''Hapalodectes'' (literal translation 'soft biter'; from ('soft, tender') and ('biter')) is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

otter Otters are carnivorous mammals in the subfamily Lutrinae. The 13 extant otter species are all semiaquatic, aquatic, or marine. Lutrinae is a branch of the Mustelidae family, which includes weasels, badgers, mink, and wolverines, among ...

-like mesonychians from the

Late Paleocene The Thanetian is, in the International Commission on Stratigraphy, ICS Geologic timescale, the latest age (geology), age or uppermost stage (stratigraphy), stratigraphic stage of the Paleocene epoch (geology), Epoch or series (stratigraphy), Serie ...

Early Eocene In the geologic timescale the Ypresian is the oldest age (geology), age or lowest stage (stratigraphy), stratigraphic stage of the Eocene. It spans the time between , is preceded by the Thanetian Age (part of the Paleocene) and is followed by th ...

, some 55million years ago. Although the first

fossils A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserved ...

were found in the Eocene

strata In geology and related fields, a stratum (: strata) is a layer of Rock (geology), rock or sediment characterized by certain Lithology, lithologic properties or attributes that distinguish it from adjacent layers from which it is separated by v ...

Wyoming Wyoming ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States, Western United States. It borders Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho t ...

, the genus originated in

Mongolia Mongolia is a landlocked country in East Asia, bordered by Russia to the north and China to the south and southeast. It covers an area of , with a population of 3.5 million, making it the world's List of countries and dependencies by po ...

, as the oldest

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

is ''H. dux'', which was found in Late Paleocene strata in the Naran Bulak Formation. Hapalodectes restoration Stanton Fink 2

The genus was once suggested to be related to the

Archaeoceti Archaeoceti ("ancient whales"), or Zeuglodontes in older literature, is an obsolete paraphyletic group of primitive cetaceans that lived from the Early Eocene to the late Oligocene (). Representing the earliest cetacean radiation, they include th ...

, such as ''

Pakicetus ''Pakicetus'' (meaning 'whale from Pakistan') is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to the Indian Subcontinent during the Ypresian (early Eocene) period, about 50 million years ago. It was a w ...

'', due to numerous similarities between the

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

and

tooth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tea ...

anatomies of the two genera. Now, however, ''Hapalodectes'' and other mesonychians are thought to be related to basal

artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...

s, while the Archaeoceti are now determined to be descended from more derived artiodactyls, like ''

Indohyus ''Indohyus'' (Meaning "India's pig" from the Greek words ''Indos'', "from India" and ''hûs'', "pig") is an extinct genus of artiodactyl known from Eocene fossils in Asia. This small chevrotain-like animal found in the Himalayas is among the clo ...

'', which are related to

hippopotamus The hippopotamus (''Hippopotamus amphibius;'' ; : hippopotamuses), often shortened to hippo (: hippos), further qualified as the common hippopotamus, Nile hippopotamus and river hippopotamus, is a large semiaquatic mammal native to sub-Sahar ...

es and

anthracothere Anthracotheriidae is a paraphyletic family of extinct, hippopotamus-like artiodactyl ungulates related to hippopotamuses and whales. The oldest genus, '' Elomeryx'', first appeared during the middle Eocene in Asia. They thrived in Africa and Eura ...

s. ''H. dux'' possessed distinct conules on its upper

molars The molars or molar teeth are large, flat tooth, teeth at the back of the mouth. They are more developed in mammal, mammals. They are used primarily to comminution, grind food during mastication, chewing. The name ''molar'' derives from Latin, '' ...

Species

*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. paradux'' Lopatin, 2023 ** ''H. serus'' Matthew et Granger, 1925

References

Mesonychia Paleocene mammals Eocene mammals Ypresian extinctions Paleogene mammals of Asia Prehistoric placental genera {{paleo-mammal-stub