A macroscopic free-swimming medusa from the middle Cambrian Burgess Shale

Abstract: Cnidarians are regarded as one of the earliest-diverging animal phyla. One of the hallmarks of the cnidarian body plan is the evolution of a free-swimming medusa in some medusozoan classes, but the origin of this innovation remains poorly constrained by the fossil record and molecular data. Previously described macrofossils, putatively representing medusa stages of crown-group medusozoans from the Cambrian of Utah and South China, are here reinterpreted as ctenophore-grade organisms. Other putative Ediacaran to Cambrian medusozoan fossils consist mainly of microfossils and tubular forms. Here we describe Burgessomedusa phasmiformis gen. et sp. nov., the oldest unequivocal macroscopic free-swimming medusa in the fossil record. Our study is based on 182 exceptionally preserved body fossils from the middle Cambrian Burgess Shale (Raymond Quarry, British Columbia, Canada). Burgessomedusa possesses a cuboidal umbrella up to 20 cm high and over 90 short, finger-like tentacles. Phylogenetic analysis supports a medusozoan affinity, most likely as a stem group to Cubozoa or Acraspeda (a group including Staurozoa, Cubozoa and Scyphozoa). Burgessomedusa demonstrates an ancient origin for the free-swimming medusa life stage and supports a growing number of studies showing an early evolutionary diversification of Medusozoa, including of the crown group, during the late Precambrian–Cambrian transition.


Allometric wing growth links parental care to pterosaur giantism

Abstract: Pterosaurs evolved a broad range of body sizes, from small-bodied early forms with wingspans of mostly 1–2 m to the last-surviving giants with sizes of small airplanes. Since all pterosaurs began life as small hatchlings, giant forms must have attained large adult sizes through new growth strategies, which remain largely unknown. Here we assess wing ontogeny and performance in the giant Pteranodon and the smaller-bodied anurognathids Rhamphorhynchus, Pterodactylus and Sinopterus. We show that most smaller-bodied pterosaurs shared negative allometry or isometry in the proximal elements of the fore- and hindlimbs, which were critical elements for powering both flight and terrestrial locomotion, whereas these show positive allometry in Pteranodon. Such divergent growth allometry typically signals different strategies in the precocial–altricial spectrum, suggesting more altricial development in Pteranodon. Using a biophysical model of powered and gliding flight, we test and reject the hypothesis that an aerodynamically superior wing planform could have enabled Pteranodon to attain its larger body size. We therefore propose that a shift from a plesiomorphic precocial state towards a derived state of enhanced parental care may have relaxed the constraints of small body sizes and allowed the evolution of derived flight anatomies critical for the flying giants.

giantism
growth
allometry
flight
pterosauria
wing shape


Evidence of artefacts made of giant sloth bones in central Brazil around the last glacial maximum

Abstract: The peopling of the Americas and human interaction with the Pleistocene megafauna in South America remain hotly debated. The Santa Elina rock shelter in Central Brazil shows evidence of successive human settlements from around the last glacial maximum (LGM) to the Early Holocene. Two Pleistocene archaeological layers include rich lithic industry associated with remains of the extinct giant ground sloth Glossotherium phoenesis. The remains include thousands of osteoderms (i.e. dermal bones), three of which were human-modified. In this study, we perform a traceological analysis of these artefacts by optical microscopy, non-destructive scanning electron microscopy, UV/visible photoluminescence and synchrotron-based microtomography. We also describe the spatial association between the giant sloth bone remains and stone tools and provide a Bayesian age model that confirms the timing of this association in two time horizons of the Pleistocene in Santa Elina. The conclusion from our traceological study is that the three giant sloth osteoderms were intentionally modified into artefacts before fossilization of the bones. This provides additional evidence for the contemporaneity of humans and megafauna, and for the human manufacturing of personal artefacts on bone remains of ground sloths, around the LGM in Central Brazil.

zooarchaeology
traceology
south america
pleistocene
bone surface modification
palaeometry


Raptorial appendages of the Cambrian apex predator <i>Anomalocaris canadensis</i> are built for soft prey and speed

