The fossil of an ancient mammalian relative, Megaconus mammaliaformis, reveals the evolutionary adaptations of a 165-million-year-old proto-mammal, providing evidence traits such as hair and fur originated well before the rise of the first true mammals, the researchers said.
"We finally have a glimpse of what may be the ancestral condition of all mammals, by looking at what is preserved in Megaconus," Zhe-Xi Luo, a professor of biology and anatomy, said. "It allows us to piece together poorly understood details of the critical transition of modern mammals from pre-mammalian ancestors."
Discovered in Inner Mongolia, China, Megaconus is one of the best-preserved fossils of the mammaliaform groups, long-extinct relatives to modern mammals that shared the Earth with feathered dinosaurs in the Jurassic era nearly 100 million years before Tyrannosaurus Rex roamed Earth.
The fossil shows a clear halo of guard hairs and underfur residue, making Megaconus -- a terrestrial animal about the size of a large ground squirrel -- only the second known pre-mammalian fossil with fur, the researchers said.
"We cannot say that Megaconus is our direct ancestor, but it certainly looks like a great-great-grand uncle 165 million years removed," Luo said. "These features are evidence of what our mammalian ancestor looked like during the Triassic-Jurassic transition."