Apatosaurus, Russian doll edition
December 3, 2007
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, but Apatosaurus is frankly pretty freaky in the cervical rib department.
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…