How big was Hudiesaurus?

January 17, 2008

In the last post, an astute commenter asked about Hudiesaurus: “A first dorsal 550 mm–isn’t that in Argentinosaurus territory?”

Well, let’s find out.

Hudiesaurus sinojapanorum was described by Dong (1997) based on a partial skeleton from the Kalazha Formation in China. The holotype, IVPP V 11120, is an anterior dorsal vertebra. Referred elements include a nearly complete forelimb, supposedly from a smaller individual of the same taxon.

I don’t actually have a copy of Dong (1997), but I do have Glut (2000), which contains a pretty good summary and a couple of pictures. Here’s the holotype dorsal in posterior view, after Glut (2000), after Dong (1997).

hudiesaurus.jpg

According to Glut, the scale bar is 15 cm–I added the “15 cm” in the image above for ease of use. Presumably ‘sp’ is ‘spine’, ‘po’ is ‘postzygapophysis’, ‘dp’ is ‘diapophysis’, and ‘ce’ is ‘centrum’. Glut says:

As measured by Dong (1997), the holotype dorsal centrum of H. sinojapanorum has a length of 42 cm, 1.5 times longer than the comparable element in the 22-meter (about 75-feet) long mounted holotype skeleton of Mamenchisaurus hochuanensis, which was the largest sauropod known from China when it was described. From these dimensions, Dong (1997) estimated the total length of H. sinojapanorum to be about 30 meters (more than 100 feet) in length.

IF the scaled figure (from Glut [from Dong]) is accurate, and if the 42 cm length (reported by Glut [reported by Dong]) is accurate–and the uncertainties involved cannot be ignored, especially after the last post–then the vertebra has the following dimensions:

  • Centrum length: 42 cm
  • Cotyle height: 39 cm
  • Cotyle breadth: 42 cm
  • Total height: 78 cm

None of these are close to 550 mm, so there’s no telling where that measurement came from or what it refers to.

UPDATE: please read comment #4 below, by Mickey Mortimer, which sets the measurement record straight. And invalidates the specific numbers used in the rest of the post, but not the overall point.

Fortunately for us, the dimensions of the vertebrae of Mamenchisaurus hochuanensis are available for free in English, along with the rest of the description (Young and Zhao 1972), courtesy of the wonderful Polyglot Paleontologist site. Here’s the paper. Let’s do some comparin’.

D1 of M. hochuanensis has a centrum length of 25 cm, cotyle height of34 cm, cotyle width of 17 cm, and total height of 64 cm. The fact that the centrum is twice as tall as wide is almost certainly an artifact of the lateral compression that affects the whole vertebral column to some extent. Let’s say for the sake of argument that the cotyle was originally circular and 25 cm in diameter. The holotype of H. sinojapanorum is 68% longer, 60% larger in diameter, and 22% taller. So if the vertebra is actually D1 and if H. sinojapanorum was built like M. hochuanensis (be sure to keep your If Counter updated), it might have been anywhere from 27-37 meters long (89-121 feet).

A couple of points before we go on. First, that’s pretty big, but it’s also a huge range. At the low end, it’s no bigger than Diplodocus; at the high end, it’s one of the longest sauropods on record. So that math suggests that it was a big sauropod but doesn’t help us pin down how big it was. Second, you have to keep in mind that Mamenchisaurus hochuanensis is basically a ridiculous neck attached to an unremarkable body (at least in terms of size). If you ignore the neck, the animal was about the same size as Cetiosaurus or Haplocanthosaurus–about 75% the size of the well-known specimens of Apatosaurus, Diplodocus, and Camarasaurus, and no where near the size of Brachiosaurus (despite having a longer neck). It’s basically a weiner dog, with most of the weiner out in the neck. Which is how Hudiesaurus could be 22% bigger and still be about the same size as Diplodocus. Even if Hudiesaurus was 60% bigger than M. hochuanensis, it would still not be in Argentinosaurus range in anything but length.

mike-and-m-hoch-500.jpg

Mike (white shirt on lift) with M. hochuanensis at the Field Museum. It is worth remembering that he would need the same lift at about the same height to work on the posterior cervicals of Brachiosaurus!

Also, assigning serial positions to isolated vertebrae is tough. What if Dong was off by a single position, and the holotype vert is actually the most posterior cervical? True, it doesn’t have fused cervical ribs, but cervical ribs can fuse pretty late in ontogeny. Furthermore, rib identities can get a little wonky in the cervico-dorsal transition. Sometimes you have a nice, well-behaved, fully-fused rib on the last cervical, and a nice, well-behaved, long mobile rib on the first dorsal, but sometimes there is a godawful Frankenstein rib that doesn’t fit neatly into either category. Anyway, we’re just playing “what if” here. Nobody should take this as gospel.

The last cervical of M. hochuanensis has a centrum length of 32.5 cm, an average cotyle diamter of 29 cm, and a total height of 66 cm. If the holotype of Hudiesaurus actually corresponds to this vert instead of D1, then it is 29% longer, 38% larger in diameter, and 18% taller. In other words, no bigger than Diplodocus. In which case, the articulated forelimb might belong with the dorsal vertebra after all. Although it was found more than a kilometer away from the vertebra, so the case for it’s referral to the same taxon is not strong. At all.

But that’s not all! Not all Chinese sauropods were hellaciously long-necked, a point made by Mickey Mortimer in his DML post on Hudiesaurus. Abrosaurus ha 13 cervicals, rather than 19 like M. hochuanensis, and its cervicals are only about a third longer than its dorsals (upshot: in neck-to-body proportions, it was built like Camarasaurus). If Hudiesaurus was built like a giant Abrosaurus, it might have approximated a large individual of Camarasaurus in both body size and neck length.

A final amusing point. Glut (2000, p. 235) includes a photograph of the articulated forelimb of Hudiesaurus on display at Dinofest ’98 in Philadelphia. Next to the forelimb is a string of 4 articulated dorsal vertebrae. What is this? The original paper only mentions one dorsal vertebra, so where did the other three come from? Sadly, they came out of the same mold as the first–if you look carefully at the photo, you can see that the exhibitors simply made four casts of the same vertebra and strung ’em together to look like something more complete.

It’s not uncommon to clone adjacent vertebrae to fill out mounted skeletons. Heck, the T. rex skeleton in the Valley Life Sciences Building at Berkeley (my old digs) has a block of 5 identical dorsals, and its caudals come in identical pairs all the way down the tail (easy to see even in the small photos here). But that’s a different case. T. rex is known from complete remains, and the cloning was only done to fill out a skeleton that was already mostly there. The exhibition of the cloned Hudiesaurus vertebrae bothers me, because it implies to observers that the animal is better known than it actually is. I wasn’t at Dinofest ’98 so I can’t tell you for certain that there wasn’t a sign right there that said, “Warning: this animal is based on one vertebra that we have cloned to show you what a string of them would look like!” but I seriously doubt that there was any indication at all (that’s no reflection on Dong; he probably had nothing to do with the choices made by the exhibitors).

Here’s the take-home message:

If you see an eyebrow-raising number tossed out regarding a giant dinosaur, don’t surrender your credulity until you or someone you trust have tracked down the sources. And anytime you see mounted material, it’s perfectly fair to ask how much of it is real.

References