The pantolestids were a small to moderate in size,
omnivorous,
semi-fossorial mammals. Members of this family formed
grade towards families
Paroxyclaenidae and
Pentacodontidae, with representatives of subfamily Dyspterninae, aswell genus
Entomodon, were anatomically most similar to them. Oldest known pantolestids were north american genera
Bessoecetor,
Leptonysson and
Paleotomus, while youngest known pantolestid was european genus
Kochictis. Members of subfamily Pantolestinae were
semiaquatic,
otter-like mammals, with a body length of about and a tail about long. The anatomy of these archaic "
insectivorous" mammals is best known through well-preserved Middle
Eocene specimens from genus
Buxolestes found at
Messel in
Germany, and a few other less complete specimens, such as the
Palaeosinopa found at
Fossil Butte in
Wyoming, estimated to have reached body weights of up to , making them relatively large early mammals. They had moderately strong
canines and multi-cusped cutting teeth supported by the strong jaw muscles to which cranial cavities were adapted. This combination of dentition and muscles has been interpreted as an early adaptation to a hard diet such as clams and snails. Freely articulated forearm bones (
radius and
ulna) permitted their powerful forelimbs wide rotational movements, while their digits had large bony claws indicating they could dig and build underground dens. Their powerful hind limbs could not be rotated in the same way, but the prominent transverse processes of the first tail vertebra suggest that they used their powerful tails to propel through the water like modern otters. In later pantolestins there is a prominent cranial crest combined with strong spinal processes, indicating the presence of strong neck muscles needed by swimmers that constantly hold their heads above the water surface. == Classification ==