Jurassic Period Animals: Early Mammals Acted More Like Reptiles, Says Study

The first mammals that roamed the Earth millions of years ago functioned and acted more like reptiles even with their already advanced body structures, a new study showed.

The research, published in Nature Communications, suggested there might be an overlap between warm-bloodedness and cold-bloodedness as mammals evolved in the past. It may be noted that mammals are considered as warm-blooded animals while reptiles are cold-blooded.

As part of the study, a team of paleontologists analyzed teeth fossils from two of the earliest mammals, the Morganucodon and Kuehneotherium, which lived alongside early dinosaurs nearly 200 million years ago. This was the first time researchers used powerful X-rays to examine ancient fossils.

The team scanned the fossilized cementum of the teeth fossils. The cementum is what attaches the teeth into the socket in the gum of mammals and it continues to grow throughout life.

The paleontologists studied the tree-like growth rings in the tooth sockets, which helped them understand the lifespan of the ancient mammals and how they evolved during the early Jurassic period.

They found that although Morganucodon and Kuehneotherium had features similar to their modern counterparts, including bigger brains, they lived more like lizards.

"They were otherwise quite mammal-like in their skeletons, skulls and teeth. They had specialized chewing teeth, relatively large brains and probably had hair, but their long lifespan shows they were living life at more of a reptilian pace than a mammalian one," Dr. Elis Newham, lead author of the study and a research associate at the University of Bristol, said in a press release.

"There is good evidence that the ancestors of mammals began to become increasingly warm-blooded from the Late Permian, more than 270 million years ago, but, even 70 million years later, our ancestors were still functioning more like modern reptiles than mammals," Newham added.

The researcher explained that even though the ancient mammals acted more like reptiles, it was found that their bone tissues endured sustained physical activities, suggesting that they were capable of foraging and hunting. They were more active than small reptiles but not as energetic as the mammals, Newham explained.