[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: New sauropod paper



> Date: Wed, 14 Sep 2005 16:54:27 -0700
> From: "T. Michael Keesey" <keesey@gmail.com>
>
>> I totally agree here. If that's the case, then say bye to Jobaria.
> 
> Only if you think _Rebbachisaurus tasmenensis_ is congeneric with
> _R.  garasbae_. Since nobody seems to think this (_R. garasbae_ is a
> diplodocoid neosauropod; _R. tasmenensis_ is a non-neosauropod
> eusauropod), it seems that _Jobaria tasmenensis_ would be the proper
> designation, and a senior synonym of _J. tiguidensis_ ...

... except that the position of Jobaria may not be particularly
secure.  The area around the base of Neosauropoda has a habit of
turning out differently in different analyses.  Sereno et al.'s (1999)
original description of _Jobaria_(*) just said:

        Despite its Cretaceous age, Jobaria is strikingly
        primitive.  Primitive features include the abbreviate
        snout, terminally positioned nares, low number of
        cervical vertebrae, simple neural spines, and many
        other features and suggest that Jobaria lies outside
        the neosauropod radiation.

Jobaria was of course too late to join the party for Upchurch 1995,
Upchurch 1998 or Wilson and Sereno 1998, but while it popped out just
outside Neosauropoda in Wilson 2002 (which the author no doubt
approved of), it emerged as a basal Macronarian (in a clade with
_Atlasaurus_ and _Bellusaurus_) in Upchurch et al. 2004 (the _D2_
analysis).

For more established maybe-in-maybe-out taxa, the situation is seen to
be more complex.  For example, Wilson and Sereno 1998 (fig. 44A,
p. 54) recovered _Haplocanthosaurus_ as a non-camarasauromorph
macronarian; Upchurch 1999 (fig. 19, p. 74) found it to be outside
Neosauropoda; Wilson 2002 (fig. 13A, p. 240) found it as a
non-diplodocimorph diplodocoid (that is, closer to Diplodocus than is
Saltasaurus, but less close to Diplodocus than is Rebbachisaurus); and
Upchurch et al. 2004 (fig. 13.18, p. 297) found it as a surprisingly
derived camarasauromorph, closer to titanosaurs than is
_Camarasaurus_.

All this just goes to prove that we have to be super-careful around
the base of the Neosauropod tree.  Given that Rebbachisauridae is the
earliest diverging branch of Diplodocoidea, I don't think it would
take much to make _Haplocanthosaurus_ a rebbachisaurid.  That's less
likely with Jobaria due to the plesiomorphic skull, but I wouldn't
want to stake the life of my first-born son on it.

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  "Looks like it's time to over-technicalize this previously tame
         post" -- Mickey Mortimer on the dinosaur mailing list


(*) If you want to call it that.