Journal of Paleontology, 92(6), 2018, p. 1107–1114 Copyright © 2018, The Paleontological Society 0022-3360/15/0088-0906 doi: 10.1017/jpa.2018.30


A new species of trionychid turtle from the Upper Cretaceous (Campanian) Fruitland Formation of New Mexico, USA


Walter G. Joyce,1 Tyler R. Lyson,2 and Joseph J.W. Sertich2


1Departement für Geowissenschaften, Universität Freiburg, Chemin du Musée 6, 1700 Freiburg, Switzerland ⟨walter.joyce@unifr.ch⟩ 2Department of Earth Sciences, Denver Museum of Nature & Science, 2001 Colorado Boulevard, Denver, Colorado 80205, USA ⟨Tyler.Lyson@dmns.org⟩, ⟨Joe.Sertich@dmns.org⟩


Abstract.—New shell material of a trionychid turtle from the Upper Cretaceous (upper Campanian) Fossil Forest Member of the Fruitland Formation of northwestern New Mexico represents a new species, Gilmoremys getty- spherensis. The material consists of right costals I–III, V, VI, and VIII, left costals V, VII, and VIII, the left half of the entoplastron, the right hypo- and xiphiplastron, and the left hyo-, hypo-, and xiphiplastron. The specimen shows great similarities to the Late Cretaceous (Maastrichtian) trionychid Gilmoremys lancensis (Gilmore, 1916) by having a relatively thin shell, carapacial sculpturing consisting of fine pits combined with extended sinusoidal ridges or grooves, free costal rib ends, presence of a preneural, a distally constricted costal I and distally expanded costal II, two lateral hyoplastral processes, low hyoplastral shoulders, and full midline contact of the elongate xiphiplastra, but differs by being smaller, having raised sinusoidal ridges on the carapace instead of grooves, less distally expanded costals II, and less elongate xiphiplastra. Phylogenetic analysis places Gilmoremys gettyspherensis n. sp. as sister to Gilmoremys lancensis near the base of the clade Plastomenidae. Like the majority of previously described plastome- nid materials, the type specimen of Gilmoremys gettyspherensis n. sp. was collected from a mudstone horizon, sug- gesting a preference for ponded environments.


UUID: http://zoobank.org/e7165061-d86b-46b7-a1f8-c31f5a8ed628 Introduction


Continental sediments of upper Campanian (Upper Cretac- eous) age are broadly exposed throughout Canada, Mexico, and the United States and have yielded exceptionally rich turtle faunas consisting of adocids, chelydroids, helochelydrids, macrobaenids, nanhsiungchelyids, trionychids, and para- cryptodires (see Brinkman, 2003, 2005; Brinkman and Rodri- guez de la Rosa, 2006; Hutchison et al., 2013; Sullivan et al., 2013; Lively, 2016; and Lyson et al., 2017 for recent summa- ries). Soft-shelled turtles (Pan-Trionychidae) are an important component of these faunas, but the majority of finds are frag- mentary, making it difficult to rigorously assess their alpha taxonomy and phylogenetic relationships (Vitek and Joyce, 2015). The pan-trionychid faunas from the late Campanian of Alberta, NewMexico, andUtah are the best understood to date. TheOldman and Dinosaur Park formations of Alberta, Canada, have yielded particularly rich material, including complete shells and skeletons, that allows recognition of four taxa, the plastomenid Aspideretoides foveatus (Leidy, 1857), the trio- nychine Axestemys splendidus (Hay, 1908), and the inde- terminate ‘Trionyx’ allani (Gilmore, 1923) and ‘Trionyx’ latus (Gilmore, 1919) (Gardner et al., 1995; Brinkman, 2005; Vitek, 2012; Vitek and Joyce, 2015). (The pan-trionychid fauna of the Fruitland and Kirtland formations of NewMexico, by contrast, mostly consists of fragments that hint at the presence of at least


four trionychids, in particular two unnamed taxa and the indeterminate ‘Trionyx’ austerus (Hay, 1908) and ‘Trionyx’ robustus (Gilmore, 1919) (Sullivan et al., 2013; Vitek and Joyce, 2015). The Kaiparowits Formation of neighboring Utah has so far yieldedmostly fragmentary remains of four unnamed pan-trionychids with uncertain affinities (Hutchison et al., 2013; Vitek and Joyce, 2015). Although the turtle faunas of Alberta, New Mexico, and Utah are broadly contemporaneous (Roberts et al., 2005, 2013), clear faunal links are still missing with the exception of an unnamed taxon with a striated car- apace reported from the lower Kirtland Formation of north- western New Mexico (Plastomeninae indet. of Sullivan et al., 2013) and the Kaiparowits Formation of southern Utah (Trio- nychidae indet. type B of Hutchison et al., 2013). The purpose of this contribution is to formally name this taxon as a new species of plastomenid pan-trionychid based on a nearly com- plete shell from the Fossil Forest Member of the Fruitland Formation of northwestern New Mexico. In addition, we pro- vide an initial assessment of the phylogenetic relationship of the newspecies and discuss biogeographic and paleoecological implications.


Geologic setting


Vertebrate fossils, including abundant remains of turtles, have been recovered from the upper Fruitland and lower Kirtland


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