Large Theropod Taxonomy

[Katieraptor]

Wow, okay.

Getting back into dinosaurs, things seemed to have changed. Megaraptor is a basal tyrannosaurid now?

So what exactly are our tetanuran groups now? And how do they all fit together? Megalosaurids, Allosaurids, Metriacanthosaurids, and Neovenatorids are all groups I've seen mentioned. A lot of these groups seem to fall under "Allosauroids". But I have to admit, this new taxonomy is getting to me. For example, I was pretty sure that Yanchuanosaurus shangyouensis was related fairly closely to Allosaurus fragilis, but it's a Metriacanthosaurid, which I thought were more similarly associated with Megalosaurids than Allosaurids?

Color this former paleontology nerd who's just starting to get back into things very confused.

[Halichoeres]

According to Zanno & Makovicky 2013, there are several basal forms (including, probably, Sinosaurus, Monolophosaurus, etc.), and then  a major split between megalosauroids (inc. spinosaurids) and everyone else. Metriacanthosaurus and its relatives are not megalosauroids under this scheme. The "everything else" side of the tree further splits into Coelurosauria and Allosauroidea. The former includes tyrannosaurs, maniraptorans, and ornithomimosaurs. The latter includes allosaurs, carcharodontosaurids, and Metriacanthosaurus/Yangchuanosaurus/Sinraptor. So Yangchuanosaurus isn't so terribly far away from Allosaurus, all things considered. Neovenatorids, under this hypothesis, constitute the sister group to the carcharodontosaurs.

Does that help at all?

[Katieraptor]

Yeah that helps a lot, thanks!

I was kind of expecting Yang to be considered an Allosaurid proper because of being referred to often as the Chinese cousin of allosaurus but I guess not.

[Sim]

The classification of Megaraptor and other megaraptorans has been controversial for some time.  As far as I've seen, palaeontologists have argued most strongly for megaraptorans being either allosauroids or tyrannosauroids, with their classification as allosauroids being the longer-standing one.  I believed their classification as tyrannosauroids was correct until from what I remember, some of the palaeontologists who had supported their classification as tyrannosauroids published a paper that suggested it was more likely megaraptorans were allosauroids.  I now think megaraptorans are most likely allosauroids, and I think this is also the most widely-held view among palaeontologists.  Something that's made it hard to work out where megaraptorans belong on the family tree is that not a single one of these animals is known from good remains.

Yangchuanosaurus is closely related to Allosaurus, it's just found to be more closely related to Sinraptor, which is why these three dinosaurs are within Allosauroidea, and Yangchuanosaurus and Sinraptor are further classified as being in Metriacanthosauridae/Sinraptoridae while Allosaurus isn't.  Metriacanthosauridae is being used instead of Sinraptoridae because the former is some years older, but I think it shouldn't be given priority since the genus it's based on - Metriacanthosaurus - is known from very poor remains that make its classification not as certain as one would like.