Mark T. Young

University of Edinburgh

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Stephen L. Brusatte

University of Edinburgh

Davide Foffa

Virginia Tech

Lorna Steel

Natural History Museum

Marco B D Andrade

Pontifícia Universidade Católica do Rio Grande do Sul

Sven Sachs

Museum für Naturkunde

Yanina Herrera

Consejo Nacional de Investigaciones Científicas y Técnicas

Michela M. Johnson

Staatliches Museum für Naturkunde Stuttgart

Lawrence M. Witmer

Ohio University

Julia A. Schwab

University of Edinburgh

Stig Walsh

National Museums Scotland

Cooperative Institutions

Centre National de la Recherche Scientifique

Natural History Museum

American Museum of Natural History

Chinese Academy of Sciences

Consejo Superior de Investigaciones Científicas

Real Jardín Botánico

Sorbonne Université

Muséum national d'Histoire naturelle

Weatherford College

École Pratique des Hautes Études

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Emptying the wastebasket: a historical and taxonomic revision of the Jurassic crocodylomorphSteneosaurus

Zoological Journal of the Linnean Society (2020)

Michela M. Johnson Mark T. Young Stephen L. Brusatte

Abstract Teleosauroidea is a clade of ancient crocodylomorphs that were integral components of coastal marine environments throughout the Jurassic. For nearly two centuries, one of the most familiar genera of teleosauroids has been Steneosaurus, encompassing nearly every teleosauroid species at some point. However, no type species has been designated for Steneosaurus under ICZN Code rules; the type specimen of the presumed type species S. rostromajorGeoffroy Saint-Hilaire, 1825 (MNHN.RJN 134c-d) is a chimera that has been largely neglected in the literature. Moreover, there is confusion as to which teleosauroid species it pertains to, and the genus Steneosaurus is often recovered as paraphyletic or polyphyletic in phylogenetic analyses. As such, the validity of Steneosaurus is uncertain. Here we formally designate S. rostromajor as the type species of Steneosaurus, designate a lectotype and re-evaluate MNHN.RJN 134c-d. We compare it with several well-known teleosauroids, including Lemmysuchus and ‘S.’ edwardsi. Due to lack of autapomorphic characters, poor preservation and a tortured taxonomic history, we find MNHN.RJN 134c-d to be an undiagnostic and unreliable specimen. Thus, we consider S. rostromajor as a nomen dubium and propose that the genus Steneosaurus is undiagnostic. This has profound implications for teleosauroid phylogenetics, which we will clarify in an upcoming paper.

Polyphyly

Paraphyly

Nomen dubium

Autapomorphy

Lampetra

10.1093/zoolinnean/zlaa027

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The ecological diversification and evolution of Teleosauroidea (Crocodylomorpha, Thalattosuchia), with insights into their mandibular biomechanics

Ecology and Evolution (2022)

Michela M. Johnson Davide Foffa Mark T. Young Stephen L. Brusatte

Abstract Throughout the Jurassic, a plethora of marine reptiles dominated ocean waters, including ichthyosaurs, plesiosaurs and thalattosuchian crocodylomorphs. These Jurassic ecosystems were characterized by high niche partitioning and spatial variation in dietary ecology. However, while the ecological diversity of many marine reptile lineages is well known, the overall ecological diversification of Teleosauroidea (one of the two major groups within thalattosuchian crocodylomorphs) has never been explored. Teleosauroids were previously deemed to have a morphologically conservative body plan; however, they were in actuality morphofunctionally more diverse than previously thought. Here we investigate the ecology and feeding specializations of teleosauroids, using morphological and functional cranio‐dental characteristics. We assembled the most comprehensive dataset to date of teleosauroid taxa (approximately 20 species) and ran a series of principal component analyses (PC) to categorize them into various feeding ecomorphotypes based on 17 dental characteristics (38 specimens) and 16 functionally significant mandibular characters (18 specimens). The results were examined in conjunction with a comprehensive thalattosuchian phylogeny (153 taxa and 502 characters) to evaluate macroevolutionary patterns and significant ecological shifts. Machimosaurids display a well‐developed ecological shift from: (1) slender, pointed tooth apices and an elongate gracile mandible; to (2) more robust, pointed teeth with a slightly deeper mandible; and finally, (3) rounded teeth and a deep‐set, shortened mandible with enlarged musculature. Overall, there is limited mandibular functional variability in teleosaurids and machimosaurids, despite differing cranial morphologies and habitat preferences in certain taxa. This suggests a narrow feeding ecological divide between teleosaurids and machimosaurids. Resource partitioning was primarily related to snout and skull length as well as habitat; only twice did teleosauroids manage to make a major evolutionary leap to feed distinctly differently, with only the derived machimosaurines successfully radiating into new feeding ecologies.

