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Fwd: Greg Paul on new description of Spinosaurus



>From Greg Paul:

---------- Forwarded message ----------
From:  <GSP1954@aol.com>
Date: Tue, Dec 2, 2014 at 2:17 PM
Subject: Posting
To: bcreisler@gmail.com


Please post the below, thanks,

Greg

http://comments.sciencemag.org/content/10.1126/science.1258750,


Ibrahim et al. have taken an assortment of incomplete spinosaur remains
found

over an enormous territory of North Africa spanning 3000 km, found in

sediments whose exact temporal correspondence is not certain, and presumed

that they represent one genus and species. This despite the specimens being

limited in overlapping comparative material, being of different ontogenetic

stages, and there being some uncertainty concerning the individuality of
some

specimens -- a large gap in the vertebrae of juvenile/s FSAC-KK 11888
between

the mid dorsals and sacrals makes the conclusion it is one individual a

matter of opinion. The unusual length of the dorsals relative to the pelvic

sacral/pelvic/hindlimb elements in 11888 is suspicious, and should not be

presumed real unless it is present in a more complete and articulated

specimen, preferably adult. An attempt by this experienced paleoillustrator

to use the array of specimens to produce a reliably proportioned composite

technical skeleton of Spinosaurus aegypticus was abandoned due to these and

other issues – it is my experience that composite skeletons of novel taxa

constructed under these circumstances later often prove substantially errant

when more complete specimens are obtained. The actual skeletal proportions
of

Spinosaurus therefore remain uncertain, and the extreme shortness of the

hindlimbs restored by Ibrahim et al. is questionable, although the

possibility that the genus had exceptionally abbreviated legs cannot be
ruled

out.

Even more open to challenge is the near equality of the length of the arms

relative to the legs, and the idea that the theropodian arms were used in

locomotion. Attempts to calculate the absolute center of mass of extinct

dinosaurs even when the specimen is a complete individual is always

debatable, and doing so with a problematically proportioned composite based

on so many individuals of differing ages from so many places risks producing

misleading results.

    Also doubtful is the designation of FSAC-KK 11888 as the neotype of S.

aegypticus. Minimal overlapping material, differing ontogenetic stages,

possible time separation, and the 3000 km separation make it very possible

that 11888 and the destroyed holotype represent different taxa. The

possibility that 11888 is more than one individual is another difficulty in

this regard.

        Ibrahim et al. appear to have over interpreted the available
fossils.</HTML>