Although the word “fossil” brings bones to mind, it can also refer to other types of preserved remains. Now, UT researchers know why other body features, such as hair, are so rarely preserved or fossilized.

A new study by researchers at the Jackson School of Geosciences found that fossilized hair is five times rarer than feathers. The findings were published in Proceedings of the Royal Society B on Sept. 6. 

UT geosciences professor Julia Clarke said the motivation behind this study came while she was writing a review on the evolution of feathers and was astonished by the absence of records from the early Mesozoic era, prompting her lab to start exploring this pattern. 

“Body coverings help organisms to hide, attract mates, stay warm and even fly,” said Chad Eliason, a researcher at the Field Museum of Natural History in Chicago, Illinois, who conducted the research while a postdoctoral fellow at UT. “Since they are the direct link between an organism and its environment, studying body coverings in the fossil record can tell us about what ancient environments were like.”

Eliason and Clarke created the largest known database on fossilized body coverings from land-dwelling vertebrates collected from lagerstatte, or fossil beds that preserve soft tissues such as hair and feathers, according to a press release. 

“We propose two possible factors, among others, as to why there are so few records of fossilized hair,” Clarke said. “The different form of keratin has a lower probability of preservation and … single hairs may not be as easily recognized.”

Keratin is a fibrous structural protein found in hair and nails. The researchers found that the lower incidence of fossilized hair may be due to differences in keratin composition which can impact the possibility of fossilization, according to the researchers. 

“Hair is made of alpha-keratin, while lizard scales and bird feathers are made of beta-keratin,” Clarke said. 

However, the researchers raised the question of whether this finding was because of physical differences, such as keratin structure, that make it difficult for hair to fossilize, or if it was an issue with collection techniques among scientists.

The researchers also used gap analysis, a technique that models the probability of finding a fossil in a particular time, to discover that hair evolved far earlier than current fossil records indicate, while feathers evolved very close chronologically to early fossils, according to a press release. 

“As we gather more data points about when and where fossilized hairs and feathers are found, we hope to make better predictions about where we can find more,” Eliason said.