A PALEOECOLOGICAL SURVEY OF VERTEBRATE PREDATORS IN THE LATE TRIASSIC USING MICROFOSSIL DIVERSITY

Late Triassic paleoecology and predation patterns remain poorly understood, primarily owing to the differential preservation potential of many vertebrate predators and their shelly prey in shallow marine environments. Microfossils of marine predators, such as teeth or dermal denticles, in shallow marine environments can indicate presence, and potentially abundance, of predator taxa. Here we present preliminary data on predator diversity and paleoecology from Early Norian marine sediments of western Nevada, USA.

Bulk samples of carbonate rock were collected from the Carbonate member of the upper Luning Formation in western Nevada, representing similar shallow-subtidal carbonate marine facies. Bulk rocks samples were disaggregated using a buffered acetic acid solution to preserve microfossils. The undissolved residue was sieved and dyed with a KOH and Alizarin Red S. Extracted teeth were identified using a morphological character matrix which was developed for Early Mesozoic vertebrate predators based on published literature. Characters used in identification include root presence, flattened to conical shape, tip angle, presence of special features such as dental palates, striations, or serrations.

Bulk sample residues contained an abundance of teeth, denticles, and fish scales. Most of the teeth present are from generalist predators, presenting as blunt cone-shaped teeth. Some specialized teeth are present, of both crushing and shearing variety. This diverse assemblage suggests that the Late Triassic shallow marine environment contained an array of fish and small sharks. Further, by observing the specialization of dentition, we can assess the relationship between shelly benthic invertebrates and benthic or demersal predators, potentially linking paleoecological changes in the former to adaptive radiations in the latter.