Characterization of Organics Consistent with β-Chitin Preserved in the Late Eocene Cuttlefish Mississaepia mississippiensis

Abstract

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 unique late Eocene coleoid cephalopod Mississaepia from Mississippi, USA: New data on cuttlebone morphology, ultrastructure, chemical composition, and their phylogenetic implications

“…Inorganic−organic composition of the cuttlebone of Missi− ssaepia, revealed here by light microscope, and SEM and EDS analyses was recently confirmed by discovery of the degraded organics consistent with b−chitin in the cuttlebones of this taxon by molecular techniques (Weaver et al 2011). Chitin composition of septa of Mississaepia, revealed here by light microscope was not analyzed by molecular techniques due to the limited number of preserved septa, there was not enough de−mineralized material for analysis.…”

“…Nevertheless, chitin composition of septa is generally supported by data on b−chitin consistent organics in Missi− ssaepia (Weaver et al 2011). Further search for more Eocene cuttlebones and their study with a focus on the phragmocone structure and septal composition will possibly reveal so far unknown taxa with chitinous septa.…”

“…3A, B). Similarly located organic laminas are present in the dorsal shield of Sepia (Weaver et al 2011: fig. 3C).…”

“…Phosphorus was recorded from the sheet−like structures in between aragonite spherulites in the dorsal shield of Mississaepia (Fig. 11B, Table 3; Weaver et al 2011: fig. 3A, B).…”

“…A bimineralic, aragonite/calcite, composition of the cuttlebone was recently suggested for Anomalosaepia (Yancey and Garvie 2011). Preservation of organics consis− tent with b−chitin within the cuttlebone of Mississaepia has recently been reported by Weaver et al (2011).…”