Two fossils recently unearthed in China show the rapid diversification of early mammals. Two members of the same taxonomic order, found at the same location show extremely specialized characteristics for their environments. One is the earliest-known tree dwelling mammal and the other the earliest known subterranean mammal. Both animals lived about 160 million years ago.

Agilodocodon scansorius, the earliest known tree dwelling mammaliaform had claws for climbing and teeth that suggest a tree-sap diest. Docofossor brachydactylus, the earliest-known subterranean mammaliaform had shovel like paws and other adaptations similar to African golden moles.

The skeletal features of Docofossor also resemble patterns in modern mammals, suggesting that the genetic features evolved before the arrival of modern mammals.

The findings, by teams at the University of Chicago and the Beijing Museum of Natural History are described in two papers published in the journal Science.

”We consistently find with every new fossil that the earliest mammals were just as diverse in both feeding and locomotor adaptations as modern mammals. The groundwork for mammalian success today appears to have been laid long ago,” said Zhe-Xi Luo, PhD, in a statement. Luo is a professor of organismal biology and anatomy at the University of Chicago and an author on both papers.

The newly discovered animals provide strong evidence that subterranean and arboreal lifestyles evolved early.

Agilodocodon, which seems to have first appeared 165 million years ago had curved, horny claws and limb proportions roughly similar to modern tree dwelling mammals. The animals have spade like teeth for gnawing on bark, similar to some modern monkeys. It is the earliest known example of a gumnivorous species, adapted for feeding on tree sap. Agilodocodon also had the flexible joints common to true climbers.

“The finger and limb bone dimensions of Agilodocodon match up with those of modern tree-dwellers, and its incisors are evidence it fed on plant sap. It’s amazing that these arboreal adaptions occurred so early in the history of mammals and shows that at least some extinct mammalian relatives exploited evolutionarily significant herbivorous niches, long before true mammals,” said study co-author David Grossnickle, graduate student at the University of Chicago.

Docofossor appears to have arrived 160 million years ago. It had shovel like fingers and the wide, short upper molars typical of subterranean mammals. Like the teeth, the animals fingers were short and wide.

The reduced bone segments in the fingers are due to the fusion of bone joints during development. This process is influenced by the genes BMP and GDF-5, which is shared by modern mammals including the African golden mole. The researchers believe the mechanism played a significant role in the early evolution of mammals.

The ribs and spines of both animals also show genetic similarities to modern mammals.

“We believe the shortened digits of Docofossor, which is a dead ringer for modern golden moles, could very well have been caused by BMP and GDF. We can now provide fossil evidence that gene patterning that causes variation in modern mammalian skeletal development also operated in basal mammals all the way back in the Jurassic,” said Luo.

The new discoveries add to growing evidence of greater diversity than previously expected among mammals in the age of dinosaurs.

“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. It appears dinosaurs did not dominate the Mesozoic landscape as much as previously thought,” said Luo