Shrinking is a key evolutionary strategy for mammals

Sept. 17 (UPI) -- Getting smaller has been an important evolutionary strategy for mammals, new research has confirmed.

Computer models showed the ability to adopt smaller proportions allowed mammals to evolve a simplified lower jaw bone. The development was an important part of the diversification of mammals over the last 200 million years.

The lower jaws of most vertebrates are composed of five or six different bones. But most modern mammals feature a single lower jaw bone. Until now, scientists have struggled to understand how mammals evolved a simpler jaw bone while still being able to feed and hear.

To find out, scientists designed four different computer models to analyze CT scans of a variety of fossil skulls and lower jaws. The simulations showed the stresses put on the lower jaw during biting and chewing were significantly reduced as mammals got smaller.

By shrinking, scientists surmised, mammals made it possible to simplify the jaw bone and still eat prey.

"Our results provide a new explanation of how the mammalian jaw evolved over 200 million years ago," Stephan Lautenschlager, a researcher at the University of Birmingham, said in a news release. "Getting very small appears to have been crucial for our mammalian ancestors. This allowed them to reduce the stresses in the jaw during feeding and made the restructuring of the jaw bones possible."

Researchers shared their analysis of the mammalian lower jaw in a paper published Monday in the journal Nature.

The findings showed the simplification of the lower jaw also freed up smaller bones to migrate upward, where they aided mammalian hearing.

"The evolution of the mammalian jaw joint has perplexed paleontologists for over 50 years," said Emily Rayfield from the University of Bristol. "Using computational methods we can offer explanations to how our mammalian ancestors were able to maintain a working jaw while co-opting bones into a complex sound detection system. Our research is about testing ideas of what makes mammals unique among the animal kingdom, and how this may have come about."

Whereas other animals, like dinosaurs, evolved larger and larger sizes, mammals have shown the ability to evolve their sizes in both directions -- getting smaller and larger. This more nuanced approach could explain the evolutionary success of mammals.