Scientists unearth ancient species of mammal-like burrowers

8 Apr 2021

Reconstruction of ancient burrowing animals. Image: Chuang Zhao

Two ancient species of ‘scratch-diggers’ have been discovered by palaentologists.

Palaeontologists at the American Museum of Natural History have discovered two new ancient species of animals that lived around 120m years ago in what is now north-eastern China.

They have described the species as “mammal-like” and distantly related. However, each evolved independent traits to allow them to dig, making them the first ‘scratch-diggers’ discovered in this particular ecosystem.

The species were mammal predecessors that used their claws to dig and burrow into the ground. They are from the early Cretaceous epoch, which means they roamed the land at the same time as many dinosaurs.

A paper on this discovery was published in Nature earlier this week. Its lead author, Jin Meng, is a curator in the museum’s palaeontology division.

“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 – not too hot in the summer and not too cold in the winter – or to find food sources like insects and plant roots,” Meng said.

“These two fossils are a very unusual, deep-time example of animals that are not closely related and yet both evolved the highly specialised characteristics of a digger.”

One of the animals was a mammal-like reptile called a tritylodontid and is the first of its kind to be identified in the region during this period. It has been named Fossiomanus sinensis and was around a foot long.

The second animal was named Jueconodon cheni. This was a eutriconodontan, making it a distant cousin of modern placental mammals and marsupials, which were common in the habitat. It measured at around seven inches in length.

Burrowing mammals have specialised traits that evolved for digging, some of which were present in these ancient species. They had shorter limbs, strong forelimbs with robust hands and a shorter tail. Both also shared an elongated vertebral column. While typical mammals have 26 vertebrae from the neck to the hip, these animals had 38 (Fossiomanus) and 28 (Jueconodon), respectively. The researchers believe this could be the result of gene mutations.

“This is the first convincing evidence for fossorial life in those two groups,” Meng said. “It also is the first case of scratch-diggers we know about in the Jehol Biota, which was home to a great diversity of life, from dinosaurs to insects to plants.”

Lisa Ardill was careers editor at Silicon Republic until June 2021