The evolutionary history of polycotylid plesiosaurians

Polycotylidae is a clade of plesiosaurians that appeared during the Early Cretaceous and became speciose and abundant early in the Late Cretaceous. However, this radiation is poorly understood. Thililua longicollis from the Middle Turonian of Morocco is an enigmatic taxon possessing an atypically lo...

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Bibliographic Details
Published in:Royal Society open science 2018-03, Vol.5 (3), p.172177-172177
Main Authors: Fischer, V., Benson, R. B. J., Druckenmiller, P. S., Ketchum, H. F., Bardet, N.
Format: Article
Language:English
Subjects:
Biology (whole Organism)
Biotic Turnover
Earth sciences & physical geography
Environmental Sciences
Evolutionary Radiation
Life Sciences
Morphology
Physical, chemical, mathematical & earth Sciences
Physique, chimie, mathématiques & sciences de la terre
Plesiosauria
Sauropterygia
Sciences de la terre & géographie physique
Sciences du vivant
Sciences of the Universe
Zoologie
Zoology
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Summary:Polycotylidae is a clade of plesiosaurians that appeared during the Early Cretaceous and became speciose and abundant early in the Late Cretaceous. However, this radiation is poorly understood. Thililua longicollis from the Middle Turonian of Morocco is an enigmatic taxon possessing an atypically long neck and, as originally reported, a series of unusual cranial features that cause unstable phylogenetic relationships for polycotylids. We reinterpret the holotype specimen of Thililua longicollis and clarify its cranial anatomy. Thililua longicollis possesses an extensive, foramina-bearing jugal, a premaxilla–parietal contact and carinated teeth. Phylogenetic analyses of a new cladistic dataset based on first-hand observation of most polycotylids recover Thililua and Mauriciosaurus as successive lineages at the base of the earliest Late Cretaceous polycotyline radiation. A new dataset summarizing the Bauplan of polycotylids reveals that their radiation produced an early burst of disparity during the Cenomanian–Turonian interval, with marked plasticity in relative neck length, but this did not arise as an ecological release following the extinction of ichthyosaurs and pliosaurids. This disparity vanished during and after the Turonian, which is consistent with a model of ‘early experimentation/late constraint’. Two polycotylid clades, Occultonectia clade nov. and Polycotylinae, survived up to the Maastrichtian, but with low diversity.
ISSN:2054-5703
2054-5703
DOI:10.1098/rsos.172177