behaviours, ecological niches, etc.) have considered a number of taxa experimenting with new body plans, allowing them to occupy new habitats and exploit new trophic resources. In the marine realm, colonization of pelagic environments by marine fishes occurred recurrently through time. Stingrays (Myliobatiformes) are a diverse clade of batoid fishes commonly known to possess venomous tail stings. Current hypotheses suggest that stingrays experimented with a transition from a benthic to a pelagic/benthopelagic habitat coupled with a transition from a non-durophagous diet to extreme durophagy. However, there is no study detailing macroevolutionary patterns to understand how and when habitat shift and feeding specialization arose along their evolutionary history. A new exquisitely preserved fossil stingray from the Eocene Konservat-Lagerstätte of Bolca (Italy) exhibits a unique mosaic of plesiomorphic features of the rajobenthic ecomorph, and derived traits of aquilopelagic taxa, that helps to clarify the evolutionary origin of durophagy and pelagic lifestyle in stingrays. A scenario of early evolution of the aquilopelagic ecomorph is proposed based on new data, and the possible adaptive meaning of the observed evolutionary changes is discussed. The body plan of †Dasyomyliobatis thomyorkei gen. et sp. nov. is intermediate between the rajobenthic and more derived aquilopelagic stingrays, supporting its stem phylogenetic position and the hypothesis that the aquilopelagic body plan arose in association with the evolution of durophagy and pelagic lifestyle from a benthic, soft-prey feeder ancestor.

durophagy
ecomorph
evolution
myliobatiformes
pelagic lifestyle
stingray


Preservational modes of some ichthyosaur soft tissues (Reptilia, Ichthyopterygia) from the Jurassic Posidonia Shale of Germany

Abstract: Abstract Konservat-Lagerstätten, such as the Toarcian (Early Jurassic) Posidonia Shale of southwestern Germany, are renowned for their spectacular fossils. Ichthyosaur skeletons recovered from this formation are frequently associated with soft tissues; however, the preserved material ranges from three-dimensional, predominantly phosphatized structures to dark films of mainly organic matter. We examined soft-tissue residues obtained from two ichthyosaur specimens using an integrated ultrastructural and geochemical approach. Our analyses revealed that the superficially-looking ‘films’ in fact comprise sections of densely aggregated melanosome (pigment) organelles sandwiched between phosphatized layers containing fibrous microstructures. We interpret this distinct layering as representing condensed and incompletely degraded integument from both sides of the animal. When compared against previously documented ichthyosaur fossils, it becomes readily apparent that a range of preservational modes exists between presumed ‘phosphatic’ and ‘carbonized’ soft-tissue remains. Some specimens show high structural fidelity (e.g. distinct integumentary layering), while others, including the fossils examined in this study, retain few original anatomical details. This diversity of soft-tissue preservational modes among Posidonia Shale ichthyosaurs offers a unique opportunity to examine different biostratinomic, taphonomic and diagenetic variables that potentially could affect the process of fossilization. It is likely that soft-tissue preservation in the Posidonia Shale was regulated by a multitude of factors, including decay efficiency and speed of phosphatic mineral nucleation; these in turn were governed by a seafloor with sustained microbial mat activity fuelled by high organic matter input and seasonally fluctuating oxygen levels.

holzmaden
ichthyosaur
jurassic
skin
soft tissue
taphonomy


What's inside a sauropod limb? First three-dimensional investigation of the limb long bone microanatomy of a sauropod dinosaur, Nigersaurus taqueti (Neosauropoda, Rebbachisauridae), and implications for the weight-bearing function

Abstract: Abstract Various terrestrial tetrapods convergently evolved to gigantism (large body sizes and masses), the most extreme case being sauropod dinosaurs. Heavy weight-bearing taxa often show external morphological features related to this condition, but also adequacy in their limb bone inner structure: a spongiosa filling the medullary area and a rather thick cortex varying greatly in thickness along the shaft. However, the microanatomical variation in such taxa remains poorly known, especially between different limb elements. We highlight for the first time the three-dimensional microstructure of the six limb long bone types of a sauropod dinosaur, Nigersaurus taqueti. Sampling several specimens of different sizes, we explored within-bone, between-bones, and size-related variations. If a spongiosa fills the medullary area of all bones, the cortex is rather thin and varies only slightly in thickness along the shaft. Zeugopod bones appear more compact than stylopod ones, whereas no particular differences between serially homologous bones are found. Nigersaurus' pattern appears much less extreme than that in heavy terrestrial taxa such as rhinoceroses, but is partly similar to observations in elephants and in two-dimensional sauropod data. Thus, microanatomy may have not been the predominant feature for weight-bearing in sauropods. External features, such as columnarity (shared with elephants) and postcranial pneumaticity, may have played a major role for this function, thus relaxing pressures on microanatomy. Also, sauropods may have been lighter than expected for a given size. Our study calls for further three-dimensional investigations, eventually yielding a framework characterizing more precisely how sauropod gigantism may have been possible.

