''Andrewsarchus'' (), meaning "
Andrews Andrews may refer to:
Places Australia
*Andrews, Queensland
*Andrews, South Australia
United States
*Andrews, Florida (disambiguation), various places
*Andrews, Indiana
*Andrews, Nebraska
*Andrews, North Carolina
*Andrews, Oregon
*Andrews, South ...
' ruler", is an extinct
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 ...
of
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 ...
that lived during the
Middle Eocene
The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...
in what is now China. The genus was
first described by
Henry Fairfield Osborn in 1924 with the
type species
In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...
''A. mongoliensis'' based on a largely complete
cranium. A second species, ''A. crassum'', was described in 1977 based on teeth. A mandible, formerly described as ''Paratriisodon'', does probably belong to ''Andrewsarchus'' as well. The genus has been historically placed in the families
Mesonychidae or
Arctocyonidae, or was considered to be a close relative of whales. It is now regarded as the sole member of its own family, Andrewsarchidae, and may have been related to
entelodonts. Fossils of ''Andrewsarchus'' have been recovered from the Middle Eocene
Irdin Manha,
Lushi, and
Dongjun Formations of
Inner Mongolia
Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an Autonomous regions of China, autonomous region of China. Its border includes two-thirds of the length of China's China–Mongolia border, border with the country of Mongolia. ...
, each dated to the
Irdinmanhan Asian land mammal age (
Lutetian
The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...
–
Bartonian stages, 48–38 million years ago).
''Andrewsarchus'' has historically been reputed as the
largest terrestrial, carnivorous mammal given its skull length of , though its overall body size was probably overestimated due to inaccurate comparisons with mesonychids. Its
incisors
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
are arranged in a semicircle, similar to entelodonts, with the second rivalling the canine in size. The premolars are again similar to entelodonts in having a
single cusp. The
crowns of the
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, '' ...
are wrinkled, suggesting it was
omnivorous
An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...
or a scavenger. Unlike many modern scavengers, a reduced
sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are excepti ...
and flat
mandibular fossa suggest that ''Andrewsarchus'' likely had a fairly weak bite force.
Taxonomy
Early history
The
holotype
A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
of ''Andrewsarchus mongoliensis'' is a mostly complete
cranium (specimen number AMNH-VP 20135). It was recovered from the lower
Irdin Manha Formation
The Irdin Manha Formation is a geology, geological formation from the Eocene located in Inner Mongolia, China, a few kilometres south of the Mongolian border.. Retrieved July 2013.
Fossil content
Mammals
U.S. paleontologists Henry Fairfield O ...
of
Inner Mongolia
Inner Mongolia, officially the Inner Mongolia Autonomous Region, is an Autonomous regions of China, autonomous region of China. Its border includes two-thirds of the length of China's China–Mongolia border, border with the country of Mongolia. ...
during a 1923 palaeontological expedition conducted by the
American Museum of Natural History
The American Museum of Natural History (AMNH) is a natural history museum on the Upper West Side of Manhattan in New York City. Located in Theodore Roosevelt Park, across the street from Central Park, the museum complex comprises 21 interconn ...
of New York.
Its discoverer was a local assistant, Kan Chuen-pao, also known as "Buckshot".''
'' It was initially identified by
Walter W. Granger as the skull of an ''
Entelodon.
'' A drawing of the skull was sent to the museum, where it was identified by
William Diller Matthew as belonging to "the primitive
Creodonta of the family
Mesonychidae".
The specimen itself arrived at the museum and was described by Osborn in 1924. Its
generic name honours
Roy Chapman Andrews
Roy Chapman Andrews (January 26, 1884 – March 11, 1960) was an American explorer, adventurer, and Natural history, naturalist who became the director of the American Museum of Natural History. He led a series of expeditions through the politi ...
, the leader of the expedition, with the
Ancient Greek
Ancient Greek (, ; ) includes the forms of the Greek language used in ancient Greece and the classical antiquity, ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Greek ...
''archos'' (
ἀρχός, "ruler") added to his surname.
A second species of ''Andrewsarchus'', ''A. crassum'', was named by Ding Suyin and colleagues in 1977 on the basis of IVPP V5101, a pair of teeth (the second and third lower
premolars) recovered from the
Dongjun Formation of
Guangxi
Guangxi,; officially the Guangxi Zhuang Autonomous Region, is an Autonomous regions of China, autonomous region of the China, People's Republic of China, located in South China and bordering Vietnam (Hà Giang Province, Hà Giang, Cao Bằn ...
.

In the 1957,
Zhou Mingzhen and colleagues recovered a mandible, a fragmentary maxilla, and several isolated teeth from the Lushi Formation of
Henan
Henan; alternatively Honan is a province in Central China. Henan is home to many heritage sites, including Yinxu, the ruins of the final capital of the Shang dynasty () and the Shaolin Temple. Four of the historical capitals of China, Lu ...
, China, which correlates to the Irdin Manha Formation. The maxilla belonged to a skull that was crushed beyond recognition; it is likely from the same individual as the mandible.
