Maobrontops

Maobrontops Temporal range:
Holotype maxilla of M. paganus (SYSU-M-4, holotype), with drawings of just the tooth crowns
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Infraclass:	Placentalia
Order:	Perissodactyla
Family:	†Brontotheriidae
Subfamily:	†Brontotheriinae
Tribe:	†Brontotheriini
Subtribe:	†Brontotheriina
Infratribe:	†Embolotheriita
Genus:	†Maobrontops Averianov et al., 20181
Species:	†M. paganus
Binomial name
†Maobrontops paganus Averianov et al., 20181

Maobrontops is an extinct genus of horned brontothere that lived in East Asia during the Late Eocene. A single species is known, M. paganus, from the Youganwo Formation in Guangdong, China. Maobrontops is known only from a single poorly-preserved maxilla.

Maobrontops paganus was described in 2018 by Alexander Averianov, Igor Danilov, Wen Chen, and Jianhua Jin. The new genus and species were based on the fragmentary left maxilla SYSU-M-4, found in an oil shale quarry near Maoming in Guangdong, China.¹ The genus name Maobrontops derives from Maoming and the genus Brontops (now considered a synonym of Megacerops).¹ The species name paganus is Latin for "rustic" and references that many fossils in the vicinity of Maoming are collected by locals.¹ SYSU-M-4 represents the southernmost known record of brontotheres in China.¹

SYSU-M-4 preserves only three of the teeth: the fourth premolar, and the first and second molar. There are also traces of the third premolar, though it is mostly destroyed.¹ The maxilla was identified as belonging to a brontothere by the molars having W-shaped ectolophs (outer shearing blades),¹ a distinctive feature of brontothere teeth,² and the lingual cusps (tooth cusps in the direction of the tongue) being isolated from each other.¹ Further dental features suggested that Maobrontops was a derived brontothere, placed in the Embolotheriita infratribe.¹ As a genus, Maobrontops is characterized mainly by combining a relatively simple fourth premolar that does not have a hypocone (one of the cusps) with relatively derived molars with large cusps on the anterolingual (towards the front of the tooth and on the side of the tongue) cingula.¹

SYSU-M-4 is poorly preserved and offers little to no information on the appearance and anatomy of the rest of the jaw or skull.¹

Maobrontops was a large brontothere.¹ Based on equations on perissodactyl body size based on the length and width of the second molar by Christine Janis, the type specimen of M. paganus is estimated to have weighed 792 kilograms (1,746 lb).¹

Averianov et al. performed a phylogenetic analysis to determine the position of Maobrontops. They used a matrix and character coding from a 2016 study by Matthew C. Mihlbachler and Joshua X. Samuels, but noted that very few characters could be coded for the fragmentary Maobrontops (19 out of 91).¹ Averianov et al. recovered Maobrontops as the sister taxon to the derived clade that includes the genera Embolotherium, Nasamplus, and Protembolotherium. Other than support from the phylogenetic analysis, the large cusps on the anterolingual cingula of the upper molar teeth is the only anatomical trait that securely unites Maobrontops with these genera.¹ Averianov et al.'s cladogram is shown below:¹

The position of Maobrontops suggests that brontotheres in southern and northern China evolved large body sizes independently, since Maobrontops is larger than the northern Protembolotherium, but not as large as the northern Embolotherium.¹

M. paganus is known from the upper part of the Youganwo Formation; the type specimen was found in oil shales that are recognized as lacustrine deposits (rock that formed in ancient lakes).¹ Based on palynomorph fossils and magnetostratigraphy, the Youganwo Formation is dated to the Middle–Late Eocene, or the Late Eocene.¹ Mammal fossils are rare in the Youganwo Formation, and include fossils from nimravids and amynodonts.¹ Reptile fossils are significantly more common, and include remains of both crocodilians (alligatorids and tomistomines) and turtles (adocids, carettochelyids, geoemydids, and trionychids).¹