bone microanatomy
graviportal
sauropodomorpha
x-ray microtomography
functional morphology
biomechanics


Palaeobiology and taphonomy of the rangeomorph Culmofrons plumosa

Abstract: Abstract The deep marine Ediacaran fossil record of Avalonia is dominated by the Rangeomorpha, a clade characterized by up to four orders of fractal-like branching. Despite their abundance, morphological diversity and the recent increase in Ediacaran studies, aspects of their palaeobiology, palaeoecology and phylogenetic position in the tree of life are still hotly debated. The clade has traditionally been interpreted as consisting of organisms that lived erect in the water column and tethered to the seafloor, based on the intuitive interpretation of their frondose body plan. However, recent work has challenged this view and instead proposes a reclining mode of life for several rangeomorphs, possibly in symbiosis with chemoautotrophic bacteria. Here, we offer a detailed description of exceptionally preserved specimens of Culmofrons plumosa from the Discovery UNESCO Global Geopark in Newfoundland, Canada. We suggest that Culmofrons plumosa should be reinterpreted as a reclining organism based on taphonomic and morphological evidence. Additionally, reproductive modes and a growth model of the species are here inferred, and they appear to be most consistent with a reclining mode of life, offering a novel palaeobiological reconstruction of the species.

rangeomorph
avalon assemblage
palaeobiology
taphonomy
reproduction
ontogeny


A new method for extracting conodonts and radiolarians from chert with NaOH solution

Abstract: Abstract Microfossils are important components of sedimentary rocks used for palaeontological, biostratigraphic, palaeoenvironmental and palaeoclimatic investigations. They are usually extracted from rocks using an acid solution, which might vary depending on the embedding rock lithology. Here we propose a new method using common NaOH (sodium hydroxide; soda) to digest cherts (micro- and cryptocrystalline quartz) instead of the standard technique based on HF (hydrofluoric acid). This new method allows the collection of undamaged specimens of different kinds of microfossils, such as conodonts, radiolarians, teeth and dermal scales, the minerology of which is still preserved (e.g. biogenic apatite in conodonts). The use of soda is thus recommended, as it is less dangerous, less expensive, and it better preserves the extracted microfossils both in shape and mineralogy.

chert
soda
conodont
radiolarian
chemical method
dissolution technique


Rise and fall of the phacopids: the morphological history of a successful trilobite family

Abstract: Abstract Phacopidae were a successful family of the Silurian–Devonian period. Although their diversity trends are well identified, their shape evolution is unknown; their morphology often considered to be conservative. We have quantified these morphologies using geometric morphometrics (landmarks) and investigated their evolution using morphological disparity indices. Results identified morphological variations between the genera, and through time. Phacopids differ from each other by the position of the facial suture linked to the size of the visual complex, the shape of the genal angle and the elongation of both cephalon and pygidium. The morphological disparity of cephala was high from the Silurian, contrary to that of pygidia. Subsequently, the morphological disparity increased in the Early Devonian with the development of narrow cephala and triangular pygidia. Morphological disparity was greater in the Emsian for both cephala and pygidia, more than 50 myr after the origination of phacopids. It constituted a perfect example illustrating that a peak of biodiversity does not necessarily happen in the early history of a clade. Subsequently, a strong decrease of morphological disparity occurred in the Middle Devonian, in conjunction with sea-level changes and anoxic events. Taxonomic richness and morphological disparity declined strongly in the Givetian, in a non-random extinction affecting particularly blind genera. The morphological disparity remained low in the Frasnian despite progressive eye reduction influenced by environmental changes. An extensive recovery occurred in the Famennian with an important increase of both taxonomic and morphological diversity. The Hangenberg event caused the final extinction of phacopids.

phacopidae
palaeozoic
morphological disparity
diversification
extinction


Taxic and morphological diversification during the early radiation of Clupeomorpha (Actinopterygii, Teleostei)

Abstract: Abstract Evolutionary radiation is a problematic concept whose definition and classification have recently changed. Radiations can be defined as the pattern of abrupt increase in diversity of a lineage. It is relevant to evaluate the presence and interaction of different types of radiation in extant and fossil organisms to adequately delimitate the radiation types and to know the diversity in the context of Earth's history. Here, we employed the superorder Clupeomorpha at the Early–Late Cretaceous boundary as a study case to investigate radiation types and their interactions, using both taxic and morphological approaches. Clupeomorpha is an extensively studied, diverse and ancient teleostean superorder with wide geographical and ecological distributions. We propose a model for calculating rates of origination in order to analyse the taxic diversification and employ geometric morphometrics to analyse the morphological diversification that occurred at the temporal boundary. The results suggest the absence of taxic radiation due to a constant increase in taxon origination. However, the expansion of the phylomorphospace occupation and the disparity increase suggest the presence of a ‘climatic–geographical’ or ‘broad diversification-like’ disparity, according to current classifications. This illustrates the incompatibility of current radiation classifications with this case study.

origin rate
phylomorphospace
disparity
clupeiformes
ellimmichthyiformes
diversification


