178-13 A new chondrichthyan fossil assemblage from the middle Campanian Cliff House Sandstone at Tsaya Canyon, New Mexico

Session: Paleontology, Diversity, Extinction, Origination

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Abstract:

The middle Campanian Cliff House Sandstone is exposed in the structural San Juan Basin of New Mexico and southwestern Colorado. It represents the transgressive phase of a regressive–transgressive wedge formed during the Campanian along the western margin of the Western Interior Seaway in North America. Despite preserving a rich assemblage of marine fauna that includes invertebrates, chondrichthyans, actinopterygians, tetrapods, and abundant trace fossils, it lacks a thorough formal description of key faunal components. Recent fieldwork and sediment sampling conducted from Tsaya Canyon in the San Juan Basin of New Mexico has revealed a diverse chondrichthyan fauna that expands upon the currently acknowledged neoselachians from the Cliff House Sandstone. The preliminary list of recovered genera from Tsaya Canyon includes the following, based off isolated teeth: Archaeolamna, Cantioscyllium, Carcharias, Cederstroemia, Ischyrhiza, Pseudohypolophus, Scapanorhynchus, Squalicorax, and Squatina. No holocephalan specimens have been recovered at the site thus far.

By far the most predominant chondrichthyan recovered at Tsaya Canyon is a small carchariid attributed to Carcharias cf. C. holmdelensis. While similar in dentition to Carcharias holmdelensis, the Tsaya Canyon Carcharias differ from the type locality specimens in that some anterior teeth possess two pairs of lateral cusplets, as opposed to one. This suggests that it is a plesiomorphic trait within Carcharias holmdelensis to possess two pairs of lateral cusplets on all tooth positions, which is retained in lateral position teeth but reduced to a single pair in later Campanian and Maastrichtian Carcharias holmdelenis anterior teeth. The second most abundant chondrichthyan recovered from Tsaya Canyon is the large mitsukurinid Scapanorhynchus texanus. Although differing in size and likely trophic level, Carcharias cf. C. holmdelensis and Scapanorhynchus texanus both possess tearing type dentitions, which could indicate similar dietary proclivities and niche partitioning by body size for the two most abundant chondrichthyans found at Tsaya Canyon. These findings refine our understanding of paleoenvironmental dynamics and marine ecosystems during the Menefee Formation−Cliff House Sandstone transition and shed light on this poorly understood marine interval.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-11258

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