Carnotaurus fossils are known from Cretaceous South America in real life, so it is possible this is where the show is set. However, this tweet from InsideTerraNova (which seems to be a legitimate account of the show's creators, since it is followed by the show's official twitter account TerraNovaonFOX) says "The geographic location of Terra Nova isn't specified in the body of the show as it doesn't affect the storyline." Also, see the Science & Speculation section of the Ankylosaurus article for a discussion of the possibility that animals from South America might have crossed to North America (or vice versa) via a land bridge that existed between the continents in the Late Cretaceous.
In Terra NovaPangaea still exists! So, all species can still roam free over all continents.
Carnotaurus's arms are unusually small--they cannot even touch each other, but they did have an unusual degree of up-and-down flexibility. On Terra Nova it is shown with feathers on its arms, although in reality Carnotaurus is unusual in that skin on nearly the entire right side of its body has been fossilized (see here), and shows no feathers.
Ecological speculations: The attacking pair might suggest Carnotaurus is monogamous and looks for prey with its mate. They are likely top predators in the area surrounding Terra Nova; the Empirosaur is the only carnivore seen so far that is larger than they are (though if the skull under Nathaniel Taylors desk is an Allosaur, Allosaurs are likely larger as well), and spinosaurs primarily subsist on fish. Their attacks on humans suggest that they will prey on anything they can catch and kill.