Quantifying the gastral mass in Early Cretaceous ornithuromorphs (Aves, Ornithothoraces) from the Jehol avifauna

Abstract: Abstract Some birds intentionally ingest stones to facilitate digestion of hard foodstuffs, a behaviour inherited from non-avian dinosaurs and present in some of the earliest birds, as evidenced by clusters of gastroliths preserved within the abdominal cavity of a wide range of dinosaurs and Cretaceous birds. For the first time, high-resolution computed laminographic and computed tomographic scans were used to reconstruct the gastral mass in two species of non-neornithine ornithuromorph birds from the Lower Cretaceous Jehol Group. Four specimens of each taxon were analysed. Preservation of the gastral mass in most of these specimens is in situ and regarded as complete or nearly so. The number of gastroliths, their total volume, and their total mass relative to the estimated body mass were calculated for each specimen. The resultant gastral mass to body mass ratios fall within the range observed in extant birds, supporting previous inferences that the digestive system in non-neornithine ornithuromorphs was comparable to that of extant taxa. Compared to available data for non-volant non-avian theropods, the gastral mass is proportionately smaller in birds suggesting that the evolution of flight constrained gastral mass size in the theropod lineage. Currently available data on gastral mass characteristics suggests that Iteravis ate larger food particles compared to Archaeorhynchus but cannot be used to determine diet more precisely. Better understanding of the relationship between gastral mass characteristics and food items across a broader range of extant taxa may provide an indirect but important method through which to infer diet and digestive function in archosaurs.

ornithuromorpha
aves
gastrolith
digestive system
ct reconstruction
diet


The dentary of hadrosauroid dinosaurs: evolution through heterochrony

Abstract: Abstract The near-global distribution of hadrosaurid dinosaurs during the Cretaceous has been attributed to mastication, a behaviour commonly recognized as a mammalian adaptation. Its occurrence in a non-mammalian lineage should be accompanied by the evolution of several morphological modifications associated with food acquisition and processing. This study investigated morphological variation in the dentary, a major element of the hadrosauroid lower jaw. Eighty-four hadrosauroid dentaries were subjected to geometric morphometric and statistical analyses to investigate their taxonomic, ontogenetic, and individual variation. Results suggest increased food acquisition and processing efficiency in saurolophids through a complex pattern of evolutionary and growth-related changes. The edentulous region grew longer relative to dentary length, allowing for food acquisition specialization anteriorly and processing posteriorly, and became ventrally directed, possibly associated with foraging low-growing vegetation, especially in younger individuals. The saurolophid coronoid process became anteriorly directed and relatively more elongate, with an expanded apex, increasing moment arm length, with muscles pulling the jaw more posteriorly, increasing mechanical advantage. During growth, all hadrosauroids underwent anteroposterior dental battery elongation by the addition of teeth, and edentulous region ventralization decreased. The dental battery became deeper in saurolophids by increasing the number of teeth per tooth family. The increased coronoid process anterior inclination and relative edentulous region elongation in saurolophids are hypothesized to have evolved through hypermorphosis and/or acceleration, peramorphic heterochronic processes; the development of an anteroposteriorly shorter but dorsoventrally taller saurolophid dentary, is probably due to post-displacement in dental battery elongation and edentulous region decreased ventral orientation, a paedomorphic heterochronic process.

hadrosaur
dentary
geometric morphometrics
heterochrony
paedomorphosis
peramorphosis


Bridging the extant and fossil record of planktonic foraminifera: implications for the Globigerina lineage

Abstract: Abstract We conducted a morphometric study and wall texture analysis on extant and fossil specimens of the planktonic foraminifera Globigerina falconensis plexus. Our global data reveal morphological inconsistencies between fossil and extant populations. Our results are significant as G. falconensis is widely used in palaeoceanographic studies in conjunction with its sister taxon G. bulloides. Morphologically these two species are similar, with the main difference being the distinctive apertural lip present in G. falconensis. We selected cores covering the entire stratigraphic range of G. falconensis, from the early Miocene to current day, spanning sites from high latitudes in the North Atlantic Ocean and the southern Indian Ocean to sites in equatorial regions. The morphology found in the modern ocean is not consistent with the Miocene holotype of Globigerina falconensis Blow described from lower Miocene sediments in Venezuela. A more lobate morphology evolved in the late Miocene, thus, a new name is required for this morphotype, coexisting in the modern oceans with G. falconensis s.s. We thus describe the new morphospecies, G. neofalconensis for the more lobate forms which evolved in the late Miocene and inhabit the modern oceans. Additionally, we report a pseudocancellate wall texture present in the G. falconensis plexus. We use the molecular sequences from the PR2 database to explore the generic attribution of the G. falconensis lineage, confirming its close relationship with G. bulloides and its retention in the genus Globigerina.