Ecomorphology

Body plan

Macroevolution

10.1002/ece3.9484

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Author response for "Skull sinuses precluded extinct crocodile relatives from cetacean-style deep diving as they transitioned from land to sea"

Mark T. Young Julia A. Schwab David Dufeau Rachel A. Racicot Thomas Cowgill

10.1098/rsos.241272/v2/response1

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Introducing the First European Symposium on the Evolution of Crocodylomorpha

Zoological Journal of the Linnean Society (2020)

Eduardo Puértolas‐Pascual Mark T. Young Christopher A. Brochu

Abstract The First European Symposium on the Evolution of Crocodylomorpha took place during the XVI Annual Meeting of the European Association of Vertebrate Palaeontologists (EAVP) organized by NOVA University of Lisbon (UNL) in Caparica, Portugal. Fourteen lectures and five posters were presented at the symposium in June 26th–July 1st, 2018. This special issue showcases twelve papers based on symposium contributions.

10.1093/zoolinnean/zlaa012

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A new metriorhynchid crocodylomorph from the Lower Kimmeridge Clay Formation (Late Jurassic) of England, with implications for the evolution of dermatocranium ornamentation in Geosaurini

Zoological Journal of the Linnean Society (2013)

Mark T. Young Marco B D Andrade Steve Etches Brian L. Beatty

A new metriorhynchid crocodylomorph from the Lower Kimmeridge Clay Formation (Kimmeridgian, Upper Jurassic) of England is described. This specimen, a three-dimensionally preserved skull and left mandibular ramus, is referred to a new species: Torvoneustes coryphaeus sp. nov. Within the genus Torvoneustes, T. coryphaeus sp. nov. is unique as it has a long anteromedial process of the frontal, ornamented dermatocranium, and the supraorbital notch forms a strongly acute angle. Our phylogenetic analysis confirms the placement of this specimen in Torvoneustes. The dentition of T. coryphaeus sp. nov., like that of the type species, has a blunt apex, crown basal–mid regions with numerous tightly packed apicobasally aligned ridges, and apical region with an anastomosed pattern of ridges that interact with the carinae. Within Thalattosuchia these dental characteristics are only found in Torvoneustes and the teleosaurid Machimosaurus. The heavily ornamented dermatocranium of T. coryphaeus sp. nov. is in contrast to the unornamented (nasals and frontal)–lightly ornamented (maxillae and premaxillae) pattern seen in Torvoneustes carpenteri. Curiously, this pattern of reduction and loss of dermatocranium ornamentation is also observed in Metriorhynchus, Dakosaurus, and the subclade Rhacheosaurini. We hypothesize that the ‘smooth’ dermatocranium of Late Jurassic metriorhynchids evolved independently in each subclade (parallel evolution), and would have reduced drag, thereby making locomotion through water more energy efficient. © 2013 The Linnean Society of London

10.1111/zoj.12082

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

Proceedings of the National Academy of Sciences (2020)

Julia A. Schwab Mark T. Young James M. Neenan Stig Walsh Lawrence M. Witmer

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.

Postcrania

Human echolocation

10.1073/pnas.2002146117

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Peer Review #1 of "A new large-bodied thalattosuchian crocodyliform from the Lower Jurassic (Toarcian) of Hungary, with further evidence of the mosaic acquisition of marine adaptations in Metriorhynchoidea (v0.1)"

Attila Ősi Mark T. Young András Galácz Márton Rabi

Based on associated and three-dimensionally preserved cranial and postcranial remains, a new thalattosuchian crocodyliform, Magyarosuchus fitosi gen.et sp.nov.from the Lower Jurassic (Upper Toarcian) Kisgerecse Marl Formation, Gerecse Mountains, Hungary is described here.Phylogenetic analyses using three different datasets indicate that M. fitosi is the sister taxon of Pelagosaurus typus forming together the basal-most sub-clade of Metriorhynchoidea.With an estimated body length of 4.67-4.83meter M. fitosi is the largest known non-metriorhynchid metriorhynchoid.Besides expanding Early Jurassic thalattosuchian diversity, the new specimen is of great importance since, unlike most contemporaneous estuarine, lagoonal or coastal thalattosuchians, it comes from an "ammonitico rosso" type pelagic deposit of the Mediterranean region of the Tethys.A distal caudal vertebra having an unusually elongate and dorsally projected neural spine implies the presence of at least a rudimentary hypocercal tail fin and a slight ventral displacement of the distal caudal vertebral column in this basal metriorhynchoid.The combination of retaining heavy dorsal and ventral armors and having a slight hypocercal tail is unique, further highlighting the mosaic manner of marine adaptations in Metriorhynchoidea.

