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''Moeritherium'' ("the beast from
Lake Moeris Lake Moeris (, genitive Μοίριδος) was an ancient endorheic freshwater lake located in the Faiyum Oasis, southwest of Cairo, Egypt, which persists today at a fraction of its former size as the hypersaline Lake Qarun (Arabic: بركة ق� ...
") is an extinct genus of basal
proboscidea Proboscidea (; , ) is a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. Three l ...
ns from the
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 ...
of North and West Africa. The first specimen was discovered in strata from the Fayum fossil deposits of
Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...
. It was named in 1901 by Charles William Andrews, who suggested that it was an early proboscidean, perhaps ancestral to mastodons, although subsequent workers considered it everything from a relative of
manatees Manatees (, family Trichechidae, genus ''Trichechus'') are large, fully aquatic, mostly herbivorous marine mammals sometimes known as sea cows. There are three accepted living species of Trichechidae, representing three of the four living spe ...
to a close relative of both clades' common ancestor. Currently, ''Moeritherium'' is seen as a proboscidean that, while fairly basal, predates the split between elephantiforms and deinotheres. Seven species have been named, though only three (''M. lyonsi'', ''M. gracile'', and ''M. chehbeurameuri''), are currently considered valid. ''Moeritherium'' is unusual even among basal proboscidean standards. Like many later members of the group, it had two sets of tusks: the ones on the upper jaw pointed downwards, while those of 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 ...
(lower jaw) were flat and formed a spade shape. In addition to these tusks, it retained its upper canines, though had lost the lower set. The morphology of the skull, particularly the nasal cavity (which was only slightly retracted), suggests that ''Moeritherium'' lacked a trunk. It may have instead possessed a small,
tapir Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a Suidae, pig, with a short, prehensile nose trunk (proboscis). Tapirs inhabit jungle and forest regions of South America, South and Centr ...
-like
proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...
, formed from the fusion of the upper lip and the nose, an evolutionary precursor of trunks. Though poorly described in the literature, ''Moeritherium'''s torso is known to have been very long, and its limbs were short. These divergent traits have led to comparisons with
desmostylians The Desmostylia (from Ancient Greek, Greek δεσμά ''desma'', "bundle", and στῦλος ''stylos'', "pillar") are an extinct order (biology), order of aquatic mammals native to the North Pacific from the early Oligocene (Rupelian) to the lat ...
, a lineage of extinct mammals formerly believed to have been relatives of manatees. ''Moeritherium'' has been suggested to have led a semi-aquatic lifestyle. While this originally stemmed from perceived similarities to sirenians (manatees and dugongs), morphological data and
isotope analysis Isotope analysis is the identification of isotopic signature, abundance of certain stable isotopes of chemical elements within organic and inorganic compounds. Isotopic analysis can be used to understand the flow of energy through a food we ...
has since lent it a great deal of support. The elongated body of ''Moeritherium'', and the high position of its eyes and ears, are likely a result of its lifestyle, and its unusual dentition is likely an adaptation for feeding on water plants.


Taxonomy


Early history

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 ...
of ''Moeritherium'', ''M. lyonsi'', was discovered in strata belonging to the Qasr el Sagha Formation in the Fayum fossil deposits of
Egypt Egypt ( , ), officially the Arab Republic of Egypt, is a country spanning the Northeast Africa, northeast corner of Africa and Western Asia, southwest corner of Asia via the Sinai Peninsula. It is bordered by the Mediterranean Sea to northe ...
. The
type specimen In biology, a type is a particular wikt:en:specimen, specimen (or in some cases a group of specimens) of an organism to which the scientific name of that organism is formally associated. In other words, a type is an example that serves to ancho ...
(CGM C.10000) consists of an almost complete mandible. It was described in 1901 by Charles William Andrews, who proposed two hypotheses for its phylogenetic position: either ''Moeritherium'' was part of the obsolete order Amblypoda, or it was an early
proboscidean Proboscidea (; , ) is a taxonomic order of afrotherian mammals containing one living family (Elephantidae) and several extinct families. First described by J. Illiger in 1811, it encompasses the elephants and their close relatives. Three liv ...
, perhaps "a generalised forerunner of the
Mastodon A mastodon, from Ancient Greek μαστός (''mastós''), meaning "breast", and ὀδούς (''odoús'') "tooth", is a member of the genus ''Mammut'' (German for 'mammoth'), which was endemic to North America and lived from the late Miocene to ...
type". In any case, he regarded it as an ungulate.


