So having never covered Allosaurus before on the Musings in what, four years, I’ve now done in twice in the last few months. Last time out it was in Japan, but this is an all-American one that’s sat (to no-one’s surprise) in the Carengie. Well, more running than sat, but you get the point. Here it is alongside an Apatosaurus, though perhaps making its way towards junior.
This being the Carnegie, there’s also an original skull to accompany the mount and let you see real bone alongside the cast. Though as Tom Holtz has pointed out in the comments, it’s Marshosaurus and not Allosaurus.
Dave Hone's Archosaur Musings 
The skull on the bottom is not Allosaurus; it is Marshosaurus.
Whoopsie! Must confess I didn’t read the large label at the time and didn’t take a photo of it for future reference – bad Dave. Still, most intriguing to learn, thanks for that Tom and squinting at the photo now, yeah, it does say that. This is what happens when you follow what you think is a consistent pattern of specimens next to mounted casts – I’ll balme the Carngie for being too good! 😉
I’ll adjust the post accordingly.
I have a question. Do we know where Coelosauria and Carnosauria split? A few weeks ago, I was wondering where the Allosaur lineage came from, and couldn’t find any answers.
Which species is this Allosaurus specimen labeled as? Its skull does not look very fragilis-like, it reminds me of BHI 126633, Allosaurus sp., with its quite longirostrine skull, the kink between maxilla and premaxilla, and the pinned and upward-pointing lacrymal processes. What do you think?
Zhen: The split between Carnosauria (Allosaurus and everything closer to it than sparrows) and Coelurosauria (sparrows and everything closer to them than Allosaurus) definitely has occurred by the Middle Jurassic, as there are members of both clades present then. Most carnosaurs look pretty similar to each other (sinraptorids and Allosaurus and Neovenator are really not too different from each other), and in general form they look pretty similar to primitive megalosauroids (such as Marshosaurus and Monolophosaurus and Piatnitzkysaurus).
The origin of the Tetanurae as a whole (megalosauroids, carnosaurs, coelurosaurs) seems to have been in the form of medium-sized (5-7 m) carnivores with deep skulls and large hands.
… thought the selection of sparrows as the internal specifier for Coelurosauria is not really ideal: it’s explicitly used in one of the PhyloCode examples as what not to do, since it invites pithering by presupposing a phylogenetic hypothesis that is still, however lamely, disputed. Not that this changes the actual point Tom was making.