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This group contains most theriosaurs, and is named because of their restricted quadrupedal stance. This group, over its existance, includes some 300+ species, and lasts the entirety of the Theriosauria.
This family are large terrestrial macropredators, convergently similar to early synapsids like Pampaphoneus or Anteosaurus. They are found on the supercontinent of Borealia, which is composed of the modern continents of Eurasia, Africa, Australia and North America. Aside from some relict large mammals in colder areas, and godzillasaurs in Africa, saberdrakes are the undisputed apex predators of most of Borealia.
Saberdrakes have several unique features for theriosaurs, the most important of which is their ability to switch between a sluggish ectothermic metabolism when inactive, to a fast endothermic metabolism in order to chase after potentially fast prey. Related to this is their stance, saberdrakes can 'high walk' similar to crocodiles, and this enables them to be efficient runners. Indeed, it is entirely possible that future descendants of saberdrakes could become fully endothermic mammal analogues.
Saberdrakes also have a heterodont dentition, with the front teeth being quite different in shape from ther rear teeth. The rear teeth are similar to that of modern varanids, sharp and serrated, but the front teeth are long, almost conicle, and very strong. The front four teeth of the jaw are hook like. Strangely, both saberdrakes and godzillasaurs both lack venom as adults, whereas the other giant theriosaurs, the fully aquatic venenosuchians, have sophisticated venom-delivering teeth, much like other smaller theriosaurs. This may suggest that larger terrestrial theriosaurs are able to rely solely on their own strength to kill.
This family are aquatic animals, generally found in large river systems, and in coastal marine settings. The family contains some 10 species in 3 genera, and range from small 2 metre piscivores to 9 metre macropredators of large bodies of water. Several of these larger species have become almost completely aquatic, and probably take over the niches that shallow water Aquavaranids held in the Postocene. This family first evolved out of basal theriosaurs about 60 million years in the future, and evolve into the next order of dominating aquatic tetrapods following the extinction of Aquavaranids in some 110 MyF. The last member of this lineage survives until some 140 MyF. Venenosuchians are some of the only theriosaurs found outside Borealia.
Arboreptanidae (Tree Snappers)Edit
The Arboreptanidae are a diverse family of theriosaurs found throughout forrested areas of Borealia, and with one small species found in South America. All genera hunt from trees, and have developed a superficially chameleon-like body, abeit on a larger scale. Arboreptanids range in size from 50 cm to over 4 metres long, depending on the size of the trees they live in, and often hunt by swinging down on their long tail and attacking before the prey can react. Their venom is strong, and is quich to dispatch prey items. Due to their long curved claws, flexible body and long fingers, Arboreptanids are relatively ungainly on the ground.
This family contains one genus and 2 species of superficially crocodile-like theriosaurs. One species is found in what was Australia, and the other in what was Africa. Neither species is very big, at about 2.5 metres long at the most, but their mildly venomous bite means they can subdue quite large prey for their size.
This group contains only the Godzillasauridae, and includes a total of 28 species between 68 and 110 MyF. Despite the name, infering that they are obligate bipeds, all godzillasaurs are capable of quadrupedal movement.
Godzillasaurs are a predominantly African group of theriosaurs that are primarily bipedal, making them convergently quite similar to some theropods such as spinosaurs. Unlike spinosaurs however, godzillasaurs are terrestrial, and will actually generally avoid water, as large freshwater venenosuchians and crocodilians, taking advantage of the warm climate and abundance of prey, are an ever-present threat to anything that attempts to drink from the rivers. Like saberdrakes, godzillasaurs have a heterodont dentition, with their front teeth being modified from the basal all purpose blade into elongated caniformes, which in large individuals can be up to 15 cm long.
Also in common with saberdrakes, adult godzillasaurs lack venom, though they hatch with the ability to produce venom, and have hollow teeth in which to do so, which are eventually replaced with solid teeth after a few short years of life at the bottom of the food chain. The offspring are cared for by the mother for several weeks, but are left to fend for themselves when they are still young, and most don't survive into adulthood.