Palaeomastodon ("ancient mastodon") is an extinct genus of basal proboscideans from the Oligocene of North Africa. The first specimen discovered was recovered from strata belonging to the Fayum fossil deposits of Egypt. It was described and named in 1901 by Charles Williams Andrews, who named its type species, P. beadnelli, after a colleague. Multiple species have been named since, though have either been reassigned to Phiomia or synonymised with P. beadnelli. Three (possible) unnamed taxa are known from Ethiopia and Libya. All remains are from strata that date to 33–27 million years ago. Palaeomastodon was fairly large for an early proboscidean. It had an estimated shoulder height of 2.2 m (7 ft 3 in), and a body mass of around 2,500 kg (5,500 lb). Similar to Phiomia, its nasal cavity was retracted and surrounded by strong muscle attachment sites, indicating that it was among the first proboscideans to possess a trunk. Like in modern elephants, the orbits (eye sockets) were positioned further back on the skull, and sat over the molars. The (lower jaw) mandible was very long, with a symphysis whose morphology suggests a long tongue was present. Like many extinct proboscideans, Palaeomastodon had two sets of tusks, one on the upper jaw and one on the lower jaws, formed from the second incisors of the maxilla and mandible respectively.
Taxonomy
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, a genus which had been briefly synonymised with Palaeomastodon. 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. In 2010, William J. Sanders et al. regarded all of the named species (except for P. minor, regarded as a synonym of Phiomia serridens) as junior synonyms of P. beadnelli. They did, however, note the possible presence of three species, two from Chilga, Ethiopia, and one from Zella, Libya.
Classification Palaeomastodon is the type genus and namesake of the family Palaeomastodontidae. Though Phiomia has been occasionally assigned to the family, generally it is recovered in a different phylogenetic position, and likely belongs to a family of its own. 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:
Description
Few postcranial remains from Palaeomastodon are known. However, based on the reported 87.5 cm (34.4 in) length of one femur, a 2016 study estimated an adult shoulder height of 2.2 m (7 ft 3 in), and a body mass of over 2,500 kg (5,500 lb). A 2004 study estimated a weight of 661 kg (1,457 lb) based on a 45 cm (18 in) long femur, while another, 67 cm (26 in) long femur was estimated at 3,691 kg (8,137 lb) and a 55 cm (22 in) long ulna was estimated at 973 kg (2,145 lb). In 2026, Asier Larramendi and Marco P. Ferretti estimated that Palaeomastodon stood 220 cm (87 in) at the shoulder and weighed 2,500 kg (5,500 lb).
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