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. Mesonychians first appeared in the early Paleocene, went into a sharp decline at the end of the Eocene, and died out entirely w ...

placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

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), ...

and

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

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

and

Asia Asia ( , ) is the largest continent in the world by both land area and population. It covers an area of more than 44 million square kilometres, about 30% of Earth's total land area and 8% of Earth's total surface area. The continent, which ...

. Hapalodectids differ from the larger and better-known

mesonychid 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 ...

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

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

'', 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 botanical subfamily names with "-oideae", and zo ...

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 o ...

, 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 (also known as orbital revolution) 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 ...

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

humerus The humerus (; : humeri) 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 (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

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

Taxa

"Hapalodectinae" was originally erected on the basis of ''Hapalodectes'', and, after promotion to family ranking, contained up to five genera based on teeth and jaw fragments with anatomies similar to ''Hapalodectes''. However, as of Ting and Li, 1987, and confirmed with Gunnell and Gingerich, 1996, the genera '' Honanodon'', '' Lohoodon'' and '' Metahapalodectes'' are no longer considered hapalodectids due to the absence of grooves on the lower molars otherwise diagnostic of ''Hapalodectes'' and '' Hapalorestes''.Gunnell, Gregg F., and Philip D. Gingerich. "New hapalodectid Hapalorestes lovei (Mammalia, Mesonychia) from the early Middle Eocene of northwestern Wyoming." (1996). 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''

References

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