OCCURRENCE AND PRESERVATION OF RARE CEPHALOPODS FROM FLORIDA'S RICH CENOZOIC DEPOSITS

Recent collecting in Florida has yielded new stratigraphic occurrences and preservation modes of the nautiloid Aturia, a genus seldom recovered from Cenozoic deposits of the state. Many of these new finds have yet to be described or illustrated and to date only two fossil species are suggested from peer-reviewed literature. Aturia alabamensis occurs in the upper Eocene Ocala Limestone and upper Eocene-lower Oligocene Bumpnose Limestone while the lower Miocene Chipola Formation contains Aturia sp. cf. A. curvilineata. To these we add Aturia from the lower Oligocene Suwannee Limestone, lower Miocene Parachula Formation, and middle Miocene Shoal River Formation. Furthermore, statoliths of the teuthoid coleoid, Loligo mississippiensis, have been reported from the Chipola Formation while we report the first guard-like sheaths of a spirulid coleoid from this deposit.

Preservation of Florida’s fossil nautiloids varies greatly throughout the Cenozoic. The most common mode of preservation is as internal and external molds of the phragmacone and sometimes the siphuncle. In rare instances, preservation as whole body fossils with much of the original aragonitic shell structure intact or as siliceous pseudomorphs is found. In the Ocala Limestone, specimens are mostly internal molds of the posterior chambers and siphuncle tubes. In some instances the external mold is preserved and can be cast using silicone rubber. Fossils from the Bumpnose Limestone and Parachucla Formation are similarly preserved, being complete to fragmentary molds of the phragmacone. Recently discovered Aturia from the Suwannee Limestone are preserved as whole-body, silicified pseudomorphs surrounded by radio-concentric growths of a clearly colonial organism (hydrozoans?). Aturia from the Chipola and Shoal River formations, are preserved as partial to complete phragmacones of the original unaltered shell. Also, in the Chipola Formation, the guard-like sheaths and statoliths of coleoid cephalopods are preserved in similar fashion.

The new occurrences may help to determine not only a more accurate diversity of Cenozoic cephalopods in Florida but provide a better understanding of the taphonomic processes that allow for their diverse modes of preservation.