Abstract
The submerged continental shelf near Venice, Sarasota County, Florida, USA, exposes clays and hard-bottom limestones of the Peace River and Tamiami formations (Late Miocene-Early Pliocene). These formations occur in <= 12 m of seawater, within 4.5 km of the modern-day shoreline, because of wave-and current-driven deposition and erosion during glacioeustactic sea-level cyclicity, shifting of the ancestral shoreline, fluvial incision, and storm activity across the shallow shelf since the Miocene. These processes have accumulated residual, fossiliferous lag deposits on the modern seafloor that contain an abundance of elasmobranch remains (primarily isolated teeth of sharks and rays) belonging to at least 45 taxa including: Squalus sp., Isistius triangulus, Heterodontus sp., Ginglymostoma cirratum, Carcharias taurus, Otodus megalodon, Parotodus benedinii, Isurus oxyrinchus, Carcharodon carcharias, C. hastalis, Scyliorhinus sp., Mustelus sp., Galeorhinus sp., Hemipristis serra, Galeocerdo aduncus, G. mayumbensis, G. cuvier, Physogaleus contortus, Rhizoprionodon sp., Negaprion brevirostris, Carcharhinus cf. C. falciformes, C. leucas, C. obscurus, C. plumbeus, C. cf. C. altimus, C. perezii, C. cf. C. brachyurus, C. cf. C. porosus, Carcharhinus limbatus, Carcharhinus brevipinna, Sphyrna cf. S. zygaena, S. cf. S. tiburo, Rhynchobatus sp., Rhinobatidae gen. indet., Pristis cf. P. pristis, Anoxypristis sp., Rajidae gen. indet., Hypanus cf. H. say, Hypanus cf. H. americanus, Rhinoptera cf. R. bonasus, Mobula cf. M. hypostoma, Mobula cf. M. birostris, Aetomylaeus sp., Myliobatis sp., and Aetobatus cf. A. narinari. These elasmobranch remains were collected exclusively by SCUBA diving off the coast of Venice, Florida and provide a unique means to observe taphonomic processes influencing vertebrate fossils on the shallow continental shelf. This represents the most diverse fossil elasmobranch assemblage reported from the state of Florida and is also one of the most diverse assemblages in the late Cenozoic fossil record in the USA. Comparison of the submerged Venice shelf elasmobranchs with those from land-based exposures in Florida and elsewhere along the Atlantic and Gulf Coastal Plains of the USA also indicates that fossils and submerged formations become geologically younger to the south. Moreover, the Venice taxa provide a unique means to assess the stratigraphic distribution of many well-known and globally occurring elasmobranchs, including large lamniforms and the megatoothed shark, Otodus megalodon, as related to habitat shifts along the west coast of Florida since the late Cenozoic.