How weird was the ilium of Brontomerus?

February 26, 2011

Sorry for the very short post. We have some longer stuff planned, but we’ve been too busy to kick it out this week, and I wanted to leave you with something cool to ponder over the weekend. Here’s the ilium of Giraffatitan overlaid on that of Brontomerus, scaled to the same acetabulum diameter (Giraffatitan is HMN J1, left ilium, modified from Janensch 1961: pl. E, fig. 2; Brontomerus is of course OMNH 66430 from Taylor et al. 2011:fig. 2).

And here’s the same thing comparing Rapetosaurus and Brontomerus (Rapetosaurus is holotype FMNH PR 2209, left ilium, modified from Curry Rogers 2009: fig. 39B). This one was tricky to scale because the ilial margin of the acetabulum is so different in the two taxa.

Here is the same trick performed with the ilium of the canonical pretty basal neosauropod Camarasaurus — specifically, Camarasaurus supremus AMNH 5761 Il. 1, left ilium, modified from Osborn and Mook (1921: fig. 87).  In this case, the proportions are so very different that it’s hard to make a meaningful superimposition: we tried to scale to equal acetabulum size, but probably that of the Camarasaurus was proportionally larger than in the other taxa illustrated in this post.  Still, here it is:

Finally, in response to Paul Barrett’s comment on a subsequent article, here is a superimposition of the ilium of Alamosaurus on that of Brontomerus:

(Sorry about the poor quality of this one, but the only figure I could find of a complete Alamosaurus ilium was the line-drawing in Lehman and Coulson (2002:fig. 8) — none of the standard descriptive works seem to illustrate a complete or near-complete ilium.)

We had a figure like these in an early draft of the paper, but we ditched it because we felt that doing a broader comparative figure would be more valuable. But I like the kick in the brainpan that these overlays provide.

References

About these ads

10 Responses to “How weird was the ilium of Brontomerus?”

  1. Heinrich Mallison Says:

    Well, quite a bit more attachment area for the iliofemoralis, that’s the first thing I note. Those guys would be adbuctors, mainly, but the flaring out of the anterior portion makes the anterior ones protractors when the limb is retracted. That ties is very nicely indeed with my theory of sauropod locomotion development: rapid protraction should, if I am right, be selected for.

    Wait a year for the paper ;)

  2. Jamie Stearns Says:

    Thunder Thighs indeed; that muscle attachment surface is ridonkulous!

  3. Andrea Cau Says:

    Since the ilium is from a juvenile, have you taken into account some kind of ontogenetic allometry as an explanation for (at least some of) these proportions?
    It would be interesting a comparison with juvenile sauropods.

  4. Mike Taylor Says:

    Andrea asked, not unreasonably, “Have you taken into account some kind of ontogenetic allometry as an explanation for (at least some of) these proportions?”

    Yes, we have. Stay tuned, we plan a post that discusses this.

  5. Marc Vincent Says:

    It (2001 instead of 2011) is at the end of the first paragraph this time. I’ll get out more tomorrow.

    Also, excellent post (again) and being able to eyeball these things means a lot to us laymen.

  6. Matt Wedel Says:

    We put those incorrect dates in as Easter eggs for our alert readers. Seriously, thanks for the catch, and for the kind words.

  7. Kennerth Carpenter Says:

    There is a not-to-minor of a problem with the images of Brontomerus. Namely, the pieces were photographed flat (presumably with the copy stand in the colections room at OMNH). An undamaged sauropod ilium does not appear two-dimnsional, rather the preacetabular process curves/flares laterally (i.e. towards the viewer in lateral view), thus foreshortening the process considerably. In Alamosaurus (UT 40597-3), this lateral curve is almost 90 degrees, resulting in significant foreshortening of the process in lateral view.

    In my re-look at the ilium of Brontomerus last week, I took the foreshortenig into account (raise the front of the preacetabular process off the table). It does not appear as long as originally illustrated, but still does appear proportionally deeper relative to acetabular length compared with most sauropods. However, ilium height does seem to decrease ontogenetically in Camarasaurus (CM 11338 > USNM 117863, both from Dino. Nat. Mon. – Carpenter in prep), so that possibility cannot be ruled out for Brontomerus.

    In the end, I have to agree with Kirkland that the quarry should have been reopened and more material than the handfull of bones been used in the original description. The presence of the adult (presumably) scapula suggests an adult ilium COULD be present. The ilium of Brotomerus might not be so werid afterall.

  8. Mike Taylor Says:

    Hi, Ken, many thanks for your comments. (One of the nice things about SV-POW! is that it provides a convenient central repository for public comments on our papers).

