December 25, 2008
But also of Christmas future.
Or, perhaps, the spirit (pneuma) of the season.
Merry Christmas to all! We’ll see you back here in 2009.
December 21, 2008
In view of all the awesome that is the Humboldt Museum’s gigantic brachiosaur mount, it’s too easy to overlook another nearly-complete Tendaguru sauropod, mounted in the very same hall, that is also worthy of respect and, yes, awe. Ladies and gentlemen, I give you: Dicraeosaurus hansemanni!
Dicraeosaurus is a member of Dicraeosauridae, the family that, together with Diplodocidae makes up the whip-tailed clade Flagellicaudata; which in turn, with rebbachisaurids and a few bits and pieces, makes up the great neosauropod clade Diplodocoidea. Dicraeosaurus was first named and briefly described by Janensch (1914:83); typically, Janensch went on to make full and detailed descriptions of its osteology, and also to describe the mounted skeleton (Janensch 1936).
It’s not really apparent from the photo above, but Dicraeosaurus is really small — like, embarrassingly small. Especially when it’s standing next to Brachiosaurus brancai. Gunga et al. (1999) estimated its mass at 12810 kg, but since that was the same paper that estimated B. b. at 74420 kg, based on a similarly grotesque baloon model, we can probably assume an accurate mass would be about one third of that, or 4000-5000 kg. Smaller than a big elephant. (I don’t know of any other published mass estimates for Dicraeosaurus; if I’ve missed any, please shout.) This is typical for dicraeosaurs: the South American Amargasaurus and Brachytrachelopan are even smaller.
Dicraeosaurs are interesting for several reasons. One is the dwarfism, and attendant shortening of the neck (which is taken to the extreme by Brachytrachelopan: reconstructed, that baby looks more like an ornithopod). But maybe most interesting is the peculiar construction of the vertebrae, which have very tall neural spines:
Check this out. The spines of C2-4 slope backwards; that of C5 is upright; from C6 onwards, they slope forwards. Very strange. Oh, and this is real: the verts are in good shape, and definitely not distorted.
One thing that Matt and I have been working on recently is the mechanics of sauropod necks, and particularly the attachment points of the epaxial ligaments and muscles. Among diplodocids and other sauropods with bifid neural spines, you occasionally find a nice clear ligament attachment knob in the floor of the trough between the metapophyses (i.e. the paired neural-spine halves) — but the Humboldt Dicraeosaurus mount is the first specimen I’ve ever seen that has such a knob at the base of every single cervical’s metapophyseal trough. See for yourself:
Unfortunately, as I was taking this last photo, and others like it, I came in a bit too close to the neck and touched one of the left cervical ribs (around C5). Aaaand off it came, to shatter on the hard flooring. It was a horrible moment … especially as I did it right in front of the curator, noted dicraeosaur lover Daniela Schwarz-Wings. With his usual impeccable tact, Matt took the opportunity of snapping a photo of me showing her the pieces, and trying to show how two of them fit together. Two more fragments lie on the floor at her feet:
Happily, the museum’s crack conservation unit swung into action immediately — I mean, literally within an hour — and I believe that rib is now back in place and as good as new. Frightening.
The tall, bifid neural spines of dicraeosaurs continue into the dorsal sequence, resulting in a “tall back” that carries through the sacrum and into the anterior part of the tail — as the posterolateral view below sort of shows. Just as the dicraeosaurid neck-shortening trend is taken to its extreme by Brachytrachelopan, so the elongation of neural spines reaches its apotheosis in Amargasaurus, which we must remember to show you one of these days.
Update (22 December)
David Hone, of Archosaur Musings fame, has sent me this photograph of the Dicraeosaurus mount in the process of being put together by the good people at RCI.
Janensch, Werner. 1914. Ubersicht uber der Wirbeltierfauna der Tendaguru-Schichten nebst einer kurzen Charakterisierung der neu aufgefuhrten Arten von Sauropoden. Archiv fur Biontologie, Berlin, III, 1 (1), pp. 81-110.
Janensch, W. 1936. Ein aufgestelltes Skelett von Dicraeosaurus hansemanni. Palaeontographica (suppl. 7), 299–308.
December 15, 2008
Here’s Mike checking out the cervicals of the mounted Cetiosaurus at the Leicester City Museum back in 2004. I like this photo because I was a ways back from Mike, and Cetiosaurus was not a particularly large or long-necked sauropod (actually in scientific terms I would describe it as being on the puny side of average), but the cervical series still goes right across the frame. Nothing but neck, as the youngsters say.
Mammals are so pathetic. To wit:
Just try to grasp Mike’s deep unhappiness as he ponders the world’s–snort!–tallest mammal, at Oxford that same spring.
December 8, 2008
A 3D reconstruction of the paranasal sinuses in a human (from Koppe et al. 1999). You also have paratympanic sinuses that pneumatize the mastoid process of the temporal bone (feel for an inferiorly-directed, thumb-size protuberance right behind each ear).
An x-ray of a pig skull, from here. Can you see the outline of the brain-shaped endocranial cavity?
How about in this x-ray of a rhino skull? Image courtesy of Kent Sanders.
A sectioned cow skull. The bottom half of the endocranial cavity is exposed in the horizontal cut. The vertical cut shows the tiers of sinuses that make up most of the volume of the skull. I think that the middle tier (the large, butterfly-shaped space) is the front part of the endocranial cavity and housed the most rostral bits of the brain; note that it is completely surrounded by sinuses.
Part of a bighorn sheep skull. The pneumatic horncores of bighorns are a useful antidote to the idea that pneumatic bones must be weak.
