A 47-million-year-old fossil of a horse with an unborn foal still inside of it has given scientists new understanding of the life and the development of the prehistoric creatures.
The fossil of the prehistoric horse identified as Eurohippus messelensis was discovered in a former coal mine pit in Germany in 2000 but detailed examination of the fossil was only undertaken in 2012, researchers at the Senckenberg Research Institute reported.
The fossil site, known as the Messel Pit, is well known for well-preserved fossils of mammals and other animals, along with birds and plants dating back to the beginning of the Eocene Epoch around 57 million years in the past.
The Eurohippus fossil revealed surprising similarities in reproductive processes to those found in modern horses, surprising given some significant differences in structure and the prehistoric creature's small size, similar to an average size modern dog, the researchers report.
The ancient horse had four toes on each of its forefeet and three on each of its hind feat.
The presence of the fetus wasn't revealed until examination of the ancient fossil with micro X-rays, they said.
"It's magnificently preserved," says institute researcher Jens Lorenz Franzen. "It turned out this was an almost complete and articulated skeleton with a fetus."
The X-rays showed a broad ligament connecting the uterus to the creature's backbone to support a developing fetus, as well as a crumpled outer uterine wall, a feature present in modern horses.
"Almost all of the bones of the fetus are still articulated in their original position," Franzen says. "Only the skull is crushed."
Although the size of the fetus suggests it was close to full term when the mother died, its position suggests the mother and foal did not die during the birth process, the scientists said.
The area where the fossil was found was once volcanic and included an ancient body of water, Lake Messel, that would have attracted many animals looking to drink who where then overcome by toxic gases, they said.
Dead animals would sink to the bottom of the lake, which was without oxygen, so anaerobic bacteria decomposing soft tissue would precipitate iron from the water, leaving behind a metallic trace of the shape of some tissues.
The preservation of the Eurohippus fossil was therefore so remarkable, Franzen said, that the researchers could make out "tips of hairs of the outer ears -- even the interior, like blood vessels, become visible in some cases."
