Cifelliodon wahkarmoosuch lived during the Cretaceous period and belonged to a group that was closely related to mammals.
Credit: Jorge A. Gonzalez
A small, furry animal with a blunt snout and beady eyes scuttled across what is now eastern Utah some 130 million years ago. And while the wee beast was surely unusual and fascinating, there’s one thing it was definitely not: half-mammal and half-reptile.
Headlines about the recent find have described it as though it were some bizarre hybrid of reptile and mammal. But while it might be amusing to imagine a beast with the front end of a lizard and the rear end of a rat, it’s not very scientific. [Real or Fake? 8 Bizarre Hybrid Animals]
The little animal, which would have stood just 3 inches (7.6 centimeters) tall and weighed about 2.5 pounds (1.1 kilograms), belonged to a group known as the haramiyidans, which emerged during the late Triassic period (251 million to 199 million years ago), and are known mostly from fossil teeth. Scientists have argued over whether haramiyidans were early mammals or a sister group — closely related to mammals, but lacking some features used by paleontologists to decide who’s a mammal and who’s not.
In a new study describing the tiny skull — which represents a new genus and species of haramiyidan called Cifelliodon wahkarmoosuch, and is thought to be between 139 million and 124 million years old — researchers determined that haramiyidans were mammal relatives, though not actual mammals. Both haramiyidans and mammals trace their origins to a reptile group known as synapsids, and though haramiyidans looked a lot like mammals, they retained more “nonmammalian” structures from their reptile ancestors than the first true mammals did, the scientists reported. [Image Gallery: 25 Amazing Ancient Beasts]
Terms such as “mammal-like reptiles” reflect the relationship between ancestral and emerging features that define animal groups. Egg-laying, for example, is a reptilian trait still found in some modern mammals, such as platypuses and spiny anteaters. So-called “true mammals” — mammals with placentas — are thought to originate from a shrew-like animal called Juramaia sinensis, which lived about 160 million years ago.
In life, the newly described haramiyidan had a long tail, teeth that could slice and crush vegetation and tiny eye sockets that suggested its eyes were small and its vision was poor. However, its olfactory bulbs were unusually large, hinting that it relied heavily on its sense of smell, according to the study.
High-resolution X-ray scans also revealed the inner cranium shape, which was “transitional between earlier stem mammals and crown Mammalia,” the researchers wrote. This means that C. wahkarmoosuch — and other haramiyidans — fall somewhere between the first reptiles that evolved mammal-like features and the group that includes mammals alive today.
The exceptional preservation of the skull — particularly its 3D shape — offered clues about the haramiyidan group that had only been guessed at before, when the only available fossils were scanty or crushed flat, lead study author Adam Huttenlocker, an assistant professor of clinical integrative anatomical sciences with the Keck School of Medicine at the University of Southern California, told USC News.
“The three-dimensional preservation of Cifelliodon highlights the primitive brain, palate and feeding structure of this special group and reinforces their position near the base of the mammalian family tree,” Huttenlocker said.
The findings were published online May 23 in the journal Nature.
Original article on Live Science.