Anteosaurus is an extinct genus of large carnivorous dinocephalian synapsid. It lived at the end of the Guadalupian (Middle Permian) during the Capitanian age, about 262 to 260 million years ago, in what is now South Africa. It is mainly known from cranial remains and few postcranial bones found in rocks of the Tapinocephalus Assemblage Zone. Measuring long and weighing about , Anteosaurus was the largest known carnivorous non-mammalian synapsid and the largest terrestrial predator of the Permian period. Occupying the top of the food chain in the Middle Permian, its skull, jaws and teeth show adaptations to capture large prey, such as giant titanosuchid and tapinocephalid dinocephalians and large pareiasaurs.
As in many other dinocephalians the cranial bones of Anteosaurus are pachyostosed (thickened), but to a lesser extent than those of tapinocephalid dinocephalians. In Anteosaurus, pachyostosis mainly occurs in the form of supraorbital protuberances, the horn- or boss-shaped prominences above the eyes. According to some paleontologists this structure would be implicated in intraspecific agonistic behaviour, including head-pushing, probably to compete with conspecifics over mating rights during the mating season. On the contrary, other scientists believe that these adaptations served to reduce cranial stresses on the bones of the skull during predation. Young Anteosaurus had fairly narrow and lean skulls, with the bones of their skull becoming progressively more pachyostosed as they grew, forming the characteristic robust skull roof of the genus.
The study of its inner ear revealed that Anteosaurus was a largely terrestrial, agile predator with highly advanced senses of vision, balance, and coordination. These studies also suggested that Anteosaurus were quite fast and would have been able to outrun competitors and prey alike. Its body was well-suited to projecting itself forward, both in hunting and competition with others. Some researchers have at times proposed a semi-aquatic lifestyle for this animal.
Anteosaurus and all other dinocephalians became extinct about 260 million years ago in a mass extinction at the end of the Capitanian, in which the large Bradysaurian pareiasaurs also disappeared. The reasons of this extinction are obscure, although some research have shown a temporal association between an important volcanism event in China (known as the Emeishan Traps) and the extinction of dinocephalians.
Etymology Some confusion surrounds the etymology of the name Anteosaurus, as David Meredith Seares Watson gave no explanation when he described and named Anteosaurus in 1921.
It is often translated as meaning "before lizard", "previous lizard" or "primitive lizard", from the Latin prefix ante meaning "before".
Alternatively, according to Ben Creisler the prefix does not come from the Latin ante, but would refer to Antaios, Latinized as Antaeus or more rarely Anteus, an opponent of Heracles in Greek mythology. The type specimen of Anteosaurus was initially classified in the genus Titanosuchus by Watson, which was named after the Titans of Greek mythology. Once this specimen was recognized as belonging to a different genus, the new name, dedicated to the giant Antaeus, established another connection with Greek mythology.
Classification and phylogeny Named by Watson in 1921, Anteosaurus was initially classified as a 'Titanosuchian Deinocephalian'. In 1954 Boonstra separated the Titanosuchians in two families: Jonkeridae (a junior synonym of Titanosuchidae) and Anteosauridae. At about the same time Yefremov erected the family Brithopodidae, in which he included the fragmentary Brithopus along with the better known Syodon and Titanophoneus.
Much later, Hopson and Barghusen argued that Brithopodidae should be discontinued and that the Russian taxa Syodon, Titanophoneus and Doliosauriscus should be placed with Anteosaurus within the family Anteosauridae in Anteosauria, to distinguish them from the Tapinocephalians, the other major dinocephalian group in which they included the titanosuchids and the tapinocephalids. They also created the taxa Anteosaurinae, containing Anteosaurus and the Russian forms Titanophoneus and Doliosauriscus, and the Anteosaurini containing only the giant forms Anteosaurus and Doliosauriscus.
Gilian King retained the incorrectly spelled 'Brithopidae' (including the subfamilies 'Brithopinae' and Anteosaurinae) and placed both Brithopidae and Titanosuchidae (including Titanosuchinae and Tapinocephalinae) in the superfamily Anteosauroidea. Ivakhnenko would later consider Brithopodidae as invalid and united Anteosauridae and Deuterosauridae (monotypic; just containing Deuterosaurus) in the superfamily Deuterosauroidea. More recently, Kammerer's systematic revision of the anteosaurs (in which Doliosauriscus become a junior synonym of Titanophoneus) demonstrated that the genus Brithopus is a wastebasket taxon and a nomen dubium, composed of the fossils of indeterminate estemmenosuchid-like tapinocephalians and indeterminate anteosaurians; Brithopodidae was also invalidated.
Kamerrer also performed the first phylogenetic analysis which included all anteosaurid taxa. Along with other subsequent phylogenetic analysis of anteosaurs, this study recovered a monophyletic Anteosauridae containing two major clades, Syodontinae and Anteosaurinae: in Kammerer's analysis, the Chinese Sinophoneus is the most basal anteosaurine and the sister group of an unresolved trichotomy including Titanophoneus potens, T. adamanteus, and Anteosaurus. The following cladogram is based on Kammerer's 2011 analysis:
When describing the Brazilian anteosaur Pampaphoneus, Cisneros et al. presented another cladogram confirming the recognition of the clades Anteosaurinae and Syodontinae. In the Fig. 2. cladogram of the main paper (which does not include Microsyodon), Titanophoneus adamanteus is recovered as the sister taxon of a clade composed of Titanophoneus potens and Anteosaurus. However, in the four cladograms within the supplementary material/supporting information of this paper, (which included Microsyodon), Anteosaurus is recovered as the sister taxon of both species of Titanophoneus. These four cladograms differ only by the position of Microsyodon within the matrix.
