So... how are these related?

[RaptorTheDoctor]

Oh man, I've been gone too long from the world of dinosauria. I used to be really into all this, and I'm just rediscovering my love of paleontology.

In any case, I was browsing dinosaur stuff the other day, and now I'm confused about how certain families are related to one another.

For example, Allosaurids, Carcharodontosaurids, Megalosaurids, and Abelisaurids.

I've seen Concavonator and Acrocanthosaurus called both Allosaurs and Carcharodontosaurs, which are they? And are the families closely related? I remember thinking as a kid that the Allosaurids evolved into Carcharodontosaurids (or at least branched out) but I can't think if that's true or not. Also, what's with this apparent split between Carcharodontosaurus and Giganotosaurus? I've seen places put Giganotosaurus and Mapusaurus into subfamily Giganotosauridae, rather than just having them as part of the Carcharodontosauridae family line. I thought that Carcha and Giga were pretty closely related, no?

Second, I have also seen Rugops called both an early Carcharodontosaurid and an Abelisaurid. Which one is true? Are Carcharodontosaurs and Abelisaurs closely related? Also, are Abelisaurs the ones that descended from Ceratosaurs? And while we're on that, aren't Ceratosaurs and Dilophosaurs closely related? I honestly don't know anymore.

Third. Megalosaurs and Allosaurs. This more concerns Torvosaurus, who I've seen called both. Which is correct? Megalosaurids used to be kind of a hodgepodge collection of whatever didn't fit anywhere else, but I think they were updated. So what's the difference between Allosaurs and Megalosaurs? Looking just at the skulls, I can see that Torvosaurus has a skull that superficially looks kind of like an early tyrannosaur (which, unless I'm totally wrong, it isn't) whereas Allosaurus has a less elongated skull that looks a little taller.

[ZoPteryx]

Excellent questions!

1)  Allosaurids, Carcharodontosaurids, Neovenatorids, and Sinraptorids are all Allosauroids (which is sometimes shortened to just Allosaurs).  They share a common ancestor, but do not necessarily lead to one another.  And so, Concavenator and Acrocanthosaurus are Cracharodontosaurid Allosauroids, although I should note that the exact position of Acrocanthosaurus is somewhat uncertain.  How distinct Neovenatorids are is uncertain, and they may prove to be just a subgroup within the Carcharodontosaurids.  As for Giga and Carcha, yes, they are very closely related, some even think they're the same genus.  However, most recent evidence points to them being in different subgroups (Giganotosaurines and Carcharodontosaurines) within the Carcharodontosaurids, but still more closely related to eachother than either is to Concavenator or Acrocanthosaurus.

2)  Rugops is a primitive Abelisaurid Abelisauroid.  Abelisauroids and Allosauroids are not particularly closely related.  The term Ceratosaurs is now typically reserved for just Ceratosaurus and its closest relatives, as these have been found to be more advanced than the Abelisauroids and Coelophysoids they were once included with.  Dilophosaurids are currently grouped with the Coelophysoids, but most recent evidence points to the Coelophysoids as being paraphyletic (a collection of relatively unrelated families), and so, Dilophosaurids will probably be split into their own group once the interelatedness of its members is sorted out (many suppossed Dilophosaurids are probably more advanced theropods).

3)  Megalosaurids are a group of primitive (& possible paraphyletic) theropods that, together with the Spinosaurids, are united under the Megalosauroids.  These are less advanced than Carnosaurs (which includes Allosauroids) & Coelurosaurs (which includes Tyrannosauroids and many others), but more advanced than other groups.  Megalosaurids are poorly understood for the most part, one unique feature is their broad pelvises and somewhat shallow snouts, but too little is known of most species to say if these traits should really be used to define the group.

Hope this helps!

[RaptorTheDoctor]

Wow, that helps a lot. I've been gone too long it seems.

I think you answered all my questions there, except the position of Torvosaurus? Megalosaur?

And one more question has been brought up by this. Why exactly are Spinosaurids and Megalosaurids grouped together? Are they really related?

[Jetoar]

Thanks Zopteryx, you have helped all us  . I didt know some answers  .

[ZoPteryx]

Glad I could be of help!

Wow, that helps a lot. I've been gone too long it seems.

I think you answered all my questions there, except the position of Torvosaurus? Megalosaur?

