Microcoprolite morphotypes from the Revueltian (Upper Triassic: Norian) age Homestead Site, Garita Creek Formation, east-central New Mexico, USA

The Homestead Site at Garita Creek is an Upper Triassic locality within the Garita Creek Formation of east-central New Mexico of Revueltian (Norian) age. In addition to abundant bones, scales, and teeth, thousands of coprolites make up a significant portion of the rich collection. Like the bones themselves, coprolites provide insight into the disparity of the assemblage, as coprolite morphologies are important indicators of paleoecological relationships. We examined a subset of 600 microcoprolites from the Homestead Site, finding that 316 (53%) preserve fossil inclusions, often ganoid scales, in either external (73%) or cross-sectional (27%) view, 22 (4%) bear abiotic inclusions, and 262 (44%) bear no visible inclusions. Most inclusions are visible externally, indicating that most coprolites do not require ‘digital dissection’ to determine whether inclusions are present. We identify four coprolite morphotypes: striated, cylindrical, spiral, and scroll, and those deemed nondiagnostic (too fragmentary and/or featureless). Of the 316 fossil-bearing coprolites, 22 (7%) are striated, 133 (42%) are cylindrical, 139 (44%) are spiral, 2 (1%) are scroll, and 20 (6%) are nondiagnostic. There is a well-defined ichnotaxonomy associated with Triassic coprolites. Striated coprolites align with the concept of Alococopros, and are interpreted to represent diapsid or temnospondyl perpetrators. Spiral coprolites align with the concept of Heteropolacopros and Saurocopros, and scroll coprolites align with the concept of Tikicopros, all of which are thought to represent spiral-valved chondrichthyan and/or sarcopterygian perpetrators. Within the context of the Homestead Site, coelacanths and lungfish are the only known taxa to have reached sufficient size to perpetrate the spiral coprolites. Cylindrical coprolites align with the concept of Eucoprus and within the context of the Homestead Site were likely perpetrated by actinopterygians. Our survey supports the hypothesis of the Homestead Site representing a diverse assemblage of fish and tetrapods interacting in a complex aquatic ecosystem