The following cladograms are those from Cisneros et al. (2012); the first is from the main article, which excludes the genus Microsyodon:
The following cladogram is based on one of the four within the supporting information of Cisneros et al. (2012), which includes Microsyodon:
In resdescribing the Chinese anteosaur Sinophoneus, Jun Lui presented a new cladogram in which Sinophoneus is recovered as the most basal Anteosauridae and so excluded from Anteosaurinae. Here Anteosaurus is the sister-taxon of Titanophoneus potens and T. adamanteus. The following cladogram is based on Jun Liu (2013):
Synonymy Genus synonymy As defined by Lieuwe Dirk Boonstra, Anteosaurus is "a genus of anteosaurids in which the postfrontal forms a boss of variable size overhanging the dorso-posterior border of the orbit." On this basis he synonymised six of the seven genera named from the Tapinocephalus zone: Eccasaurus, Anteosaurus, Titanognathus, Dinosuchus, Micranteosaurus, and Pseudanteosaurus. Of these, he considers Dinosuchus and Titanognathus can safely be considered synonyms of Anteosaurus. Eccasaurus, with a holotype of which the cranial material consists of only few typical anteosaurid incisors, appears to be only determinable to family level. The holotypes of Pseudanteosaurus and Micranteosaurus were previously considered to be distinct on account of their small size but is better interpreted as young specimens of Anteosaurus. Boonstra still considered the genus Paranteosaurus as valid, which is defined as a genus of anteosaurids in which the postfrontal is not developed to form a boss. This is probably an example of individual variation and hence another synonym of Anteosaurus.
Species synonymy Anteosaurus was once known by a large number of species, but it is currently thought that these merely represent different growth stages of A. magnificus.
Possible synonyms Archaeosuchus cairncrossi is a dubious species of anteosaur from the Tapinocephalus Assemblage Zone. It was named by Broom in 1905 on the basis of a partial maxilla. It was interpreted as a titanosuchid by Boonstra, but Kammerer determined it was an anteosaur indistinguishable from Anteosaurus and Titanophoneus. As Anteosaurus magnificus appears to be the only valid large anteosaur in the Tapinocephalus Assemblage Zone, Archaeosaurus cairncrossi is very likely to be a specimen of it, but due to poor preservation, the specimen lacks any features that would allow the synonymy to be proven.
Eccasaurus priscus is a dubious species of anteosaur from the Tapinocephalus Assemblage Zone. It was named by Broom in 1909 on the basis of a fragmentary skeleton, of which Broom only described the humerus. As with Archaeosuchus cairncrossi, Eccasaurus priscus is very likely to be synonymous with Anteosaurus magnificus. As Eccasaurus was named before Anteosaurus and thus has priority, a petition to the ICZN would be needed to conserve the name Anteosaurus magnificus if this synonymy were to be proven.
Description Size
Anteosaurus is one of the largest known carnivorous non-mammalian synapsids and anteosaurids, measuring around long and weighing about The juvenile specimen BP/1/7074 has an estimated body mass of about , showing extreme disparity in size with adult Anteosaurus.
Skull The skull of Anteosaurus is large, measuring between in the largest specimens (TM265 and SAM-PK-11293), with a heavily pachyostosed skull roof possessing a developed frontal boss. The main features of the skull are the massively pachyostosed postfrontals that form strong horn-like bosses projected laterally. Another boss, characteristically oval in shape, is also present on the angular bone of the lower jaw. The morphology of this angular boss is different between each anteosaurid species. In Anteosaurus the boss is oval in shape, roughly the same thickness throughout its length, with blunt anterior and posterior edges. Some individuals may have also a jugal boss more or less pronounced. Like other anteosaurids, the postorbital bar is strongly curved anteroventrally in such way that the temporal fenestra undercuts the orbit. An additional typical character of anteosaurs is the premaxilla oriented upwards at an angle of about 30–35° with respect to the ventral edge of the maxilla. However, unlike most anteosaurs in which the ventral margin of the premaxilla is directed upwards in a straight line, in Anteosaurus the anterior end of the premaxilla is curved ventrally, producing a concave alveolar border of the region preceding the canines. The skull shows also a concave dorsal snout profile. On the top of the skull, the pineal boss is exclusively formed by the parietals as is the case in other anteosaurines (and in more basal anteosaurs such as Archaeosyodon and Sinophoneus) while this boss is made up of both frontals and parietals in the other anteosaur subgroup, the syodontines. Contrary to what is observed in the latter, the frontals and the pineal boss of the anteosaurines do not participate in the attachment site of the mandibular adductor musculature. On the palate, the transverse processes of pterygoids are massively enlarged at their distal end, giving them a palmate shape in ventral view, as is the case in Titanophoneus and Sinophoneus. As in other anteosaurs, two prominent palatal bosses carried several small teeth. In Anteosaurus (and in other anteosaurines), these two palatal bosses are well separated from each other while in syodontines the two bosses are very close or interconnected.
It is estimated that approximately 48% of the anteosaurid's endocast volume would have housed non-neural tissue.
Dentition