Moeritherium

File:Map_of_Fayum_area.png

The type species of Moeritherium, M. lyonsi, was discovered in strata belonging to the Qasr el Sagha Formation in the Fayum fossil deposits of Egypt.{{Cite journal |last=Matsumoto |first=Hikoshichirō |last2=Andrews |first2=Charles William |date=1923 |title=A contribution to the knowledge of Moeritherium. Bulletin of the AMNH ; v. 48, article 4. |url=https://digitallibrary.amnh.org/items/fca96909-0303-46ab-8cd7-0e3fc3627a5e |journal=Bulletin of the American Museum of Natural History}} The type specimen (CGM C.10000) consists of an almost complete mandible.{{Cite journal |last=Andrews |first=Charles William |author-link=Charles William Andrews |date=1901 |title=II.—Preliminary Note on some Recently Discovered Extinct Vertebrates from Egypt. (Part I.) |url=https://www.cambridge.org/core/journals/geological-magazine/article/abs/iipreliminary-note-on-some-recently-discovered-extinct-vertebrates-from-egypt-part-i/27D7F26260C46DA8EFEB19FFBB4AB200 |journal=Geological Magazine |language=en |volume=8 |issue=9 |pages=400–409 |doi=10.1017/S0016756800179282 |issn=1469-5081}}{{Cite journal |last=Delmer |first=Cyrille |last2=Mahboubi |first2=Mohamed |last3=Tabuce |first3=Rodolphe |last4=Tassy |first4=Pascal |date=2006 |title=A New Species of Moeritherium (proboscidea, Mammalia) from the Eocene of Algeria: New Perspectives on the Ancestral Morphotype of the Genus |url=https://onlinelibrary.wiley.com/doi/10.1111/j.1475-4983.2006.00548.x |journal=Palaeontology |language=en |volume=49 |issue=2 |pages=421–434 |doi=10.1111/j.1475-4983.2006.00548.x |issn=1475-4983|url-access=subscription }} 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, perhaps "a generalised forerunner of the Mastodon type". In any case, he regarded it as an ungulate.

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.{{Cite journal |last=Andrews |first=Charles William |date=1902 |title=II.—Preliminary Note on some Recently Discovered Extinct Vertebrates from Egypt. (Part III.) |url=https://www.cambridge.org/core/journals/geological-magazine/article/abs/iipreliminary-note-on-some-recently-discovered-extinct-vertebrates-from-egypt-part-iii/7E8E5F1FFA556952E15664345C428802 |journal=Geological Magazine |language=en |volume=9 |issue=7 |pages=291–295 |doi=10.1017/S0016756800181178 |issn=1469-5081|url-access=subscription }} 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.{{Cite journal |last=Andrews |first=Charles William |date=1904 |title=Further notes on the mammals of the Eocene of Egypt (Part I) |journal=Geological Magazine |series=New Series, Decade V |volume=1 |pages=109–115}} (equivalent to the Jebel Qatrani Formation){{Cite journal |last=Badawy |first=Hanan S. |date=2018-03-01 |title=Termite nests, rhizoliths and pedotypes of the Oligocene fluviomarine rock sequence in northern Egypt: Proxies for Tethyan tropical palaeoclimates |url=https://linkinghub.elsevier.com/retrieve/pii/S0031018217308209 |journal=Palaeogeography, Palaeoclimatology, Palaeoecology |volume=492 |pages=161–176 |doi=10.1016/j.palaeo.2017.12.021 |issn=0031-0182|url-access=subscription }} 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.{{Cite journal |last=Deraniyagala |first=Paulus Edward Pieris |author-link=Paulus Edward Pieris Deraniyagala |date=1955 |title=Some extinct elephants, their relatives and the two living species |journal=Ceylon National Publications, Colombo}}

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.{{Cite journal |last=Schlosser |first=Max |author-link=Max Schlosser (zoologist) |date=1911 |title=Beiträge zur Kenntnis der oligozänen Landsäugetiere aus dem Fayum, Ägypten |journal=Beiträge zur Paläontologie und Geologie Österreich-Ungarns |volume=24 |pages=1–167}} This classification, however, has been rejected. In 1971, German zoologist Heinz Tobien opted to synonymise the entire genus with M. lyonsi,{{Cite journal |last=Tobien |first=Heinz |date=1971 |title=Moeritherium, Palaeomastodon, Phiomia aus dem Paläeogen Nordafrikas und die Abstammung der Mastodonten (Proboscidea, Mammalia). |journal=Mitteilungen aus dem Geologischen Institut der Technischen Universität, 10, 141–163. |volume=10 |pages=141–163}} 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. 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.

