Topic
Stratesaurus
About: Stratesaurus is a research topic. Over the lifetime, 2 publications have been published within this topic receiving 135 citations.
Papers
TL;DR: High rhomaleosaurid diversity immediately following the Triassic-Jurassic boundary supports the gradual model of Late Triassic extinctions, mostly predating the boundary itself.
Abstract: Invasion of the open ocean by tetrapods represents a major evolutionary transition that occurred independently in cetaceans, mosasauroids, chelonioids (sea turtles), ichthyosaurs and plesiosaurs. Plesiosaurian reptiles invaded pelagic ocean environments immediately following the Late Triassic extinctions. This diversification is recorded by three intensively-sampled European fossil faunas, spanning 20 million years (Ma). These provide an unparalleled opportunity to document changes in key macroevolutionary parameters associated with secondary adaptation to pelagic life in tetrapods. A comprehensive assessment focuses on the oldest fauna, from the Blue Lias Formation of Street, and nearby localities, in Somerset, UK (Earliest Jurassic: 200 Ma), identifying three new species representing two small-bodied rhomaleosaurids (Stratesaurus taylori gen et sp. nov.; Avalonnectes arturi gen. et sp. nov) and the most basal plesiosauroid, Eoplesiosaurus antiquior gen. et sp. nov. The initial radiation of plesiosaurs was characterised by high, but short-lived, diversity of an archaic clade, Rhomaleosauridae. Representatives of this initial radiation were replaced by derived, neoplesiosaurian plesiosaurs at small-medium body sizes during a more gradual accumulation of morphological disparity. This gradualistic modality suggests that adaptive radiations within tetrapod subclades are not always characterised by the initially high levels of disparity observed in the Paleozoic origins of major metazoan body plans, or in the origin of tetrapods. High rhomaleosaurid diversity immediately following the Triassic-Jurassic boundary supports the gradual model of Late Triassic extinctions, mostly predating the boundary itself. Increase in both maximum and minimum body length early in plesiosaurian history suggests a driven evolutionary trend. However, Maximum-likelihood models suggest only passive expansion into higher body size categories.
TL;DR: One of the oldest plesiosaurians, Stratesaurus taylori from the earliest Hettangian of the United Kingdom, is provided, due to its plesiomorphic morphology and well-characterized anatomy, to be recommended as an ingroup representative of Plesiosauria for future cladistic analyses of Triassic sauropterygians.
Abstract: We provide a complete description of one of the oldest plesiosaurians, Stratesaurus taylori from the earliest Hettangian of the United Kingdom. At least 25 apomorphies distinguish S. taylori from the sympatric Thalassiodracon hawkinsii, to which all three specimens of S. taylori were originally referred. Several features of the skull of S. taylori suggest specialization on small prey items, or sieve feeding. In particular, it has anteriorly inclined premaxillary and mesial maxillary teeth and an only weakly heterodont maxillary dentition. This indicates niche partitioning among sympatric small-bodied plesiosaurians: T. hawkinsii has a pronouncedly heterodont dentition. With a body length estimated around 2 m, S. taylori is one of the smallest plesiosaurians, comparable to T. hawkinsii. Our anatomical review of S. taylori suggests difficulty determining its precise phylogenetic affinities. This is consistent with a general lack of phylogenetic resolution among earliest Jurassic plesiosaurians, which may result from missing data on their Triassic ancestry. However, due to its plesiomorphic morphology and well-characterized anatomy, we recommend S. taylori as an ingroup representative of Plesiosauria for future cladistic analyses of Triassic sauropterygians.
Related Topics (5)
Performance Metrics
| Year | Papers |
|---|---|
| 2015 | 1 |
| 2012 | 1 |