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RE: The skinny on Apato versus Brontosaurus



Upchurch et al. (2004) state the ajax holotype has the following diagnostic 
characters of Apatosaurus- cervical ribs very short and robust, with rounded 
processes projecting from the dorsal margin immediately posterior to the 
tuberculum; cervical ribs set well below and lateral to the centrum, so that 
the height of the vertebra exceeds its length; coracoid with quadrangular 
lateral profile.  It's more closely related to excelsus and parvus than louisae 
due to having a scapular blade that curves ventrally toward its distal end.  It 
shares proximal caudal centra with concave posterior articular surfaces and a 
distal scapula expanded <1.5 times minimum blade width with other specimens 
assigned to A. ajax.  So the scapula itself would be sufficient to assign it to 
ajax, and a cervical would be sufficient to assign it to Apatosaurus.  While it 
may have been risky at the time to assign all of the current A. ajax material 
to one species, now that we have associated specimens with the same character 
distribution (e.g. NSMT-PV 20375), postulating the ajax holotype is a chimaera 
that just happens to agree with other specimens in morphology seems implausible.

As louisae is outside the (excelsus+ajax) clade, it cannot be in the same genus 
as excelsus but a different one than ajax.  Unless you're using 
paraphyletic/polyphyletic genera, which no modern dinosaur worker advocates.  
Make excelsus Brontosaurus, and parvus Elosaurus (since it's not necessarily 
closer to ajax or to excelsus) if you wish, but louisae will need a new genus 
too.  Then we've accomplished nothing scientific, since we'd just have four 
monospecific genera instead of four species in one genus.

Mickey Mortimer

----------------------------------------
> Date: Mon, 29 Apr 2013 19:21:48 -0400
> From: GSP1954@aol.com
> To: dinosaur@usc.edu
> Subject: The skinny on Apato versus Brontosaurus
>
> The holotype of Apatosaurus ajax is very fragmentary, and is not really
> diagnostic at the species or even genus level (have examined it at Yale).
> Worse, nothing was
 quarry, so
> the bones assigned to the holotype could belong to multiple individuals
> (very possible) and even taxa (less likely but possible). It could therefore 
> be
> a chimeria that gives misleading taxonomic information. It's a very bad
> type:-(
>
> The mounted Yale holotype of Brontosaurus excelsus is most of the skeleton
> (the vertebrae are badly beat up, I suspect from incompetent excavation and
> transport in the day before jacketing, and from chucking the naked bones
> into straw filled wood boxes). It is an excellent holotype for a genus:-)
>
> Also, A. ajax is from high in the Morrison, B. excelsus from the middle.
> Probably 3 million years separating them. Assigning the latter to the same
> genus as the former is correspondingly very dubious when the A. ajax type is 
> so
> poor. (Also mid Morrison A. or B. louisae is definitely the same genus but
> probably not same species as B. or A. excelsus).
>
> Riggs blew it at a time when the importance of high quality types etc was
> not appreciated. He should have declared the A. ajax type inadequate and kept
> Brontosaurus. Would have avoided the chronic name confusion, and kept the
> popular name going.
>
> I was thinking of doing so now. But that requires for the first time
> actually describing the A. ajax type in proper detail to then sink it, and it
> would be good to do the same for B. excelsus skeleton (should be done when it 
> is
> dismantled during the hall redo).
>
> GSPaul</HTML>