And one more question has been brought up by this. Why exactly are Spinosaurids and Megalosaurids grouped together? Are they really related?

Yes, Torvosaurus is a Megalosaurid, and one of the best known at that.

Some Megalosaurids have rather elongated snouts and vertebral spines, nearly conical teeth, and relatively long and muscular arms.  These features, combined with the broad pelvises and other primitive characteristics shared between the Megalosaurids and Spinosaurids, have been used to unite the groups.  However, with that said, Megalosauroidea is still poorly understood (it contains many genera that have proven difficult to place) and could very well be split in the future.

[Splonkadumpocus]

I still want to know why Allosauroidea seems to be the preferred term for that group of dinosaurs instead of Carnosauria, which contains all the allosauroids and only a few other taxa. Carnosauria has much more historical precedent and has much fewer syllables.

Whenever I've used the term "carnosaur" people seem to be under the mistaken impression that it's an obsolete term that means "Allosauroidea+Tyrannosauroidea" which it doesn't.

[Horridus]

I still want to know why Allosauroidea seems to be the preferred term for that group of dinosaurs instead of Carnosauria, which contains all the allosauroids and only a few other taxa. Carnosauria has much more historical precedent and has much fewer syllables.

'Allosauroidea' makes it a bit more obvious what sorts of animals you're talking about, I suppose. To play devil's advocate.

What hasn't been mentioned yet, and might be worthwhile for someone in need of some quick catch-up, is the split between tetanurine and non-tetanurine theropods. Tetanurae is a clade containing the majority of theropods, including megalosaurs, allosaurs and coelurosaurs (including birds), but more 'primitive' (or more properly, basal) non-tetanurines survived until the end of the Cretaceous in the form of the abelisaurs.

[RaptorTheDoctor]

I still want to know why Allosauroidea seems to be the preferred term for that group of dinosaurs instead of Carnosauria, which contains all the allosauroids and only a few other taxa. Carnosauria has much more historical precedent and has much fewer syllables.

'Allosauroidea' makes it a bit more obvious what sorts of animals you're talking about, I suppose. To play devil's advocate.

What hasn't been mentioned yet, and might be worthwhile for someone in need of some quick catch-up, is the split between tetanurine and non-tetanurine theropods. Tetanurae is a clade containing the majority of theropods, including megalosaurs, allosaurs and coelurosaurs (including birds), but more 'primitive' (or more properly, basal) non-tetanurines survived until the end of the Cretaceous in the form of the abelisaurs.

Really? Wow, I wasn't aware Abelisaurs were so unique!

I've mostly only see Late Jurassic/Cretacious Abelisaurs. What's the earliest known one? And do they have any close relatives?

[Splonkadumpocus]

I still want to know why Allosauroidea seems to be the preferred term for that group of dinosaurs instead of Carnosauria, which contains all the allosauroids and only a few other taxa. Carnosauria has much more historical precedent and has much fewer syllables.

'Allosauroidea' makes it a bit more obvious what sorts of animals you're talking about, I suppose. To play devil's advocate.

What hasn't been mentioned yet, and might be worthwhile for someone in need of some quick catch-up, is the split between tetanurine and non-tetanurine theropods. Tetanurae is a clade containing the majority of theropods, including megalosaurs, allosaurs and coelurosaurs (including birds), but more 'primitive' (or more properly, basal) non-tetanurines survived until the end of the Cretaceous in the form of the abelisaurs.

Really? Wow, I wasn't aware Abelisaurs were so unique!

I've mostly only see Late Jurassic/Cretacious Abelisaurs. What's the earliest known one? And do they have any close relatives?

Abelisaurs were the most derived members of an earlier lineage called ceratosaurs. The earliest ceratosaurs would be Sarcosaurus and Berberosaurus from the Early Jurassic of Britain and North Africa respectively. The group also includes the ornithomimid-like elaphrosaurs, known from Jurassic Asia (Limusaurus) and Africa (Elaphrosaurus, Spinostropheus), as well as Ceratosaurus from North America. A couple of non-abelisaurid ceratosaurs made it into the mid-Cretaceous in the southern continents; these are Genyodectes from South America and Deltadromeus/Bahariasaurus from Africa.

The earliest definite abelisaur is Eoabelisaurus from mid-Jurassic Argentina, though Berberosaurus may be an abelisaur as well.