Hapalodectidae (literal translation 'soft biters': ('soft, tender'), ('biter')) is an extinct family of relatively small-bodied ()

mesonychia Mesonychia ("middle claws") is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely ...

placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsup ...

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur or ...

s from the

Paleocene The Paleocene, ( ) or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), E ...

and

Eocene The Eocene ( ) Epoch is a geological epoch (geology), epoch that lasted from about 56 to 33.9 million years ago (mya). It is the second epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), Era. The name ''Eocene' ...

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

and

Asia Asia (, ) is one of the world's most notable geographical regions, which is either considered a continent in its own right or a subcontinent of Eurasia, which shares the continental landmass of Afro-Eurasia with Africa. Asia covers an area ...

. Hapalodectids differ from the larger and better-known

mesonychid Mesonychia ("middle claws") is an extinct taxon of small- to large-sized carnivorous ungulates related to artiodactyls. Mesonychids first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely ...

s by having teeth specialized for cutting (presumably meat), while the teeth of other mesonychids, such as ''

Mesonyx ''Mesonyx'' ("middle claw") is a genus of extinct mesonychid mesonychian mammal: fossils of the various species are found in Early to Late Eocene-age strata in the United States and Early Eocene-aged strata in China, 51.8—51.7 Ma ( AEO). Wh ...

'' or ''

Sinonyx ''Sinonyx'' ("Chinese claw") is a genus of extinct, superficially wolf-like mesonychid mammals from the late Paleocene of China (about 56 million years ago). It is within the family Mesonychidae, and cladistic analysis of a skull of ''Sinonyx'' ...

'', are more specialized for crushing bones. Hapalodectids were once considered a

subfamily In biological classification, a subfamily (Latin: ', plural ') is an auxiliary (intermediate) taxonomic rank, next below family but more inclusive than genus. Standard nomenclature rules end subfamily botanical names with "-oideae", and zoologi ...

of the

Mesonychidae Mesonychidae (meaning "middle claws") is an extinct family of small to large-sized omnivorous-carnivorous mammals. They were endemic to North America and Eurasia during the Early Paleocene to the Early Oligocene, and were the earliest group of la ...

, but the discovery of a skull of '' Hapalodectes hetangensis'' showed additional differences justifying placement in a distinct family. In particular, ''H. hetangensis'' has a

postorbital bar The postorbital bar (or postorbital bone) is a bony arched structure that connects the frontal bone of the skull to the zygomatic arch, which runs laterally around the eye socket. It is a trait that only occurs in mammalian taxa, such as most strep ...

closing the back of the

orbit In celestial mechanics, an orbit is the curved trajectory of an object such as the trajectory of a planet around a star, or of a natural satellite around a planet, or of an artificial satellite around an object or position in space such as a p ...

, a feature lacking in mesonychids. The skeleton of hapalodectids is poorly known, and of the postcranial elements, only the

humerus The humerus (; ) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius and ulna, and consists of three sections. The humeral upper extremity consists of a roun ...

has been described. The morphology of this bone indicates less specialization for terrestrial locomotion than in mesonychids.

Species

Family Hapalodectidae *Genus '' Hapalodectes'' ** ''H. anthracinus'' Zhou et Gingerich, 1991 ** ''H. dux'' Lopatin, 1999 ** ''H. hetangensis'' Ting et Li, 1987 ** ''H. huanghaiensis'' Tong et Wang, 2006 ** ''H. leptognathus'' Osborn et Wortman, 1892 ** ''H. lopatini'' Solé et al., 2017 ** ''H. paleocenus'' Beard et al., 2010 ** ''H. serus'' Matthew et Granger, 1925 *Genus '' Hapalorestes'' **''H. lovei'' *Genus '' Honanodon'' **''H. chow'' **''H. hebetis'' **''H. lushiensis'' **''H. macrodontus'' *Genus '' Lohoodon'' **''L. lushiensis'' *Genus '' Metahapalodectes'' **''M. makhchinus''

References

Mesonychids Eocene extinctions Paleocene first appearances Prehistoric mammal families {{paleo-mammal-stub