Camarasaurus sacra of the AMNH
July 18, 2012
Thanks to the wonder of Osborn and Mook (1921), we have already seen multiview illustrations of the pubis and ischium of Camarasaurus. Now we bring you their Camarasaurus sacrum.
This is the sacrum of Camarasaurus supremus AMNH 5761. Top row: dorsal view, with anterior to left. Middle row, from left to right: anterior, left lateral and posterior views. Bottom row: ventral view, with anterior to left. Modified from Ostrom and Mook (1921:figs. 43-44).
It’s instructive to compare with the “Apatosaurus” minimus sacrum. Direct comparison is somewhat hindered for two reasons: first, the ilia are fused to that sacrum but not to this; and second, different views are available, so I put the composites together differently. We can’t do anything about the ilia. But to facilitate comparison, here is a reworked version of the “Apatosaurus” minimus illustration with the right-lateral view discarded, a ventral-view silhouette added, and the composition mirroring that of Osborn and Mook’s Camarasaurus:
One thing is for sure: whatever else “Apatosaurus” minimus might be, it ain’t Camarasaurus.
Sauropod Vertebra Picture of the Week 
July 19, 2012 at 12:58 pm
How unlikely is it that A. minimus is A. ajax? Looking at Upchurch et al., 2004, its transverse processes / sacral ribs and neural spines look very similar, the centra are amphiplatyan, the flared ilia are not that much more flared than those of NSMT-PV 20375, and also the anterior four neural spines of this specimen could be interpreted as being about to fuse, a process completed in A. minimus. Maybe the sixth vertebra incorporated in to the sacrum of A. minimus was a dorsal, which then forced the ilia to flare more widely than observed in NSMT-PV 20375? Ten dorsals from that specimen were found and it only has five sacrals… and it’s sacrum is shorter than in A. minimus! Maybe it is Apatosaurus after all… is the quarry data for it extant?
July 19, 2012 at 9:16 pm
Hi, Steve P. It’s not Apatosaurus — on that, everyone from McIntosh (1990) to Upchurch et al. (2004) is agreed. See the first illustration in Neural spine bifurcation in sauropods, Part 5: is Haplocanthosaurus a juvenile of a known diplodocid?, which is Hatcher (1903:plate IV). It shows articulated pelvis/sacrum complexes, in lateral view, of Apatosaurus, Diplodocus and Haplocanthosaurus. The sacral spines, ilium and ischium are all visibly different from those of “Apatosaurus” minimus.
That said, I agree that the Apatosaurus sacrum-ilium in Upchurch et al (2005:fig. 9) is superficially much more similar to that of our baby. But the lateral-only view can be very deceptive, and their plate 4 shows a lot of differences. Also, the ischium in their fig. 11 more obviously differs from ours.
July 19, 2012 at 11:15 pm
[…] and re-composed in the same format as the Camarasaurus and “Apatosaurus” minimus from last time, for easy […]
July 20, 2012 at 2:14 am
I’m seeing a Camarasaurus supremus sacrum missing vertebrae. That, or there is an age-based discrimination here in which extra vertebrae are eventually incorporated into the sacral series, especially notable by the lack of fusion of the sacral spines into series, the lateral versus cranially oriented first and last sacral transverse processes in minimus, which is distinct from the radial array of the others (a quick look at titanosaurid sacral incorporation seems to suggest a similar pattern, say when posterior dorsals and the first “caudal” is added to the sacral series). Sacral spine shape seems particularly off, though: distally expanded, club-shaped in the one, very narrow in the other.
Shaping up to be a pretty interesting sauropod.
July 20, 2012 at 8:16 am
Wait, are you saying that’s what you think “Apatosaurus” minimus is? That would make no sense: our baby has six coalesced sacrals, whereas Osborn and Mook’s Camarasaurus sacrum has only four. If anything, you’d expect theirs to pick up two more sacrals (a dorso-sacral and a caudo-sacral) through ontogeny, to bring it up to the full complement of six. Except we know that Camarasaurus doesn’t do that, because the sacrum of Jensen’s geriatric Camarasaurus lewisi still only has five sacrals despite being about the most elderly known sauropod individual.
Also, the Camarasaurus sacrum is notably tall, whereas ours is not. And, as you say, the neural spines are completely different.
July 20, 2012 at 9:10 am
No, no: I am saying that it looks like supremus there is missing sacrals. I then referred to minimus. It was not in my argument to conflate the two taxonomically, as I hoped my last sentence would imply. The idea here is that some factors of the minimus sacrum’s peculiarity are, sadly, those of a particularly aged individual.
I am curious, though: What aging methods have been done for the Morrison sauropods?
July 20, 2012 at 9:35 am
Oh, right. That makes more sense. Yes, we know by comparing with the otherwise fairly similar lewisi sacrum that there is another sacral centrum still to coalesce.
It does look that way; yet there are places in that sacrum where it’s not fully fused, e.g. S1 sacral ribs not fully fused to centrum. Ageing sauropods is complicated. And so:
Ah, you’ll be wanting to read the skeletochronology section of Matt’s and my in-review manuscript :-) I can give you a sneak preview of the conclusion (thought it will seem hauntingly familiar to anyone who read that last paragraph of this message): it’s complicated.
August 15, 2012 at 1:18 am
[…] shown a lot of sauropod sacra around here lately (for example here, here, and here), so here’s a little look back down the […]
August 11, 2015 at 9:34 am
[…] other sacra for comparative purposes. One of them you’ve already seen — that of the Camarasaurus supremus holotype AMNH 5761. Here is […]