Anthracotheriidae
Encyclopedia
Anthracotheriidae is a family of extinct, hippopotamus
-like artiodactyl ungulate
s related to hippopotamus
es and whale
s. The oldest genus, Elomeryx
, first appeared during the Middle Eocene
in Asia. They thrived in Africa and Eurasia, with a few species ultimately entering North America
during the Oligocene
, and eventually died out in Europe and Africa during the Miocene
, possibly due to a combination of climatic changes and competition with other artiodactyls, including pigs and true hippopotami. The youngest genus, Merycopotamus
, died out in Asia during the late Pliocene
. The family is named after the first genus
discovered, Anthracotherium
, which means "coal beast," as the first fossils of it were found in Paleogene
-aged coal beds in France
. Fossil remains of the anthracothere genus were discovered by the Harvard University and Geological Survey of Pakistan joint research project (Y-GSP) in the well-dated Middle and Late Miocene deposits of the Pothohar Plateau
in northern Pakistan.
In life, the average anthracothere would have resembled a skinny hippopotamus with a comparatively small, narrow head and most likely pig-like in general appearance. They had four or five toes on each foot, and broad feet suited to walking on soft mud. They had a full set of approximately 44 teeth with five semi-crescentric cusps on the upper molars, which, in some species, were adapted for digging up the roots of aquatic plants.
The nature of the sediments in which they are fossilized implies that anthracotheres were amphibious, which supports the view based on anatomical evidence that they were ancestors of the hippopotami. In many respects, especially the anatomy of the lower jaw, Anthracotherium, as with other members of the family, is allied to the hippopotamus, of which it is probably an ancestral form.
However, one study suggests that, instead of anthracotheres, another pig-like group of artiodactyls called palaeochoerids are the true stem group of Hippopotamidae
.
Recent evidence gained from comparative gene sequencing further suggests that hippos are the closest living relatives of whales, so if anthracotheres are stem hippos, they would also be related to whales.
However, the earliest known anthracotheres appear in the fossil record in the Middle Eocene
, well after the archaeocetes
had taken up a totally aquatic lifestyle. Although phylogenetic analyses of molecular data on extant animals strongly support the notion that hippopotamids are the closest relatives of cetaceans (whales, dolphins and porpoises) (REF), it is unlikely that the two groups are closely related when extant and extinct artiodactyls are analyzed. One reason hypothesizes that cetaceans originated about 50 million years ago in south Asia, whereas the family Hippopotamidae is only 15 million years old and the first hippopotamids are only 6 million years old. Yet, analyses of fossil clades have not resolved the issue of cetacean relations.
Another study has offered a suggestion that anthracotheres are part of clade that also consists of entelodont
s and even Andrewsarchus that is a sister clade to other cetancodonts, with Siamotherium as the most basal member of the clade Cetacodontamorpha
.
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
-like artiodactyl ungulate
Ungulate
Ungulates are several groups of mammals, most of which use the tips of their toes, usually hoofed, to sustain their whole body weight while moving. They make up several orders of mammals, of which six to eight survive...
s related to hippopotamus
Hippopotamus
The hippopotamus , or hippo, from the ancient Greek for "river horse" , is a large, mostly herbivorous mammal in sub-Saharan Africa, and one of only two extant species in the family Hippopotamidae After the elephant and rhinoceros, the hippopotamus is the third largest land mammal and the heaviest...
es and whale
Cetacea
The order Cetacea includes the marine mammals commonly known as whales, dolphins, and porpoises. Cetus is Latin and is used in biological names to mean "whale"; its original meaning, "large sea animal", was more general. It comes from Ancient Greek , meaning "whale" or "any huge fish or sea...
s. The oldest genus, Elomeryx
Elomeryx
Elomeryx is an extinct genus of artiodactyl ungulate, and is among the earliest known anthracotheres. The genus was extremely widespread, first being found in Asia in the middle Eocene, in Europe during the latest Eocene, and having spread to North America by the early Oligocene.Elomeryx was about...
, first appeared during the 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...
in Asia. They thrived in Africa and Eurasia, with a few species ultimately entering North America
North America
North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...
during the Oligocene
Oligocene
The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...
, and eventually died out in Europe and Africa during the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
, possibly due to a combination of climatic changes and competition with other artiodactyls, including pigs and true hippopotami. The youngest genus, Merycopotamus
Merycopotamus
Merycopotamus is an extinct genus of Asian anthracothere that appeared during the Middle Miocene, and died out in the Late Pliocene. At the height of the genus' influence, species ranged throughout southern Asia. With the extinction of the last species, M. dissimilis, the lineage of...