planktonic foraminifera
extant
globigerina
taxonomy
genetic
morphometric


Limited convergence in the postcranium of aquatic Crocodylomorpha

Abstract: Abstract Thalattosuchia (Early Jurassic to Early Cretaceous) and Dyrosauridea (Late Cretaceous to Early Eocene) are crocodylomorph archosaurs which diversified in fluvial and marine environments and endured extinction events (i.e. Jurassic–Cretaceous boundary for Thalattosuchia; Cretaceous–Palaeogene for Dyrosauridea). Their postcrania remain globally undervalued in anatomical descriptions and diagnoses, shrouding the locomotive adaptations that possibly underpinned their radiations and longevity. We thoroughly surveyed the postcranial morphology of Dyrosauridea and Thalattosuchia, recreated their girdles in three-dimensions using tens of high-precisions 3D scans, and analysed their shape using geometric morphometrics. Dyrosauridea and Thalattosuchia have clearly distinct postcrania, even when found within similar environments, suggesting the existence of clade-specific features limiting the strength of evolutionary convergence. Moreover, the range of postcranial morphologies evolved by dyrosaurids and thalattosuchians is large compared to extant crocodylians, making the latter unsatisfactory functional analogues for every group of extinct crocodylomorphs. Our work reveals the previously unsuspected potential of postcranial anatomy as an abundant source of phylogenetic and taxonomic characters to assess the relationships within Crocodylomorpha. Incorporation of postcranial anatomy therefore appears crucial to fully assess the ecology, disparity, and relationships of crocodylomorphs.

archosauria
postcranium
phylogenetic signal
thalattosuchia
dyrosauroidea
appendicular morphology


Putting the F into FBD analysis: tree constraints or morphological data?

Abstract: Abstract The fossilized birth–death (FBD) process provides an ideal model for inferring phylogenies from both extant and fossil taxa. Using this approach, fossils are directly integrated into the tree, leading to a statistically coherent prior on divergence times. Since fossils are typically not associated with molecular sequences, additional information is required to place fossils in the tree. We use simulations to evaluate two different approaches to handling fossil placement in FBD analyses: using topological constraints, where the user specifies monophyletic clades based on established taxonomy, or using total-evidence analyses, which use a morphological data matrix in addition to the molecular alignment. We also explore how rate variation in fossil recovery or diversification rates impacts these approaches. We find that the extant topology is well recovered under all methods of fossil placement. Divergence times are similarly well recovered across all methods, with the exception of constraints which contain errors. We see similar patterns in datasets which include rate variation, however, relative errors in extant divergence times increase when more variation is included in the dataset, for all approaches using topological constraints, and particularly for constraints with errors. Finally, we show that trees recovered under the FBD model are more accurate than those estimated using non-time calibrated inference. Overall, we show that both fossil placement approaches are reliable even when including uncertainty. Our results underscore the importance of core taxonomic research, including morphological data collection and species descriptions, irrespective of the approach to handling phylogenetic uncertainty using the FBD process.

fossilized birth–death
total-evidence
taxonomy
morphological data
topological constraints
phylogenetic inference


Inaccurate fossil placement does not compromise tip-dated divergence times

Abstract: Abstract Time-scaled phylogenies underpin the interrogation of evolutionary processes across deep timescales, as well as attempts to link these to Earth's history. By inferring the placement of fossils and using their ages as temporal constraints, tip dating under the fossilized birth–death (FBD) process provides a coherent prior on divergence times. At the same time, it also links topological and temporal accuracy, as incorrectly placed fossil terminals should misinform divergence times. This could pose serious issues for obtaining accurate node ages, yet the interaction between topological and temporal error has not been thoroughly explored. We simulate phylogenies and associated morphological datasets using methodologies that incorporate evolution under selection, and are benchmarked against empirical datasets. We find that datasets of 300 characters and realistic levels of missing data generally succeed in inferring the correct placement of fossils on a constrained extant backbone topology, and that true node ages are usually contained within Bayesian posterior distributions. While increased fossil sampling improves the accuracy of inferred ages, topological and temporal errors do not seem to be linked: analyses in which fossils resolve less accurately do not exhibit elevated errors in node age estimates. At the same time, inferred divergence times are biased, probably due to a mismatch between the FBD prior and the shape of our simulated trees. While these results are encouraging, suggesting that even fossils with uncertain affinities can provide useful temporal information, they also emphasize that palaeontological information cannot overturn discrepancies between model priors and the true diversification history.

tip dating
time calibration
morphological clock
fossilized birth–death model


Dental microwear texture analysis reveals a likely dietary shift within Late Cretaceous ornithopod dinosaurs

Abstract: Abstract Dinosaurs were the dominant megaherbivores during the Cretaceous when angiosperms, the flowering plants, emerged and diversified. How herbivorous dinosaurs responded to the increasing diversity of angiosperms is largely unknown due to the lack of methods that can reconstruct diet directly from body fossils. We applied dental microwear texture analysis (DMTA), an approach that quantifies microtopography of diet-induced wear marks on tooth surfaces, to ornithopods, the dinosaur clade that includes taxa with the most sophisticated masticatory system. We found that Late Cretaceous ornithopods have significantly rougher dental microwear texture (DMT) compared to pre-Late Cretaceous ornithopods, and DMT variation increased in hadrosaurids, a derived Late Cretaceous ornithopod clade. These changes indicate a likely temporal dietary shift towards more abrasive foodstuffs within ornithopods, probably due to the increased ingestion of phytoliths (amorphous silica bodies in plants). Phytoliths are a main source of rough DMT in modern herbivores, along with exogenous dust and grit, and were generally more concentrated in Late Cretaceous angiosperms than in other major plant groups. Our results show that DMTA of the occlusal enamel surface can be used to reconstruct the diets of herbivorous dinosaurs, with a resolution superior to conventional methods.

