The oldest known remains of a mammalian placenta have been found inside the 48-million-year-old fossil of an early ancestor of a horse – with its unborn foal still inside.
The remarkably well-preserved body of a horse-like species known as Eurohippus messelensism was discovered at the Messel Pit, a disused shale quarry in Darmstadt, Germany.
While in the same family as a horse, the Eurohippus messelensism is much smaller, has four toes on each forefoot, three toes on each hindfoot, and is about the size of a small dog.
Analysis of the mare has revealed she was nearing delivery when she died, but the fetus, along with some of the tissue from the uterus and placenta, have remained amazingly intact. This soft tissue, referred to as the uteroplacenta, represents the earliest known fossil record of the uterine system of a placental mammal.
You can read the full findings which have been published as “Description of a Well Preserved Fetus of the European Eocene Equoid Eurohippus messelensis” in the interdisciplinary journal, PLOS ONE.