Taxonomy, systematics and ecomorphological diversity of Teleosauroidea (Crocodylomorpha, Thalattosuchia), and the evaluation of the genus ‘Steneosaurus’
View/ Open
Date
10/12/2019Author
Johnson, Michela Maria Angeline
Metadata
Abstract
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.