dental microwear texture analysis
ornithopod dinosaurs
angiosperm
cretaceous
dietary reconstruction


Uncovering a phylogenetic signal in plant biopolymer chemistry: a comparison of sporopollenin isolation approaches for use in palynological research

Abstract: Abstract Sporomorphs (pollen and spores) are a mainstay of research into past vegetation, and increasingly sporomorph chemistry is being used as a palaeoecological tool. To make extant sporomorphs directly comparable to fossil specimens, fresh material is processed to remove labile compounds and isolate the sporopollenin wall. A range of processing approaches are currently in use, but the chemistries produced by these different techniques have not yet been compared across a range of taxa. It is therefore not clear how they compare in terms of efficiently isolating sporopollenin without changing its chemical structure, and what impact they have on relative chemical similarities and differences among taxa (i.e. whether more closely related species will always appear chemically more similar, regardless of how they have been processed). Here, we test this by applying five different processing approaches to sporomorphs from 15 taxa from across the vascular plant phylogeny. We show that each approach has its own idiosyncrasies in terms of impacts on sporomorph chemistry. For the most part a common pattern of among-taxon chemical variability is uncovered, and a phylogenetic signal within sporopollenin chemistry is supported. Working with spectral derivatives generally increases agreement among the different processing approaches, but decreases the strength of the phylogenetic signal. No one processing approach is ideal, and the choice of which to use is likely to depend on the goal of the study, the type and quantity of material being processed, and the laboratory facilities available for processing.

fourier transform infrared (ftir) microspectroscopy


Developmental models shed light on the earliest dental tissues, using Astraspis as an example

Abstract: Abstract Fossils of extinct jawless vertebrates are pivotal to deciphering the evolutionary paths that led to the various forms of the vertebrate skeleton. For example, Pteraspidomorphs (stem-gnathostomes), such as the Ordovician Astraspis, display some of the oldest remains of bony and ‘dental’ (dentine and enameloid) tissues. However, the identification of the very nature of these early mineralized tissues has been hampered by a lack of unambiguous diagnostic characters. As development is key to identifying the derivation of these tissues, we developed an integrative and generic histogenetic model, testing several ontogenetic scenarios. We illustrate our approach on the basis of the well-preserved Astraspis samples and show how this can be used to infer key developmental features from extinct species. This study suggests that in the odontodes of Astraspis: (1) the initial curvature of the epithelium was close to the shape of the final external surface; (2) the mesenchymal cells differentiate synchronously in the whole inner periphery; and (3) the capping tissue was produced by both mesenchymal and epithelial cells (enameloid rather than enamel). Astraspis specimens also provide evidence of a dual growth periodicity, possibly homologous to Andresen and von Ebner growth lines observed in amniotes, suggesting this type of dual periodicity may be shared by most vertebrates. We estimated that an Astraspis odontode grew up in around 60–70 days at a rate of 0.5–5 μm/day. The new developmental approach proposed in this study could be a robust framework for critically evaluating the tissues of extinct taxa in the future.

developmental model
dental tissue
odontode
enameloid
palaeohistology
early vertebrate


Machine-learning-based morphological analyses of leaf epidermal cells in modern and fossil ginkgo and their implications for palaeoclimate studies

Abstract: Abstract Leaf stomata form an essential conduit between plant tissue and the atmosphere, thus presenting a link between plants and their environments. Changes in their properties in fossil leaves have been studied widely to infer palaeo-atmospheric-CO2 in deep time, ranging from the Palaeozoic to the Cenozoic. Epidermal cells of leaves, however, have often been neglected for their usefulness in reconstructing past-environments, as their irregular shape makes the manual analyses of epidermal cells a challenging and error-prone task. Here, we used machine-learning (using the U-Net architecture, which evolved from a fully convolutional network) to segment epidermal cells automatically, to efficiently reduce artificial errors. We furthermore applied minimum bounding rectangles to extract length-to-width ratios (RL/W) from the irregularly shaped cells. We applied this to a dataset including over 21 000 stomata and 170 000 epidermal cells in 114 Ginkgo leaves from 16 locations spanning three climate zones in China. Our results show negative correlations between the RL/W and specific climatic parameters, suggesting that local temperature and precipitation conditions may have affected the RL/W of epidermal cells. We subsequently tested this methodology and the observations from the modern dataset on 15 fossil ginkgoaleans from the Lower to the Middle Jurassic (China). It suggested that the RL/W values of fossil ginkgo generally had a similar negative response to warmer climatic backgrounds as modern G. biloba. The automated analyses of large palaeo-floral datasets provide a new direction for palaeoclimate reconstructions and emphasize the importance of hidden morphological characters of epidermal cells in ginkgoaleans.

