Four-Toed Horse Reveals Secrets About Ancient Mares

Fifty million years ago, horses were certainly not the tall and regal animals they are today. In fact, they were about the size of your average pig, and boasted three or four thick-nailed toes, not hooves to boot! Now, a well-preserved fossil of an ancient pregnant mare is helping paleontologists learn more about what traits of ancient horses still persist in the animals today.

The ancient mare in question (Eurohippus messelensis) was reportedly found in Germany's renowned Messel Pit fossil site back in 2000. It was estimated to be about 46 million years old. However, it wasn't until 2009 that Jens Lorenz Franzen, a researcher at the Senckenberg Research Institute, and his colleagues studied the specimen with a micro X-ray to look for details that might tell experts more about the once-tiny animals.

Franzen revealed his findings last week at the 2014 annual meeting of the Society of Vertebrate Paleontology in Berlin. According to the researcher and his team, they found out they were not only looking at a complete mare skeleton, but one coupled with an immaculately preserved and intact fetus.

Even the microbiome in and around the fetus could be observed with the help of the X-ray scans - which in turn helped the researchers see details that otherwise would have been impossible to notice.

"The bacteria helped a lot and in a very wonderful way," Franzen told Live Science. "Tips of hairs of the outer ears - even the interior, like blood vessels, become visible in some cases."

He explained how the decomposition of anaerobic bacteria in the specimen's skin produced carbon dioxide, which precipitated iron that was present in the lake's water. Bacterial residue then essentially imprinted the structure of the surrounding soft tissue, remaining as faint images sitting lightly on the mare's fossilized bones.

According to the authors' abstract, the fetus was likely close to term when its mother died from what is suspected to have been a sudden plume of deadly volcanic gases. The foal had been developing in a way that was stunningly similar to modern horses, showing that while these ancestors were smaller and toed, basic biological structure has not altered much over the last 46 million years.