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.{{cite journal |last1=Osborn |first1=H. F. |year=1909 |title=The Feeding Habits of Mœritherium and Palæomastodon |journal=Nature |volume=81 |issue=2074 |pages=139–140 |bibcode=1909Natur..81..139O |doi=10.1038/081139a0 |doi-access=free}} In 1921, however, he rejected this view, and divided Proboscidea into four suborders or superfamilies: Moeritherioidea, Deinotherioidea, Mastodontoidea, and Elephantoidea.{{Cite journal |last=Osborn |first=Henry Fairfield |author-link=Henry Fairfield Osborn |date=1936 |title=Proboscidea. Vol. 1: Moeritherioidea, Deinotherioidea, Mastodontoidea. |journal=Amer. Mus. Press, New York.}} 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.{{Cite journal |last=Tassy |first=Pascal |date=1988 |title=THE CLASSIFICATION OF PROBOSCIDEA: HOW MANY CLADISTIC CLASSIFICATIONS? |url=https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1096-0031.1988.tb00467.x |journal=Cladistics |language=en |volume=4 |issue=1 |pages=43–57 |doi=10.1111/j.1096-0031.1988.tb00467.x |issn=0748-3007|url-access=subscription }} 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.{{Cite journal |last1=Hautier |first1=Lionel |last2=Tabuce |first2=Rodolphe |last3=Mourlam |first3=Mickaël J. |last4=Kassegne |first4=Koffi Evenyon |last5=Amoudji |first5=Yawovi Zikpi |last6=Orliac |first6=Maëva |last7=Quillévéré |first7=Frédéric |last8=Charruault |first8=Anne-Lise |last9=Johnson |first9=Ampah Kodjo Christophe |last10=Guinot |first10=Guillaume |date=2021-10-13 |title=New Middle Eocene proboscidean from Togo illuminates the early evolution of the elephantiform-like dental pattern |journal=Proceedings of the Royal Society B: Biological Sciences |language=en |volume=288 |issue=1960 |doi=10.1098/rspb.2021.1439 |issn=0962-8452 |pmc=8511763 |pmid=34641726}}

A cladogram of Proboscidea based on the phylogenetic analysis of Hautier et al. 2021 is below:{{clade|{{clade

|1=Eritherium

|2={{clade

|1=Phosphatherium

|2={{clade

|1=Daouitherium

|2={{clade

|1=Numidotherium

|2={{clade

|1=Barytherium

|2={{clade

|1=Arcanotherium

|2={{clade

|1=Omanitherium

|2={{clade

|1=Saloumia

|2=Moeritherium

|3={{clade

|1=Deinotheriidae

|label2=Elephantiformes

|2={{clade

|1=Dagbatitherium

|2={{clade

|1=Palaeomastodon

|2={{clade

|1=Phiomia

|2=Elephantimorpha

}}}}}}}}}}}}}}}}}}}}}}}}|label1=Proboscidea}}

File:Moeritherium_lyonsi.svg

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 {{convert|230|cm|ft|abbr=on}}. At the shoulder, this species measured only {{convert|70|cm|ft|abbr=on}}, and it had a body mass of {{convert|235|kg|lb|abbr=on}},{{Cite journal | last1 = Larramendi | first1 = A. | year = 2016 | title = Shoulder height, body mass and shape of proboscideans | journal = Acta Palaeontologica Polonica | volume = 61 | doi = 10.4202/app.00136.2014 | url = https://www.app.pan.pl/archive/published/app61/app001362014.pdf | doi-access = free }} though Moeritherium exhibited strong sized-based sexual dimorphism, so this estimate should be considered a crude average.