ginkgo
epidermal cell
micro-character
machine learning
palaeoclimate parameter


Macroscopic fossils from the Chuanlinggou Formation of North China: evidence for an earlier origin of multicellular algae in the late Palaeoproterozoic

Abstract: Abstract Multicellular algae are the core topic for understanding the early life evolution on Earth. The timing of origin and cellular differentiation of multicellular algae, however, remains poorly constrained. The Palaeoproterozoic to early Mesoproterozoic is a critical period during which multicellular algae began to occur and evolve in marine environments. This paper reports well-preserved multicellular fossils from shales of the Chuanlinggou Formation (c. 1.64 Ga) in North China, with emphasis on their holdfast and putative cellular structures. These macroalgal fossils are reasonably diversified and include Chuaria circularis, Tawuia sinensis, Tawuia robusta, Glossophyton ovalis, Glossophyton sp., Tuanshanzia sp. and Changchengia sp.; mainly preserved as carbonaceous compressions, with a few sideritized forms. Field emission scanning electron microscope (FESEM) observation revealed multicellular structures in Chuaria, confirming its biological attributes of a multicellular eukaryote and providing direct evidence that multicellular algae had already originated by the terminal Palaeoproterozoic, earlier than previously speculated. Tuanshanzia sp. and Changchengia sp. developed with a bare rhizome holdfast, suggesting that they had a benthic sessile lifestyle in their late Palaeoproterozoic oceanic habitat.

palaeoproterozoic
multicellular macroalgal fossil
holdfast structure
chuanlinggou formation
north china platform


Quantitative ichnology: a novel framework to determine the producers of locomotory trace fossils with the ichnogenus Gordia as a case study

Abstract: Abstract Trace fossils record the interactions between organisms and their surroundings, and can therefore provide unique insights into the coevolution of trace makers and the environment. However, identifying the producers of trace fossils is challenging because different animals can create very similar traces and many ichnotaxa can therefore only be attributed to broad morphological grades. For example, simple horizontal traces like Gordia are generally suggested to have been produced by vermiform organisms, potentially encompassing a range of animal phyla. This uncertainty makes it difficult to decipher their palaeobiological significance through major evolutionary events and episodes of environmental change. We have developed new mathematical approaches for identifying previously unrecognized signatures left by the trace makers of simple marine locomotory traces. We calculated the deviation angle series of self-crossing traces made by extant isopods, polychaetes, gastropods and nematodes, computing the frequency spectrum and autocorrelation function in each case. The results reveal that each of these taxa left unique markers during the trace-making process, reflecting differences in their anatomy and locomotory behaviour. We were able to identify the possible trace makers of several early Palaeozoic Gordia specimens, demonstrating that ichnospecies within the same ichnogenus can be created by distantly related animals with very different morphologies and/or behaviours. This novel mathematical framework has great potential for identifying the possible producers of diverse trace fossils through deep time, helping to uncover the earliest evidence of certain animals or behaviours. It also has great potential for quantifying ichnotaxonomy, consolidating the link between ichnology and palaeobiology.

trace fossil
locomotory trace
gordia
repeating pattern
frequency spectrum
autocorrelation function


Germ-soma differentiation and reproduction in a new species of early Cambrian acritarch

Abstract: Abstract As a significant evolutionary innovation, multicellularity has independently evolved multiple times throughout the evolutionary history of eukaryotes, making a substantial contribution to their diversity. In retracing the multicellularity of eukaryotes, deep-time fossil records play an irreplaceable role. In this paper, we report a new acritarch Concavaesphaera ornata gen. et sp. nov. from the early Cambrian Kuanchuanpu biota (535 Ma). These fossils are generally spherical, with diameters ranging from 450 to 950 μm, and feature an envelope with complex ornament. Inside, there are two groups of cells varying in size. Larger cells are relatively fewer in number and each resides within a sac-like cavity distributed along the inner wall of the envelope. Statistical data show a positive correlation between the diameter and cavity volume during the development of large cells. Small cells are numerous, have a diameter of about 15 μm, and fill the entire interior of the specimens. We interpret the large cells as reproductive cells and the small cells as somatic cells. These observations show that Concavaesphaera evolved multicellular complexity equivalent to that of modern Volvox, with germ-soma differentiation and separation. Available evidence suggests that the similarities between Concavaesphaera and Volvox are more likely to be the result of convergent evolution. Therefore, Concavaesphaera may represent an extinct multicellular eukaryote which evolved during the Cambrian explosion and probably documented an independent innovation of multicellularity in eukaryotic evolutionary history. This implies that multicellularity evolved many more times in eukaryotes than previously estimated.

concavaesphaera ornata
germ-soma differentiation
multicellularity
cambrian
acritarch
kuanchuanpu biota