Zhou described it in 1959 as ''Paratriisodon henanensis'', and assigned it to
Arctocyonidae. He further classified it as part of the subfamily
Triisodontinae (now the family Triisodontidae) based on close similarities of the
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, '' ...
and
premolars to those of ''
Triisodon''.
A second species, ''P. gigas'', was named by Zhou and colleagues in 1973 for a
molar also from the Lushi Formation. Three molars and an
incisor from the Irdin Manha Formation were later referred to ''P. gigas''.
Comparisons between the two genera were drawn as far back as 1969, when Frederick Szalay suggested that they either evolved from the same arctocyonid ancestors or that they were an example of convergent evolution. ''Paratriisodon'' was first properly synonymised with ''Andrewsarchus'' by
Leigh Van Valen in 1978, who did so without explanation.
Regardless, their synonymy was upheld by Maureen O'Leary in 1998, based on similarities between the molars and premolars of the two genera and their comparable body sizes.
Classification
''Andrewsarchus'' was initially regarded as a mesonychid,
and ''Paratriisodon'' as an
arctocyonid.
In 1995, the former became the sole member of its own
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 ...
, Andrewsarchinae, within
Mesonychia.
The subfamily was elevated to family level by
Philip D. Gingerich in 1998, who tentatively assigned ''Paratriisodon'' to it. In 1988,
Donald Prothero and colleagues recovered ''Andrewsarchus'' as the
sister taxon to whales. It has since been recovered as a more
basal member of
Cetancodontamorpha, most closely related to
entelodonts,
hippos, and
whales
Whales are a widely distributed and diverse group of fully Aquatic animal, aquatic placental mammal, placental marine mammals. As an informal and Colloquialism, colloquial grouping, they correspond to large members of the infraorder Cetacea ...
.
In 2023, Yu and colleagues conducted a phylogenetic analysis of
ungulates, with a particular focus on entelodontid artiodactyls. ''Andrewsarchus'' was recovered as part of a clade consisting of itself, ''
Achaenodon'', ''
Erlianhyus'', ''
Protentelodon'', ''
Wutuhyus'', and
Entelodontidae. It was found to be most closely related to ''Achaenodon'' and ''Erlianhyus'', with which it formed a
polytomy. A
cladogram
A cladogram (from Greek language, Greek ''clados'' "branch" and ''gramma'' "character") is a diagram used in cladistics to show relations among organisms. A cladogram is not, however, an Phylogenetic tree, evolutionary tree because it does not s ...
based on their phylogeny is reproduced below:
Description

When first describing ''Andrewsarchus'', Osborn believed it to be the largest terrestrial, carnivorous mammal. Based on the length of the ''A. mongoliensis''
holotype
A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...
skull, and using the proportions of ''
Mesonyx'', he estimated a total body length of and a body height of .
However, considering cranial and dental similarities with
entelodonts, Frederick Szalay and
Stephen Jay Gould
Stephen Jay Gould ( ; September 10, 1941 – May 20, 2002) was an American Paleontology, paleontologist, Evolutionary biology, evolutionary biologist, and History of science, historian of science. He was one of the most influential and widely re ...
proposed that it had proportions less like mesonychids and more like them, and thus that Osborn's estimates were likely inaccurate.
Skull
The holotype skull of ''Andrewsarchus'' has a total length of , and is wide at the
zygomatic arches. The snout is greatly elongated, measuring one-and-a-half times the length of the
basicranium,
and the portion of the snout in front of the canines resembles that of entelodonts.
Unlike entelodonts, however, the
postorbital bar is incomplete.
The
sagittal crest
A sagittal crest is a ridge of bone running lengthwise along the midline of the top of the skull (at the sagittal suture) of many mammalian and reptilian skulls, among others. The presence of this ridge of bone indicates that there are excepti ...
is reduced, and the
mandibular fossa is relatively flat. Together, these attributes suggest a weak
temporalis muscle and a fairly weak bite force. The
hard palate is long and narrow.
The mandibular fossa is also offset
laterally and
ventrally from the
basicranium, similar to the condition seen in mesonychids. The
mandible
In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla).
The jawbone i ...
itself is long and shallow, characterised by a straight and relatively shallow
horizontal ramus.
The masseteric fossa, the depression on the mandible to which the
masseter
In anatomy, the masseter is one of the muscles of mastication. Found only in mammals, it is particularly powerful in herbivores to facilitate chewing of plant matter. The most obvious muscle of mastication is the masseter muscle, since it is the ...
attaches, is shallow.
Symphyseal contact between the two mandibles is limited.
Dentition

The holotype cranium of ''Andrewsarchus'' demonstrates the typical placental
tooth formula, of three
incisors
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
, one
canine, four
premolars and three
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, '' ...
per side,
though it is not clear whether the same applies to the mandible. The upper
incisors
Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
are arranged in a semicircle in front of the canines, a trait that is shared with entelodonts. The second incisor is enlarged, and is almost the size of the canines.
This is partly because, while the canines were originally described as being "of enormous size",
they are relatively small in proportion to the rest of the dentition.
