Biochemistry and adaptive colouration of an exceptionally preserved juvenile fossil sea turtle

Abstract

The holotype (MHM-K2) of the Eocene cheloniine Tasbacka danica is arguably one of the best preserved juvenile fossil sea turtles on record. Notwithstanding compactional flattening, the specimen is virtually intact, comprising a fully articulated skeleton exposed in dorsal view. MHM-K2 also preserves, with great fidelity, soft tissue traces visible as a sharply delineated carbon film around the bones and marginal scutes along the edge of the carapace. Here we show that the extraordinary preservation of the type of T. danica goes beyond gross morphology to include ultrastructural details and labile molecular components of the once-living animal. Haemoglobin-derived compounds, eumelanic pigments and proteinaceous materials retaining the immunological characteristics of sauropsid-specific β-keratin and tropomyosin were detected in tissues containing remnant melanosomes and decayed keratin plates. The preserved organics represent condensed remains of the cornified epidermis and, likely also, deeper anatomical features, and provide direct chemical evidence that adaptive melanism – a biological means used by extant sea turtle hatchlings to elevate metabolic and growth rates – had evolved 54 million years ago.

Paleoproteomics of Mesozoic Dinosaurs and Other Mesozoic Fossils

“…Recent data suggest that other modes of preservation may also yield molecular data (e.g., refs. []); thus, specimens should be evaluated on a “case‐by‐case” basis.…”

“…However, unlike true impressions, these fossils are often histologically distinct from surrounding sediments, and instead retain distinct tissue microstructure (e.g., Figure , refs. []). In particular, fossilized feathers, when not preserved in amber (e.g., ref.…”

“…Marine environments (e.g., refs. []) have also produced fossils from which original molecules have been reported.…”

“…[] and references therein), and, more recently, transmission electron microscopy (TEM, e.g., refs. []) and atomic force microscopy (AFM, refs. []).…”

The molecular evolution of feathers with direct evidence from fossils

“…S5 and S6 and Table S4). However, it differentiates β-keratin-containing tissues from those composed of α-keratins or other proteins (27,28). Both immunofluorescence (IF) and immunogold (IG) labeling revealed the presence of specific epitopes consistent with β-keratins in Anchiornis feathers ( Fig.…”