The reproductive system in animals was already highly developed during the Paleocene era that lasted from about 66 to 56 million years ago, or possibly even earlier, the study of a 48 million year-old horse-like equoid foetus suggests.
The fossil was discovered at the Messel pit near Frankfurt, Germany, and studied by Jens Lorenz Franzen and colleagues from Senckenberg Research Institute, Frankfurt.
The foetus looked well-preserved, with almost all bones present and connected, except for the skull, which appeared to have been crushed.
The well-preserved condition of the fossil allowed the researchers to reconstruct the original appearance and position of the foetus.
They estimated that the mare may have died shortly before birth, but do not believe the death was related to birth.
The authors also found preserved soft tissue, like the uteroplacenta and one broad uterine ligament, which may represent the earliest fossil record of the uterine system of a placental mammal.
More From This Section
The observable details correspond largely with living mares, which lead the authors to posit that the reproductive system was quite developed during the Paleocene.
The study was published in the open-access journal PLOS ONE.