The first documented fossil records of Isistius and Squatina (Chondrichthyes) from Florida, with an overview of the associated vertebrate fauna

Abstract

In October 2016, an email inquiring about the geologic age of a creek in Sarasota County led to the serendipitous ‘discovery’ of fossil teeth of the sharks Isistius triangulus and Squatina sp. in Florida. Up to that point, no fossils of Isistius or Squatina from Florida were present in the vertebrate paleontology collections at the Florida Museum of Natural History, nor had they been listed in any scientific publication. However, public inquiries revealed that the presence of both genera in the Florida fossil record has been known among the amateur paleontology community for well over a decade. Once co-author Marks was made aware that the Isistius teeth represented something novel, more rigorous collecting was conducted to procure more specimens. A total of 94.5 kg of matrix from four gravel deposits within the creek, informally known as Cookiecutter Creek, were screenwashed and picked to produce 186 whole or partial lower teeth of Isistius triangulus and four teeth belonging to Squatina. In addition, a diverse vertebrate fauna was recovered that ranged from Pliocene to Pleistocene in age. Screenwashing of 7.5 kg of matrix from the in situ Pleistocene Caloosahatchee Formation revealed no specimens of Isistius or Squatina, which implies their actual source is the underlying Pliocene Tamiami Formation. The unprecedented occurrence of Isistius triangulus, with such a high density in Cookiecutter Creek relative to other sites in Florida, may indicate that Cookiecutter Creek preserves a unique deep-water facies within the Tamiami Formation. The associated vertebrate fauna includes taxa from marine, brackish, freshwater, and fully terrestrial paleoenvironments; providing evidence of local sea-level fluctuations during the Pliocene to Pleistocene. The temporally mixed accumulation in these gravel deposits inhibits a more accurate reconstruction of these sea-level fluctuations.