In press

Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water

Schwab, J.A., Young, M.T., Neenan, J.M., Walsh, S.A. Witmer, L.M., Herrera, Y., Allain, R., Brochu, C.A., Choiniere, J.N., Clark, J.M., Dollman, K.N., Etches, S., Fritsch, G., Gignac, P.M., Ruebenstahl, A., Sachs, S., Turner, A.H., Vignaud, P., Wilberg, E.W., Xu, X., Zanno, L.E. & Brusatte, S.L. (in press) Inner ear sensory system changes as extinct crocodylomorphs transitioned from land to water, Proceedings of the National Academy of Sciences. [Request a pdf]

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Major evolutionary transitions, in which animals develop new body plans and adapt to dramatically new habitats and lifestyles, have punctuated the history of life. The origin of cetaceans from land-living mammals is among the most famous of these events. Much earlier, during the Mesozoic Era, many reptile groups also moved from land to water, but these transitions are more poorly understood. We use computed tomography to study changes in the inner ear vestibular system, involved in sensing balance and equilibrium, as one of these groups, extinct crocodile relatives called thalattosuchians, transitioned from terrestrial ancestors into pelagic (open ocean) swimmers. We find that the morphology of the vestibular system corresponds to habitat, with pelagic thalattosuchians exhibiting a more compact labyrinth with wider semicircular canal diameters and an enlarged vestibule, reminiscent of modified and miniaturized labyrinths of other marine reptiles and cetaceans. Pelagic thalattosuchians with modified inner ears were the culmination of an evolutionary trend with a long semiaquatic phase, and their pelagic vestibular systems appeared after the first changes to the postcranial skeleton that enhanced their ability to swim. This is strikingly different from cetaceans, which miniaturized their labyrinths soon after entering the water, without a prolonged semiaquatic stage. Thus, thalattosuchians and cetaceans became secondarily aquatic in different ways and at different paces, showing that there are different routes for the same type of transition.

Metriorhynchid crocodylomorphs from the lower Kimmeridgian of Southern Germany

Abel, P., Sachs, S. & Young, M. & (in press) Metriorhynchid crocodylomorphs from the lower Kimmeridgian of Southern Germany, Alcheringa. [Request a pdf]

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Over the last two centuries, numerous exquisitely preserved thalattosuchian crocodylomorph skeletons have been found in the Jurassic strata of Southern Germany. While the majority of these specimens occur in Toarcian and upper Kimmeridgian–lower Tithonian deposits, thalattosuchian
remains are otherwise rare in strata representing different stages of the Jurassic. Here, we describe skeletal elements from two large-bodied thalattosuchians attributable to the family Metriorhynchidae – these were recovered from lower Kimmeridgian sediments in Bavaria and Baden-W€urttemberg, respectively. These new metriorhynchid fossils are closely comparable in both stratigraphic age and dental morphology, and thus may be congeneric. Furthermore, our phylogenetic analysis suggests affinity with metriorhynchid remains from France, Switzerland, and the UK. We interpret these taxa as members of an as-yet unnamed geosaurine metriorhynchid lineage (herein termed the ‘E-clade’) from the  Kimmeridgian and Tithonian of Europe, which appears to be related to species of Torvoneustes from England and Mexico, and Purranisaurus potens from Argentina, collectively contributing to ‘Subclade T’ of the tribe Geosaurini. Finally, the metriorhynchid material described herein suggests preservation as a ‘bloat and float’ carcass that underwent diagenetic dispersal within a limestone-marl-alternation deposited in an off-shore epicontinental marine environment.

Evidence of thalattosuchian crocodylomorphs in the Portland Stone Formation (Late Jurassic) of England, and a discussion on Cretaceous teleosauroids

 Young, M. & Sachs, S. (in press) Evidence of thalattosuchian crocodylomorphs in the Portland Stone Formation (Late Jurassic) of England, and a discussion on Cretaceous teleosauroids, Historical Biology. [Request a pdf]

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We report the first definite specimen of a thalattosuchian crocodylomorph from the Portland Stone Formation of England. This specimen (an isolated tooth crown) can be referred to the teleosauroid genus Machimosaurus based on its conical shape, distinctive enamel ornamentation and lack of carinae. Understanding the faunal composition of the Portland Stone Formation is key to elucidating the distinct shift in crocodylomorph taxa that occurred during the Tithonian-to-Berriasian in Europe. One of the most striking aspects of this faunal shift is the hypothesised extinction of Teleosauroidea in Europe. The presence of Machimosaurus in the Portland Stone Formation supports the hypothesis that the localised marine regression in Europe at the Jurassic–Cretaceous boundary, and the resultant habitat loss, contributed to the absence of teleosauroids in Europe during the Berriasian. However, the fossil record of thalattosuchians during the Cretaceous is notorious scarce. We review the purported Cretaceous record of teleosauroids, and agree that closer to the equator this clade survived for at least 20 million years after the Jurassic–Cretaceous boundary.

2020

Enigmatic plesiosaur vertebral remains from the middle Turonian of Germany

Sachs, S., Madzia, D., Püttmann, T. & Kear, B.P. (2020) Enigmatic plesiosaur vertebral remains from the middle Turonian of Germany, Cretaceous Research 110, 104406. [Request a pdf]

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The Turonian (93.9-89.8 Ma) was a key transitional interval of plesiosaur evolution, during which pliosaurid apex predators (dominant since the Middle Jurassic) rapidly declined, and polycotylids correspondingly radiated as middle trophic-level pursuit hunters. Paradoxically, however, the fossil record of Turonian plesiosaurs is globally sparse, especially in continental Europe where only a handful of fragmentary specimens have been recovered from localities in the Czech Republic, Germany and Poland. Here, we report on a new European Turonian plesiosaur occurrence from the Bochum Grünsand Member of the Duisburg Formation in the city of Unna, western Germany. These remains comprise a series of eight mid-series cervical vertebrae with articulated ribs that can be precisely correlated to the lower middle Turonian UC8aeUC8b calcareous nannofossil biozones. The vertebrae display a distinctive character state combination, including transversely broad lozenge-shaped centra that are anteroposteriorly compact, bear amphicoelous articular surfaces, inset lateral sides, and large zygapophyses that are broader than the corresponding centra. Although phylogenetically inconclusive, these features are compatible with coeval polycotylids. The Bochum Grünsand Member vertebrae thus augment the currently scant knowledge of Turonian plesiosaurs from Europe, and support assertions that the regional
assemblage was taxonomically diverse at that time.