University College London

Mike Taylor

The hot news on the block right now is the description of the new
sauropod *Abydosaurus mcintoshi*, which, amazingly, is known from four
more or less complete skulls (Chure et al. 2010).  This is unheard of
--- absolutely unprecedented.  There are few enough sauropods for which
a skull is known at all; but four of them, all in decent nick, is
breathtaking.

And here is one of them, the holotype:

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image-caption="Abydosaurus mcintoshi holotype skull DINO 16488, from Chure et al. (2010:fig. 3)
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Abydosaurus mcintoshi holotype skull DINO 16488, from Chure et al.
(2010:fig. 3)
:::

It's a real shame that, presumably due to space limitations, this is the
only one of the skulls that's figured in the paper; but the good news is
that some of the referred material is illustrated in the supplementary
information, which --- like the paper itself --- is freely available,
thanks to the wonder of open-access publishing.

According to the phylogenetic analysis in the paper, *Abydosaurus* is a
brachiosaurid --- it is recovered in all MPTs as the sister taxon to
Chure et al.'s "*Brachiosaurus*" OTU (on which, see below).  Since it's
from the mid Cretaceous (Cenomanian-Albian, from the Mussentuchit Member
of the Cedar Mountain Formation), it's likely about 105 million years
old, which means it lived the best part of 50 million years after the
better known brachiosaurs *Brachiosaurus* and *Giraffatitan*.  It was
evidently attracted by the *Giraffatitan* component of the compound OTU,
since the skull and neck are effectively unknown in *Brachiosaurus* (see
Taylor 2009 for a review of the holotype and referred material).
 Because it lived in pretty much the same time and place as
*Sauroposeidon*, there is the tantalising possibility that it is
actually the skull of that animal; on the other hand, the four recovered
skulls are all too small to fit the *Sauroposeidon* holotype, so unless
they were all subadult, that appealing idea is probably wrong.

Unlike *Giraffatitan* --- the only other brachiosaur with decent cranial
material, so far as I recall --- *Abydosaurus* has narrow teeth ,
superficially similar to those of diplodocids and titanosaurs.  Chure et
al. show that this seems to be part of a general trend of sauropods
evolving progressively narrower tooth crowns through time, perhaps
because narrow teeth can be replaced more quickly and turnover rate is
more important than robustness.

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Abydosaurus mcintoshi, reconstruction of skull and anterior neck based
on holotype and referred specimens (from Chure et al. 2010:fig. 4). Note
your weekly helping of sauropod-vertebra goodness in the upper-right
corner, in the form of a transverse slice though cervical 3 just behind
the diapophyses.
:::

One aspect of this paper particularly pleases me, and that is that the
new species is named after John McIntosh.  For anyone out there who
doesn't know who McIntosh is, he's been working on sauropods since
forever: he's produced a stream of important papers on the skulls of
diplodocids, among many other things, and wrote the Sauropoda chapter in
the original *The Dinosauria* (McIntosh 1990).  All of this in his spare
time, mind you, because as his day-job he was a professor of theoretical
physics at Yale and Princeton.  He's probably seen more sauropod
material than anyone else alive.  And on top of all that, he is one of
the good guys.  I drew the long straw at the Austin SVP in 2007, and got
to sit next to him at the informally convened sauropod-workers' lunch,
and it was a revelation to see his face light up as I tried to describe
the weird morphology of the as-yet-unpublished vertebra that we now know
as
*[Xenoposeidon](http://svpow.wordpress.com/papers-by-sv-powsketeers/xenoposeidon-week/)*.
 At an advanced age --- I don't know exactly how old he is, but you can
get some idea from the fact that he flew over Hiroshima and Nagasaki
less than a week after the bombs were dropped --- his enthusiasm remains
undimmed, and he is truly an inspiring example to every avocational
palaeontologist.

So it's sort of scandalous that it took so long before McIntosh got a
sauropod of his own.  (Jensen did name *Ultrasaurus* after him, but [as
has been much
discussed](http://svpow.wordpress.com/2008/09/10/its-ultrasaurus-i-mean-um-ultrasauros-err-supersaurus/),
that ended up synoymised with *Supersaurus*).  I know there's at least
one more new sauropod in the works that's slated to be named after him,
and I'm in favour.