Additional species

In 1902, after conducting a more thorough examination of specimens collected by himself and his colleague, Hugh John Llewellyn Beadnell, he named a second species from the Qasr el Sagha, ''M. gracile''; a third was recognised in the same paper, though he did not provide a name, and referred to it simply as ''M.'' sp. The two species were distinguished from ''M. lyonsi'' by a more gracile build and a larger body size respectively. The lack of material overlap has made it difficult to determine how ''M. gracile'' actually relates to ''M. lyonsi'', as their holotypes consist of different skull elements; the type specimen of the former (CGM C.10003) is a palate with no associated lower teeth. Regardless, they are treated as belonging to the same genus, and are likely separate. Two years later, a fourth taxon, ''M. trigodon'', was described, also by Andrews, based on remains recovered from the " fluvio-marine beds"Matsumoto, H. 1922. Revision of ''Palæomastodon'' and ''Mœritherium''. ''Palæomastodon intermedius'', and ''Phiomia osborni'', new species. ''American Museum Novitates''. Number 51, November 21. (equivalent to the
Jebel Qatrani Formation The Jebel Qatrani Formation (also Gebel Qatrani, Gabal Qatrani or Djebel Qatrani) is a geologic formation located in the Faiyum Governorate of central Egypt. It is exposed between the Jebel Qatrani escarpment and the Qasr el Sagha escarpment, nor ...
) around the lake Birket-el-Qurun. In 1955, over half a century after the genus' initial naming, Sri Lankan artist and palaeontologist Paulus Edward Pieris Deraniyagala named two additional species, ''P. latidens'' and ''P. pharaonensis'', based on isolated mandibular fragments. In 1911, German zoologist Max Schlosser divided ''M. lyonsi'' into two species: ''M. lyonsi'', restricted to the Qasr el Sagha Formation, and ''M. andrewsi'', restricted to the Jebel Qatrani. This classification, however, has been rejected. In 1971, German zoologist Heinz Tobien opted to synonymise the entire genus with ''M. lyonsi'', though he chose to altogether disregard, Deraniyagala's species, likely as they were poorly diagnostic. In 2006, Cyrile Delmer et al. published a paper describing a new ''Moeritherium'' species, ''M. chehbeurameuri'', from Bir El Ater,
Algeria Algeria, officially the People's Democratic Republic of Algeria, is a country in the Maghreb region of North Africa. It is bordered to Algeria–Tunisia border, the northeast by Tunisia; to Algeria–Libya border, the east by Libya; to Alger ...
. In their paper, they treated most of the above species (with the exception of ''M. latidens'' and ''M. pharaonensis'') as valid. While the paper was not intended as a systematic revision, they chose to treat at the very least three species as valid: the type species ''M. lyonsi'', ''M. gracile'', and ''M. chehbeaurameuri''.


Classification

Henry Fairfield Osborn, in 1909, suggested that ''Moeritherium'' was more similar to sirenians (manatees and dugongs, and their extinct kin) to any living or extinct proboscidean. In 1921, however, he rejected this view, and divided Proboscidea into four suborders or superfamilies: Moeritherioidea, Deinotherioidea, Mastodontoidea, and Elephantoidea. In a 1988 paper discussing the systematics of proboscideans, Pascal Tassy abandoned this system and neglected to provide any superfamily-rank clades. Erecting the suborder Elephantiformes, Tassy placed ''Moeritherium'' outside it, alongside '' Barytherium'', '' Numidotherium'', and the Deinotheriidae. He considered ''Moeritherium'' among the most basal proboscideans, with ''Numidotherium'' being the most basal and ''Barytherium'' being only slightly less basal than that. In a 2021 paper describing a new genus (''Dagbatitherium tassyi'') Lionel Hautier et al. ran a phylogenetic analysis which recovered ''Moeritherium'' as sister to a clade including deinotheres and elephantiforms. A cladogram of Proboscidea based on the phylogenetic analysis of Hautier et al. 2021 is below:


Description

''Moeritherium'' was a fairly small, very elongate taxon. It was smaller than most later proboscideans. The species ''M. lyonsi'' has an estimated body length of . At the shoulder, this species measured only , and it had a body mass of , though ''Moeritherium'' exhibited strong sized-based
sexual dimorphism Sexual dimorphism is the condition where sexes of the same species exhibit different Morphology (biology), morphological characteristics, including characteristics not directly involved in reproduction. The condition occurs in most dioecy, di ...
, so this estimate should be considered a crude average.


