The research team of Nikos Solounias, Ph.D., and Matthew Mihlbachler, Ph.D., has found a strong link between the evolution of horses and changes in their environment.

NYIT Researchers Reveal Secrets of Horses and Hearts

By Nikita Japra

As a three-year-old boy in Samos, Greece, Nikos Solounias, Ph.D., had a peculiar habit of hiding bones he found under his bed.

Eight thousand miles away and six decades later, in the Riland Academic Health Center at NYIT-Old Westbury, the paleontologist is researching fossils of prehistoric horses with colleague Matthew Mihlbachler, Ph.D., and has concluded that you are, in fact, what you eat.

The two NYIT professors, who can be found in the third-floor anatomy lab of Riland teaching gross anatomy to eager first-year medical students, also travel the world conducting research on the evolution of ungulates, or plant-eating hoofed mammals such as rhinos, camels, giraffes, gazelles, wildebeests, goats, cows, sheepÑand horses, of course.

Or, more specifically, horse teethÑwhich scientists have speculated follow a model of evolution that is linked to the abrasive nature of their grass-based diets. Today's horses have relatively flat, tall molars. As horses age, their teeth wear down though they are still big enough to accommodate the excessive wear, which enables the animals to continue feeding.

Mihlbachler and Solounias determined that horses could help answer questions about the history and evolution of life on Earth because, unlike humans who manufacture their own environments and have only existed for four million years, horses have a 55-million-year history that is documented in fossil collections.

"The zebra, donkey, and horse are the last chapter in the course of this animal's evolution," explains Solounias. "The oldest horse fossils reveal very short, very tiny, pointed teeth."

Solounias helped develop a methodology known as dental mesowear analysis to reconstruct the diets of the extinct species by measuring food-related wear and tear on fossil teeth. Working with colleagues in Massachusetts and Spain, he and Mihlbachler examined the teeth of 6,500 fossil horses representing 222 different populations of more than 70 extinct horse species.

Although the numbers sound daunting, Mihlbachler says the collection of data is the easier part of the research. The more time-consuming tasks involved creating a methodology for turning the different molar cusp shapes they encountered into data; it took another several months to determine how to analyze the data statistically. In total, the process took more than five years.

"The bones speak back to you," says Solounias. "They help you conceptualize the hidden information that is unknown to mankind."

The team examined the patterns present in the specimens' dental wear to see if horse diets were actually changing as their teeth were evolving. They analyzed their data alongside records of North American climate changes that would have shifted the animals' feeding patterns from rainforest fruits and woody, leafy vegetation to the more abrasive diets found in the grasslands that spread across North America at the start of the Miocene epoch 23 million years ago.

Doing so allowed them to create a seven-point scale for the different-sized molar cusps of horses throughout time. In the end, the study produced a classic example of how the evolution of horse teeth and other ungulates relates to the evolution of ecosystems and vegetation. Their findings were published in the March 4, 2011, issue of Science, the prestigious bi-weekly international journal.

"One of the things our study shows is that animals are strongly impacted by how environments change," says Mihlbachler. He adds that their results indicate a critical lag time between the evolution of horse teeth and dietary changes resulting from climate change. "If we had found, for instance, that the evolutionary changes in teeth preceded the dietary changes, the hypothesis of evolution by natural selection would have been nonsensical. But the observation that dental changes followed dietary changes is consistent with evolution due to adaptation."

Through their extensive survey of available fossil data, Mihlbachler and Solounias also determined that as the number of horse species dwindled in the last few million years, the types of horse diets were also greatly reduced. Modern horses and their relatives today are primarily grass-eaters, which was not necessarily the case for the extinct ancestral horse species. The mesowear data indicate that living horses are anything but typical examples of the dietary ecology of this once diverse group of mammals.

Both scientists agree that their study highlights the importance of understanding the interrelation of environment and evolution. Moving forward, Mihlbachler will explore hot spotsÑareas that raise more questions than answers in the horse fossil records.

As for his partner, Solounias will continue to collaborate with his colleague but he is also writing a book on giraffes, a subject that brings him back to his boyhood days in Greece.

"The very first bone I found belonged to an extinct giraffe called Samotherium," says Solounias. "But now I keep it in my office."

Next: Heart Research That Sounds Fishy

More Features

Spring 2011 Table of Contents