University of California, Merced

Matt Wedel

[![apato-growth-series-500.jpg](https://svpow.files.wordpress.com/2007/12/apato-growth-series-500.jpg)](http://svpow.files.wordpress.com/2007/12/apato-growth-series.jpg "apato-growth-series.jpg")

My favorite room in the world is the big bone room at BYU's Earth
Science Museum. It is the only place on the planet that has good
material of all six of the best-known Morrison sauropods: *Apatosaurus*,
*Barosaurus*, *Brachiosaurus*, *Camarasaurus*, *Diplodocus*, and
*Haplocanthosaurus*. So if you are looking at, say, a middle cervical of
*Apatosaurus* and you think, "Hmm, I wonder how this looks in *X*,"
where *X* is one of the other five genera listed above, you can just
**go look**. It's phenomenal.

The big vert here is a posterior cervical of *Apatosaurus*. Those big
loops on the side are formed by the diapophyses and parapophyses
(sticking out from the vertebra) and the capitula and tubercula of the
cervical ribs. Capitula are rib heads, and they articulate with the
parapophyses, which are the lower of the two sets of rib articulations
on the vertebral centrum. Tubercula are rib tubercles, and they
articulate with the diapophyses, which are at the ends of the massive
transverse processes sticking out sideways from the neural arch. Here's
a labeled version, just in case the verbal description made no sense. I
know Mike covered this stuff back in [Tutorial
2](http://svpow.wordpress.com/2007/10/04/tutorial-2-basic-vertebral-anatomy/),
but *Apatosaurus* is frankly pretty freaky in the cervical rib
department.

[![apato-growth-labeled-500.png](https://svpow.files.wordpress.com/2007/12/apato-growth-labeled-500.png)](http://svpow.files.wordpress.com/2007/12/apato-growth-labeled-500.png "apato-growth-labeled-500.png")

You'll notice that the neural spine is split down the middle, which is
the case in many diplodocoids but not all of them. Bifurcated neural
spines are also found in *Camarasaurus*, some titanosaurs, and to a
lesser extent in some mamenchisaurs, so the character definitely evolved
more than once. More about bifid neural spines another day...

At last, to the point. In front of the big vert you can see a smaller
one, about the size of a fist. That's a vertebral centrum from the same
part of the neck from a much smaller individual of *Apatosaurus*,
probably somewhere between horse- and elephant-size. And that's not
all--in front of the scale bar, wrapped up in plastic, is a centrum from
a wee little baby *Apatosaurus* about the size of poodle. Why is the
vert in plastic? Because it was going off to the micro-CT scanner at the
University of Utah, which is in a cleanroom, so all specimens have to be
hermetically sealed. I didn't think to shoot this little growth series
lineup until the vert was already bagged, and I haven't been back since
to set it up again.

Alas, the baby *Apatosaurus* vert and the CTs of its internal structure
will **also** have to wait for another day. We're such teases...


My favorite room in the world is the big bone room at BYU’s Earth Science Museum.

Apatosaurus, Russian doll edition

University of Portsmouth

Mike Taylor

After eight consecutive posts on *Xenoposeidon*, I have to admit that
even I am getting just a tiny bit bored of it, so I can only imagine how
the rest of you feel. So now for something completely different:

[![BMNH 96
"Chondrosteosaurus"](https://svpow.files.wordpress.com/2007/11/bmnh-r96-chondrosteosaurus-500px.jpeg)](http://svpow.files.wordpress.com/2007/11/bmnh-r96-chondrosteosaurus.jpeg "BMNH 96 “Chondrosteosaurus”")

You see before you a badly battered cervical vertebra, BMNH R96, which
if I remember correctly is catalogued as belonging to
"*Chondrosteosaurus*". That genus, like so many from the Wealden, was
erected on non-diagnostic material, and there is really no reason to
think that R96 belongs to the same taxon as the *Chondrosteosaurus* type
specimen BMNH R46869. It's best regarded as Neosauropoda indet. (and,
no, before you ask, we will not be naming it and promoting it as "The
world's second most amazing sauropod").

The interesting thing about this specimen is that its condyle is
completely eroded away. We're looking at it in anterior view, right into
the front of the centrum, and we can see a classic camellate pattern.
The network of thin lines is bone; everything in between, now filled
with matrix, used to be filled with air when the animal was alive. A
while back, Matt ran the number on this photo and concluded that this
vertebra was 78% air --- a very high proportion even by sauropod
standards, exceeded only by *Sauroposeidon* (the world's third most
amazing sauropod).

Of course it's a shame that this bone is so poorly preserved; on the
other hand, if it were complete, we wouldn't be able to see the internal
structure. Matt's firmly of the opinion that bone not broken is a bone
wasted, and I sometimes think that if he had his way, he'd go through
the world's sauropod collections with a sledgehammer, smashing all the
vertebrae open in search of pneumaticity. (Note to collections staff:
Just kidding! Har har!) It's certainly true that more is known about the
"Angloposeidon" vertebra than would be known if it weren't snapped in
two; and of course, we'd not have known about [the internal structure of
the *Xenoposeidon*
vertebra](http://svpow.wordpress.com/2007/11/17/xenoposeidon-week-day-3-the-basic-beast-inside/)
were the condyle not blasted off.

Up till now, internal structure has been badly neglected in terms of
informing sauropod phylogeny, despite Matt's work on its evolution and
distribution (Wedel 2003a, 2003b). The analyses of Wilson (2002) and
Upchurch et al. (2004) each included just a single character for
presacral bone texture in their matrices; and the Grand Unified Analysis
of Harris (2006), which merged the Wilson and Upchurch matrices,
discarded even this one character, as discussed in the supplementary
data. That may be fair enough: we might not yet know enough about
vertebral bone texture to code it well. But hopefully that will soon
change, because there is a lot of information out there that's not
getting used.

