158 Paleontology: Taphonomy, Paleoecology, and Diversity Dynamics (Posters)

Tuesday, 6 November 2012
9:00 AM - 6:00 PM
Hall B

POSTMORTEM MINERALOGY OF GLADII OF THE CONIACIAN-CAMPANIAN (LATE CRETACEOUS) "SQUID" TUSOTEUTHIS LONGA (CEPHALOPODA: COLEOIDEA), NORTH AMERICA: A KEY TO THEIR ORIGINAL COMPOSITION

Paper number: 158-5
Program: Technical Sessions
Time: 9:00 AM – 6:00 PM

Authors

Abstract

Extant squids and vampyromorphs (Cephalopoda: Coleoidea) have a non-biomineralized chitinous internal shell or gladius. Fossil gladii, known since Late Permian, are preserved as mineralized structures. Jurassic and Cretaceous gladii are commonly phosphatized which lead to the hypothesis that gladii of fossil “squids” are biomineralized. However, the micro-lamination and fibrous ultrastructure of laminas in gladii of Jurassic Trachyteuthis, Loligosepia and Teudopsis, from Germany, indicate a chitinous or aragonite/chitin composition. Evidence of diagenetic substitution of chitin by calcium phosphate in these fossil gladii is the absence of crystal-shaped units and presence of micro-globular ultrastructure with about 1 µm (microbial-sized) globules. The latter suggests the role of phosphorus accumulating bacteria during fossilization of gladii. In anoxic paleoenvironments, chitinous gladii served as a template for phosphorus accumulating bacteria which allowed for preservation of gladii as phosphatized pseudomorphs.

The present study is focused on determining the postmortem mineralogy and original composition of Tusoteuthis longa gladii from different paleoenvironments of the Late Cretaceous of North America. Thus far, the mineral composition of eleven (of 36 available) gladii have been analyzed using X-ray defractometry (XRD). All analyzed specimens from the calcareous units, (Smoky Hill Chalk and the Carlile Formation) and three specimens from non-calcareous units (Millwood and Pembina Members of the Pierre Formation) are apatitic. Poorly preserved gladii from the Gammon Ferruginous and Pembina Members of the Pierre Formation are gypsum that shows presence of sulfur instead of phosphorus. One gladius from the Smoky Hill Chalk shows some barite indicating sulfur, as well as, apatite indicating phosphorus. These analyses suggest the possibility that the gladii of Tusoteuthis longa may have been partially mineralized in life. Alternatively, they could have been preserved as pseudomorphs due to metabolism of phospho-accumulating bacteria very early in the diagenetic process. Further analyses of more specimens, by FTIR, electron microprobe and Scanning Electron Microscopy from Kansas, North Dakota, Manitoba and Wyoming may clarify this issue.