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Re: Megaraptor



At 09:39 PM 11/25/97 PST, jaemei@hotmail.com wrote:
>"*Megaraptor*" is supposedly the first South American dromaeosaur, and 
>bigger than *Utahraptor*. Of that I have no doubt, but it is its 
>classification that I doubt.
>
>Firstly, only north Africa and Australia seem to see dromaeosaur 
>fossils, and even those are doubtful, and could belong to a sister 
>branch of the "raptors," or to dinosaurs similar to *Noasaurus*.

No, the claws of the North African form (and Megaraptor) are distinctly
different from Noasaurus, which has a pit on the ventral surface.

Having seen photos & drawings of Megaraptor, I can say that it is very
similar to dromaeosaurids if it isn't a true dromaeosaur.  Of course, there
is another big avialian in the same sediments, for which we don't have
overlapping material, so it may be that Megaraptor will lose its name in time...

(And, as a general warning, beware of taxonomy by biogeography.)

>This could be the same situation as in *Baryonyx*, so I doubt the South 
>American super-raptor.

Why don't people wait to actually see the fossils... :-S

>The Asian and North American (Asiamericanan) 
>raptors are known from many fossils, many times articulated, so we know 
>that they were there; but for the European and far-east Asian, there 
>isn't enough evidence (teeth) to base anything on, for they aren't 
>diagnostic.

Excuse me?  There are most definite European dromaeosaurid material, both
teeth and bones.

>I'm not saying for sure they weren't raptors, but Laurasia 
>seems to be where all the valid dromaeosaurids have been found, and the 
>troodontids, so I am having difficulty believing in Gondwanan raptors: 
>the African, Australian, and South American "raptors" could all be 
>spinosauroid,

The Megaraptor material is most certainly not similar to Baryonyx!  If a
spinosauroid, it is one which is extraordinarily convergent upon coelurosaurs.

>To support my thoery, there are supposed "spinosaurid" remains from 
>South America anyway (*Angaturama,* *Irritator,* and *Asiamericana*) and 
>it is feasible that a baryonychid may have come from the Argentine rocks 
>of the Rio Neuquen Formation, a viable grave of dinosaurs. I don't know 
>what formations those are from, aside from the Santana (*Irritator*), so 
>"*Megaraptor*" _could_ be one of those, a plausible synonomy that 
>should, in my opinion, be followed.

Asiamericana is Asian (hence half of its name), and may well be a fish.
Angaturama and Irritator are both Santanan.

Megaraptor is younger than these forms, and comes from a formation which
also includes an arctometatarsalian, troodontid-type form (unnamed at
present) and the avialian Unenlagia.  So, coelurosaurs were definitely
present in the Rio Neuquen.

>And then there's *Noasaurus*, a 
>raptor-like ornitholestoid from Argentina; as I've never seen the claw 
>in question -- what if?

Noasaurus is an abelisauroid neoceratosaur, not an Ornitholestes-like form.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661