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Antetonitrus



(Posted for Adam Yates)
____

Iâd just like to say a few words about Antetonitrus
and early sauropodomorph phylogeny in general. Firstly
many may be struck by the large-scale differences
between the phylogeny in Yates and Kitching and the
phylogeny published a few months earlier in Journal of
Systematic Palaeontology, in reality almost two years
worth of work and observations of actual specimens
separates the two. It is because of the long time it
takes to get large papers like the J Syst Pal paper
published, that they appeared so close in time. It
could have been even worse, the Antetonitrus paper
could have come first! Anyway my iterations of basal
sauropodomorph analyses have stabilised and a topology
like the one in Yates and Kitching constantly comes
up. 

Mickey Mortimer suggested that it is a simple change
in taxonomy that has resulted in these early sauropods
and that not so long ago Antetonitrus would have been
classified as a prosauropod. Well what-if games are
hard to play and thoroughly untestable, but I like to
think that had Antetonitrus been thoroughly looked at
back when a melanorosaurids were thought to be part of
a monophyletic prosauropoda it would still have been
called a Norian sauropod. Thankyou to Matt Bonnan for
eloquently stating from a non-systematists point the
importance of this new work. To Tim I would say that
Lessemsaurus, Blikanasaurus and Anchisaurus HAVE got a
whole lot more sauropod-like. Antetonitrus and
Lessemsaurus are VERY similar and quite distinctive.
They share the distally flaring neural spines (they
look like a wedge of cheese balanced on its thin
edge). There are also derived similarities between the
large undescribed appendicular elements from the Los
Colorados Formation and those of Antetonitrus. These
elements cannot be referred to Lessemsaurus with
complete certainty but it now seems very likely. Using
the more complete anatomy of Antetonitrus we can see
that there is so much of their anatomy that is derived
compared to Riojasaurus and Melanorosaurus. I doubt
Antetonitrus would ever have been called a prosauropod
(but then again, even Vulcanodon was once called a
prosauropod so who can say?) Even little Anchisaurus
hosts a whole lot of derived sauropod-like
characteristics (maybe even a buttload? Iâm not sure,
Tom hasnât provided a precise definition of this
measure!) that have not been previously recognised.
But to see this evidence Iâm afraid you're going to have
to âwait for the paperâ.

I also notice that Mickey suggests that Euskelosaurus
might be another basal sauropod, following the J.
Syst. Pal. paper. I strongly doubt this now.
Euskelosaurus is based on a very poor type and there
are at least two taxa within the Lower Elliot that it
could belong to, so I recommend abandoning the name as
a nomen dubium (A practice I know Mickey doesnât like
but some of these old names are so bothersome, Iâm
happier with a relaxed attitude towards dismissing
taxa as nomen dubia). Anyway the codings for
Euskelosaurus in the J. Syst. Pal. paper were taken
from the Kromme Spruit material described in the 70âs
by Van Heerden. The next available name for this
material is Plateosauravus cullingworthi and this is
name I now use. So what is Plateosauravus and why
isnât it in Yates and Kitchingâs analysis? Mainly
because when scored from the Kromme Spruit material
alone the taxon is highly unstable (could be a basal
sauropodomorph, a prosauropod or a sauropod) and also
because a much more complete specimen has been found
(with skull) that is probably referable to
Plateosauravus. Until I get a chance to examine that
specimen Iâd rather leave the taxon out.
Matt Bonnan raised the possiblility that Prosauropoda
may still just represent a grade (as in the J. Syst.
Pal. paper). While this is topology is now definitely
less parsimonious than the Y & K topology there is
still support for a fully pectinate early
Sauropodomorpha within the matrix of Y & K, so I guess
we should not rule this possibility out. (I would
however rule out any chance of a fully inclusive
Prosauropoda with all taxa from Saturnalia to
Melanorosaurus being found to be monophyletic)
As for where other taxa not included might lie, Iâm as
anxious to find out as the next person. I really canât
wait to get good anatomical data for the
yunnanosaurids (I havenât yet seen either
Yunnanosaurus or Jingshanosaurus). 
Gongxianosaurus will almost certainly be a sauropod
but one more basal than Antetonitrus (based on the
dorsal vertebrae). 

Lastly Iâd like to add that you havenât seen the last
of the impressive finds from the Lower Elliot. Iâve
just spent just four days in the northern exposures of
this unit and saw four or five specimens that need to
be excavated. Now all I need is time and money.
Well I think thatâs enough rambling for now. Oh
finally the name does mean âbefore the thunderâ and it
is a reference to Brontosaurus (there is no problem
with using well-known synonyms to generate new names â
just think of Eobrontosaurus for starters). As for
ingenipes being spelt incorrectly, my little latin
dictionary told me that âingensâ was latin for
massive, if this is wrong then â DâOH.


Cheers all,

Adam