Scientists unearthed two fossils belonging to “scratch-diggers” that lived in the northeastern part of China sometime between 145 million and 100 million years ago (probably closer to around 120 million years ago). These are the first of the ancient burrowing mammal-like animals found from that time period – specifically the Jehol Biota which includes living creatures that lived during the Early Cretaceous Period in northeast China.
These two new species were distant relatives but they each developed their own unique digging skills. One of the fossils belonged to a foot-long mammal-like reptile called a Tritylodontidae and this new species has been named Fossiomanus sinensis. The second fossil was a 7-inch-long type of Eutriconodontan called Jueconodon cheni that was a distant cousin of today’s placental mammals and marsupials.
As for why these two species were diggers, Professor Jin Meng, who is from the American Museum of Natural History and an author of the study, explained, “There are many hypotheses about why animals dig into the soil and live underground.” “For protection against predators, to maintain a temperature that's relatively constant, or to find food sources like insects and plant roots. These two fossils are a very unusual, deep-time example of animals that are not closely related and yet both evolved the highly specialized characteristics of a digger.”
These newly discovered species had specific characteristics that helped them dig, such as short limbs, powerful forelimbs, strong hands with sharp claws, and a short tail. The type of digging they conducted is called “scratch digging” where they mainly used their forelimb claws.
Additionally, they had an elongated vertebral column. While today’s mammals normally have 26 vertebrae, the Fossiomanus species had 38 and the Jueconodon had 28.
Dr. Fangyuan Mao, who is from the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) of the Chinese Academy of Sciences and another author of the study, weighed in on the newly discovered mammals by noting, “This is the first convincing evidence for fossorial life in those two groups,” adding, “It also is the first case of scratch diggers we know about in the Jehol Biota, which was home to a great diversity of animals, from dinosaurs and insects to plants.” (A picture of the fossils can be seen here.)
Their study was published in the journal Nature where it can be read in full.