A cross-section of an elephant skull, courtesy of Project Gutenberg. The cavity at the back marked ‘b’ is the endocranial cavity that holds the brain. The big tube running through the middle is the nasal airway. Everything else is pneumatic. Note that the brain is entirely surrounded by sinuses.
A blown skull of a proboscidean from the bone cellar at the Humbolt Museum. I snapped this on the last day in collections, on a mad scramble to get whatever non-sauropod pics (gasp!) I might want later. The bumps to the upper right are the occipital condyles; the skull is in left lateral view facing down and to the left.
Paratympanic sinuses (green) surrounding the brain (blue) of an alligator, from David Dufeau’s homepage. Go there for a lot more mind-blowing images of sinuses. The snout of this gator is filled with paranasal sinuses, they’re just not shaded in here.
Sectioned skull of a rhinoceros hornbill, which is pretty much completely filled with paranasal and paratympanic sinuses. Even the lower jaw is pneumatized.
Okay, so now you know that mammals, crocs, and birds are all air-heads. What does any of this have to do with sauropods? Well…
- Archosaurs and mammals evolved cranial pneumaticity independently. Does that mean that cranial pneumaticity is easy to evolve (since it evolved more than once) or hard to evolve (since it only evolved twice)? This is relevant to the question of how many times postcranial pneumaticity evolved.
- Archosaurs evolved cranial pneumaticity before they evolved postcranial pneumaticity. Does that mean that postcranial pneumaticity is the application of a pre-existing developmental program (bone pneumatization) to a new anatomical region (the postcranial skeleton)? Or did the developmental control of pneumatization have to evolve de novo in the postcranium?
- The development of cranial pneumatization in mammals and postcranial pneumatization in birds seems to follow similar rules. Does that mean that we can apply lessons learned from, say, the development of human sinuses to understand the development of sauropod vertebrae?
- Sauropods and big-headed mammals like elephants have this in common: at the front end they’ve got a big chunk of pneumatic bone. In sauropods, it’s the neck; in elephants, it’s the head. In both cases the big pneumatic organ makes up close to a tenth of the animal’s volume. I don’t know what else to make of that, but maybe you can get mileage out of it at a cocktail party.
I posted these because I was inspired by Darren’s post on dome-headed elephants, because they’re cool, to maybe demystify sauropod pneumaticity a little, or perhaps to re-mystify skeletal pneumatization in general. You have a pneumatic cavity between your brain and your monitor right now. How much time have you spent thinking about that (when you didn’ t have a sinus headache)?
Next time: more Berlin goodness.
UPDATE: By utter coincidence, Ohio University put out a news story about Larry Witmer’s work on sinuses yesterday. Hat tips to Yasmani Ceballos Izquierdo, who posted the link on the DML, and to Mike for sending it on to me. As long as you’re going over there, remember that Larry is one of the Good Guys and puts his papers up for public consumption; the new dino sinus paper is here. It’s great, but it makes the pictures I used here look pretty pathetic. Go have fun!
December 3, 2008
Brachiosaurus: uglier than you think (we’re sorry, but it’s true).
UPDATE: Fig. 1 from Witmer (2001) showing hypothesized position of the fleshy nostrils in Brachiosaurus.
How awesome was our trip to Germany? I’ll tell you: it was easily the best conference AND the best research trip I’ve ever been on.
We started out with three solid days of sauropod talks at the University of Bonn. I’ve been going to SVP for ten years, and usually I’m lucky if there are three or four sauropod talks at the whole meeting, plus maybe half a dozen posters. There was so much going on in Bonn that after the first day, there were always two sets of talks running concurrently. Talk about your dilemmas! The best part of the workshop was talking to all of the people there who don’t work on sauropods primarily or at all, like nutritionist Peter Van Soest, ecologist Brian McNab, and physiologists Roger Seymour and Steve Perry (Seymour and Perry have both written important papers on sauropods, but those are tiny parts of their much broader research programs). These folks were genuinely interested in the problems of sauropod paleobiology, and they brought tons of experience and data from living animals that really grounded all of our discussions. Most of this stuff is in the literature and its not like paleontologists have completely ignored it, but there is a big difference between knowing that a paper exists somewhere and having the person who wrote it explain exactly what they’ve found and why it matters.
The field trip was great not only for the places we visited, but also to have three days to ride around with a busload of sauropodologists–some newly minted–and talk about all of the stuff that came up during the conference.
And then Berlin was…well, we took lots of pictures, so I’ll let them do the talking.
The overall effect of the trip was to pour a few tankers worth of gasoline on our intellectual fires (well, mine anyway–Mike got petrol). I went with a blank notebook and came home with enough ideas and measurements to keep me going for a long, long time. Mike and I took more than 1500 digital photos between us, and we’ll be mining those for data and for figures for the rest of our careers.
However big you think Brachiosaurus is, it’s bigger in person. I promise. You’ll recognize cervical 8 of the HM SII mounted skeleton from several of our tutorials.
The best thing about the trip was that we learned so much and had such a good time doing it. Often in academia we talk about an institution achieving a critical mass of workers in a particular field. It’s an apt metaphor–when you get a bunch of people together who share a common interest, the effect is more than additive. That’s even true if you just put two people together. I’ve been on loads of museum visits, many solo, and the research trips I’ve taken with Mike have been more than doubly productive. Two sets of eyes will notice a lot more than one, and two brains can attack a problem from many more angles. Now that I’ve gotten the damned dissertation out of the way, it may be a while before I write another single-authored paper. Cuz, why?