Pantolestidae is an extinct family

Family (biology)

In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...

 of semi-aquatic, placental mammals that took part in the first placental evolutionary radiation

Evolutionary radiation

An evolutionary radiation is an increase in taxonomic diversity or morphological disparity, due to adaptive change or the opening of ecospace. Radiations may affect one clade or many, and be rapid or gradual; where they are rapid, and driven by a single lineage's adaptation to their environment,...

 together with other early mammals such as the leptictids

Leptictida

Leptictida is an extinct order of placental mammals. According to cladistic studies, they may be related to Euarchontoglires , although they are more often regarded as the first branch to split from basal eutherians.- Description :The leptictids are a characteristic example of the...

.
Forming the core of the equally extinct order Pantolesta, the pantolestids evolved as a series of increasingly otter-like forms, ranging from the Middle Paleocene (60 mya) Bessoecetor to the Middle Eocene (50-40 mya) Buxolestes. They first appear in North America from where they spread to Europe.

Description

The pantolestids were fish predators with a body length of about 50 centimetres (19.7 in) and a tail about 35 centimetres (13.8 in) long. The anatomy of these archaic "insectivorous

Insectivora

The order Insectivora is a now-abandoned biological grouping within the class of mammals...

" mammals is best known through well-preserved Middle Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 Buxolestes specimens found at Messel

Messel pit

The Messel Pit is a disused quarry near the village of Messel, about southeast of Frankfurt am Main, Germany. Bituminous shale was mined there. Because of its abundance of fossils, it has significant geological and scientific importance...

 in Germany and a few other less complete specimens, such as the Palaeosinopa found at Fossil Butte

Fossil Butte National Monument

Fossil Butte National Monument is a unit of the National Park Service located 15 miles west of Kemmerer, Wyoming; the national monument was established on October 23, 1972. The site preserves the best paleontological record of Tertiary aquatic communities in North America and possibly the world,...

 in Wyoming

Wyoming

Wyoming is a state in the mountain region of the Western United States. The western two thirds of the state is covered mostly with the mountain ranges and rangelands in the foothills of the Eastern Rocky Mountains, while the eastern third of the state is high elevation prairie known as the High...

, estimated to have reached body weights of up to 1400 grams (3 lb), making them relatively large early mammals.

They had moderately strong canines

Canine tooth

In mammalian oral anatomy, the canine teeth, also called cuspids, dogteeth, fangs, or eye teeth, are relatively long, pointed teeth...

 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

Radius (bone)

The radius is one of the two large bones of the forearm, the other being the ulna. It extends from the lateral side of the elbow to the thumb side of the wrist and runs parallel to the ulna, which exceeds it in length and size. It is a long bone, prism-shaped and slightly curved longitudinally...

 and ulna

Ulna

The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form and runs parallel to the radius, which is shorter and smaller. In anatomical position The ulna is one of the two long bones in the forearm, the other being the radius. It is prismatic in form...

) 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 pantolestids 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

Family: †Pantolestidae (Cope

Edward Drinker Cope

Edward Drinker Cope was an American paleontologist and comparative anatomist, as well as a noted herpetologist and ichthyologist. Born to a wealthy Quaker family, Cope distinguished himself as a child prodigy interested in science; he published his first scientific paper at the age of nineteen...

, 1884)

Subfamilies

†Pentacodontinae (Simpson

George Gaylord Simpson

George Gaylord Simpson was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern evolutionary synthesis, contributing Tempo and mode in evolution , The meaning of evolution and The major features of...

, 1937)

†Pantolestinae (Cope, 1884)

†Dyspterninae (Kretzoi

Miklós Kretzoi

Miklós Kretzoi was a Hungarian geologist, paleontologist and paleoanthropologist and Széchenyi Prize winner....

, 1943)