Skull and dentition

The skull of ''Moeritherium'' was long, slender, and very low for the entirety of its length. The cranial region is nearly twice as long as the facial region. 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 ...
(eye socket) occupied a fairly anterodorsal position, meaning that it sat towards the front and top of the skull, and resembled that of
sirenians The Sirenia (), commonly referred to as sea cows or sirenians, are an order (biology), order of fully aquatic, herbivorous mammals that inhabit swamps, rivers, estuaries, marine wetlands, and coastal marine waters. The extant Sirenia comprise tw ...
. Unlike later proboscideans, the naris (nasal cavity) was fairly close to the front of the skull, which, in conjunction with the length of the mandible, suggests that a conventional trunk was absent in ''Moeritherium''. It may have instead possessed a wide, mobile unit comprising the nose and
upper lip The lips are a horizontal pair of soft appendages attached to the jaws and are the most visible part of the mouth of many animals, including humans. Mammal lips are soft, movable and serve to facilitate the ingestion of food (e.g. sucklin ...
, similar to the
proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular arthropod mouthparts, mouthparts used for feeding and sucking. In vertebrates, a pr ...
of modern
tapirs Tapirs ( ) are large, herbivorous mammals belonging to the family Tapiridae. They are similar in shape to a Suidae, pig, with a short, prehensile nose trunk (proboscis). Tapirs inhabit jungle and forest regions of South America, South and Centr ...
. The external ear would have been high up on the skull, which may have been an adaptation for a semiaquatic lifestyle; the same, however, is observed in other proboscideans that are unlikely to have been aquatic, such as ''
Gomphotherium ''Gomphotherium'' (; "nail beast" for its double set of straight tusks) is an extinct genus of gomphothere proboscidean from the Neogene of Eurasia, Africa and North America. It is the most diverse genus of gompothere, with over a dozen valid sp ...
'' and '' Palaeomastodon''. ''Moeritherium'' has a
dental formula Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...
of . The first lower
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 ...
sit close together, forming a spade shape, while the equivalent set on the upper jaw, actually the second incisors (as in later genera), were modified into short, curved tusks. ''Moeritherium'' still retained the first and third upper incisors, and the upper canines, though in a highly reduced form. The cheek teeth (the
premolars The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mout ...
and
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, '' ...
) were bunodont, bearing rounded cusps, though were also lophodont, bearing large ridges called lophs between cusps. The premolars are large and broad in relation to the molars, a condition not seen in more derived proboscideans, though similar to in manatees.


Postcranial skeleton

The postcranial anatomy of ''Moeritherium'' has been compared to
desmostylians The Desmostylia (from Ancient Greek, Greek δεσμά ''desma'', "bundle", and στῦλος ''stylos'', "pillar") are an extinct order (biology), order of aquatic mammals native to the North Pacific from the early Oligocene (Rupelian) to the lat ...
, such as ''
Pezosiren ''Pezosiren portelli'', also known as the "walking manatee", is a basal sirenian from the early Eocene of Jamaica, 50 million years ago. The type specimen is represented by a Jamaican fossil skeleton, described in 2001 by Daryl Domning, a marine ...
''. Both taxa have an extremely elongated, broad torso, possibly an adaptation for diving in both taxa. Little of the cervical (neck)
vertebrae Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spinal ...
is known, save for the
atlas An atlas is a collection of maps; it is typically a bundle of world map, maps of Earth or of a continent or region of Earth. Advances in astronomy have also resulted in atlases of the celestial sphere or of other planets. Atlases have traditio ...
and some of the middle cervical vertebrae. Most of the vertebral column, save for some cervical vertebrae and one of the
thoracic The thorax (: thoraces or thoraxes) or chest is a part of the anatomy of mammals and other tetrapod animals located between the neck and the abdomen. In insects, crustaceans, and the extinct trilobites, the thorax is one of the three main ...
(upper body) vertebrae, is known from a specimen that was at some point catalogued as C. 10005, probably belonging to ''M. lyonsi''. A more complete specimen of ''Moeritherium'' is known, though has not been described in detail. Like modern proboscideans, there twenty-three presacral vertebrae (those preceding the
sacrum The sacrum (: sacra or sacrums), in human anatomy, is a triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part of the pelvic cavity, ...
). The lumbar (lower back) region was longer proportionally than in modern proboscideans, while the thoracic region was slightly shorter. ''Moeritherium'''s limbs were extremely short compared to those of later taxa, being roughly half as big, proportionally, as those of extant
elephant Elephants are the largest living land animals. Three living species are currently recognised: the African bush elephant ('' Loxodonta africana''), the African forest elephant (''L. cyclotis''), and the Asian elephant ('' Elephas maximus ...
s.


