Palaeomastodon

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Palaeomastodon
Temporal range: Oligocene, 33–27  Ma
Palaeomastodon beadnelli.jpg
P. beadnelli skull
Scientific classification OOjs UI icon edit-ltr.svg
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Proboscidea
Family:† Palaeomastodontidae
Genus:† Palaeomastodon
Andrews, 1901
Type species
†Palaeomastodon beadnelli
Andrews, 1901
Synonyms [1]
Synonyms of P. beadnelli
  • †P. parvus Andrews, 1906
  • †P. wintoniAndrews, 1906
  • †P. intermedius Matsumoto, 1922

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.

Contents

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 Similar to Phiomia, its nasal cavity was retracted and surrounded by strong muscle attachment sites, indicating that it was among the first proboscideans to possess a trunk.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

Map of the Fayum area of Egypt, from which Palaeomastodon beadnelli originates Map of Fayum area.png
Map of the Fayum area of Egypt, from which Palaeomastodon beadnelli originates

Early history

The first specimens of Palaeomastodon were recovered from lower Oligocene strata, part of the Fayum fossil deposits of Egypt. [2] 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, [1] formerly referred to as the "fluvio-marine formation". [3] [4] 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. [5]

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 considred a "co-type". [6] In a 1922 revision of the genus' taxonomy, Japanese palaeontologist Matsumoto Hikoshichirō reassigned P. minor and P. wintoni to Phiomia , [3] a genus which had been briefly synonymised with Palaeomastodon. [7] 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. [3] 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. [1]

Classification

Palaeomastodon is the type genus and namesake of the family Palaeomastodontidae. [4] 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. [8] [9] 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"). [10] 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. [11] A 2021 phylogenetic analysis of basal proboscideans performed by Lionel Hautier et al. recovered similar results: Palaeomastodon was within the suborder Elephantiformes, though was basal to Phiomia and Elephantimorpha. [9]

Below is a cladogram depicting the results of Hautier et al. (2021): [9]

Proboscidea

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). [12] 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). [13]

Skull and dentition

Palaeomastodon's skull was similar in many regards to that of Phiomia. [14] The naris (nasal cavity) was retracted, and sat just in front of the orbits (eye sockets). [15] 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. [14] This is contrary to Henry Fairfield Osborn's suggestion that Palaeomastodon was trunkless, and instead had a large upper lip. [16] The orbits, too, had shited backwards, and sat above the molars as in modern elephants. [1] The occipital region was high and the nuchal crest was very large, possibly to counterbalance the elongated mandible, tusks, and trunk. [14] Unlike later proboscideans, Palaeomastodon had a sagittal crest, and the braincase was small and fairly low. [1] The mandibular symphysis is extremely elongated, [14] [15] with a dorsal surface that bears a deep and wide supra-symphyseal groove, indicating that Palaeomastodon possessed a long tongue. [14]

Palaeomastodon had a dental formula of 1.0.3.31.0.2.3 × 2 = 26. [1] [a] Like Phiomia and many other extinct proboscideans, it possessed tusks on both the maxilla and the mandible. The maxillary tusks were mid-sized, slightly curved, and oriented downwards, while the mandibular tusks were broad and procumbent (protruding), and sat very close together. Behind the tusks on both upper and lower jaws was a very large diastema (gap), separating them from the cheek teeth, separating them from the cheek teeth (the premolars and molars). Palaeomastodon's cheek teeth were brachydont (possessing fairly low crowns), and lophodont, meaning that between each crown were small ridges called lophs. The premolars, relative to the molars, were fairly long. [1] Unlike later proboscideans (though like Phiomia), the teeth erupted vertically, rather than horizontally. [17]

Palaeoenvironment

Palaeomastodon, depicted by Heinrich Harder Paleomastodon.jpg
Palaeomastodon, depicted by Heinrich Harder

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. [18] 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. [19] 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 . [20] 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. [21] 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. [22]

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. [1]

Notes

  1. ↑ 1 incisor, no canine, 3 premolars and 3 molars in each half of the upper jaw, and 2 incisors, no canines, 2 premolars and 3 molars in each half of the lower jaw, resulting in 26 teeth in total

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<i>Moeritherium</i> Extinct genus of mammals

Moeritherium is an extinct genus of basal proboscideans from the Eocene of North and West Africa. The first specimen was discovered in strata from the Fayum fossil deposits of Egypt. 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 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, are currently considered valid.

<span class="mw-page-title-main">Gomphothere</span> Extinct family of proboscidean mammals

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<i>Arsinoitherium</i> Extinct genus of mammals

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<span class="mw-page-title-main">Deinotheriidae</span> Prehistoric family of mammals

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<i>Phiomia</i> Genus of mammals

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<span class="mw-page-title-main">Jebel Qatrani Formation</span> Geologic formation in Egypt

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References

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  7. ↑ Andrews, Charles William (1908). "IX. On the skull, mandible, and milk dentition of Palæomastodon, with some remarks on the tooth change in the proboscidea in general". Philosophical Transactions of the Royal Society of London. Series B, Containing Papers of a Biological Character. 199 (251–261): 393–407. doi:10.1098/rstb.1908.0009.
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  11. ↑ Tassy, Pascal (1988). "The Classification of Proboscidea: How Many Cladistic Classifications?". Cladistics. 4 (1): 43–57. doi:10.1111/j.1096-0031.1988.tb00467.x. ISSN   0748-3007.
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  16. ↑ Osborn, H. F. (1909). "The Feeding Habits of Mœritherium and Palæomastodon". Nature. 81 (2074): 139–140. Bibcode:1909Natur..81..139O. doi: 10.1038/081139a0 .
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  19. ↑ Rasmussen, D.T.; Olson, S.L.; Simons, E.L. (1987). "Fossil birds from the Oligocene Jebel Qatrani formation Fayum Province, Egypt". Smithsonian Contributions to Paleobiology. 62 (62): 1–20. doi:10.5479/si.00810266.62.1.
  20. ↑ Murray, A.M. (2004). "Late Eocene and early Oligocene teleost and associated ichthyofauna of the Jebel Qatrani Formation, Fayum, Egypt". Palaeontology. 47 (3): 711–724. Bibcode:2004Palgy..47..711M. doi:10.1111/j.0031-0239.2004.00384.x. S2CID   140627361.
  21. ↑ Rasmussen, D. T.; Simons, E.L.; Hertel, F.; Judd, A. (2001). "Hindlimb of a giant terrestrial bird from the upper Eocene, Fayum, Egypt". Palaeontology. 44 (2): 325–337. Bibcode:2001Palgy..44..325R. doi:10.1111/1475-4983.00182. S2CID   130033734.
  22. ↑ Kampouridis, P.; Hartung, J.; Augustin, F.J. (2023). "The Eocene–Oligocene Vertebrate Assemblages of the Fayum Depression, Egypt". The Phanerozoic Geology and Natural Resources of Egypt. Advances in Science, Technology & Innovation. pp. 373–405. doi:10.1007/978-3-030-95637-0_14. ISBN   978-3-030-95636-3.
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