| Anteosaurs | |
|---|---|
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| Life restoration ofAnteosaurus | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Synapsida |
| Clade: | Therapsida |
| Suborder: | †Dinocephalia |
| Infraorder: | †Anteosauria |
| Subgroups | |
see Taxonomy | |
| Synonyms | |
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Anteosaurs are a group of large, primitivecarnivorousdinocephaliantherapsids with large canines and incisors and short limbs, that are known from theMiddle 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. They died out at the end of the Middle Permian, possibly as a result of the extinction of the herbivorousTapinocephalia on which they may have fed.
The Anteosauria are distinguished from the Tapinocephalia by several features, such as very largecanines, cheek teeth with bulbouscrowns, and an upturning of thepremaxilla, so that the front of mouth curves strongly upwards. There is a tendency especially in more advanced forms such asAnteosaurus 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.
The early Russian (Boonstra 1972) and Chinese (Rubidge & Sidor 2001) anteosaurs are generally considered the most primitive of the dinocephalians, although it has also been suggested (Kemp, 1982, King 1988) that theestemmenosuchids are morebasal. They have featured in common withpelycosaurs (Carroll 1988) andBiarmosuchians (Chudinov 1965), and, with the Tapinocehalia, are part of the first major evolutionary radiation of the Therapsida (Rubidge & Sidor 2001). So far, little work has been done on detailedphylogenetic relationships between the varioustaxa.
The stance of a typical anteosaur, such asTitanophoneus, 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 contemporaryAnteosaurus 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,pachycephalosauriandinosaurs,titanothere ungulates, andgoats were or are completely terrestrial. Perhaps these animals spent some time in the water but were active on land during the mating season, and probably quite able to get about on land to hunt for prey.
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 armoredpareiasaurs (Lee, 1997) andenormoustapinocephalid dinocephalians (Rubidge, 1995).[1]
The large anteosaurs were efficient predators, more specialized than earlier and more primitivebiarmosuchid andeotitanosuchid 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.[1]
James Hopson and Herbert Barghusen in 1986 provided the firstcladistic 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.[2]
Thecladogram below follows an updated (2012) version of Kammerer's analysis by Juan Carolos Cisneros and colleagues.[3]
The group was originally defined as asuperfamily byL. D. Boonstra in 1962 to include thefamiliesBrithopodidae andAnteosauridae.
Gillian King in a 1988 review of theAnomodontia (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 ongoingEncyclopedia 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".
After Kammereret al., 2011.
