Its discoverers sampled 268 characters from all major Mesozoic mammal clades and principal eutherian families of the Cretaceous period . As a result , they claim Eomaia is at the root of the eutherian `` family tree '' with a few other fossils . Its discoverers claim that , on the basis of 268 characters sampled from all major Mesozoic mammal clades and principal eutherian families of the Cretaceous , Eomaia is placed at the root of the eutherian `` family tree '' along with Murtoilestes and Prokennalestes .