SIATS

Upon discovery, Zanno and Makovicky announced Siats as the first megaraptoran neovenatorid carcharodontosaurian allosauroid known from North America. Geographically, it's the youngest allosauroid yet discovered in North America too. But it's ginormous, third only to Acrocanthosaurus (whom it succeeded) and Tyrannosaurus (whom it preceded) in the all time American theropod charts, size-wise. And, like the two super-predators it was sandwiched inbetween, Siats would have dominated its time and place.

Contrary to press sensationalism, Siats didn't "terrorize" Tyrannosaurus rex, because in Siats' time, there were no Tyrannosaurus rex to terrorize. There were tyrannosauroids, the modestly-sized T.rex ancestors that were no more than a mild annoyance to the apex predator. But when Siats and its carcharodontosaurian brethren died out during the early-Late Cretaceous, some 10 million years later than palaeontologists had previously thought, the top-of-the-food-chain niche became vacant and tyrannosauroid super-sizing began. A further thirty million years passed before Tyrannosaurus rex — the Tyrant lizard king — took his throne.

Late in 2013, Novas et al. restudied Neovenatoridae and found that Megaraptora, the neovenatorid sub-group to which Siats has been assigned, were actually tyrannosauroids. However, most palaeontologists opine that this particular branch of the theropod family tree needs more study to substantiate such a claim. Lead author Zanno (pers.comms.) insists that Siats is definitely not a tyrannosauroid.