How big was Brachiosaurus‘s forelimb?

June 1, 2011

In a new comment on an oldish post, Peter Adlam asked:

I recently happened upon a picture of the late Jim Jenson standing beside the huge front leg of “Ultrasauros”, which leads me to ask a few questions. Did he really find a complete forelimb? Was the leg from Brachiosaurus altithorax? If that leg is valid at actual size how tall/long was the whole animal? It looks to be about 40% to 50% taller than the berlin Giraffatitan, I am guessing the leg is a constructed representation of how the leg would look rather than a cast of the actual leg because if the whole front leg was found they would probably be the most talked about sauropod bones in the world and the fact is I’ve heard pretty much nothing about these remains for years.

I answered this in a followup comment, but because the answer involved a few nice images, I thought it ought to be promoted into a post of its own.  So here it is, in expanded form.

I believe I know the picture Peter was talking about: it was either the one on the right, of Jensen working on the limb in the lab, or the one below of the same limb, again with Jensen, this time out in the desert.

As an aside: based on a post by ReBecca Hunt-Foster (scroll down to the 12th picture), it looks like this forelimb may have ended up in the New Mexico Museum of Natural History and Stuff (NMMNHS).

Anyway, the bad news is that, no, this is not a complete forelimb fossil. The worse news is that the limb is not even partly cast from real material: it’s a pure sculpture, based presumably on the forelimb of Giraffatitan brancai, but scaled up according to Jensen’s idea of how big “Ultrasauros” was. The only part of the model that probably was cast from real material is not part of the limb proper, but the scapulocoracoid — which is the only real brachiosaur element that Jensen found and described from the Dry Mesa quarry.  In fact, the scap in these photos (and in ReBecca’s) does look very much like BYU 9462, the element that Jensen meant to designate as the “Ultrasauros” holotype, but didn’t, instead plumping for … ah, you all know the story.

"Ultrasauros" scapulocoracoid BYU 9462 (almost certainly a cast), with Graeme Elliott for scale.

But in fact, the scapulocoracoid in the whole-forelimb pictures above looks much too small in comparison with the other elements; or to put it the right way round, since only the scap is based on an actual fossil, all the other elements are too big — which suggests that Jensen exaggerated the sizes of the sculpted limb bones well beyond what the scapulocoracoid warranted.  (In any case, the idea that this scap represents a much larger brachiosaurid than any previously known specimen was shown by Curtice et al. (1996) to be mistaken — it’s from an animal pretty similar in size to, and probably a little smaller than, the largest known Tendaguru specimens.)

But the good news is, Peter’s sense of awe is not misplaced. Real brachiosaur forelimbs are actually not much less impressive than this. See for example me next to the right forelimb of the Berlin Giraffatitan mount, which is real bone — as shown in our classic post Shedloads Of Awesome:

Or here I am again, this time with the Chicago Brachiosaurus mount. (The Chicago mount is a cast, based on a hybrid of real Brachiosaurus elements, some bits of Giraffatitan, and some sculptures, but the scaling is good.)

My rule of thumb, based on a lot of posing for photos around the Chicago mount, is that if I stand next to the forelimb and reach up, I can just rest my hand on the top of the ulna without stretching.  I’m about six feet tall, if that helps.

Jim Jensen was 4% taller than me — 6’3″.  Bearing that in mind, and looking at the second photograph above (the first one is useless because of the forced perspective), Jensen’s inability to reach close to the top of the ulna suggests that his model is inflated by maybe 30%.  Which means that it represents an animal about 1.3^3 = 2.2 times as voluminous and heavy as it should be.  But let’s not forget that among the Giraffatitan material in Berlin is the isolated fibula XV 2, which at 134 cm in length is 12.6% longer than the 119 cm tibia of S II.  So that is from animal about half way between S II and Jensen’s Imaginary Monster in size.

So.  Real brachiosaurs are awesome enough.

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10 Responses to “How big was Brachiosaurus‘s forelimb?”

  1. Heinrich Mallison Says:

    this IS a cast, at best, and located at the SMNS (Staatliches Museum für Naturkunde Stuttgart)

  2. ReBecca Says:

    I will check my pictures and see if I have a better picture of that cast. I have been down to NMMNHS many times since the old pictures on my website, so I may have a better shot of it….

  3. Graeme Says:

    I’m 6’2″ if anyone wants to standardize me….

  4. Gregory Says:

    After following a few links to other stories via this article, I found out that I never realized how few examples we had of some of these creatures. Is it common to only have 1-3 full skeletons of a dinosaur? I was just watching a NOVA episode on microraptor and they mentioned that just over the past two decades they’ve found 30 skeletons in China. Is that unusually high, or is the average about in-between?

  5. Mike Taylor Says:

    Hi, Gregory. Yes, it’s the exception rather than the rule to have as many as 30 skeletons of a single dinosaur. It’s obviously easier with smaller dinosaurs, where you can find mass graves and hoik out a dozen skeletons in a single block. For sauropods, each specimen is a big deal to collect. I’ve not run the numbers but I would guess that the majority of sauropod genera, maybe as many as 80%, are known only from a single specimen each. See also on the startling rarity of complete sauropod necks.

  6. Hi Mike:

    Another “annoyance” to point out in all this is that the radius and ulna are inverted in the Jensen pix — the ulna is lining up with the thumb! No tetrapod on earth has this configuration, unless something unfortunate has happened. =) The three claws on the manus are also a bit troubling.

    For anyone interested in my own rambling research on sauropod forelimbs and hands:

    The biggest problem we seem to have with restoring dinosaur forelimbs is that we want to make them like mammals — or invert bones. =)

  7. Ronald Says:

    Just a question concerning the apparently exaggerated size of Jim Jensen’s Ultrasauros foreleg:
    Is it possible/likely/known that the largest brachiosaurids did indeed reach this size?

    I am referring here to Sauroposeidon, ‘Brachiosaurus’ nougharedi, Breviparopus, …

    See also the post:

    and Nima’s Brachiosaur Parade:

  8. Mike Taylor Says:

    Ronald, my gut feeling is that, yes, the leg that Jensen sculpted is probably about as big as the biggest brachiosaurs we have any kind of evidence for — Sauroposeidon vertebrae, Breviparopus tracks, etc. (I don’t think the “Brachiosaurusnougaredi sacrum can be trusted, its proportions are all wrong for a brachiosaur.) But there are multiple layers of caveats surrounding such a conclusion,of course.

  9. [...] Hm, is that a Brachiosaurus or a Giraffatitan? It looks a few years old (the shape, not the model), thus I bet it is a typical Giraffatitan-based “Brachiosaurus” (see SVPOW posts here, here). [...]

  10. [...] in which I considered the possible size and identity of the Recapture Creek femur fragment, which “Dinosaur Jim” Jensen (1987: page 604) said was “the largest bone I have ever [...]

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