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48-Million-Year-Old Fossil of Horse-Like Fetus Analyzed; Material Included Preserved Soft Tissue Like the Uteroplacenta and One Broad Uterine Ligament; May Be Earliest Fossil Record of Uterine System of Placental Mammal

Analysis of a 48-million-year-old fossil of a horse-like equoid fetus discovered, together with the fossil of its mother, in 2000 at the Messel pit near Frankfurt, Germany, is reported in a study published online on October 7, 2015 in the open-access journal PLOS ONE. The report was authored by Jens Lorenz Franzen, Ph.D., from Senckenberg Research Institute in Frankfurt, Germany, and also from the Naturhistorisches Museum in Basel, Switzerland, together with colleagues. The article is titled “Description of a Well Preserved Fetus of the European Eocene Equoid Eurohippus messelensis.” The authors of this study completed their investigation of the fetus from a 48-million-year-old horse-like equoid uncovered near Frankfurt, Germany, in 2000. They evaluated the bones and anatomy and used scanning electronic microscopy (SEM) and high-resolution micro-x-ray technologies to describe the ~12.5 cm fetus. The fetus appears to be well-preserved, with almost all bones present and connected, except for the skull, which appears to have been crushed. The well-preserved condition of the fossil allowed the researchers to reconstruct the original appearance and position of the fetus. They estimate that the mare may have died shortly before birth, but they don't 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. Applying SEM, the authors discovered a bacterial lawn replacing the soft tissues, as is common with other specimens found in that area. The observable details correspond largely with living mares, which lead the authors to posit that the reproductive system was already highly developed during the Paleocene era, and possibly even earlier. The image shows the skeleton of a mare of Eurohippus messelensis with a fetus (white ellipse). The specimen was discovered and excavated by a team of the Senckenberg Research Institute Frankfurt at the Grube Messel in Germany. (Credit: Senckenberg Forschungsinstitut Frankfurt, Sven Tränkner). Please go to the press release (via link below), to see a larger, higher-resolution image of the mare and small fetus that is shown within a white oval drawn in the image.

[Press release] [PLOS ONE article]