Apatosaurus sacra of the National Science Museum, Tokyo
July 19, 2012
In a comment on the previous post, Steve P. asked whether “Apatosaurus” minimus might not be a Apatosaurus specimen after all — particularly, an Apatosaurus ajax individual resembling NSMT-PV 20375, the one in the National Science Museum, Tokyo, that Upchurch et al. (2005) so lavishly monographed.
Initially, I dismissed this idea out of hand, because the “Apatosaurus” minimus sacrum-pelvis complex is so very different to that of the “Brontosaurus” illustrated by Hatcher (1903: fig. 4), as seen in an earlier post. But on going back to the Upchurch et al. monograph I realised that their sacrum-ilium complex is very different from Hatcher’s. Here it is, cleaned up from scans and re-composed in the same format as the Camarasaurus and “Apatosaurus” minimus from last time, for easy comparison.
Sacrum and fused ilia of Apatosaurus ajax NSMT-PV 20375. Top row: dorsal view with anterior to left. Middle row, left to right: anterior, right lateral (reversed), posterior. Bottom row: ventral view with anterior to left. Modified from Upchurch et al. (2005: plate 4 and text-figure 9).
Here’s Hatcher’s “Brontosaurus” illustration (from his plate 4) again:
I’m not sure what to make of this. The Tokyo Apatosaurus seems to be intermediate in some respects between Hatcher’s specimen and “Apatosaurus” minimus.
One important difference is that the neural spines are much taller in Hatcher’s illustration than in the Tokyo Apatosaurus. Could that be ontogenetic? (IIRC the Tokyo individual is subadult). Or are they in fact different species? Or is it just individual variation?
I don’t know. Anyone?
References
- Hatcher, J.B. 1903. Osteology of Haplocanthosaurus with description of a new species, and remarks on the probable habits of the Sauropoda and the age and origin of the Atlantosaurus beds; additional remarks on Diplodocus. Memoirs of the Carnegie Museum 2:1-75.
- Upchurch, Paul, Yukimitsu Tomida, and Paul M. Barrett. 2005. A new specimen of Apatosaurus ajax (Sauropoda: Diplodocidae) from the Morrison Formation (Upper Jurassic) of Wyoming, USA. National Science Museum Monographs No.26. Tokyo.
Upchurch et al. (2005)
Sauropod Vertebra Picture of the Week 
July 20, 2012 at 10:52 am
I’m not sure that neural spines are genuinely taller. If you look at the Hatcher illustration you’ll notice substantial portions of the sacral ribs projecting above the dorsal margin of the ilium. The ilium in this illustration/specimen is likely to be ventrally displaced, allowing the distal ends of the ribs to be seen (they would normally be totally obscured as they’d be contacting the ilium along their total lengths). If you correct for this there’s no real difference in the neural spine height.
July 20, 2012 at 12:32 pm
which is why I hope to get a good 3D model done soon – we just need photos of the other specimens, too.
July 24, 2012 at 9:20 am
Hi, Paul, thanks for that. Sorry for the slow response, we’ve just hosted a houseparty over the long weekend, so I am only now catching up with blogs and email.
An important clarification. Matt and I had trouble, when we were coding the “Apatosaurus” minimus specimen into the Harris 2006 matrix, with character 161 ‘Dorsoventral length of sacral ribs’, scored as ‘low (not projecting beyond dorsal margin of ilium)’ or ‘high (extending to or beyond dorsal margin of ilium)’. Is that character fundamentally flawed? Wilson’s (2002) character 112 is essentially the same, and it seems that Upchurch et al.’s (2004) character 168 is also similar, though I’ve lost my copy of the supplementary information and can’t verify that.
Still, I don’t think it at all explains the variation we’re seeing here:
I tried it. First, I tweaked Hatcher’s illustration by hand, moving the ilium up until it “looked about right”:
In this view, the sacral ribs for the middle three vertebrae are all obscured, but that of S5 is still visible above the ilium. I guess that’s probably correct, as it’s the condition we see in “Apatosaurus” minimus. But measuring from this modified illustration, the height of the tallest spine is still 45% of total ilium length (210/462 pixels) whereas in the Tokyo illustration it’s only 21% (167/771 pixels).
So next, I tried moving Hatcher’s ilium up until the neural spine height above the ilial margin is in the same ratio to ilium length as in the Tokyo specimen — i.e. 21%, which comes to 100 pxiels. Here’s the result:
From a quick glance, it doesn’t look obviously wrong; but when I wing down the opacity of the ilium layer, you can see what’s actually going on:
And that’s obviously not right.
So I think we have to conclude that, even when ilium displacement is taken into account, Hatcher’s “Brontosaurus” sacrum really does have much taller neural spines — more than twice as tall — as the Tokyo specimen.
What about other specimens? Gilmore (1936:fig. 19) gives Apatosaurus louisae CM 3018 an outline with tall spines similar to Hatcher’s, and the rear view of Apatosaurus excelsus CM 563 in fig. 31 looks compatible with those proportions. (Is that specimen the same as UWGM 15556?) And Riggs (1903:plate L) also shows spines that look similarly tall to the naked eye.
So it looks like the Tokyo specimen may be the odd one out.
July 24, 2012 at 11:24 pm
So it looks like the Tokyo specimen may be the odd one out.
A possible apomorphy of A. ajax, relative to other diplodocids?
July 25, 2012 at 12:07 am
What does Marsh’s holotype sacrum of A. ajax look like in dorsal view, one wonders?
July 25, 2012 at 8:54 am
Yes, an important question. And in lateral, anterior and posterior views. Marsh’s own plate, unused in his lifetime but reproduced in Ostrom and McIntosh’s (1966) Marsh’s Dinosaurs, shows it only in ventral view. It’s a great regret of mine that, having twice visited the YPM collections, I’ve never dug out that sacrum.
August 1, 2012 at 4:59 am
Actually, it was figured as part of Plate XVII in Marsh’s 1896 publication Dinosaurs of North America…
August 4, 2012 at 10:20 pm
Steve P says:
Yes; but as I noted, only in ventral view. In fact, the illustration in Marsh 1896 is the same one that appears in Ostrom & McIntosh.
August 15, 2012 at 1:18 am
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