    Regarding the shape of the Brontomerus ilium, I’ll quote what we said in the paper:

    As with many sauropods, the preacetabular lobe of the ilium flares laterally. However, in most sauropods this flaring is progressive, so that in dorsal or ventral view the most posterior part of the preacetabular lobe is nearly parallel with a line drawn between the pubic and ischiadic peduncles, and smooth lateral curvature inclines the more anterior parts increasingly laterally, so that the more anterior part is almost at right angles to this line and the ilium appears smoothly curved in dorsal or ventral view–for example, Apatosaurus Marsh, 1877 (Upchurch et al. 2004b: pl. 4: D, E), Haplocanthosaurus Hatcher, 1903b (Hatcher 1903a: pl. 5: 1) and Saltasaurus Bonaparte and Powell, 1980 (Powell 1992: fig. 17). In Brontomerus, by contrast, the blade of the ilium appears to be “hinged”–deflected laterally at a point directly anterior to the public peduncle–so that the preacetabular lobe is straight in dorsal or ventral view, and directed anterolaterally by an angle of about 30° to the sagittal.
    […]
    The Brontomerus ilium is laterally compressed, and unlike most sauropod ilia the dorsal margin is not deflected laterally relative to the more ventral part, so that in ventral view it appears very thin (Fig. 2B).

    (As a matter of fact, we’ve not talked about that strange ventral view anywhere near as much as we ought to have done — it’s one of the weirdest things about the ilium.)

    You are of course right that sauropod ilia are not flat plates but complex three-dimensional objects, and every possible view of them is ultimately misleading. (As an example, there are big differences in ilia all referred to Camarasaurus that are not at all apparent in lateral view but impossible to miss “in the flesh” — one of the reasons that I think the genus Camarasaurus is overlumped. But I digress.)

    Still, within the limits of 2D photography, the best we can do is to be consistent, and that is to present a uniform perspective. The standard way to depict sauropod ilia seems to be in lateral aspect, i.e. with the camera on a line perpendicular to the plane of the acetabulum, and this is what we did for Fig. 2a of the paper. You can see this from the photograph that that figure was prepared from: note the sandbags propping up the preacetabular blade to lift it off the table. The result is that the Brontomerus ilium appears foreshortened in our figure — as do all the other ilia shown in the comparative Fig. 3, of course. Anyway, as best we could, we compared like with like. (For a different perspective on the Brontomerus ilium, taken more nearly perpendicular to the preacetabular blade than the acetabulum, see this photo, in which the preacetabular blade appears even more proportionally enlarged!

    BTW., there are more photos of the Brontomerus material at http://www.miketaylor.org.uk/dino/brontomerus/extras.html#3

    On the matter of ontogenetic change in the proportions of sauropod ilia: as Matt will soon show in the looong-awaited post on this very subject, our investigations into this subject have shown that they seem to grow isometrically through ontogeny, although the sample size is small enough that it can’t be demonstrated conclusively as it has been for sauropod long bones. I’d be interested to see your camarasaur ilia, but it certainly looks to me as though the ilium illustrated for the juvenile CM 11338 by Gilnmore (1925:pl. XVII) is identical in proportional height to that of the adult AMNH 5761 II as shown by Osborn and Mook (1921:fig. 87). But do we actually know what the ilium of CM 11338 looked like? The caption of Gilmore’s plate XV says that “the left ilium of another individual has been introduced” but includes no details, and what he has to say about the right ilium in the text is not very enlightening (p380):

    The pelvic arch is represented by the articulated ilium, pubis, and ischium of the right side, and the pubis of the left side. The left ilium and ischium are missing. In the present position of the skeleton the right ilium is almost entirely hidden from view by the overlying sacrum, except a portion of its anterior extremity and the acetabular border. The parts exposed are in conformity with those of the described ilia of this genus.

    Has the right ilium been prepped out since Gilmore wrote this?

    Finally, on Jim’s feeling that “the quarry should have been reopened and more material than the handful of bones been used in the original description” — I think everyone agrees that this would have been great. But the facts of the matter are that no-one was showing the slightest interest in re-opening the quarry at the time that we started this project — in fact, it was one of the express goals of this descriptive work that it would provoke more work on the quarry, and indeed Matt and I were delighted when Rich told us, a few days after publication, that this does seem to be in the works now.

    Like you, I greatly hope that the work uncovers an ilium of the adult individual that provided that scapula; but unlike you, I am confident that (so long as the scapula really is from the same taxon as the holotype ilium, of course) the adult ilium will indeed exhibit all the same unusual properties as the holotype.

    Anyway, many thanks once more for chipping in. This kind of feedback is really helpful: apart from anything else, it makes us realise how much we should have said in the paper but didn’t think to!

  9. Mike Taylor Says:

    (Is there a way that I can get a DOI assigned for that last comment? Just kidding … I think.)


  10. […] while in other species it’s 52 percent” could do with some substantiation — I think we’ve shown pretty convincingly how different the ilium is from anything else out […]


Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

Follow

Get every new post delivered to your Inbox.

Join 414 other followers

%d bloggers like this: