19 The Campanian Crucible: A synthesis of vertebrate paleobiogeography and ecosystem dynamics in Laramidia

Laramidia’s Campanian deposits reveal vertebrate diversification, geographic isolation, and provincialism, and its fossil record informs paleoecology and biogeography. This session synthesizes research on evolution, endemism, WIS dynamics, and underexplored geochronology across this Late Cretaceous landscape.

Tuesday, 19 May 2026
8:00 AM - 12:00 PM
Alvarado C

A New Well-preserved Shell of the Baenid Turtle Scabremys from the Menefee Formation of New Mexico

Paper number: 19-8
Program: Technical Sessions
Time: 10:20 AM – 10:40 AM

Authors

Abstract

The baenid turtle Scabremys ornata is known exclusively from a few shells from Upper Cretaceous deposits in the San Juan Basin of New Mexico. Three specimens have been reported from the De-na-zin and Hunter Wash Members of the Kirtland Formation, but of these, only the holotype has been figured and described. A partial fourth shell was recently documented by our team from the Allison Member of the Menefee Formation, and we describe here a nearly complete fifth specimen, also from the Allison Member. Originally referred as Baena ornata by Gilmore, the taxon was later placed within Denazinemys, a more widespread southern Laramidian baenid genus that was coeval in the San Juan Basin and shared a similar nodose, pustulate shell ornamentation. Both genera have their oldest occurrences in the Menefee Formation where they co-occur. Scabremys was later placed in its own genus and differentiated from Denazinemys nodosa by shell shape, anterior shell scalation (i.e., lack of prepleural and gular scales), and morphology and extent of shell texture. The distinctive textures of these taxa aid in identifications based on fragmentary material, and Scabremys differs in this regard from Denazinemys by more elongate pustules that are mostly arranged in rows and constrained to the midline. The two taxa were also differentiated by a limited phylogenetic analysis that included several other Late Cretaceous baenids. Despite the apparent rarity of Scabremys, co-ossification and infilling have facilitated the preservation of relatively complete shell material. However, taphonomic damage and its characteristic shell topology have confounded documentation of some aspects of its morphology, particularly in patterns of scale and bone arrangements. Description and high resolution visualization of additional material improves our understanding of the Menefee specimens in particular and allows comparison with Kirtland material, which is approximately 3 million years younger. Descriptions of the two undescribed Kirtland shells will be undertaken in the future, and this increase in sample size will potentially be informative regarding intraspecific variation and habitat preferences. A more thorough morphological coding of Scabremys also permits a more extensive phylogenetic analysis including the numerous baenid species that have been erected in the 15 years since the genus was defined and may result in a better understanding of baenid evolution in the Campanian.

Geological Society of America Abstracts with Programs. Vol. 58, No. 4

doi: 10.1130/abs/2026RM-410584

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