Unusual lizard fossil from the Miocene of Nebraska and a minimum age for cnemidophorine teiids

Abstract

Teiid lizards are well represented in the fossil record and are common components of modern ecosystems in North and South America. Many fossils were referred to the cnemidophorine teiid group (whiptails, racerunners and relatives), particularly from North America. However, systematic interpretations of morphological features in cnemidophorines were hampered by the historically problematic taxonomy of the clade, and the biogeography and chronology of cnemidophorine evolution in North America is poorly understood from the fossil record. Few fossil cnemidophorines were identified with an apomorphy-based diagnosis, and there are almost no fossil cnemidophorines that could be used to anchor node calibrations. Here, I describe a cnemidophorine from the Miocene Ogallala Group of Nebraska and diagnose the fossil using apomorphies. In that process, I clarify the systematic utility of several morphological features of cnemidophorine lizards. I refer the fossil to the least inclusive clade containing Aspidoscelis , Holcosus and Pholidoscelis . The most conservative minimum age of the locality of the fossil is a fission-track date of 6.3 Ma, but mammal biochronology provides a more refined age of 9.4 Ma, which can be used as a minimum age for the crown cnemidophorine clade in divergence time analyses. The fossil indicates that a cnemidophorine lineage that does not live in Nebraska today inhabited the area during the Miocene. I refrain from naming a new taxon pending discovery of additional fossil material of the lineage to which the fossil belonged.

Identification of Late Pleistocene and Holocene fossil lizards from Hall’s Cave and a primer on morphological variation in North American lizard skulls

“…Fossils in this study were previously excavated from Hall's Cave and are accessioned at the University of Texas Vertebrate Paleontology Collections (TxVP), locality 41229. We largely restricted our osteological comparative material to North American (NA) lizard taxa (see table 1 in Scarpetta et al 2020) including those that today live on or north of the Isthmus of Panama, as well as those that inhabit Caribbean islands. Our comparative dataset was chiefly based on dry skeletal specimens; however, we also examined skeletons from specimens scanned using highresolution computed tomography (CT).…”

“…Xantusia differs from pleurodontans in having a fused spleniodentary (Mead and Bell 2001). Teiids differ in having a tall and open Meckelian groove and substantial cementum deposits at the tooth bases (Estes et al 1988;Scarpetta 2020). In gymnophthalmoids, the Meckelian groove is not bounded by suprameckelian and inframeckelian lips or is completely fused to almost the level of the posterior-most tooth position (Bell et al 2003).…”

“…Morphotype A: Dentaries of Morphotype A share with Pleurodonta and some teiids pleurodont teeth and an inframeckelian lip that curls dorsolingually, producing a medial exposure of the Meckelian groove along the mid-length of the dentary (Gauthier et al 2012;Bochaton et al 2017). Fossil dentaries differ from teiids in lacking a broad subdental shelf (Estes et al 1988), lacking asymmetric bicuspid teeth, and lacking large amounts of cementum deposits at base of teeth (Estes et al 1988;Nydam et al 2007;Scarpetta 2020). Fossils are assigned to Pleurodonta.…”

Morphometric analyses of the vertebrae of Ambystoma (Tschudi, 1838) and the implications for identification of fossil salamanders

“…Fossil identifications are the foundation upon which paleoecological analyses are based and often play an important role in evolutionary analyses. As examples, fossil identifications can have substantial impacts on evolutionary and ecological inferences because they can directly affect investigations relating morphological evolution to past environmental changes (e.g., Moroz et al, 2021), investigations on the mechanisms and timing of lineage diversification through time (e.g., Scarpetta, 2020), and investigations on ecosystem changes over time (e.g., Smith et al, 2016). Therefore, the methods by which we identify fossils require detailed study and attention to recognize limits in our abilities to identify fossil material (Bell et al, 2010).…”

A Palaeogene stem crotaphytid ( Aciprion formosum ) and the phylogenetic affinities of early fossil pleurodontan iguanians

“…some phrynosomatids, crotaphytids, corytophanids and liolaemids) and in some sphenomorphine skinks, but to my knowledge does not occur in other squamates. Anterior restriction of the Meckelian groove by dorsoventral expansion of the suprameckelian lip occurs in some teiids [ 111 ]. A.9.…”