A remarkably complete fossil of a newly identified mammal, Tamirkhan balcarceli, shows that zhelestids belonged with zalambdalestoids rather than representing early relatives of modern placental mammals. The fossil combines the distinctive rounded teeth previously used to classify zhelestids with a skull and long, slender hind limbs that reveal a very different evolutionary relationship. The discovery highlights the dangers of reconstructing entire extinct animals from teeth alone because similar dental adaptations can evolve independently in unrelated lineages. A small fossil from the windswept Gobi Desert is forcing scientists to rethink a long chapter in the story of mammal evolution. For decades, researchers believed a group of ancient mammals called zhelestids were early relatives of modern placental animals. That idea now appears to be wrong The newly described species, Tamirkhan balcarceli, offers the clearest picture yet of what these mysterious mammals actually looked like. More importantly, it reveals that zhelestids belonged to a completely different branch of the mammal family tree. The finding overturns nearly 40 years of assumptions based largely on fossil teeth. “This discovery illustrates …