Anteosaur

Anteosaurs Temporal range: Middle Permian, As. S Artin. Kung. Road. W Ca. Wu. C
Life restoration of Anteosaurus
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Clade:	Synapsida
Clade:	Therapsida
Suborder:	†Dinocephalia
Infraorder:	†Anteosauria
Subgroups
see Taxonomy
Synonyms
Anteosauroidea Boonstra, 1962

Anteosaurs are a group of large, basal carnivorous dinocephalian therapsids with large canines and incisors and short limbs, that are known from the Middle Permian of South Africa, Russia, China, and Brazil. Some grew very large, with skulls 50–80 centimetres (20–31 in) long, and were the largest predators of their time. Anteosaurs, as well as other dinocephalians, would die out during the Capitanian mass extinction, which marked the end of the Middle Permian.^[1][2]

The Anteosauria are distinguished from the Tapinocephalia by several features, such as very large canines, cheek teeth with bulbous crowns, and an upturning of the premaxilla, so that the front of the mouth curves strongly upwards. There is a tendency especially in more advanced forms such as Anteosaurus towards thickening of the bones of the top of the skull, indicating head-butting behavior. There is a large canal for the pineal organ (third eye); probably tied in with the animal's diurnal and seasonal cycles.

The shoulder girdle is fairly light, with a narrow interclavicle, clavicle, and scapular blade. The femur (thigh bone) is slender and curved. These were, despite their size, probably quite agile animals. The limbs are short and the skull is long, narrow, and heavy. The tail is very long in at least some genera.

Initially, it has been suggested that the estemmenosuchids are the most basal of the dinocephalians.^[3][4] However, most experts now recover anteosaurs as the most basal of the dinocephalians,^[5][6][7] with the Russian anteosaurs considered the clade.^[5][8] They have featured in common with pelycosaurs (Carroll 1988) and biarmosuchians (Chudinov 1965), and, with the tapinocephalians, are part of the first major evolutionary radiation of the therapsids.^[5]

James Hopson and Herbert Barghusen in 1986 provided the first cladistic study of the Therapsida. They used the term "Anteosauria" and synonymised the families Brithopodidae and Anteosauridae. In 2010, Christian Kammerer published a re-evaluation of anteosaurian relationships.^[7]

The cladogram below follows an updated (2012) version of Kammerer's analysis by Juan Carolos Cisneros and colleagues.^[9]

The group was originally defined as a superfamily by L. D. Boonstra in 1962 to include the families Brithopodidae and Anteosauridae.

• Superfamily Anteosauroidea Boonstra, 1962
  • Family Brithopidae Efremov, 1954
  • Family Anteosauridae Boonstra, 1954

Gillian King in a 1988 review of the Anomodontia (including the Dinocephalia - however the view that the Dinocephalia are a subset of the Anomodontia is no longer held) as part of Gutsav Fischer Verlag's ongoing Encyclopedia of Paleoherpetology series of volumes, uses a more traditional Linnaean arrangement, but includes the herbivorous forms under the superfamily Anteosauroidea as well. The "Titanosuchidae" here is equivalent to the "Tapinocephalia".

• Superfamily Anteosauroidea Boonstra, 1962
  • Family Brithopidae Boonstra, 1972
    • Subfamily Brithopodinae Efremov, 1954
    • Subfamily Anteosaurinae Boonstra, 1954
  • Family Titanosuchidae Boonstra, 1972
    • Subfamily Titanosuchinae Broom, 1903
    • Subfamily Tapinocephalinae Lydekker, 1890

After Kammerer et al., 2011.

• Class Synapsida
  • Order Therapsida
    • Suborder Dinocephalia
      • Clade Anteosauria
        • Family Anteosauridae
          • Archaeosyodon
          • Microsyodon
          • Subfamily Anteosaurinae
            • Sinophoneus
            • Titanophoneus
            • Anteosaurus
          • Subfamily Syodontinae
            • Australosyodon
            • Notosyodon
            • Pampaphoneus
            • Syodon
        • Family Brithopodidae
          • Admetophoneus
          • Brithopus
          • Chthomaloporus
          • Eosyodon
          • Mnemeiosaurus
        • Family Deuterosauridae
          • Deuterosaurus

The stance of a typical anteosaur, such as Titanophoneus, was primitive. Rather than the limbs being drawn in under the body, the stance was more sprawling. Olson (1962) notes that the Russian dinocephalian assemblages indicate environments tied to water, and Boonstra considered that the roughly contemporary Anteosaurus was a slinking crocodile-like semi-aquatic form. The long tail, weak limbs, and sprawling posture do indeed suggest some sort of crocodile-like existence. However, the thickened skull-roof indicates that these animals were quite able to get about on land, if they were to practice the typically dinocephalian head-butting behavior. All other head-butters, pachycephalosaurian dinosaurs, titanothere ungulates, and goats were or are completely terrestrial. Bhat et al. (2021) suggested that Anteosaurus may have occasionally inhabited shallow and short-lived pools, similar to modern day hippopotamus, based on its bone histology.^[8]

On the other hand, analysis on the brain of a juvenile Anteosaurus specimen suggested Anteosaurus weren't sluggish predators. X-ray imaging and 3-D reconstructions showcase that Anteosaurus were fast, agile animals in spite of their great size: the inner ears were larger than those of its closest relatives and competitors, suggesting that Anteosaurus was well-suited to the role of an apex predator that could outrun both its rivals and prey alike. The area of its brain responsible for coordinating the movements of the eyes with the head was also determined to have been exceptionally large, an important feature to ensure that they could track their prey accurately. As a result, Anteosaurus is thought to be well-adapted to pursuing land-based prey.^[10]

Anteosaurs were evolved to prey on particularly large animals and were among the most highly predaceous of all synapsids (Sennikov, 1996), potential prey included the bull-sized armored pareiasaurs (Lee, 1997) and enormous tapinocephalid dinocephalians (Rubidge, 1995).^[11]

The large anteosaurs were efficient predators, more specialized than earlier and more primitive biarmosuchid and eotitanosuchid carnivorous therapsids, as the temporal opening behind the eye socket was larger, indicating a greater muscle mass available for closing the lower jaw. Large pterygoid flanges indicate a well-developed Kinetic-Inertial system in anteosaurs, and increased vertical alignment of the temporalis muscles suggests an expanded Static-Pressure component of the bite cycle.^[11]

• Boonstra, L.D., 1972, Discard the names Theriodontia and Anomodontia: a new classification of the Therapsida. Annals of the South African Museum 59:315-338.
• Carroll, R. L., 1988, Vertebrate Paleontology and Evolution, WH Freeman & Co.
• Chudinov, P. K. 1965, "New Facts about the Fauna of the Upper Permian of the USSR", Journal of Geology, 73:117-30
• Hopson, J.A. and Barghusen, H.R., 1986, An analysis of therapsid relationships in N Hotton III, PD MacLean, JJ Roth and EC Roth, The Ecology and Biology of Mammal-like Reptiles, Smithsonian Institution Press, pp. 83–106
• King, G.M., 1988, "Anomodontia" Part 17 C, Encyclopedia of Paleoherpetology, Gutsav Fischer Verlag, Stuttgart and New York,
• Rubidge, B.S. & Sidor, C.A. 2001, Evolutionary patterns among Permo-Triassic therapsids. Annu. Rev. Ecol. Syst. 32: 449-480.

• "Therapsida: Anteosauria". Palaeos. Archived from the original on 2006-03-13.
• "†Anteosauria". Mikko's Phylogeny Archive. Archived from the original on 2006-01-17.