Mosaic

10.7287/peerj.4668v0.1/reviews/1

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Paranasal sinus system and upper respiratory tract evolution in Mesozoic pelagic crocodylomorphs

The Anatomical Record (2021)

Thomas Cowgill Mark T. Young Julia A. Schwab Stig Walsh Lawrence M. Witmer

Abstract Thalattosuchians were a predominately marine clade of Mesozoic crocodylomorphs, including semi‐aquatic teleosauroid and obligately pelagic metriorhynchid subclades. Recent advances in our understanding of thalattosuchian endocranial anatomy have revealed new details of the evolutionary transition from terrestrial to marine to pelagic taxa. Paranasal sinuses, however, have received little attention. Herein, we investigate the evolution of the paranasal sinus system and part of the upper respiratory system (nasopharyngeal ducts) in Thalattosuchia, by reconstructing the nasal and paranasal anatomy in CT scans of seven thalattosuchian skulls: one teleosauroid, two basal metriorhynchoids and four metriorhynchids. Our outgroups were: three extant crocodylian species (including adult and subadult skulls) and the basal crocodyliform Protosuchus . We found thalattosuchians exhibit exceptionally reduced paranasal sinus systems, solely comprising the antorbital sinus, as has been previously proposed. The semi‐aquatic basal thalattosuchians Palgiopthalmosuchus gracilirostris and Pelagosaurus typus both have an antorbital sinus partially located medial to a reduced external antorbital fenestra and broadly communicating with the dorsal alveolar canal. In pelagic metriorhynchids, the antorbital cavity is more extensive than in basal taxa and possibly had an active function associated with a hypothesized accessory suborbital diverticulum, but our reconstructions are insufficient to confirm or reject the presence of such a diverticulum. The nasopharyngeal ducts of metriorhynchids are dorsoventrally enlarged, possibly enabling stronger ventilation. The sequence of acquisition of craniofacial adaptations show a mosaic pattern and appears to predate many skeletal adaptations, suggesting these changes occurred early in the thalattosuchian marine transition.

Sinus (botany)

Basal (medicine)

10.1002/ar.24727

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Steneosaurus edwardsi(Thalattosuchia: Teleosauridae), the largest known crocodylomorph of the Middle Jurassic

Biological Journal of the Linnean Society (2015)

Michela M. Johnson Mark T. Young Lorna Steel Yves Lepage

Teleosaurids were a clade of marine crocodylomorphs that were globally distributed during the Jurassic Period. They evolved a wide range of body sizes, from small (∼2–3 m) to very large (> 9 m). Until now, the largest known Middle Jurassic teleosaurid was 'Steneosaurus' obtusidens, from the Oxford Clay Formation of the UK. Here, we re-examine a very large Oxford Clay specimen (ilium, ischium, and femur) that had been tentatively attributed to 'S.' obtusidens. Based on comparative anatomical study with the 'S.' obtusidens holotype and referred specimens of Steneosaurus edwardsi and Steneosaurus leedsi, we conclude that this very large individual actually pertains to S. edwardsi. Based on comparisons with the Machimosaurus mosae neotype (which has a complete femur and skeleton), we estimate a total length in excess of 7 m for this large S. edwardsi individual, making it the largest known Middle Jurassic teleosaurid. Therefore, along with the closely related genus Machimosaurus, this clade of large-bodied Middle–Late Jurassic teleosaurids were the largest species during the first 100 million years of crocodylomorph evolution.

10.1111/bij.12525

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Citations (19)

The Braincase and Neurosensory Anatomy of an Early Jurassic Marine Crocodylomorph: Implications for Crocodylian Sinus Evolution and Sensory Transitions

The Anatomical Record (2016)

Stephen L. Brusatte Amy Muir Mark T. Young Stig Walsh Lorna Steel

ABSTRACT Modern crocodylians are a morphologically conservative group, but extinct relatives (crocodylomorphs) experimented with a wide range of diets, behaviors, and body sizes. Among the most unusual of these fossil groups is the thalattosuchians, an assemblage of marine‐dwellers that transitioned from semiaquatic species (teleosaurids and kin) into purely open‐ocean forms (metriorhynchids) during the Jurassic and Cretaceous Periods (ca 191–125 million years ago). Thalattosuchians can give insight into the origin of modern crocodylian morphologies and how anatomy and behavior change during a major evolutionary transition into a new habitat. Little is known, however, about their brains, sensory systems, cranial sinuses, and vasculature. We here describe the endocranial anatomy of a well‐preserved specimen of the Jurassic semiaquatic teleosaurid Steneosaurus cf. gracilirostris using X‐ray micro‐CT. We find that this teleosaurid still had an ear well attuned to hear on land, but had developed large internal carotid and orbital arteries that likely supplied salt glands, previously thought to be present in only the fully pelagic metriorhynchids. There is no great gulf in endocranial anatomy between this teleosaurid and the metriorhynchids, and some of the features that later permitted metriorhynchids to invade the oceanic realm were apparently first developed in semiaquatic taxa. Compared to modern crocodylians, Steneosaurus cf. gracilirostris has a more limited set of pharyngotympanic sinuses, but it is unclear whether this relates to its aquatic habitat or represents the primitive condition of crocodylomorphs that was later elaborated. Anat Rec, 299:1511–1530, 2016. © 2016 Wiley Periodicals, Inc.

Endocast

Sinus (botany)

10.1002/ar.23462

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Citations (69)