Scientists have unearthed a fossil of a mammal the size of a chipmunk that skittered around with the dinosaurs, with a key feature in the evolution of mammals.
WASHINGTON: Scientists have unearthed a fossil of a mammal the size of a chipmunk that skittered around with the dinosaurs, with a key feature in the evolution of mammals—the middle ear bones—fabulously preserved.
Writing in the journal Nature on Wednesday, the scientists said the unusual critter retrieved from a fossil-rich rock formation in northern China provides rare insight into a crucial element of mammalian evolution: ear structure that enabled highly sensitive hearing.
The mammal, named Yanoconodon for the Yan Mountains in China’s Hebei Province, lived 125 million years ago during the Cretaceous period. Its body was shaped very oddly for a mammal — with an elongated torso and short, stubby limbs. “In a way, it’s sort of a salamander-like body form in a mammal,” lead researcher Zhe-Xi Luo of the Carnegie Museum of Natural History in Pittsburgh said.
The scientists think Yanoconodon—5 inches long and weighing about 30 grams—was nocturnal and ate insects. It lived in a lush environment with fresh-water lakes, early flowering plants and many other animals. Yanoconodon is particularly important because it displays an intermediate stage in the evolution of mammalian ear structure. Mammals possess hearing superior to all other vertebrates, and that trait has been fundamental to mammalian life.
Scientists believe ear bones evolved from the bones of the jaw hinge in the reptiles from which mammals are thought to have evolved. Luo said the Yanoconodon provided a definitive piece of evidence of this evolution. The ear bones in Yanoconodon are fully like that of modern mammals, but remain connected to the lower jaw, which is not the case with modern mammals.
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