Original dinosaur claw sheath proteins preserved for 75 million years
New research from North Carolina State University shows that a 75-million-year-old Mongolian oviraptor, preserved while brooding its eggs, also preserved the original keratinous claw sheath that covered its digits. The work adds to the body of evidence that original organic materials can preserve over time.
|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 [Credit: Alison Moyer et al]
During preparation of the specimen, the scientists noticed that there was a thin lens of white material extending beyond one of the bony claws on a forelimb that differed in texture and color from both the sediment and the bone. It was also located where a claw sheath would be.
In modern birds, claw sheaths cover the claw at the end of a digit much like fingernails in humans and serve a number of functions - aiding them in defense, movement, or catching and holding prey. The sheaths in modern birds are composed of two types of keratin: alpha-keratin, the softer form found on the interior of the sheath; and beta-keratin, a harder and more durable keratin that comprises the sheath's exterior.
|Higher magnification of the dinosaur claw sheath reveals a fibrous texture |
[Credit: Alison Moyer et al]
Moyer and her NC State colleagues first used scanning and transmission electron microscopy to get microscopic details of both the tissue's surface and its internal structure. The results showed that the sample was structurally similar to claw sheaths from modern birds, so the team decided to proceed with immunohistochemical (IHC) testing.
IHC testing utilizes antibodies that react against a particular protein. If the protein is present, the antibodies bind to small regions of the protein and indicate where the protein is located in the tissue. Moyer used beta-keratin antibodies derived from modern bird feathers. In initial IHC testing, results were inconclusive, which led Moyer to look more closely at the specimen. She found an unusually high concentration of calcium in the fossil claw - much higher than would be found in claws from the living birds used in comparison or from the sediment surrounding the fossil. Theorizing that the calcium might be affecting results, Moyer removed the calcium and did further IHC testing on the claw sheath material.
|An entire emu claw sheath, used for comparison, with boxed region showing approximate |
location sampled for comparative SEM analysis [Credit: Alison Moyer et al]
"It's probable the incorporation of calcium in the tissue helped preserve it," says Moyer, "but that same calcium had to be removed in order to see the underlying molecular composition. Because this study used multiple, well-tested methods, it not only supports the longevity of proteins in the rock record, it reveals a lot about how these might be preserved."
The research appears in Proceedings of the Royal Society B.
Source: North Carolina State University [November 08, 2016]