BackgroundPreservation of original organic components in fossils across geological time is controversial, but the potential such molecules have for elucidating evolutionary processes and phylogenetic relationships is invaluable. Chitin is one such molecule. Ancient chitin has been recovered from both terrestrial and marine arthropods, but prior to this study had not been recovered from fossil marine mollusks.Methodology/Principal FindingsOrganics consistent with β-chitin are recovered in cuttlebones of Mississaepia mississippiensis from the Late Eocene (34.36 million years ago) marine clays of Hinds County, Mississippi, USA. These organics were determined and characterized through comparisons with extant taxa using Scanning Electron Microscopy/Energy Dispersive Spectrometry (SEM/EDS), Field Emission Scanning Electron Microscopy (Hyperprobe), Fourier Transmission Infrared Spectroscopy (FTIR) and Immunohistochemistry (IHC).Conclusions/SignificanceOur study presents the first evidence for organics consistent with chitin from an ancient marine mollusk and discusses how these organics have been degraded over time. As mechanisms for their preservation, we propose that the inorganic/organic lamination of the cuttlebone, combined with a suboxic depositional environment with available free Fe2+ ions, inhibited microbial or enzymatic degradation.

A new family, Mississaepiidae, from the Sepia-Spirula branch of decabrachian coleoids (Cephalopoda), is erected on the basis of the following, recently revealed, morphological, ultrastructural and chemical traits of the cuttlebone in the late

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A new genus Mississaepia and one new species Mississaepia mississippiensis is described based on two specimens of guard-like sheaths from the Bartonian (Eocene) Moodys Branch Formation, Town Creek, Jackson, Hinds County, Mississippi and twenty-nine specimens from the Priabonian (Eocene) Yazoo Clay, Miss Lite Clay Pit, Cynthia, Hinds County, Mississippi. Mississaepia mississippiensis n. gen. differs from Belosaepia Voltz, in having a reduced more blunt spine, having a thin ventro-lateral wall which tapers anteriorly and lacking a pronounced ventral plate. The new genus also differs from Belemnosella Naef known from the Moodys Branch Formation, Gosport Sand and Cook Mountain Formation in having a curved phragmocone. Due to its curved phragmocone and other belosaepiid-like morphological features, Mississaepia mississippiensis n. gen. is tentatively assigned to the family Belosaepiidae.

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