A famous fossil – an oviraptorid dinosaur that died brooding its unhatched eggs – still has 75 million-year-old proteins present in the sheath of its claw.

The fossil sheath was compared with a claw sheath from ostriches and emus and the researchers found that the microstructure of the sheath had similar features to the birds, even after 75 million years. The findings are published in the Proceedings of the Royal Society B.

Structural similarities

The team used antibodies as biological markers that bind to keratin, a protein found in the sheath, as well as in human hair and nails. They found that the chemical as well as the physical features of the claw sheath were very similar to that of present-day birds.

The structure extending from the claw was first spotted in 1995 when the fossil was being prepped for the original publication of the discovery of the dinosaur in the journal Nature. Study author Alison Moyer, a former PhD student at North Carolina State University in the US, who is now a postdoctoral researcher at Drexel University in Philadelphia and lead author of a paper, told IBTimes UK that identification of this structure as a claw sheath 20 years later was unexpected.

"It does come as a surprise because it could well have been something else – a mineral lens, for example. But it was pretty remarkable when studying it just how similar [it was] to [a] modern claw," she says.

Dinosaur claw sheath
A lower magnification image of the claw sheath, clearly differentiated from surrounding sediment by colour and texture. The sand is red and granular and the sheath is white, dense and cohesive. Alison Moyer et al

Calcium preservation

Exactly how the keratin sheath has survived for so long is not clear, Moyer says. "We're not exactly sure of the mechanisms of how it's being preserved but betakeratin is a protein, its molecular composition as well as its structure is very tough," she says. "Keratin is in scales, feathers, beaks claws – they're tough structures because they're interacting with the animal's environment."

Dinosaur claw sheath
Higher magnification of the dinosaur claw sheath reveals a fibrous texture Alison Moyer et al

Keratin – unlike proteins such as collagen – is not associated with bone and so does not get protection from a mineral complex, Moyer says. However, she did observe high levels of calcium in the protein sheath. This calcium may have a role in the preservation process. Without further analysis, it's not possible to say whether the calcium is from the bone underlying the sheath or from the environment, she says.

Emu claw sheath
An entire emu claw sheath, used for comparison, with boxed region showing approximate location sampled for comparative SEM analysis Alison Moyer et al

The fossil was discovered in the Djadokhta Formation of Mongolia in 1995. The dinosaur's forelimbs encompass the eggs, with the hindlimbs tucked underneath it. The dinosaur and its eggs are encased in sandstone, which suggests that a fatal sandslide quickly covered the dinosaur and its brood. The dinosaur was about the size of an emu and lived in what is now Mongolia during the Cretaceous period.