The upper
premolars are elongate and consist of a
single cusp, resembling those of entelodonts. The fourth premolar retains the
protocone, though in a
vestigial form.
Their roots are not
confluent and lack a
dentine platform, which are both likely to be adaptations to prolong the tooth's functional life after crown abrasion. The first molar is the smallest. The second is the widest, but has been heavily worn since fossilisation. The third has largely avoided that wear. The premolars and molars have wrinkled
crowns, similar to the condition seen in
suids and other omnivorous artiodactyls.
The tooth structure of the mandible (IVPP V5101) is difficult to determine, as nearly all are
worn or broken. All of the right mandible's teeth are preserved save for the first premolar, which is instead preserved on the left mandible. The lower canine and the first premolar both point forwards.
The third molar is large, with
talonids that have two cusps.
Diet
In his paper describing ''Andrewsarchus'', Osborn suggested that it may have been
omnivorous
An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...
based on comparisons with entelodonts.
This conclusion was supported by Szalay and Gould, who use the heavily wrinkled crowns of the molars and premolars as supporting evidence,
as well as the close phylogenetic relationship between ''Andrewsarchus'' and entelodonts.
R.M. Joeckel, in 1990, suggested that it was likely an "omnivore-scavenger", and that it was an ecological analogue to entelodonts. Lars Werdelin further suggested that it was a scavenger, or that it might have preyed on
brontotheres.
Palaeoecology

For much of the Eocene, a hothouse climate with humid, tropical environments with consistently high precipitations prevailed. Modern mammalian orders including the
Perissodactyla, Artiodactyla, and
Primates
Primates is an order of mammals, which is further divided into the strepsirrhines, which include lemurs, galagos, and lorisids; and the haplorhines, which include tarsiers and simians ( monkeys and apes). Primates arose 74–63 ...
(or the suborder Euprimates) appeared already by the Early Eocene, diversifying rapidly and developing dentitions specialized for folivory. The
omnivorous
An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize ...
forms mostly either switched to folivorous diets or went extinct by the Middle Eocene (
Lutetian
The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...
–
Bartonian, 48–38 million years ago) along with the archaic "
condylarths". By the Late Eocene (
Priabonian
The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between . The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage ...
, 38–34 million years ago), most of the ungulate form dentitions shifted from bunodont cusps to cutting ridges (i.e. lophs) for folivorous diets.
The
Irdin Manha Formation
The Irdin Manha Formation is a geology, geological formation from the Eocene located in Inner Mongolia, China, a few kilometres south of the Mongolian border.. Retrieved July 2013.
Fossil content
Mammals
U.S. paleontologists Henry Fairfield O ...
, from which the holotype of ''Andrewsarchus'' was recovered, consists of
Irdinmanhan strata dated to the Middle Eocene.
''Andrewsarchus mongoliensis'' comes from the IM-1 locality, dated to the lower
Irdinmanhan,
from which the
hyaenodontine ''Propterodon'', the
mesonychid ''
Harpagolestes'', at least three unnamed mesonychids,
the artiodactyl ''
Erlianhyus'',
the perissodactyls ''
Deperetella'' and ''
Lophialetes'', the
omomyid ''
Tarkops'', the
glirian ''
Gomphos'', the rodent ''
Tamquammys,'' and various indeterminate glirians are also known.
The Lushi Formation, from which the ''Paratriisodon henanensis'' specimen was recovered, was deposited at around the same time as the Irdin Manha Formation. The mesonychid ''
Mesonyx'', the pantodont ''
Eudinoceras'', the dichobunid ''
Dichobune'', the
helohyid ''
Gobiohyus'', the brontotheres ''
Rhinotitan'' and ''
Microtitan'', the perissodactyls ''
Amynodon'' and ''Lophialetes'', the
ctenodactylid ''
Tsinlingomys'', and the
lagomorph
The lagomorphs () are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (rabbits and hares) and the Ochotonidae ( pikas). There are 110 recent species of lagomorph, of which 109 species in t ...
''
Lushilagus'' have been identified from the Lushi Formation. The Dongjun Formation, from which ''A. crassum'' originates, is similarly Middle Eocene. It preserves the
nimravid ''
Eusmilus'', the
anthracotheriid ''
Probrachyodus'', the pantodont ''Eudinoceras'', the brontotheres ''
Metatelmatherium'' and cf. ''
Protitan'', the deperetellids ''
Deperetella'' and ''
Teleolophus'', the hyracodontid ''
Forstercooperia'', the rhinocerotids ''
Ilianodon'' and ''
Prohyracodon'', and the amynodonts ''
Amynodon'', ''
Gigantamynodon'', and ''
Paramnyodon''.
References
{{Taxonbar, from=Q133214
Cetancodontamorpha
Eocene Artiodactyla
Enigmatic mammal taxa
Eocene mammals
Eocene mammals of Asia
Lutetian genus first appearances
Priabonian genus extinctions
Fossil taxa described in 1924
Taxa named by Henry Fairfield Osborn
Prehistoric Artiodactyla genera