Abstract: The stem-group euarthropod Anomalocaris canadensis is one of the largest Cambrian animals and is often considered the quintessential apex predator of its time. This radiodont is commonly interpreted as a demersal hunter, responsible for inflicting injuries seen in benthic trilobites. However, controversy surrounds the ability of A. canadensis to use its spinose frontal appendages to masticate or even manipulate biomineralized prey. Here, we apply a new integrative computational approach, combining three-dimensional digital modelling, kinematics, finite-element analysis (FEA) and computational fluid dynamics (CFD) to rigorously analyse an A. canadensis feeding appendage and test its morphofunctional limits. These models corroborate a raptorial function, but expose inconsistencies with a capacity for durophagy. In particular, FEA results show that certain parts of the appendage would have experienced high degrees of plastic deformation, especially at the endites, the points of impact with prey. The CFD results demonstrate that outstretched appendages produced low drag and hence represented the optimal orientation for speed, permitting acceleration bursts to capture prey. These data, when combined with evidence regarding the functional morphology of its oral cone, eyes, body flaps and tail fan, suggest that A. canadensis was an agile nektonic predator that fed on soft-bodied animals swimming in a well-lit water column above the benthos. The lifestyle of A. canadensis and that of other radiodonts, including plausible durophages, suggests that niche partitioning across this clade influenced the dynamics of Cambrian food webs, impacting on a diverse array of organisms at different sizes, tiers and trophic levels.

cambrian
anomalocaris
predation
kinematics
biomechanics
computational fluid dynamics


A giant armoured skink from Australia expands lizard morphospace and the scope of the Pleistocene extinctions

Abstract: There are more species of lizards and snakes (squamates) alive today than any other order of land vertebrates, yet their fossil record has been poorly documented compared with other groups. Here, we describe a gigantic Pleistocene skink from Australia based on extensive material that includes much of the skull and postcranial skeleton, and spans ontogenetic stages from neonate to adult. Tiliqua frangens substantially expands the known ecomorphological diversity of squamates. At approximately 2.4 kg, it was more than double the mass of any living skink, with an exceptionally broad, deep skull, squat limbs and heavy, ornamented body armour. It probably filled the armoured herbivore niche that land tortoises (testudinids), absent from Australia, occupy on other continents. Tiliqua frangens and other giant Plio-Pleistocene skinks suggest that small-bodied groups that dominate vertebrate biodiversity might have lost their largest and often most morphologically extreme representatives in the Late Pleistocene, expanding the scope of these extinctions.

pleistocene megafauna australia tiliqua reptile extinction


Developmental and functional controls on enrolment in an ancient, extinct arthropod

Abstract: Three-dimensional models reveal how the mechanics of exoskeletal enrolment changed during the development of a model organism for insights into ancient arthropod development, the 429-million-year-old trilobite Aulacopleura koninckii. Changes in the number, size and allocation of segments within the trunk, coupled with the need to maintain effective exoskeletal shielding of soft tissue during enrolment, necessitated a transition in enrolment style about the onset of mature growth. During an earlier growth phase, enrolment was sphaeroidal, with the venter of the trunk fitting exactly against that of the head. In later growth, if lateral exoskeletal encapsulation was to be maintained trunk length proportions did not permit such exact fitting, requiring an alternative, non-sphaeoridal enrolment style. Our study favours the adoption of a posture in later growth in which the posterior trunk extended beyond the front of the head. This change in enrolment accommodated a pattern of notable variation in the number of mature trunk segments, well known to characterize the development of this species. It suggests how an animal whose early segmental development was remarkably precisely controlled was able to realize the marked variation in mature segment number that was related, apparently, to life in a physically challenging, reduced oxygen setting.

biomechanics kinematics ontogeny tagmosis trilobites silurian


A new dolphin with tusk-like teeth from the late Oligocene of New Zealand indicates evolution of novel feeding strategies

Abstract: All extant toothed whales (Cetacea, Odontoceti) are aquatic mammals with homodont dentitions. Fossil evidence from the late Oligocene suggests a greater diversity of tooth forms among odontocetes, including heterodont species with a variety of tooth shapes and orientations. A new fossil dolphin from the late Oligocene of New Zealand, Nihohae matakoi gen. et sp. nov., consisting of a near complete skull, earbones, dentition and some postcranial material, represents this diverse dentition. Several preserved teeth are horizontally procumbent, including all incisors and canines. These tusk-like teeth suggest adaptive advantages for horizontally procumbent teeth in basal dolphins. Phylogenetic analysis places Nihohae among the poorly constrained basal waipatiid group, many with similarly procumbent teeth. Features of N. matakoi such as its dorsoventrally flattened and long rostrum, long mandibular symphysis, unfused cervical vertebrae, lack of attritional or occlusal wear on the teeth and thin enamel cover suggest the rostrum and horizontally procumbent teeth were used to injure and stun prey though swift lateral head movements, a feeding mode that did not persist in extant odontocetes.

