Stunning fossil shows pregnant mare and fetus

Forty-seven million years ago, a pregnant mare and its unborn foal lost their lives, perhaps chased into a lake, where they drowned. Where they died, however, was a stroke of luck for 21st century paleontologists. Their fossilized remains were discovered in the Messel Pit , a former coal and oil shale mine near Frankfurt, Germany, that is famous for its exquisitely preserved fossils. The mare and her fetus are now giving scientists an unprecedented glimpse into the anatomy and reproduction of this early horse species, Eurohippus messelensis. Like other early horses, the mare was small, only about the size of a fox terrier, says Jens Franzen, a paleontologist at the Senckenberg Research Institute and Natural History Museum in Frankfurt, who presented the prepared fossil for the first time yesterday at the Society of Vertebrate Paleontology annual meeting here. Not only were most of the bones of the mare and fetus intact, but scientists can also detect the placenta. This organ was not fossilized directly, but is visible as a dark shadow left by bacteria that consumed the tissue and then were fossilized. Researchers can also see the broad ligament that helps attach the uterus to the backbone. (Although the skull of the fetus was crushed, its ribs and legs are clearly visible.) Under a scanning electron microscope, scientists could see the cellular structure of the colon and the plant remains of the mare’s final meals. The position of the foal suggests that it wasn’t fully in position to be born, but was close to mature, and suggests that ancient horses gave birth in a similar way to their modern cousins. It is only the second example of a fossil where the placenta can be identified, Franzen says.

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