Brusatte, Stephen

Young, Mark

Wood, Rachel

Johnson, Michela Maria Angeline

other

2019-12-20T11:03:38Z

2019-12-20T11:03:38Z

2019-12-10

Teleosauroidea represented an extraordinary group of crocodylomorphs that thrived in predominately shallow marine environments during the Mesozoic Era. While they have previously been considered as ‘marine gharials’ of the Jurassic, teleosauroids were in fact morphofunctionally diverse and evolved a bizarre body-plan (which included proportionally enlarged heads and femora). During the Jurassic, they attained a near-global distribution, expanded into various palaeoenvironments and became the first crocodylomorphs to grow to truly large sizes (> 7 m in length). In addition, teleosauroids were one of the first fossil crocodylomorphs to be described (1758) and named (1814), making them a historically important fossil group. Despite an increase in research over the past decade (particularly for the well-known clade Machimosaurini), the ecology and systematics of Teleosauroidea are still poorly understood and little studied. The question “What is ‘Steneosaurus’?”, a waste-basket genus that nearly every teleosauroid species has been placed into at some point, is a taxonomic conundrum that has hampered previous attempts to elucidate and examine teleosauroid evolutionary relationships. To rectify these issues, I examined approximately 550 specimens from 12 countries, and using this material, I created the largest and most comprehensive teleosauroid phylogenetic dataset to date; this dataset includes 502 characters and 153 crocodylomorph taxa (twenty-seven of which are teleosauroids), and was run in both TNT 1.5 and MrBayes 3.2.6. The results of both the parsimony and Bayesian analyses are consistent with one another, with two large subclades (Teleosauridae and Machimosauridae) within Teleosauroidea recovered; each one is morphologically distinct, with differing biogeographic distributions (one being Laurasian and the other Sub-Boreal European-Gondwanan) and feeding strategies. In addition, there was a significant divergence in ecomorphological characters between these subclades. While the SubAbstract Boreal subclade attained larger body-sizes (≥ 5 m) and evolved durophagy, the Laurasian subclade was more phenotypically plastic (including an east- Asian freshwater clade, a near-pelagic clade, and a heavily armoured clade). Based on my first-hand comparative anatomical and phylogenetic results, I propose major taxonomic revisions to Teleosauroidea, including: (1) redefining Teleosauridae and introducing Machimosauridae; (2) the resurrection of several historical genera; (3) erecting seven new genera; and (4) referring to the infamous genus ‘Steneosaurus’ as a nomen dubium. With this improved teleosauroid phylogenetic framework and updated alpha taxonomy (which allows thorough examination of their anatomical and ecological diversity), a new window has been opened on our understanding of these historically important crocodylomorphs.

https://hdl.handle.net/1842/36656

en

The University of Edinburgh

Foffa D, Johnson MM, Young MT, Stee L, Brusatte SL. 2019. Revision of the Late Jurassic deep-water teleosauroid crocodylomorph Teleosaurus megarhinus Hulke, 1871, and evidence of pelagic adaptations in Teleosauroidea. PeerJ 7: 6646.

Johnson MM, Young MT, Steel L, Lepage Y. 2015. Steneosaurus edwardsi (Thalattosuchia, Teleosauridae), the largest known crocodylomorph of the Middle Jurassic. Biological Journal of the Linnean Society 115: 911- 918.

Johnson MM, Young MT, Steel L, Foffa D, Smith AS, Hua S, Havlik P, Howlett EA, Dyke G. 2017. Re-description of ‘Steneosaurus’ obtusidens Andrews, 1909, an unusual macrophagous teleosaurid crocodylomorph from the Middle Jurassic of England. Zoological Journal of the Linnean Society 1: 1-34. DOI:10.1093/zoolinnean/zlx035.

Johnson MM, Young MT, Brusatte SL, Thuy B, Weis R. 2018. A catalogue of teleosauroids (Crocodylomorpha: Thalattosuchia) from the Toarcian and Bajocian (Jurassic) of southern Luxembourg. Historical Biology: DOI:10.1080/08912963.2018.1427090.

Johnson MM, Young MT. Brusatte SL. 2019. Re-description of two contemporaneous mesorostrine teleosauroids (Crocodylomorpha, Thalattosuchia) from the Bathonian of England, and insights into the early evolution of Machimosaurini. Zoological Journal of the Linnean Society zlz037: https://doi.org/10.1093/zoolinnean/zlz037

Sachs S, Johnson MM, Young MT, Abel P. 2019b. The mystery of Mystriosaurus Kaup, 1834: redescribing the poorly known Early Jurassic teleosauroid thalattosuchians Mystriosaurus laurillardi Kaup, 1834 and Steneosaurus brevior Blake, 1876. Acta Palaeontologica Polonica 64: 565- 579.

fossil crocodylomorphs

thalattosuchians

teleosauroids

teleosauroid evolution

taxonomy

Taxonomy, systematics and ecomorphological diversity of Teleosauroidea (Crocodylomorpha, Thalattosuchia), and the evaluation of the genus ‘Steneosaurus’

Thesis or Dissertation

Doctoral

PhD Doctor of Philosophy