File:Moeritherium lyonsi RBCM.jpg

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.{{Cite book |last=Andrews |first=Charles William |author-link=Charles William Andrews |url=https://www.biodiversitylibrary.org/bibliography/55134 |title=A descriptive catalogue of the Tertiary Vertebrata of the Fayûm, Egypt. Based on the collection of the Egyptian government in the Geological museum, Cairo, and on the collection in the British museum (Natural history), London |date=1906 |publisher=Printed by order of the Trustees of the British museum |location=London}} The orbit (eye socket) occupied a fairly anterodorsal position, meaning that it sat towards the front and top of the skull, and resembled that of sirenians. Unlike later proboscideans, the naris (nasal cavity) was fairly close to the front of the skull,{{Cite journal |last=Nabavizadeh |first=Ali |date=2024 |title=Of tusks and trunks: A review of craniofacial evolutionary anatomy in elephants and extinct Proboscidea |url=https://anatomypubs.onlinelibrary.wiley.com/doi/10.1002/ar.25578 |journal=The Anatomical Record |language=en |doi=10.1002/ar.25578 |issn=1932-8494 |pmid=39380178|url-access=subscription }} 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, similar to the proboscis of modern tapirs. 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 and Palaeomastodon.

Moeritherium has a dental formula of {{DentalFormula|upper=3.1.3.3|lower=2.0.3.3}}.{{efn|3 incisors, 1 canine, 3 premolars and 3 molars in each half of the upper jaw, and 2 incisors, no canines, 3 premolars and 3 molars in each half of the lower jaw}}{{Cite book |last=Sanders |first=William J. |url=https://www.google.co.uk/books/edition/Evolution_and_Fossil_Record_of_African_P/P_rJEAAAQBAJ? |title=Evolution and Fossil Record of African Proboscidea |date=2023-09-15 |publisher=CRC Press |isbn=978-1-351-64521-8 |pages=67–68 |language=en}} The first lower incisors 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 and molars) 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.

The postcranial anatomy of Moeritherium has been compared to desmostylians, such as Pezosiren. Both taxa have an extremely elongated, broad torso, possibly an adaptation for diving in both taxa. Little of the cervical (neck) vertebrae is known, save for the atlas and some of the middle cervical vertebrae. Most of the vertebral column, save for some cervical vertebrae and one of the thoracic (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.{{Cite journal |last=Domning |first=Daryl P. |last2=Ray |first2=Clayton E. |last3=McKenna |first3=Malcolm C. |date=1986 |title=Two New Oligocene Desmostylians and a Discussion of Tethytherian Systematics |url=https://www.biodiversitylibrary.org/bibliography/159042 |journal=Smithsonian Contributions to Paleobiology |language=en |issue=59 |pages=1–56 |doi=10.5479/si.00810266.59.1}} Like modern proboscideans, there twenty-three presacral vertebrae (those preceding the sacrum). 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 elephants.{{Cite journal |last=Belyaev |first=Ruslan I. |last2=Boeskorov |first2=Gennady G. |last3=Kuznetsov |first3=Alexander N. |last4=Rotonda |first4=Mathys |last5=Prilepskaya |first5=Natalya E. |date=2025 |title=Comparative study of the body proportions in Elephantidae and other large herbivorous mammals |url=https://onlinelibrary.wiley.com/doi/10.1111/joa.14143 |journal=Journal of Anatomy |language=en |volume=246 |issue=1 |pages=63–85 |doi=10.1111/joa.14143 |issn=1469-7580 |pmid=39395275|pmc=11684385 }}