Adult branchiosaurid temnospondyls: the life cycle of Xerodromeus gracilis

Abstract: Abstract The Branchiosauridae form a clade of tiny newt-like, extinct amphibians of overall larval appearance. Although their status as neotenic (perennibranchiate) forms had long been universally accepted, adult specimens are known from only one taxon that was hitherto referred to as Melanerpeton (Apateon) gracile. Here we study this life cycle in depth, which includes the only well-documented metamorphosis-like transformation in an early tetrapod outside Lissamphibia. Based on various newly recognized features, Melanerpeton gracile is attributed to a new genus, Xerodromeus. Xerodromeus gracilis is characterized by a short postorbital skull table, wide supratemporal, quadrate condyles well posterior to the occipital ones, ossified endocranial elements, carpals, coracoid and pelvis as well as wedge-shaped intercentra and cylindrical pleurocentra, of which the latter are identified for the first time in branchiosaurids. The studied size classes are referred to four phases: (A) integration of jaw and cheek, longer snout; (B) stronger teeth, robust limbs, incipient ossification of exoccipital, coracoid and pelvis, change in dermal ornament; (C) larger gape, wider skull, polygonal ornament; and (D) quadrate, coracoid, carpals and vertebral centra ossified, during which a probably terrestrial adult morph developed. Adult X. gracilis is more massively built than amphibamids, and its non-pedicellate dentition indicates that it was probably feeding on different prey.

amphibamiformes development dissorophoidea phylogeny temnospondyli


The last horned armadillos: phylogeny and decline of Peltephilidae (Xenarthra, Cingulata)

Abstract: Abstract Peltephilidae (Xenarthra, Cingulata) is an ancient lineage of medium–large-sized ‘armadillos’ from South America, characterized by chisel-shaped molariforms, a U-shaped dental arcade, and cephalic osteoderms modified into hornlike structures. Although the biochron of the group extends from the early Eocene to the Late Miocene, the most abundant and complete records come from the Early Miocene of Patagonia. Remains from the Late Miocene are very scarce, and the last records of the group are from the Chasicoan Stage (Tortonian). The only taxon known from this interval is Epipeltephilus kanti from the Arroyo Chasicó Formation (9.23 ± 0.09 Ma; Buenos Aires Province, Argentina), a species previously represented only by a few isolated osteoderms. Here we report new remains assigned to E. kanti from the Late Miocene of Loma de Las Tapias Formation (c. 9.0–7.8 Ma; San Juan Province, Argentina), including a hemimandible and several fixed and mobile osteoderms. These new specimens constitute the youngest record of Peltephilidae. The inclusion of E. kanti within Epipeltephilus and the monophyly of the genera Peltephilus and Epipeltephilus are corroborated for the first time through a cladistic analysis. The decline and eventual disappearance of this ‘armadillo’ group in the Late Miocene is chronologically coincident with the replacement of subtropical/tropical environments by more open and arid ones and with the proliferation of other large armadillos such as Vetelia, Macrochorobates, and Macroeuphractus.

cenozoic
epipeltephilus
evolutionary history
miocene
peltephilus
xenarthra


The dental system of †Kazanichthys viatkensis (Actinopterygii, Acrolepididae) from the middle Permian of European Russia: palaeobiological and palaeoecological inferences

Abstract: Abstract Among ray-finned fishes (Actinopterygii), the crushing, durophagous feeding strategy first evolved in the early Carboniferous period, with the †Eurynotiformes possessing dentitions with single layers of partially to fully fused blunt teeth. In the †‘Platysomidae’ (Permian), a new form of crushing dentition evolved (phyllodonty), in which multiple layers of superimposed crushing teeth developed intraosseously, within the jaw. The phyllodont durophagous dentition is also recovered from later-occurring taxa originating mainly in the Mesozoic, such as the †Bobastraniiformes, the neopterygians †Pycnodontiformes and Ginglymodi, and in the teleost group †Phyllodonta. By comparison, †Kazanichthys viatkensis, an actinopterygian from the middle Permian of European Russia, is characterized by a third, putatively durophagous dentition, with anterior conical teeth and closely packed molariform teeth on the buccal dental plates (a potential similarity with eurynotiforms). Whereas the conical teeth are similar to those of basal actinopterygians, the molariform teeth superficially resemble teeth of some teleosts (Characiformes, Tetraodontiformes), but are unique among known fossil and living Actinopterygii in being crowned by anastomosing, sharp apical ridges. Teeth are ankylosed to the jaw and acrodont in implantation. There is neither evidence of plicidentine, nor cavities corresponding to intraosseous crypts. Most replacement teeth formed extraosseously, differing from the phyllodont dentition, but similar to several more phylogenetically basal actinopterygians. The dental system morphologically resembles recent Sparidae (Teleostei; Perciformes), possibly indicating a similar trophic adaptation. Based on these comparisons and patterns of wear, we propose that †K. viatkensis was a generalist durophagous feeder, with the ability to switch prey types with its unique and complex dentition.

actinopterygii permian durophagy evolution


New insights into the sea spider fauna (Arthropoda, Pycnogonida) of La Voulte-sur-Rhône, France (Jurassic, Callovian)

