Intraspecific versus interspecific variation in Miocene Great Basin mylagaulids: implications for systematics and evolutionary history

Abstract

The Mylagaulidae are a family of burrowing rodents abundant in Miocene faunas from western North America. Recent taxonomic revisions of mylagaulids from the Great Plains suggest that their systematics may be best understood on a regional basis. Previous studies addressed the taxonomy and evolutionary history of mylagaulids from the Great Basin, but recent discoveries of specimens, new phylogenetic data, and more detailed stratigraphical information necessitate a thorough reanalysis of their relationships and occurrences. We present a revision of the systematics of the mylagaulids from the Great Basin. In addition to rare large mylagaulids of uncertain taxonomic affinity, we recognize four species of mylagaulids distributed throughout Oregon and Nevada from the late Hemingfordian through to the early late Hemphillian: Alphagaulus vetus, Hesperogaulus gazini, Hesperogaulus wilsoni, and a new species from the genus Hesperogaulus. All species are known from large sample sizes of isolated premolars, allowing consideration of ontogenetic variation in determining the key morphological differences that allow recognition of different species. Although the number of enamel lakes varies within a given taxon, the presence of some of these lakes is taxonomically significant. This result emphasizes the importance of understanding ontogeny in describing species of fossil hypsodont mammals.

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

“…Feranec et al . ; McGuire ; Calede & Hopkins ; Davis & Calede ; Davis & McHorse ). This work has often focused on teeth because of their utility in mammalian taxonomy and abundance in the fossil record (see Smith & Wilson ) but it can be complicated by the change in apparent tooth shape with wear in hypsodont taxa (e.g.…”

The first tetrapod from the mid-Miocene Clarkialagerstätte(Idaho, USA)

“…Although a diverse fauna of mylagaulids is known from the Inland Northwest ( Barnosky et al, 2007 ; Calede & Hopkins, 2012a ; Calede, Hopkins & Davis, 2011 ), most genera are much larger than UWBM 113209 ( Calede, Hopkins & Davis, 2011 ). Only the genus Mesogaulus is similar in size to UWBM 113209 ( Dorr, 1956 ; Hopkins, 2007 ).…”

“…The teeth of mesogauline mylagaulids (including Mesogaulus ) are also very much unlike those of UWBM 113209. They are typically very large, high-crowned, and display a complex occlusal surface composed of enamel lakes ( Calede & Hopkins, 2012a ; Shotwell, 1958 ). The postcranial skeleton of UWBM 113209 provides additional evidence that the Clarkia rodent is not a mylagaulid, given its gracile forelimbs unlike those found in mylagaulids ( Calede & Hopkins, 2012b ; Fagan, 1960 ; Galbreath, 1984 ; Korth, 2000 ).…”

New occurrences of mammals from McKay Reservoir (Hemphillian, Oregon)

“…Shotwell (1955a) argued that the taphonomy of the McKay Reservoir fossils indicated a pondbank environment and built on this by including the McKay Reservoir fauna in a pioneering analysis of landscape paleoecology in the Columbia River Basin (Shotwell, 1958). The site's continuing importance as a paleobiological study system is underscored by the many subsequent studies incorporating McKay Reservoir fossils to address questions regarding mammalian body-size evolution (Orcutt andHopkins, 2013, 2016), morphological variation in mylagaulid rodents (Calede and Hopkins, 2012), the biogeography of arvicoline rodents (Martin, 2010), the origin of sigmodontine rodents (Ronez et al, 2021), rhinocerotid paleopathology (Stilson et al, 2016), and felid functional morphology and systematics (Orcutt and Calede, 2021). As extensively and intensely as it has been studied, the McKay Reservoir faunal list continues to grow, due to taxonomic revisions, to previously described taxa, and to new collections made by Gonzaga University field crews in 2017 and 2021.…”