phylogeny
dolphin
evolution
functional morphology
palaeoecology
evolution


Multivariate mapping of ontogeny, taphonomy and phylogeny to reconstruct problematic fossil taxa

Abstract: Exceptionally preserved fossils of soft-bodied organisms provide unique evidence of evolutionary history, but they are often contentious; different approaches frequently produce radically different reconstructions of taxa and their affinities. Conflict arises due to difficulties in disentangling the three non-independent factors that underlie all morphological variation within and between fossils: ontogeny, taphonomy and phylogeny. Comparative data from extant organisms can be extremely powerful in this context, but is often difficult to apply given the multi-dimensionality of anatomical variation. Here, we present a multivariate ordination method using discrete morphological character data from modern taxa at different ontogenetic and taphonomic stages (semaphoront and ‘semataphonts’). Analysing multiple axes of morphological variation simultaneously allows us to visualize character combinations that are likely to exist in fossil specimens at intersecting stages of growth and decay, and thus constrain interpretation of fossils. Application to early vertebrates finds variation in fossil specimens to be accounted for by all three axes: primarily decay in Mayomyzon, ontogeny in Priscomyzon and phylogeny in ‘euphaneropoids’ and Palaeospondylus. Our demonstration of empirical multi-factorial variation underscores the power of multivariate approaches to fossil interpretation, especially non-biomineralized taxa. As such, this conceptual approach provides a new method for resolving enigmatic taxa throughout the fossil record.

ontogeny
taphonomy
early vertebrates
soft-tissue
fossil
non-metric multidimensional scaling


Colonial coral resilience by decreasing size: reaction to increased detrital influx during onset of the late Palaeozoic Ice Age

Abstract: Modern coral reefs and associated biodiversity are severely threatened by increasing terrestrial runoff. Similar scenarios could be suspected for geological times, but reef coral resilience is still an enigma. In late Visean-Serpukhovian (Mississippian foraminiferal zones/MFZ 14-16) times, a major glaciation phase of the late Palaeozoic Ice Age (LPIA) associated with enhanced terrestrial weathering and runoff coincides with a biodiversity crisis and coral reef decline. In this study, the impact of enhanced terrestrial runoff is tested on size variations of colonial corals Aulina rotiformis and Lithostrotion decipiens along a gradient of contemporaneous (Serpukhovian) open marine carbonate to near-shore siliciclastic facies in South China. Along this gradient, their sizes decrease from carbonate, through intermediate carbonate-siliciclastic, to siliciclastic facies. This is consistent with increasing abundance of terrestrial materials of high silicon, aluminium and phosphorus values. On a larger million-year-long interval (MFZ14-16) and for several palaeocontinents, size data of Lithostrotion decipiens and Siphonodendron pauciradiale show a distinct decline in late Visean, when enhanced terrestrial weathering occurred commonly with palaeosols developed during regression. This suggests that terrestrial sediment and nutrient input may have mainly controlled phenotypic plasticity in Mississippian reef corals, with a decrease in size as a component of resilience across the LPIA onset.

terrestrial runoff
reef coral
phenotypic plasticity
facies
biodiversity crisis
mississippian


A 2200-year record of Andean Condor diet and nest site usage reflects natural and anthropogenic stressors

Abstract: Understanding how animals respond to large-scale environmental changes is difficult to achieve because monitoring data are rarely available for more than the past few decades, if at all. Here, we demonstrate how a variety of palaeoecological proxies (e.g. isotopes, geochemistry and DNA) from an Andean Condor (Vultur gryphus) guano deposit from Argentina can be used to explore breeding site fidelity and the impacts of environmental changes on avian behaviour. We found that condors used the nesting site since at least approximately 2200 years ago, with an approximately 1000-year nesting frequency slowdown from ca 1650 to 650 years before the present (yr BP). We provide evidence that the nesting slowdown coincided with a period of increased volcanic activity in the nearby Southern Volcanic Zone, which resulted in decreased availability of carrion and deterred scavenging birds. After returning to the nest site ca 650 yr BP, condor diet shifted from the carrion of native species and beached marine animals to the carrion of livestock (e.g. sheep and cattle) and exotic herbivores (e.g. red deer and European hare) introduced by European settlers. Currently, Andean Condors have elevated lead concentrations in their guano compared to the past, which is associated with human persecution linked to the shift in diet.

palaeoecology volcano condor diet birds nest