Eating plants and blinking: Western Pa. scientists research evolutionary path of ancient mammal ancestors

Blinking — all of us do it, all the time.

But research by scientists in Western Pennsylvania is shedding new light on how something as simple as blinking helped ancient animals begin the transition from water to land, and how some of them developed into plant-eaters.

At Seton Hill University, assistant biology professor Brett Aiello and counterpart Thomas Stewart at Penn State University recently published a study into how the ancestors of humans and tetrapods — the group of animals that includes mammals, birds, reptiles and amphibians — began to evolve adaptations for life on land.

The study focuses on the specific adaptation of blinking, looking at the mudskipper fish as an example.

The mudskipper evolved independently into an amphibious lifestyle and spends much of its life out of the water. It developed a blinking eye which serves many of the same purposes it does in humans — keeping the eye moist, protecting it from dust, dirt and other particles, etc. — and provides some clues about traits that evolved to allow tetrapods to transition to a life on land 375 million years ago.

“Blinking in mudskippers appears to have evolved through a rearrangement of existing muscles that changed their line of action and also by the evolution of a novel tissue, the dermal cup,” Aiello said. “This is a very interesting result because it shows that a very rudimentary, or basic, system can be used to conduct a complex behavior. You don’t need to evolve a lot of new stuff to evolve this new behavior — mudskippers just started using what they already had in a different way.”

According to the study, published in the Proceedings of the National Academy of Sciences, “both mudskippers and tetrapods, blinking appears to have originated coincident with (a transition to living on land). We predict that similar selective demands have acted upon the visual systems of these lineages and propose that blinking is a key adaptation that has facilitated for a major shift in niche occupancy and life on land.”

Meanwhile, researchers at the Carnegie Museum of Natural History have collaborated with colleagues from the Smithsonian and Harvard University in studying a new species that provides clues about how some land-dwelling animals developed into herbivores.

They announced the discovery of Melanedaphodon hovaneci, the earliest known edaphosaurid synapsid, ancient precursors of mammals recognized in popular culture and science textbooks for the spine-supported sails along their backs.

Their study looked at two fossils recovered in eastern Ohio dating back to the Moscovian Age (between 307 million and 315 million years ago).

“With its large, bulbous and cusped marginal teeth, together with numerous teeth on its palate (i.e., the roof of the mouth), Melanedaphodon differs from all other known species of Edaphosauridae,” according to the study published in the journal Scientific Reports. “The presence of such teeth suggests that adaptations for processing tough plant material first appeared among the earliest mammal precursors. The researchers propose that durophagy — feeding on organisms with hard shells or exoskeletons—eventually enabled the eating of plants.”

The team named Melanedaphodon hovaneci in honor of the late A. George Hovanec, a native of West Mifflin, whose financial contributions made the study possible.

“This is such an exciting find,” said Amy Henrici, one of the authors and collection manager of vertebrate paleontology at Carnegie Museum of Natural History. “We now have a much better understanding of how terrestrial animals first adapted as plant eaters, which had a profound impact on global ecosystems.”