Palaeobiology


Lifestyle

The notion of ''Moeritherium'' being semi-aquatic dates as far back as 1909, when Henry Fairfield Osborn suggested that it was not only related to sirenians, but resembled them in habits. In his 1923 paper discussing the genus' morphology, Japanese zoologist Matsumoto Hikoshichirō listed adaptations that indicated a semi-aquatic lifestyle (such as the high position of the eyes and ears), though also listed several that were evidence against it (such as its dentition, which to him seemed better-suited to a terrestrial forager). In his view, ''Moeritherium'' was unlikely to be semi-aquatic. However, similarities with desmostylians have been noted in the postcranial skeleton, and its unusual limb proportions have been cited as the product of a semi-aquatic lifestyle. In 2008, stable isotopic analysis lent further credence to the semiaquatic model, with its oxygen isotope ratios more closely resembling those of aquatic ones than fully terrestrial ones, with it being suggested that ''Moeritherium'' likely consumed freshwater plants.


Palaeoenvironment

The environment of the Jebel Qatrani Formation, from which some specimens of ''Moeritherium'' are known, have been described as a
subtropical The subtropical zones or subtropics are geographical zone, geographical and Köppen climate classification, climate zones immediately to the Northern Hemisphere, north and Southern Hemisphere, south of the tropics. Geographically part of the Ge ...
to
tropical The tropics are the regions of Earth surrounding the equator, where the sun may shine directly overhead. This contrasts with the temperate or polar regions of Earth, where the Sun can never be directly overhead. This is because of Earth's ax ...
lowland plain by Bown, who further suggests the presence of streams and ponds. Based on the occurrence of birds that are associated with water (such as ospreys, early flamingos, jacanas,
herons Herons are long-legged, long-necked, freshwater and coastal birds in the family Ardeidae, with 75 recognised species, some of which are referred to as egrets or bitterns rather than herons. Members of the genus '' Botaurus'' are referred to as ...
,
storks Storks are large, long-legged, long-necked wading birds with long, stout Beak, bills. They belong to the family (biology), family Ciconiidae, and make up the order Ciconiiformes . Ciconiiformes previously included a number of other families, suc ...
, cormorants and shoebills), Rasmussen and colleagues similarly inferred that the environment featured slow-moving freshwater with a substantial amount of aquatic vegetation. Although
lithology The lithology of a rock unit is a description of its physical characteristics visible at outcrop, in hand or core samples, or with low magnification microscopy. Physical characteristics include colour, texture, grain size, and composition. Lit ...
suggests that most fossils were deposited on sandbanks after being transported by currents, the authors argue that
swamps A swamp is a forested wetland.Keddy, P.A. 2010. Wetland Ecology: Principles and Conservation (2nd edition). Cambridge University Press, Cambridge, UK. 497 p. Swamps are considered to be transition zones because both land and water play a role in ...
could have easily formed along the banks of the river that was present during the Oligocene and may account for the mudstone found in certain quarries. They furthermore suggest that the fossil birds of Fayum, due to their affinities with modern groups, should be considered a more valuable indicator of the environment when compared with the fossil mammals, many of which belonged to families lacking modern examples. The absence of other birds typical for such an environment may be explained either through sampling bias or due to the fact that said groups had simply not yet been present in Oligocene Africa. Generally, Rasmussen and colleagues compare the environment of Jebel Qatrani to freshwater habitats in modern Central Africa. The discovery of snakehead fossils seem to support Rasmussen's interpretation, as the ''Parachanna'' today prefers slow-moving backwaters with plenty of vegetation. Other fish present meanwhile, notably ''Tylochromis'', suggest that deep, open water was likewise present. The river channels may have been overgrown with reeds,
papyrus Papyrus ( ) is a material similar to thick paper that was used in ancient times as a writing surface. It was made from the pith of the papyrus plant, ''Cyperus papyrus'', a wetland sedge. ''Papyrus'' (plural: ''papyri'' or ''papyruses'') can a ...
and featured floating vegetation like water lilies and ''
Salvinia ''Salvinia'' or watermosses is a genus of free-floating aquatic ferns in the family Salviniaceae. The genus is named in honor of 17th-century Italian naturalist Anton Maria Salvini, and the generic name was first published in 1754 by French bo ...
''. In a 2001 paper Rasmussen et al''.'' argued that the sandstone and mudstone of the formation likely formed as sediments were aggraded by a system of river channels that emptied towards the west into the Tethys. Here they reconstructed the environment as a tropical lowland swamp forest intermingled with marshes. They furthermore suggest that the environment would have experienced
monsoons A monsoon () is traditionally a seasonal reversing wind accompanied by corresponding changes in precipitation but is now used to describe seasonal changes in atmospheric circulation and precipitation associated with annual latitudinal oscil ...
. Overall this indicates that this region was a part of an extensive belt of tropical forest that stretched across what is now northern Africa, which would gradually give rise to open woodland and even steppe the further one was to travel inland.


Notes


References

{{Taxonbar, from=Q131232 Eocene proboscideans Eocene mammals of Africa Prehistoric placental genera Transitional fossils Taxa named by Charles William Andrews Fossil taxa described in 1901