AMHERST, Mass. - A series of fossils unearthed in China by a University of Massachusetts paleontologist has revealed evidence that now-extinct mammals which lived roughly 55 million years ago grew hair. The discovery, by biology professor Jin Meng, is detailed in a report in the Feb. 20 issue of Nature, and is significant because it helps scientists to better pinpoint the evolution of mammals. This is Meng’s third article in the prestigious scientific journal.
Meng is a new faculty member at the University. Before joining the University, he was associated with a number of institutions including the Smithsonian Institution in Washington, D.C., and the American Museum of Natural History in New York City.
The fossils were found in the Gobi Desert of Inner Mongolia, China. Meng’s discovery helps scientists determine when mammals began growing hair. Hair is commonly regarded as a feature unique to mammals, and is believed to be an evolutionary development which keeps animals warm. Meng’s find suggests that hair may have appeared as long ago as 210 million years, during the late Triassic and early Jurassic era.
Meng’s fossils are unusual: they are the fossils of bird pellets - food materials regurgitated by birds feeding their young - and fossilized organic waste, which scientists call coprolites. The hair is so well preserved in these structures that its microscopic scale pattern is visible when it is magnified under a scanning electron microscope. Some of the hair measures just 40 to 80 microns in diameter. (A micron is a unit of length equal to one millionth of a meter.)
Fossils showing impressions and casts of hair are extremely unusual, because animal hair is a "soft" tissue that disintegrates quickly - usually before it can be preserved. Meng believes that the area from which the fossils were discovered was a quiet pond or lake area, with very little wave or wind motion, allowing the samples to become fossilized as they were covered by sediments.
The fossils reveal not just hair, but also skeletal bits of four species of tiny "micromammals" which are long since extinct: a hoofed animal that may have originated in South America, as well as two types of rodent-like animals and a multituberculate (the scientific term for an animal whose teeth has many ridges). Cemented within the pellets and coprolites are portions of skulls, teeth, and even limbs, which enable Meng to identify associated hair to species.
"The multituberculates are interesting as an extinct group because their relationship to living mammals is unclear," said Meng. "They could be related either to the platypus (monotremes) or to therians - a group which includes human beings."
Hair from the multituberculates that Meng found is the first evidence that this anatomic feature existed in the third mammal group, besides monotremes and therians.
The samples also reveal ecological activities: some of the coprolites show grooves and holes, which Meng says are the results of beetles feeding on the materials before they were fossilized, an uncommon finding in fossils. There is also minute fossilization of bacteria - some just one micron across.