The fossils of two ancient, shrew-like mammals were recently discovered in China, and are telling scientists that mammalian diversity started to take place more than 160 million years ago, according to a new study.
The findings were published in two separate papers in the journal Science.
These creatures, hailing from the Jurassic Period, represent the oldest-known tree-climbing and burrowing mammals and show that early mammals were surprisingly diverse. Agilodocodon scansorius, an omnivore that lived roughly 165 million years ago, possessed paws with curved claws for climbing and spade-like teeth for eating tree sap and bark - akin to those of New World monkeys. It also had limb proportions characteristic to other tree-dwelling mammals and flexible elbow, wrist and ankle joints that made them expert climbers.
The other fossil, Docofossor brachydactylus, is the earliest-known subterranean mammal, living around 160 million years ago. It had a skeletal structure and body proportions strikingly similar to the modern day African golden mole, as well as shovel-like fingers good for digging.
Both about the size of the shrew and belonging to the long-extinct mammalian order called Docodonta, these mammal ancestors had unique adaptations that were tailored to their respective ecological habitats.
"We know that modern mammals are spectacularly diverse, but it was unknown whether early mammals managed to diversify in the same way. These new fossils help demonstrate that early mammals did indeed have a wide range of ecological diversity," researcher Zhe-Xi Luo, who worked on both papers, said in a news release.
Agilodocodon was discovered first in 2011 in deposits from a dried up lake bed in Inner Mongolia. Just a year later, the fossil of Docofossor was unearthed in lake deposits of the Ganggou Fossil Site in China's Hebei province, Live Science reports.
Docofossor was even smaller than Agilodocodon's mere 1.4-ounce (40 grams) frame. It probably stood just 3.5 inches tall and weighed up to 0.6 ounces (17 grams), the researchers said.
But despite their small size, these shrew-like creatures managed to survive during an era when dinosaurs dominated the landscape, developing striking mammalian diversity all the while.
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