Juramaia is an
extinct genus of very
basal eutherian mammal from the
Late Jurassic (
Oxfordian stage) deposits of western Liaoning,
China; it is a small shrew-like mammal of body length approximately 70-100 mm.
Juramaia is known from the
holotype BMNH PM1343, an
articulated and nearly complete
skeleton including incomplete
skull preserved with full
dentition. It was collected in the Daxigou site,
Jianchang, from the
Tiaojishan Formation dated at about . It was first named by Zhe-Xi Luo, Chong-Xi Yuan, Qing-Jin Meng and Qiang Ji in
2011 and the
type species is
Juramaia sinensis. The discovery of
Juramaia provides new insight into the evolution of placental mammals by showing that their lineage diverged from that of the marsupials 35 million years earlier than previously thought. Furthermore, its discovery fills gaps in the fossil record and helps to calibrate modern, DNA-based methods of dating the evolution. Based on climbing adaptations found in the forelimb bones, it has been suggested that the basal stock of Eutheria was arboral.