Euharamiyida, a newly-discovered group of ancient mammals that ruled the Earth 160 million years ago, could push back the record of mammals on Earth by 40 million years.
Fossils from members of three species of Euharamiyida were unearthed in Liaoning Province in China. The long-extinct animals resembled modern squirrels in many ways, according to paleontologists.
The tiny creatures weighed between just one and 10 ounces, roughly the size of a contemporary mouse. Using unique, pointed teeth, the diminutive mammal ate nuts, fruits and insects.
Mammals may have evolved over 200 million years ago, this new finding suggests.
Haramiyida were an ancient group of mammals, and the earliest-known herbivores in the class of animals. Euharamiyida were placed in this grouping after their recent discovery. Prior to this discovery, grouping of animals were known just from samples of preserved teeth.
"For decades, scientists have been debating whether the extinct group, called Haramiyida, belongs within or outside of Mammalia. Previously, everything we knew about these animals was based on fragmented jaws and isolated teeth. But the new specimens we discovered are extremely well preserved... which confirms that they are, indeed, mammals," Jin Meng, at the American Museum of Natural History told the press.
Discovery of the ancient species could help provide evidence for how the world's first mammals started to diversify, leading to the wide range of mammal species we see today.
Euharamiyida may have evolved in a wide range of modern mammals, from the duck-billed platypus to human beings. Study of the artifacts revealed the three species last broke off from a common ancestor 208 million years in the past.
The ancient mammal ancestor was likely adapted for holding branches, spending more time in trees than modern squirrels. Running on flat ground may have been a challenge for the tiny animals, since their hands and feet were not well-designed for such a movement.
Human molars have up to five cusps, or points, on each tooth. Euharamiyida had teeth with two rows of cusps, containing up to seven points each. Most biologists believe all mammals evolved from a common ancestor which possessed teeth containing three cusps. The complex history of teeth in mammals has been an intricate puzzle facing biologists for decades. One common characteristic all mammals, including the new species, have in common is a trio of bones in the inner ear.
Mammals were thought to have originated between 176 and 161 million years ago, but recent DNA research has suggested a divergence date of between 235 and 201 million years in the past. Study of Euharamiyida lends support in favor of the earlier origin.
Discovery of Euharamiyida and study of its place as an early ancestor to modern mammals was published in the journal Nature.
