Shedloads of Awesome, part 3: Dicraeosaurus
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 hansemanni mounted skeleton, Humboldt Museum, Berlin. Anterolateral view. Matt Wedel for scale.
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:
Dicraeosaurus neck. Left lateral view.
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:
Ligament attachment knobs in intermetapophyseal trough of Dicraeosaurus neck. Posterodorsal view.
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:
Me apologising to Daniela for breaking a Dicraeosaurus cervical rib
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.
A farewell to Dicraeosaurus. Right posterolateral view. Also in view: the stinkin' stegosaur Kentrosaurus (left), Diplodocus (nearly obscured by Dicraeosaurus) and Brachiosaurus brancai (right and, er, top).
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.
RCI building the Humboldt Dicraeosaurus mount.
References
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.
Sauropod Vertebra Picture of the Week 
December 21, 2008 at 10:45 pm
How long is the femur (approximately) of the mounted Dicraeosaurus?
December 21, 2008 at 11:40 pm
My German’s not good enough to be sure (at least without putting some actual work in), but it seems likely that the femur in the mounted skeleton is m 5, which Janensch (1961:209) gave as 122 cm long. (That is the only D. hansemanni femur for which he gives measurements.)
December 22, 2008 at 1:09 pm
“Dicraeosaurus is really small — like, embarrassingly small.”
It’s not about the size of your sauropod, but what you do with it.
Incidentally, why are ligament attachment knobs rare in other diplodocids?
December 22, 2008 at 9:08 pm
One thing those pictures do show is how big, compared to a human, even a very small sauropod is.
December 23, 2008 at 5:54 am
One thing those pictures do show is how big, compared to a human, even a very small sauropod is.
This was brought home to us in a very direct fashion when we started measuring the ribcages of the mounted specimens. For Brachiosaurus, Mike had to ascend to fall-and-kill-yourself heights on a ladder to reach up as high as he could to put the first of our three taped-together meter tapes at the widest point of the ribcage. I crouched on the ground and put a binder clip on the lowest of the meter tapes just above the ground, to act as a plumb bob and hold the train perfectly vertical. Then I placed a quarter on the ground right beneath the binder clip. Then Mike descended, we moved the styrofoam pads that kept the ladder from either tearing up or getting torn up by the ridiculously sharp textured concrete of the pedestal, and he went up the ladder on the other side of the ribcage and we repeated the whole process. Finally we measured the distance between the two quarters. We only did this once, at the widest pair of ribs. For the curious, the width of the ribcage at D5 is 212 cm, or 6 feet, 11.5 inches. (Remember that this is a measurement of a mount, with all the caveats that entails!)
Next we did Diplodocus. This time Mike set up the ladder three times, once in the front third of the ribcage, once in the middle, and once at the back end, and he measured the width of every pair of ribs by the simple expedient of holding out his arms. The ribcage is widest at D6, where it is 140 cm, or 4 feet, 7 inches.
Finally, for Dicraeosaurus, we didn’t use a ladder at all. Mike crouched down to duck under the ribs, and once he was inside he kept his elbows in to keep from knocking against the ribs. The ribcage is widest from D4 to D6; all three pairs had a maximum span of 102 cm, or 3 feet, 4 inches.
That’s less than half the width of ribcage of Brachiosaurus and, all else being equal, one eighth of the volume (all else is not equal, though; that Dicraeosaurus is more slab-sided than either of the other mounts). And yet the ribcage of that mounted Dicraeosaurus is more voluminous than those of all terrestrial mammals other than proboscideans and indricotheres. It pays not to get too blase about this stuff.
December 23, 2008 at 6:56 pm
Any theories as to why dicraeosaurids developed such strange necks?
December 23, 2008 at 9:40 pm
Zach,
I’ve not given it much thought — certainly not as much as I ought. So that can be my New Year Resolution for 2009: to think more about dicraeosaur necks. (I’m sure Matt will join me.)
December 24, 2008 at 2:04 am
It looks like the neural spines a little in front of the shoulders are weirdly splayed out, especially in the first picture. Is that real, or an artifact of mounting or photography? If it’s real, does it mean something?
December 24, 2008 at 9:54 am
William, the “splaying” of the cervical neural spines is real — that is, the more anterior spines project posterodorsally and the more posterior spines anterodorsally. It’s possible, though, that one or two of the individual spines are a little distorted, making the transition appear more abrupt than it would have been in life. As for what it means — I’ve already promised to think more about dicraeosaur necks in 2009, so ask me in a year’s time :-)
December 31, 2008 at 9:07 pm
Mike,
Brave of you to Admit to Breaking a Fossil!
(that’s what I like on SV-POW, the straight-upfulness of everyone here).
Seriously though, that must have been one heart-stopping moment… I feel for you…
…So let the joshing begin!
Daniela looks a bit shaken (she’s gone all blurry).
…and I bet they said something like:
“Hmm, it’s a bit more than a crack, innit, mate? It’s completely broke!”
or
“‘Conserve’ it? Conserve it? It’s already been bloomin’ Marmalised!
…I ‘spose we could put the bits in a jar labelled Golden Shred… ‘Cos now you find yourself in a bit of a jam, sunshine… as these ‘ere fossils are Worth Their Weight in know-what-i-mean?”
Seriously though, Mike,
Never mind.
It was well-dead already.
And after what it’s already been through, I don’t suppose it suffered much, extra.
And it twer an axey dent.
It’s not as if you went in there bent on mad manic mayhem saying “Die, Dicraeosaurus!” or “Break, Brachiosaurus!”
Anyway, nothing lasts for ever, does it?
Amazing it had lasted as long as it did, come to think of it.
There’s prob’ly plenty more like it stashed in the basement.
etc
:-)
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