Pendraig milnerae, a new small-sized coelophysoid theropod from the Late Triassic of Wales

Spiekman, Stephan N F; Ezcurra, Martà­n D; Butler, Richard J; Fraser, Nicholas C; Maidment, Susannah C R

Pendraig milnerae, a new small-sized coelophysoid theropod from the Late Triassic of Wales

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Spiekman, Stephan N F

Ezcurra, Martàn D

Butler, Richard J

Fraser, Nicholas C

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Maidment, Susannah C R

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October 6, 2021

Abstract

We describe a new small-bodied coelophysoid theropod dinosaur, Pendraig milnerae gen. et sp. nov, from the Late Triassic fissure fill deposits of Pant-y-ffynnon in southern Wales. The species is represented by the holotype, consisting of an articulated pelvic girdle, sacrum and posterior dorsal vertebrae, and an associated left femur, and by two referred specimens, comprising an isolated dorsal vertebra and a partial left ischium. Our phylogenetic analysis recovers P. milnerae as a non-coelophysid coelophysoid theropod, representing the first-named unambiguous theropod from the Triassic of the UK. Recently, it has been suggested that Pant-y-ffynnon and other nearby Late Triassic to Early Jurassic fissure fill faunas might have been subjected to insular dwarfism. To test this hypothesis for P. milnerae, we performed an ancestral state reconstruction analysis of body size in early neotheropods. Although our results indicate that a reduced body size is autapomorphic for P. milnerae, some other coelophysoid taxa show a similar size reduction, and there is, therefore, ambiguous evidence to indicate that this species was subjected to dwarfism. Our analyses further indicate that, in contrast with averostran-line neotheropods, which increased in body size during the Triassic, coelophysoids underwent a small body size decrease early in their evolution.