Geometric morphometric analyses of worn cheek teeth help identify extant and extinct gophers (Rodentia, Geomyidae)

Abstract

Studies of the biostratigraphy and palaeoecology of fossil vertebrate assemblages require large samples of accurately identified specimens. Such analyses can be hampered by the inability to assign isolated and worn remains to specific taxa. Entoptychine gophers are a diverse group of burrowing rodents found in Oligo‐Miocene deposits of the western United States. In both entoptychines and their extant relatives the geomyines, diagnostic characters of the occlusal surface of the teeth are modified with wear, making difficult the identification of many isolated fossil teeth. We use geometric morphometrics to test the hypothesis that tooth shape informs taxonomic affinities and expected levels of morphological variation across gopher taxa. We also incorporate data from microcomputer tomography to investigate changes in occlusal surface shape through wear within individuals. Our analyses demonstrate the usefulness of our approach in identifying extant geomyines to the genus, subgenus and species levels, and fossil entoptychines to the genus and, in some cases, the species level. Our results cast doubt on the validity of some species within Entoptychus and suggest future revisions to entoptychine taxonomy. The amounts of morphological divergence observed among fossil and extant genera are similar. Fossil species do not differ greatly from extant ones in that regard either. Further work evaluating the morphological variation within and across entoptychine species, including unworn teeth and osteological material, will allow revised analyses of the biostratigraphy and palaeoecology of important Oligo‐Miocene mammalian assemblages of the western United States and help to infer the phylogenetic relationships and evolution of gophers.

Locomotory adaptations in entoptychine gophers (Rodentia: Geomyidae) and the mosaic evolution of fossoriality

“…We also present here new Pleurolicus material from the Arikareean‐aged middle Cabbage Patch beds of western Montana (Table ). Previously reported in part by Rasmussen (), Souza (), Calede (, ), and Calede and Glusman (), but never analyzed, this material represents the most complete remains of Pleurolicus known. It includes a complete skeleton of “ Pleurolicus nelsoni” (Figure ), as well as the skull and partial skeleton of “ Pleurolicus rensbergeri ” (Figure ).…”

“…The fossil record of entoptychine gophers is rich in partial jaws and isolated teeth (Calede & Glusman, ), but skulls and postcranial remains are rare and often fragmentary (Rensberger, , ; Stevens, ), thus presenting an obstacle to rigorous analyses of locomotion in entoptychines. In an effort to resolve the apparent conflict between ichnological and osteological evidence, we herein present new skeletal material for three entoptychine species from Montana, including an almost complete skeleton of the genus Pleurolicus .…”

Dental measurements do not diagnose modern artiodactyl species: Implications for the systematics of Merycoidodontoidea

“…If intraspecific variation were constant across the animal kingdom, the lack of artiodactyl-specific studies should not matter. Recent papers have explored dental variation on several extant mammalian groups, with particular emphasis on carnivores (e.g., Pengilly, 1984;Polly, 1998;Szuma, 2002;Meiri et al, 2005), elephants (e.g., Roth, 1989Roth, , 1992, primates (e.g., Gingerich and Schoeninger, 1979;Cope, 1993), and rodents (e.g., Austin and Stangl, 1995;Polly, 2003;Carrasco, 2004;Polly and Head, 2004;Caumul and Polly, 2005;Cordeiro-Estrela et al, 2006;Calede and Glusman, 2017). The abundant research on variation has made it clear that there exists a wide range of variation in mammalia, both by morphology measured and by species -one size range does not fit all groups.…”

Ecological correlates of the morphology of the auditory bulla in rodents: Application to the fossil record

“…These quantitative analyses have focused on the proportions of postcranial skeletons (e.g., Calede et al, 2019;Candela & Picasso, 2008;Carrizo et al, 2014;Elissamburu & de Santis, 2011;Elissamburu & Vizcaíno, 2004;Essner, 2007;Ginot et al, 2016;Lessa and Thaeler, 1989;Samuels & Van Valkenburgh, 2008) as well as the analyses of mostly complete skulls (Bertrand et al, 2016;Calede et al, 2019;Samuels & Van Valkenburgh, 2009). However, such remains are quite rare in the North American fossil record of the Oligocene and Miocene (see Calede & Glusman, 2017;Calede & Hopkins, 2012;Calede et al, 2019); this hampers the determination of locomotory modes for a large majority of fossil species. Our analysis explores a different approach that focuses on one adaptation to locomotion: hearing.…”