, died out in Asia during the late Pliocene
Pliocene
The Pliocene Epoch is the period in the geologic timescale that extends from 5.332 million to 2.588 million years before present. It is the second and youngest epoch of the Neogene Period in the Cenozoic Era. The Pliocene follows the Miocene Epoch and is followed by the Pleistocene Epoch...
. The family is named after the first genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
discovered, Anthracotherium
Anthracotherium
Anthracotherium was a genus of extinct artiodactyl ungulate mammals, characterized by having 44 teeth, with five semi-crescentic cusps on the crowns of the upper molars. The genus ranged throughout the Oligocene period, having a distribution throughout Europe, Asia, and North America...
, which means "coal beast," as the first fossils of it were found in Paleogene
Paleogene
The Paleogene is a geologic period and system that began 65.5 ± 0.3 and ended 23.03 ± 0.05 million years ago and comprises the first part of the Cenozoic Era...
-aged coal beds in France
France
The French Republic , The French Republic , The French Republic , (commonly known as France , is a unitary semi-presidential republic in Western Europe with several overseas territories and islands located on other continents and in the Indian, Pacific, and Atlantic oceans. Metropolitan France...
. Fossil remains of the anthracothere genus were discovered by the Harvard University and Geological Survey of Pakistan joint research project (Y-GSP) in the well-dated Middle and Late Miocene deposits of the Pothohar Plateau
Pothohar Plateau
The Pothohar Plateau is a plateau in north-eastern Pakistan and the western parts of Pakistan-administered Kashmir. The area was the home of the Soanian Culture, which is evidenced by the discovery of fossils, tools, coins, and remains of ancient archaeological sites...
in northern Pakistan.
In life, the average anthracothere would have resembled a skinny hippopotamus with a comparatively small, narrow head and most likely pig-like in general appearance. They had four or five toes on each foot, and broad feet suited to walking on soft mud. They had a full set of approximately 44 teeth with five semi-crescentric cusps on the upper molars, which, in some species, were adapted for digging up the roots of aquatic plants.
Evolutionary relationships
Some skeletal characters of anthracotheres suggest they are related to hippos.The nature of the sediments in which they are fossilized implies that anthracotheres were amphibious, which supports the view based on anatomical evidence that they were ancestors of the hippopotami. In many respects, especially the anatomy of the lower jaw, Anthracotherium, as with other members of the family, is allied to the hippopotamus, of which it is probably an ancestral form.
However, one study suggests that, instead of anthracotheres, another pig-like group of artiodactyls called palaeochoerids are the true stem group of Hippopotamidae
Hippopotamidae
Hippopotamuses are the members of the family Hippopotamidae. They are the only extant artiodactyls which walk on four toes on each foot.- Characteristics :...
.
Recent evidence gained from comparative gene sequencing further suggests that hippos are the closest living relatives of whales, so if anthracotheres are stem hippos, they would also be related to whales.
However, the earliest known anthracotheres appear in the fossil record in the 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...
, well after the archaeocetes
Archaeoceti
Archaeocetes, or "ancient whales", are a paraphyletic group of cetaceans that gave rise to the modern cetaceans.The archaeocetes were once thought to have evolved from the mesonychids, based on dental characteristics...
had taken up a totally aquatic lifestyle. Although phylogenetic analyses of molecular data on extant animals strongly support the notion that hippopotamids are the closest relatives of cetaceans (whales, dolphins and porpoises) (REF), it is unlikely that the two groups are closely related when extant and extinct artiodactyls are analyzed. One reason hypothesizes that cetaceans originated about 50 million years ago in south Asia, whereas the family Hippopotamidae is only 15 million years old and the first hippopotamids are only 6 million years old. Yet, analyses of fossil clades have not resolved the issue of cetacean relations.
Another study has offered a suggestion that anthracotheres are part of clade that also consists of entelodont
Entelodont
Entelodonts, sometimes nicknamed hell pigs or terminator pigs, is an extinct family of pig-like omnivores endemic to forests and plains of North America, Europe, and Asia from the middle Eocene to early Miocene epochs , existing for approximately .-Taxonomy:Entelodontidae was named by Richard...
s and even Andrewsarchus that is a sister clade to other cetancodonts, with Siamotherium as the most basal member of the clade Cetacodontamorpha
Cetacodontamorpha
Cetancodontamorpha is a total clade of artiodactyls defined, according to Spaulding et al., as "Cetancodonta plus all extinct taxa more closely related to extant members of Cetancodonta than to any other living species." Cetancodonta is the crown clade containing Cetacea and hippopotamuses...
.