Abstract: Abstract Three species of sea spider (Arthropoda, Pycnogonida) have been described from the Middle Jurassic (Callovian) Konservat-Lagerstätte of La Voulte-sur-Rhône: Palaeopycnogonides gracilis, Colossopantopodus boissinensis and Palaeoendeis elmii. These fossils were initially attributed to three extant families or superfamilies, justifying their use as calibration points in a recent tree-dating analysis. However, their taxonomic affinities are still debated. Our knowledge of the morphology of these Jurassic sea spiders is limited by prior investigation with only light microscopy and radiographs, such that further morphological details such as cephalic appendages (chelifores, palps, ovigers) remain poorly documented. Here, we reinvestigate the La Voulte-sur-Rhône fossils using x-ray microtomography and reflectance transformation imaging. A new specimen, tentatively attributed to P. gracilis, was found using x-ray microtomography, while another fossil initially interpreted as Palaeoendeis elmii may also be related to this species. We attribute all fossils to Pantopoda, crown-group Pycnogonida. Palaeopycnogonides gracilis had ovigers in at least one sex and had chelifores and palps that were either reduced or absent. Together, the cephalic appendage set and the structure of the ovigers are unique among Pantopoda, and this species is reassigned to the new family Palaeopycnogonididae. Colossopantopodus boissinensis lacked chelifores but had palps and ovigers, the latter with the typical structure shown by extant Colossendeinae, to which we attribute the fossil. The absence of chelifores and palps in Palaeoendeis elmii and the structure of its ovigers indicate affinities with Endeidae. The impact of these new taxonomic assignments on the way Jurassic sea spiders can be used as fossil calibrations is discussed.

pycnogonida
pantopoda
konservat-lagerstätte
jurassic
reflectance transformation imaging
x-ray microtomography


Cryptic moulting behaviour of some Carboniferous Ostracoda

Abstract: Abstract Monospecific accumulations of ostracods, represented by spine-bearing Janischewskya? sp. and a smooth-shelled Cavellina? sp., were detected inside the body chamber, siphuncle and camerae of three cephalopod specimens (a nautiloid and two goniatites) from the Carboniferous (Mississippian) Cracoean reefs of North Yorkshire, UK. The ostracods occur as isolated valves packed together and are well-preserved, with delicate spines of Janischewskya? sp. still intact on numerous specimens. Such a mode of ostracod preservation inside the cephalopod conchs and their paucity in the surrounding matrix outside the shells indicate that the valves were not concentrated due to sedimentary processes. Rather, the ostracods deliberately entered the empty cephalopod shells in order to seek sheltered habitats for moulting. In the case of the smooth-shelled Cavellina? sp., the ostracod valves preserved inside a camera of the nautiloid have similar size, indicating that a synchronized mass moulting took place in this species. Additionally, the presence of putative eggs closely associated with the spine-bearing Janischewskya? sp. valves inside a siphuncle of the nautiloid shows that the empty conchs could have also served as safe places for egg deposition. The present finds are thus the first examples of cryptic moulting behaviour in ostracods. They also imply that such behaviour in this group of arthropods has a long evolutionary history, at least since the Carboniferous, and potentially may persist in present day ostracods.

arthropoda ostracoda ecdysis palaeoecology mississippian palaeozoic


Eucera bees (Hymenoptera, Apidae, Eucerini) preserved in their brood cells from late Holocene (middle Neoglacial) palaeosols of southwest Portugal

Abstract: Abstract The c. 100 myr extensive fossil record of bee brood nests and cells (calichnia) in siliciclastic sedimentary deposits, or palaeosols, is virtually devoid of the presence of their producers. The absence of a more specific assignment to a producer of the different ichnogenera of the ichnofamily Celliformidae precludes their use in phylogenetic and palaeobiogeographic studies. Omission surfaces developed in incipient carbonate palaeosols during the late Holocene (middle Neoglacial), c. 2975 yr cal BP, on the southwest coast of mainland Portugal show insect calichnia in dense ichnofabrics dominated by shallow discrete cells (Palmiraichnus castellanosi) and cells at the terminus of vertical shafts. At Carreira Brava, one of the studied sites, bees ready to abandon their cells were found in an exceptional state of preservation inside the sealed brood chambers. The chambers also preserve the inner cell hydrophobic polymerized membrane and remains of the monospecific Brassicaceae-type pollen provision. Although the cause of mass mortality remains a mystery, oxygen depletion due to sudden flooding of the nesting substrate and consequent or overnight temperature drop, just before emergence, are plausible causes. The anaerobic conditions and later rapid carbonate diagenetic lithification are the likely causes of the preservation of the bees and the inner cell organic membrane. The favourable climate conditions for the development of successive, dense ichnofabrics from an omission suite dominated by bee brood cells may be the result of slightly colder and higher-precipitation winters during the Neoglacial interval.

brood cell
palmiraichnus castellanosi
eucera
palaeosol
neoglacial
portugal