Using light to describe the ancient world

Chitin, a nearly fantastical, yet completely biogenic compound, has recently been reported from a Late Eocene cuttlefish. The discovery reported by Weaver and colleagues extends the preservation age of intact chitin from 25 million to 36 million years. Image from Wikimedia.

Chitin is a natural compound with fantastical properties. Pure chitin is see-through, bendy, strong, and chemically adaptable. Plasticky and leathery pure chitin can be easily modified: adding calcium carbonate can produce armour plating and food shredding surfaces. The dynamic properties of chitin have made it a target for research, and the natural compound is now weaved into much of civilisation. New medical applications for chitin have recently been developed that might see substantial improvements for patients recovering from ear, nose and throat surgeries. All considered, chitin is natural Clarkian magic, which is perhaps surprising for a compound that has probably existed on Earth for more than 540 million years.

Chitin is an organic compound that does not preserve well in the fossil record. Recognisable arthropods are known from the Cambrian Explosion but their chitinous composition is only assumed. A discovery reported in 1997 placed the oldest tangible evidence for fossil chitin at 25 million years. In early 2011 George Cody and colleagues extended the age of fossil chitin to 417 million years on the basis of protein remnants. Very recently, however, Patricia Weaver and colleagues reported the discovery of intact fossil chitin dated to 36 million years, extending the preservation age of chitin into the Late Eocene. Evidence for the chitin was provided in part by vibrational spectroscopy.

Weaver and colleagues analysed a cuttlebone from a fossil cuttlefish (Mississaepia mississippiensis), which, as the name subtly hints at, was collected in the state of Mississippi, USA. Using Fourier Transform infrared spectroscopy, the authors observed “…[p]eaks at 1649 cm-1… and 1544 cm-1 in cuttlefish, squid and fossil spectra indicat[ing] organics consistent with β-chitin…”. These bands are attributed to carbonyl (C=O), amide (N-H) and other functional groups typical of protein. “…Closer examination of the region ca. 600–1400 cm-1…shows the principle change in M. mississippiensis is the loss of peaks in Amide III region. Amide I and II peaks may arise from chitin, but also from proteins, humics or other chemicals. It is parsimonious to assume the presence of chitin-like molecules rather than an admixture of substances displaying a similar spectrum…” The exceptional preservation of chitin in M. mississippiensis has been attributed to an originally anoxic, clay-rich depositional environment – ideal conditions for establishing physical and geochemical resistance from microbial, chemical and physical degradation. Apart from the exciting discovery of a complex, biogenic compound with almost 40 million years of antiquity, the preservation of organic molecules opens up new avenues of phylogenetic research. “Future work will focus on comparisons with other Eocene cuttlefish and the phylogenetic implications of chitinous structures with regards to the origin cuttlefish…”

Weaver PG, Doguzhaeva LA,Lawver DR, Tacker RC, Ciampaglio CN, Crate JM, Zheng W. (2011) Characterization of Organics Consistent with b-Chitin Preserved in the Late Eocene Cuttlefish Mississaepia mississippiensis. PLoS ONE 6: e28195. doi:10.1371/journal.pone.0028195

Image from Wikimedia.


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