For nearly 40 years, paleontologists have been puzzled by a group of extinct mammals called zhelestids. Their teeth looked like those of early placental mammals, leading many researchers to treat them as ancient relatives of the group that includes humans, bats, and whales. But the teeth may have been a misleading clue.
A newly described fossil from Mongolia’s Gobi Desert, named Tamirkhan balcarceli, is beautifully preserved and provides the clearest look yet at the anatomy of a zhelestid. According to the ScienceDaily report, that anatomy shows zhelestids were not early relatives of modern placental mammals after all, despite their suggestive teeth.
The finding resolves a contradiction that had lingered since the 1980s. With the fossil in hand, researchers can now place zhelestids elsewhere in the mammal family tree, demonstrating how even well-studied groups can be misread when only teeth are available for comparison.