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,{{Cite journal |last=Simons |first=Elwyn |last2=Wood |first2=Albert |date=1968-01-01 |title=Early Cenozoic mammalian faunas, Fayum Province, Egypt: Part I. African Oligocene mammals: Introduction, history of study, and faunal succession. Part II. The African Oligocene Rodentia. Part II. The African Oligocene Rodentia. |url=https://elischolar.library.yale.edu/peabody_museum_natural_history_bulletin/28/ |journal=Bulletin of the Peabody Museum of Natural History |issue=28}} 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.{{Cite journal |last1=Liu |first1=Alexander G. S. C. |last2=Seiffert |first2=Erik R. |last3=Simons |first3=Elwyn L. |date=2008-04-15 |title=Stable isotope evidence for an amphibious phase in early proboscidean evolution |journal=Proceedings of the National Academy of Sciences |language=en |volume=105 |issue=15 |pages=5786–5791 |bibcode=2008PNAS..105.5786L |doi=10.1073/pnas.0800884105 |issn=0027-8424 |pmc=2311368 |pmid=18413605 |doi-access=free}}

File:Moeritherium.jpg. The proportions of the body are incorrect, as the torso should be longer and the limbs should be shorter.]]

The environment of the Jebel Qatrani Formation, from which some specimens of Moeritherium are known, have been described as a subtropical to tropical lowland plain by Bown, who further suggests the presence of streams and ponds.{{Cite journal |last1=Bown |first1=T. M. |last2=Kraus |first2=M. J. |date=1988 |title=Geology and paleoenvironment of the Oligocene Jebel Qatrani Formation and adjacent rocks, Fayum Depression, Egypt |url=https://pubs.usgs.gov/publication/pp1452 |journal=USGS Report |language=en |page=14 |bibcode=1988usgs.rept...14B |doi=10.3133/pp1452 |issn=2330-7102}}

Based on the occurrence of birds that are associated with water (such as ospreys, early flamingos, jacanas, herons, storks, cormorants and shoebills), Rasmussen and colleagues similarly inferred that the environment featured slow-moving freshwater with a substantial amount of aquatic vegetation. Although lithology suggests that most fossils were deposited on sandbanks after being transported by currents, the authors argue that swamps 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.{{Cite journal |last1=Rasmussen |first1=D.T. |last2=Olson |first2=S.L. |last3=Simons |first3=E.L. |year=1987 |title=Fossil birds from the Oligocene Jebel Qatrani formation Fayum Province, Egypt |url=https://www.biodiversitylibrary.org/bibliography/159058 |journal=Smithsonian Contributions to Paleobiology |volume=62 |issue=62 |pages=1–20 |doi=10.5479/si.00810266.62.1}} 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 and featured floating vegetation like water lilies and Salvinia.{{Cite journal |last1=Murray |first1=A.M. |year=2004 |title=Late Eocene and early Oligocene teleost and associated ichthyofauna of the Jebel Qatrani Formation, Fayum, Egypt. |url=https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.0031-0239.2004.00384.x |journal=Palaeontology |volume=47 |issue=3 |pages=711–724 |bibcode=2004Palgy..47..711M |doi=10.1111/j.0031-0239.2004.00384.x |s2cid=140627361|url-access=subscription }}

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.{{Cite journal |last1=Rasmussen |first1=D. T. |last2=Simons |first2=E.L. |last3=Hertel |first3=F. |last4=Judd |first4=A. |year=2001 |title=Hindlimb of a giant terrestrial bird from the upper Eocene, Fayum, Egypt. |url=https://onlinelibrary.wiley.com/doi/pdf/10.1111/1475-4983.00182 |journal=Palaeontology |volume=44 |issue=2 |pages=325–337 |bibcode=2001Palgy..44..325R |doi=10.1111/1475-4983.00182 |s2cid=130033734|url-access=subscription }}

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.{{Cite book |last1=Kampouridis |first1=P. |title=The Phanerozoic Geology and Natural Resources of Egypt |last2=Hartung |first2=J. |last3=Augustin |first3=F.J. |year=2023 |isbn=978-3-030-95636-3 |series=Advances in Science, Technology & Innovation |pages=373–405 |chapter=The Eocene–Oligocene Vertebrate Assemblages of the Fayum Depression, Egypt |doi=10.1007/978-3-030-95637-0_14}}

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