THE PLIO-PLEISTOCENE VERTEBRATE FAUNA OF COOKIECUTTER CREEK (SARASOTA COUNTY, FLORIDA), INCLUDING TWO NEW CHONDRICHTHYAN TAXA FOR THE FLORIDA FOSSIL RECORD

In October 2016, a run-of-the-mill email inquiring about the geologic age of a creek in South Florida led to the serendipitous ‘discovery’ of Isistius cf. I. triangulus and Squatina subserrata. Up to that point, no specimens of Isistius or Squatina from Florida were present in the vertebrate paleontology collections at the Florida Museum of Natural History. However, a call out to the public 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 the collector and co-author of this manuscript, Ken 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 cf. I. triangulus and four teeth belonging to Squatina subserrata. 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 they are sourced from the underlying Pliocene Tamiami Formation. The unprecedented occurrence of Isistius cf. I. triangulus, with such a high density in Cookiecutter Creek relative to other sites in Florida, may indicate that Cookiecutter Creek captures 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. Although, the temporal accumulation reflected in these gravel deposits inhibits a more accurate reconstruction of these sea-level fluctuations.