Ben Creisler
Some recent non-dino papers:
Pay-walled:
Jelle Heijne, Nicole Klein & P. Martin Sander (2019)
The uniquely diverse taphonomy of the marine reptile skeletons (Sauropterygia) from the Lower Muschelkalk (Anisian) of Winterswijk, The Netherlands.
PalZ (advance online publication)
Having provided dozens of articulated, and even more disarticulated skeletons of marine reptiles with varying degrees of completeness, the Middle Triassic fossil deposit of Winterswijk, The Netherlands, might be considered the richest within the entire Germanic Basin concerning associated and partially articulated remains. Aside from these remains, a high number of isolated bones are also found. Among the various marine reptile taxa, the pachypleurosaur Anarosaurus and the nothosaur Nothosaurus are the most common. The skeletons and remains show diverse disarticulation patterns. These patterns range from mostly complete articulated skeletons to clustered and isolated bones. Interestingly, a large number of isolated articulated limbs is found, a pattern which is not known from other marine localities. Although numerous reports have been made on the taxa from Winterswijk, the taphonomy of the locality still remains poorly understood. Here, a series of methods are used to describe the taphonomy of 327 marine reptile specimens from the locality of Winterswijk in a qualitative manner. Furthermore, it is tested whether biofilms such as microbial mats could have had an influence on the preferential preservation of several body regions. Upon investigation, it is concluded that the taphonomy of Winterswijk is very complex and indeed depends on various factors such as: current activity, microbial activity, and anatomical differences between taxa. Finally, a total of 12 recurring patterns were identified within the dataset, which could largely be explained by the aforementioned factors.
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Free pdf:
Robert Lemanis, Andrew S. Jones, Richard J Butler, Philip S.L. Anderson & Emily J. Rayfield (2019)
Comparative biomechanical analysis demonstrates functional convergence between slender-snouted crocodilians and phytosaurs.
PeerJ Preprints 7:e27476v1
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Morphological similarities between the extinct Triassic archosauriform clade Phytosauria and extant crocodilians have formed the basis of long-proposed hypotheses of evolutionary convergence. These hypotheses have informed the reconstructions of phytosaur ecology and biology, including feeding preferences, body mass, soft tissue systems, mating behaviours, and environmental preferences. However, phytosaurs possess numerous cranial apomorphies that distinguish them from modern crocodilians and potentially limit ecomorphological comparisons. Here, we present the first computational mechanical comparison of phytosaur cranial strength to several extant crocodilian taxa using two biomechanical approaches: beam theory and finite element analysis. We demonstrate mechanical convergence between the slender-snouted phytosaur Ebrachosuchus neukami and modern slender-snouted crocodilians. We provide evidence that the phytosaurian premaxillary palate is functionally equivalent to the crocodilian secondary palate. The premaxillary palate is associated with greater resistance to biting induced stress, lower strain energy, higher resistance to bending and torsion, as well as increased performance under tension. In all tests, Ebrachosuchus performed worse than all tested crocodilians, showing higher stress under equivalent loading conditions. These findings have implications for the proposed feeding ecology of slender-snouted phytosaurs and corroborate previous broad assessments of phytosaur ecology based on morphological comparisons to crocodilians; however, we urge caution in overextending those assessments given the current paucity of comparative functional data.
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Free pdf:
Natascha Westphal, Kristin Mahlow, Jason James Head and Johannes MÃller (2019)
Pectoral myology of limb-reduced worm lizards (Squamata, Amphisbaenia) suggests decoupling of the musculoskeletal system during the evolution of body elongation.
BMC Evolutionary Biology 19:16
Background
The evolution of elongated body forms in tetrapods has a strong influence on the musculoskeletal system, including the reduction of pelvic and pectoral girdles, as well as the limbs. However, despite extensive research in this area it still remains unknown how muscles within and around bony girdles are affected by these reductions. Here we investigate this issue using fossorial amphisbaenian reptiles, or worm lizards, as a model system, which show substantial variation in the degree of reductions of girdles and limbs. Using iodine-based contrast-enhanced computed tomography (diceCT), we analyze the composition of the shoulder muscles of the main clades of Amphisbaenia and their outgroups relative to the pectoral skeleton.
