Anteosaurus magnificus

Anteosaurus (meaning “Antaeus reptile”) is an extinct genus of large carnivorous synapsids. It lived during the Capitanian epoch of the Guadalupian (266-260 million years ago) in what is now South Africa. Like the well-known Moschops, they were dinocephalians, a clade of large-bodied therapsids that flourished from 270 to 260 million years ago and then went extinct without descendants.
Paleontologists
 surmise that Anteosaurus hunted rather like crocodiles, pulling land
animals into the water. In particular, scientists point to the animal’s
strong tail and weak, sprawling legs. Its body was well-suited to
projecting itself forward, both in hunting and evidently in
head-butting.

Anteosaurus had a tall, narrow skull, which is 80 centimetres (31 in) long. It was perhaps the largest known carnivorous non-mammalian synapsid, estimated at 5–6 m (16–20 ft) in length and 500 to 600 kg (1,100 to 1,300 lb) in weight.
The
 teeth are another identifying characteristic of Anteosaurus. The teeth
 on the roof of the mouth are enlarged and confined in a cluster near
the outer tooth row. The "normal teeth" include the anterior, canine and cheek teeth.
 A prominent feature of the dinocephalians is the ledge on the anterior
 teeth. The canine teeth are big, and there are usually about ten cheek
 teeth present. The front of the mouth curves up due to the premaxillary bone of the upper jaw.

Species
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 says, 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 as to family. The
skull fragment forming the holotype of Pseudanteosaurus can best be
considered as an immature specimen of Anteosaurus. Micranteosaurus, the
holotype of which contains a small snout, was previously considered a
new genus on account of its small size but is better be interpreted as a
 young specimen of Anteosaurus. And likewise, the large number of
species attributed to the genus Anteosaurus can also be considered
synonyms. Boonstra still considers as valid the genus Paranteosaurus,
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 the current thinking
on this is that they merely represent different growth stages of the
same type species, A. magnificus.
We have 32 skulls of Anteosaurus, of which 16 are reasonably well preserved and on them ten species …

During the Permian, two clades of amniotes came to dominate terrestrial
niches: the sauropsids and the synapsids. The synapsids included top
predators, such as Dimetrodoon and Gorgonopsia. Anteosaurus were
therapsids, a clade within Synapsida that includes the Permian ancestors
 of mammals.
Ecology
Olson notes that the Russian dinocephalian
 assemblages indicate environments tied to water, and Boonstra
considered that the roughly contemporary Anteosaurus were slinking
crocodile-like semi-aquatic forms. 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 behaviour. All other
head-butters (pachycephalosaurians, titanotheres, and goats)
 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.
Head-butting behavior
Anteosaurus like other related therapsids had a thickened skull (pachyostosis), and this has been suggested as an adaptation for head butting, or perhaps more aptly for head pushing. Also like with Moschops,
 the overall build seems to have been for projecting its body weight
forwards. Not only could this have been useful in dominance head pushing
 contests, but it may have also been a technique to knock over
unsuspecting or weakened prey.