The leptictids are a characteristic example of the non-specialized placental mammals that took part in the late
Cretaceous-
Paleocene evolutionary radiation, originally bunched together in the order
Insectivora. The leptictids became extinct during the
Oligocene. Their archaic cranium and dentition make it difficult to determine their relationship to other groups. Leptictid
postcranial anatomy has been studied from the well-preserved middle
Eocene Leptictidium specimens found at
Messel, Germany. Judging from these specimens, lepticids were small placentals with a body length ranging from . The head had a long and slender snout, probably featuring a short trunk, which may have been used for scratching the undergrowth in search of insects and worms. The mouth's archaic dentition included two or three incisors, a canine, and V-shaped cheek-teeth - four premolars and three molars. Their forelegs were shortened, but their hind legs were elongated. While this anatomy is reminiscent of small kangaroos and
jerboas, suggesting a jumping locomotion, the structure of the
tarsal bones hints at a specialization for terrestrial running. Perhaps these animals were capable of both modes of locomotion; running slowly in search for food, and jumping quickly to avoid threats. Additionally, the Messel specimens feature a surprisingly long tail, unique among modern placental mammals, formed by 40 vertebrae and probably used for balance. ==Classification==