Results
All investigated amphisbaenian taxa retain the full set of 17 shoulder muscles, independent of the degree of limb and girdle reductions, whereas in some cases muscles are fused to complexes or changed in morphology relative to the ancestral condition. Bipes is the only taxon that retains forelimbs and an almost complete pectoral girdle. All other amphisbaenian families show more variation concerning the completeness of the pectoral girdle having reduced or absent girdle elements. Rhineura, which undergoes the most severe bone reductions, differs from all other taxa in possessing elongated muscle strands instead of discrete shoulder muscles. In all investigated amphisbaenians, the shoulder muscle agglomerate is shortened and shifted anteriorly relative to the ancestral position as seen in the outgroups.
Conclusions
Our results show that pectoral muscle anatomy does not necessarily correspond to the loss or reduction of bones, indicating a decoupling of the musculoskeletal system. Muscle attachment sites change from bones to non-skeletal areas, such as surrounding muscles, skin or connective tissue, whereas muscle origins themselves remain in the same region where the pectoral bones were ancestrally located. Our findings indicate a high degree of developmental autonomy within the musculoskeletal system, we predict that the observed evolutionary rearrangements of amphisbaenian shoulder muscles were driven by functional demands rather than by developmental constraints. Nevertheless, worm lizards display a spatial offset of both pectoral bones and muscles relative to the ancestral position, indicating severe developmental modifications of the amphisbaenian body axis.
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Pay-walled:
Jason D. PARDO, Robert HOLMES and Jason S. ANDERSON (2019)Â
An enigmatic braincase from Five Points, Ohio (Westphalian D) further supports a stem tetrapod position for aÃstopods.
Environmental Science Transactions of The Royal Society of Edinburgh (advance online publication)
We describe a new specimen of the aÃstopod Oestocephalus from Five Points, Ohio, which preserves much of the posterior braincase. The specimen, the largest aÃstopod skull described, preserves the postorbital region to the occiput. The posterior braincase has coossified the basioccipital, exoccipitals, and opisthotic. The parasphenoid is rostrally restricted, toothless, and highly vaulted along the cultriform process. The lateral walls of the cultriform process are further reinforced by large longitudinally running, ventral flanges from the parietals. Two large endochondral ventral projections from the basioccipital, previously interpreted as basal tuberosities for hypaxial muscle insertion, are here instead interpreted as articulations for the branchial skeleton. This interpretation is further supported by traces of vasculature that is consistent with what is seen in gill-bearing species. A model for the reorganisation of the basicranial region on the transition from hyomandibula to stapes is proposed, which suggests that gills, or gill-support skeletal elements, might be further distributed along the tetrapod stem than previously thought. These data further support the placement of aÃstopods in the tetrapod stem group and require a reconsideration of our understanding of early tetrapod evolution.
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Free pdf:
Julia A. Schwab, JÃrgen Kriwet, Gerhard W. Weber & Cathrin PfaffÂ
Carnivoran hunting style and phylogeny reflected in bony labyrinth morphometry.
Scientific Reports 9, Article number: 70
Carnivorans are a highly diverse and successful group of mammals, found on the top of the food chain. They originated in the Palaeocene (ca. 60âMa) and have developed numerous lifestyles, locomotion modes and hunting strategies during their evolutionary history. Mechanosensory organs, such as the inner ear (which houses senses of equilibrium and hearing), represent informative anatomical systems to obtain insights into function, ecology and phylogeny of extant and extinct vertebrates. Using ÂCT scans, we examined bony labyrinths of a broad sample of various carnivoran species, to obtain new information about hunting behaviours of ancient carnivorans. Bony labyrinths were digitally reconstructed and measurements were taken directly from these 3D models. Principal component analyses generally separated various hunting strategies (pursuit, pounce, ambush and occasional), but also support their phylogenetic relationships (Canoidea vs. Feloidea). The height, width and length of all three semicircular canals show functional morphological adaptations, whereas the diameter of the canals, the height of the cochlea and particularly the angle between the lateral semicircular canal and the cochlea indicate a phylogenetic signal. The results demonstrate that the bony labyrinth provides a powerful ecological proxy reflecting both predatory habits as well as phylogenetic relationships in extinct and extant carnivorans.