## References

- [Harris, Jerald D. 2006. The significance of *Suuwassea emiliae*
  (Dinosauria: Sauropoda) for flagellicaudatan intrarelationships and
  evolution. Journal of Systematic Palaeontology 4:
  185-198.](http://cactus.dixie.edu/jharris/Flagellicaudatan_Phylogeny.pdf)
- [Wedel, Mathew J. 2003. The Evolution of Vertebral Pneumaticity in
  Sauropod Dinosaurs. Journal of Vertebrate Paleontology 23 (2):
  344-357.](http://www.sauroposeidon.net/Wedel_2003b_evolution-of-pneumaticity.pdf)
- [Wedel, Mathew J. 2003. Vertebral pneumaticity, air sacs, and the
  physiology of sauropod dinosaurs. Paleobiology, 29 (2):
  243-255.](http://www.sauroposeidon.net/Wedel_2003a_sauropod-pneumaticity.pdf)
- Upchurch, Paul, Paul M. Barrett and Peter Dodson. 2004. Sauropoda. pp.
  259-322 in D. B. Weishampel, P. Dodson and H. Osmólska (eds.), The
  Dinosauria, 2nd edition. University of California Press, Berkeley and
  Los Angeles. 861 pp.
- [Wilson, Jeffrey A. 2002. Sauropod dinosaur phylogeny: critique and
  cladistic analysis. Zoological Journal of the Linnean Society 136:
  217-276.](http://www-personal.umich.edu/~wilsonja/JAW/Publications_files/Wilson2002.pdf)


After eight consecutive posts on

 Xenoposeidon

, I have to admit that even I am getting just a tiny bit bored of it, so I can only imagine how the rest of you feel.

Well, not Xenoposeidon, anyway

I see now that Mike has beaten me to the punch in providing your
at-least-weekly dose of sauroponderous vertebrawesome. And a nice job it
is. Still, I feel funny about you not getting a *new* picture
([ahem](http://svpow.wordpress.com/2007/10/04/tutorial-2-basic-vertebral-anatomy/)),
so I'm posting my late entry anyway. For some reason, despite--or
perhaps because of--my ardent devotion to cervicals, I have taken it on
myself to push the anatomical boundaries of SV-POW!
[again](http://svpow.wordpress.com/2007/10/15/the-promised-land/).

[![amnh-diplodocus-500.jpg](https://svpow.files.wordpress.com/2007/11/amnh-diplodocus-500.jpg)](http://svpow.files.wordpress.com/2007/11/amnh-diplodocus-pelvis.jpg "amnh-diplodocus-500.jpg")

Here's a partial pelvis of *Diplodocus* in the American Museum of
Natural History, in left lateral view. The big, vertically-oriented slab
is the ilium. The semicircular concavity on the bottom of the ilium is
the top half of the acetabulum, or hip socket. The bottom half of the
acetabulum was formed by the other two pelvic bones, the pubis, which
pointed down and forward, and the ischium, which pointed down and back.
Behind the ilium you can see five sacral vertebrae, and the sacral ribs
that connect the ilium to the vertebral column. The neural spines of the
middle three vertebrae are fused together. The first and fifth have free
neural spines, but all five are fused together at the centra.

The number of sacral vertebrae increased several times in the evolution
of sauropodomorphs (sauropods and "prosauropods"). Almost all
"prosauropods" have three sacrals, basal sauropods have four, most
neosauropods have five, most titanosaurs and some elderly individuals of
*Camarasaurus* have six, and *Neuquensaurus* is reported to have seven.
It is a little weird that sacral count increases so regularly and
straightforwardly up the tree. The sacrum is the only bony connection
between limbs and the vertebral column (recall that the shoulder girdle
"floats" in a sling of muscles and ligaments), so it's pretty important
mechanically. You might expect that bigger sauropods would have more
sacral vertebrae and smaller sauropods would have fewer, but that's not
the case. Monsters like *Apatosaurus* and *Brachiosaurus* only have
five, and little ole titanosaurs like *Malawisaurus* and *Saltasaurus*
have six ("little" in this case means up to the size of an elephant--big
for an animal, kinda pathetic for a sauropod). Now, granted, there were
much bigger titanosaurs, like *Argentinosaurus*, *Puertasaurus*, and
*Paralititan*, but the sixth sacral shows up early in titanosaurian
history, in the little guys. So there does not seem to be much of a
connection between sacral count and body size. Which raises the
question: what was driving the increase?


I see now that Mike has beaten me to the punch in providing your at-least-weekly dose of sauroponderous vertebrawesome. And a nice job it is. Still, I feel funny about you not getting a

 new

picture (ahem), so I’m posting my late entry anyway. For some reason, despite–or perhaps because of–my ardent devotion to cervicals, I have taken it on myself to push the anatomical boundaries of SV-POW! again.

The sacral and the profane

[![three-giant-dorks-500px.jpg](https://svpow.files.wordpress.com/2007/10/three-giant-dorks-500px.jpg)](http://svpow.files.wordpress.com/2007/10/three-giant-dorks-500px.jpg "three-giant-dorks.jpg")

Figure 1. *Sauroposeidon proteles*, eighth cervical vertebra (top) and
posterior portion of seventh cervical (bottom). Mike Taylor (left) and
Matt Wedel (right) for scale.


Figure 1.

 Sauroposeidon proteles

, eighth cervical vertebra (top) and posterior portion of seventh cervical (bottom). Mike Taylor (left) and Matt Wedel (right) for scale.

Postagens de Rogue Scholar

Apatosaurus, Russian doll edition

Well, not Xenoposeidon, anyway

The sacral and the profane

Three big dorks