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image-title="ScienceDaily-brooks-britt-with-abydosaurus"
image-description=""
image-caption="Brooks Britt (a co-author on the paper) with one of the skulls of Abydosaurus. Stolen from Science Daily.
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Brooks Britt (a co-author on the paper) with one of the skulls of
Abydosaurus. Stolen from Science Daily.
:::

# A note on brachiosaur taxonomy

I suppose I ought to mention this, only because if I don't, everyone
will just ask me about it.  Chure et al. (2010) refer to *Giraffatitan*
by the old name "*Brachiosaurus*" *brancai* throughout, and explain why
they do so on page 2:

Taylor (2009) recently suggested that the North American species
*Brachiosaurus altithorax* is generically distinct from the African
species *Brachiosaurus brancai*, which is known from abundant material
including a complete skull and many craniodental elements. Based on
numerous differences between overlapping parts of both holotypes, Taylor
(2009) proposed that the African species should be known as
*Giraffatitan brancai*. While we are open to this possibility, we do not
believe that it is sufficiently justified at present because the
identified differences have not been defended as separating genera,
rather than species, populations, or individuals. The sister-taxon
relationship between the two species recovered in the phylogenetic
analysis performed by Taylor (2009) neither supports nor refutes their
generic-level separation. At this point, we consider the decision to
recognize the African species as a genus apart to be arbitrary. We
choose to retain the original nomenclature in this contribution,
distinguishing between the two species where appropriate.

I am sort of nonplused by this.  I'm certainly not saying that [my 2009
paper](http://svpow.wordpress.com/papers-by-sv-powsketeers/taylor-2009-on-brachiosaurus-and-giraffatitan/)
is unassailable: as soon anyone comes along with evidence that
*Brachiosaurus* and *Giraffatitan* should after all be considered
congeneric, I'll be first in line to hear them out.  But I do feel that
now 26 osteological differences have been described between the species,
the null hypothesis has shifted, and the burden of proof is now on those
who wish to synonymise the genera.  "We choose to retain the original
nomenclature" is not an argument, and doesn't really advance
understanding.  So I'm afraid I think this was a regrettable misstep.

Anyway --- I don't want to end on that note!  The big deal here is that
we now have four fantastic new brachiosaur skulls, no doubt to be
described in more detail hereafter, and John McIntosh has a beautiful
sauropod named after him.  Happy days!

# References

::: {#_mcePaste}
- [Chure, Daniel, Brooks B. Britt, John A. Whitlock and Jeffrey A.
 Wilson.  2010.  First complete sauropod dinosaur skull from the
 Cretaceous of the Americas and the evolution of sauropod dentition.
 Naturwissenschaften (online, unpaginated).
  doi:10.1007/s00114-010-0650-6](http://www.springerlink.com/content/lpn30h8tx2231223/)
- McIntosh, John S.  1990.  Sauropoda.  pp. 345-401 in: D. B.
 Weishampel, P. Dodson and H. Osmólska (eds.), The Dinosauria.
 University of California Press, Berkeley and Los Angeles.
- [Taylor, Michael P.  2009.  A re-evaluation
 of](http://www.miketaylor.org.uk/dino/pubs/taylor2009/Taylor2009-brachiosaurus-and-giraffatitan.pdf)
 *[Brachiosaurus
 altithorax](http://www.miketaylor.org.uk/dino/pubs/taylor2009/Taylor2009-brachiosaurus-and-giraffatitan.pdf)*
 [Riggs 1903 (Dinosauria, Sauropoda) and its generic separation
 from](http://www.miketaylor.org.uk/dino/pubs/taylor2009/Taylor2009-brachiosaurus-and-giraffatitan.pdf)
 *[Giraffatitan
 brancai](http://www.miketaylor.org.uk/dino/pubs/taylor2009/Taylor2009-brachiosaurus-and-giraffatitan.pdf)*
 [(Janensch 1914).  Journal of Vertebrate Paleontology
 29(3):787-806.](http://www.miketaylor.org.uk/dino/pubs/taylor2009/Taylor2009-brachiosaurus-and-giraffatitan.pdf)
:::

The hot news on the block right now is the description of the new sauropod

 Abydosaurus mcintoshi

, which, amazingly, is known from four more or less complete skulls (Chure et al. 2010).  This is unheard of — absolutely unprecedented.  There are few enough sauropods for which a skull is known at all; but four of them, all in decent nick, is breathtaking.

Postagens de Rogue Scholar

Say hello to Abydosaurus mcintoshi