Gobi Desert fossil clarifies Cretaceous mammal evolution

A fossil discovery in the Gobi Desert is reshaping scientific understanding of Cretaceous mammal evolution. The specimen, named Tamirkhan balcarceli, is the most complete known example of a mysterious group of small mammals called zhelestids.

For approximately 40 years, paleontologists relied on isolated teeth and skeletal fragments to study zhelestids. Their low, rounded teeth led researchers to hypothesize a close relationship to early placental mammals, the lineage including humans. However, a study published in the journal Nature by researchers from the American Museum of Natural History and various U.S. universities suggests this was a case of convergent evolution.

The new fossil, measuring 15 to 18 centimeters in length, preserves critical skull and hind limb features. Analysis of the long, slender hind limbs and distinct ankles indicates that zhelestids actually belonged to the zalambdalestoid lineage, a separate group of small Cretaceous mammals, rather than being primitive placental mammals.