Palaeomastodon

Early history The first specimens of Palaeomastodon were recovered from lower Oligocene strata, part of the Fayum fossil deposits of Egypt. The first specimen to be discovered, consisting of a partial mandible (lower jaw) with two premolars and three molars, was recovered from the Jebel Qatrani Formation, formerly referred to as the "fluvio-marine formation". It was described in 1901 by British palaeontologist Charles William Andrews, who named its type species, P. beadnelli, after his colleague, Hugh John Llewellyn Beadnell. Other species Four years after describing P. beadnelli, Andrews named two additional Palaeomastodon species: P. parvus, based on a partial right mandible, bearing premolars and molars; and P. wintoni, based on two near-complete, articulated mandibles, lacking only the angular and the anterior (front) right cheek teeth. Andrews noted a second mandible housed in Cairo, which he considered a "co-type". In a 1922 revision of the genus' taxonomy, Japanese palaeontologist Matsumoto Hikoshichirō reassigned P. minor and P. wintoni to Phiomia, In addition, he described a fourth species, P. intermedius, based on a partial left mandibular ramus that bore all of the molars and parts of the last premolars. Three more specimens were also known, including a large skull fragment consisting mostly of the palate. Writing in 1926, Henry Fairfield Osborn suggested that Palaeomastodon was a direct, if remote, ancestor of gomphotheres and mammutids (which he referred to under the umbrella of "mastodonts"). In a 1988 paper discussing the taxonomy of proboscideans, Pascal Tassy suggested that Palaeomastodon fell under the suborder Elephantiformes, being phylogenetically closer to modern elephants than to taxa like Deinotherium and Moeritherium, though was still more basal than Phiomia. A 2021 phylogenetic analysis of basal proboscideans performed by Lionel Hautier and colleagues recovered similar results: Palaeomastodon was within the suborder Elephantiformes, though was basal to Phiomia and Elephantimorpha. Below is a cladogram depicting the results of Hautier and colleagues' 2021 analysis:}}}}}}}}}}}}}}}}}}}}|label1=Proboscidea}} == Description ==

Few postcranial remains from Palaeomastodon are known. However, based on the reported length of one femur, a 2016 study estimated an adult shoulder height of , and a body mass of over . A 2004 study estimated a weight of based on a long femur, while another, long femur was estimated at and a long ulna was estimated at . In 2026, Asier Larramendi and Marco P. Ferretti estimated that Palaeomastodon stood at the shoulder and weighed . Skull and dentition Palaeomastodon's skull was similar in many regards to that of Phiomia. The naris (nasal cavity) was retracted, and sat just in front of the orbits (eye sockets). Around the naris were attachment sites for strong muscles, and together, these attributes suggest the presence of a small trunk, a precursor to that seen in later proboscideans. The orbits, too, had shifted backwards, and sat above the molars as in modern elephants. == Palaeoenvironment ==

The environment of the Jebel Qatrani Formation, from which Palaeomastodon is known, has been described as a subtropical to tropical 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, storks, cormorants and shoebills), Rasmussen and colleagues inferred that the environment featured slow-moving freshwater with a substantial amount of aquatic vegetation, which matches the prior hypothesis. 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. The discovery of snakehead fossils seem to support Rasmussen's interpretation, as the genus 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. 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. 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. == Chronology ==

All specimens of Palaeomastodon are known from the Oligocene, between 33-27 Ma. The strata from which P. beadnelli is known have been dated to ca. 33–30 Ma. The two Ethiopian taxa, which both come from the Chilga Formation, have both been dated to 28–27 Ma. The taxon from Libya, whose stratigraphic unit is unclear, has been tentatively dated to the early Oligocene, though no specific time frame has been given. == Notes ==