Leptictidium (a Latinized diminutive of the name of its relative Leptictis, which means "graceful weasel" in Ancient Greek) is an extinct genus of small mammals that were likely bipedal. Comprising eight species, they resembled today's bilbies, bandicoots, and elephant shrews. They are especially interesting for their combination of characteristics typical of primitive eutherians with highly specialized adaptations, such as powerful hind legs and a long tail which aided in locomotion. They were omnivorous, their diet a combination of insects, lizards and small mammals. Lepticidium and other lepticids are not placentals, but are non-placentral eutherians, although closely related. They appeared in the Lower Eocene, a time of warm temperatures and high humidity, roughly fifty million years ago. Although they were widespread throughout Europe, they became extinct around thirty-five million years ago with no descendants, probably because they were adapted to live in forest ecosystems and were unable to adapt to the open plains of the Oligocene. Description Leptictidium is a special animal because of the way its anatomy combines quite primitive elements with elements which prove a high degree of specialization. It had small fore legs and large hind legs, especially at the distal side (that further from the body). The lateral phalanges of its forelegs (fingers I and V) were very short and weak, finger III was longer and fingers II and IV were roughly equal in size, and slightly shorter than finger III. The tips of the phalanges were elongated and tapered. The ankles and the sacroiliac joint were quite loosely fixed, while the pelvis had a flexible joint with only one coccygeal vertebra. The anteorbital muscle fenestrae in their crania suggest they probably had a long and mobile snout, similar to that of elephant shrews. Leptictidium had wide diastemata in the antemolar row, its upper molar teeth were more transverse than those of the North American leptictids and its fourth premolars were molariform. Its C1 canines were incisiviform. Its dentition was quite small in comparison to the size of the mandible and the animal as a whole. It varied between in length (more than half of which belonged to the tail), and in height. It weighed a couple of kilograms. These sizes could vary from one specimen to another. Leptictidium tobieni from Messel (Germany) is the largest known leptictid with skull long, head with trunk long, and tail long. Locomotion One of the mysteries about Leptictidium is whether