Mamenchisaurus tail club, again
March 30, 2010
In color, this time, with multiple views, thanks to Xing et al. (2009). They also did a finite element analysis of the tail club and concluded that it was a fairly pathetic weapon. Xing et al. closed by supporting the contention of Ye et al. (2001) that the tail club was a sensory organ. As they stated at the end of the abstract:
The tail club of Mamenchisaurus hochuanensis probably also had limitations as a defense weapon and was more possibly a sensory organ to improve nerve conduction velocity to enhance the capacity for sensory perception of its surroundings.
One thing Xing et al. (2009) cite in support of this is the expanded neural canal inside the club, which they compare to the sacral enlargement in stegosaurs and to the glycogen bodies of birds. They rule out a glycogen body on the grounds that the sacral enlargement in stegosaurs is much bigger than the brain volume, whereas the neural canal enlargement in the M. hochuanensis tail club is much smaller (if you don’t follow that logic, don’t worry, neither do I).
I’m not sure what to make of this thing. On one hand, it would be nice to have more than one club available to rule out the possibility that it’s just a weird paleopathology. On the other hand, it looks oddly regular to be pathological, and the definitive clubs in Shunosaurus and Omeisaurus are at least weak support for this being a genuine feature, although the clubs of the former taxa look very different.
Furthermore, I don’t understand how the authors can rule out the presence of a glycogen body based on the size of the neural expansion alone–especially since the functions of glycogen bodies in extant taxa are very poorly understood (as you may remember from this dustup). Nor can I fathom how a titchy little nerve bundle–if such existed–down at the end of the tail could do much to improve nerve conduction velocity up the rest of the tail. Either my understanding of neuroscience is completely shot, or this hypothesis…lacks support. I am open to being enlightened either way.
Finally, I am disappointed that the authors didn’t pursue the cutting-edge pseudohead hypothesis that has figured prominently here and elsewhere in the blogosphere. There’s a Nobel lurking in there, I just know it.
References
- Xing, L, Ye, Y., Shu, C., Peng, G., and You, H. 2009. Structure, orientation, and finite element analysis of the tail club of Mamenchisaurus hochuanensis. Acta Geologica Sinica 83(6):1031-1040.
- Ye, Y., Ouyang, H., and Fu, Q.-M. 2001. New material of Mamenchisaurus hochuanensis from Zigong, Sichuan. Vertebrata PalAsiatica 39(4):266-271.
Tornieria caudals
March 23, 2010
For various arcane reasons, the SV-POW!sketeers are all neck-deep in work, so the blog may actually become somewhat more of the APOD-style picture-n-paragraph thing we originally envisioned, and less of the TetZoo-style monograph-of-the-week thing it’s often leaned toward, at least for a while.
I like it when people decorate their papers with megapixels of vertebral goodness, so here are some caudal vertebrae of the African diplodocine Tornieria, from Remes (2006:fig. 5). Click through to see the figure at its massive native resolution. And check out that pneumaticity! Really, the only question about this image is whether you can settle for just using it as your desktop background, or if you need to print out a wall-sized poster for your bedroom. So the next time you see Kristian Remes, buy him a beer for doing solid work here, on the Humbolt sauropod remount, and on pretty much everything else (including this).
Reference
Remes, K. 2006. Revision of the Tendaguru sauropod Tornieria africana (Fraas) and its relevance for sauropod paleobiogeography. Journal of Vertebrate Paleontology 26 (3): 651–669.
Um, dude, there’s a thing on your neck
March 15, 2010
On the off chance that the postparapophyses of Shunosaurus weren’t enough to sate your appetite for Sino-pod rib-related weirdness, here are a couple of fused cervicals of Klamelisaurus, from the Middle Jurassic of China (from Zhao 1993:plate 1). These are weird for a couple of reasons. First, although fused caudals are pretty common in sauropods (see here), and fused dorsals turn up a lot (see discussion here), and the fusion of the atlas to the axis is not unheard of (see here and here), fusion of the middle or posterior cervicals is rare. Which makes intuitive sense–presumably fusing up your food-reaching organ is counterproductive. The only other example I know of is the pair of fused posterior cervicals in the AMNH 5761 Camarasaurus supremus (which, oddly enough, I don’t think we’ve covered yet on SV-POW!). If you know of others, please let me know.
Anyway, what’s really weird about the Klamelisaurus verts is not the fusion but the bar of bone connecting the cervical rib of the first vertebra back to one or more of the centra. I think that the weird pseudo-parapophysis-thingy is not the parapophysis of the second vert, which is hanging down just behind, but some kind of extra ossification off the postero-ventro-lateral corner of the first vert’s centrum. Admittedly, that’s a lot of interpretation to hang on one grainy photo of a specimen I’ve never seen. But I’ve seen something similar in some bird cervicals, where there is sometimes a prong or hook of bone from that corner of the centrum sweeping down and out to brace against the longus colli ventralis tendon that comes off the cervical rib. One of the Apatosaurus cervicals on the wall at Dinosaur National Monument has a similar pair of hooks on its posterior centrum. Irritatingly, I don’t have any digitized photos of the Apato vert, and I can’t find any photos at all that show what I’m talking about in birds. Sorry to tantalize, I learned it from Darren. When I get pix, I’ll post ’em.
In the meantime, you can amuse yourself by pondering the strangeness of the fused Klamelisaurus verts, and by watching the Dinosaur National Monument Quarry Visitor Center get demolished here.
Reference
Zhao X. 1993. A new mid-Jurassic sauropod (Klamelisaurus gobiensis gen. et sp. nov.) from Xinjiang, China. Vertebrata PalAsiatica 31(2):132-138.
Shunosaurus lii is a basal eusauropod from the Middle Jurassic of China. Outside of palaeontological circles, it’s not at all well known — which is kind of surprising, as it’s one of the best represented of all sauropods. It’s known from numerous complete skeletons, including skulls, and has been described in detail in Zhang’s (1988) monograph: 89 pages and 15 plates. Here’s a skeleton of one individual, as found in the ground:
Shunosaurus lii, referred adult individual ZDM T5402, skeleton as found. From Zhang (1988:fig. 2)
Apart from being so well represented, Shunosaurus is known mostly for its tail club, which at the time of its discovery was unique among sauropods. Despite recent discoveries of Mamenchisaurus hochuanensis individuals with preserved tail-clubs, and of Spinophorosaurus, the Shunosaurus tail-club is the best developed and best preserved.
But I don’t want to show you that. I want to show you something I’ve been wanting to see for many years, and today finally saw for the first time: a feature of the dorsal vertebrae totally unique to Shunosaurus, known as postparapophyses.
Shunosaurus lii, referred juvenile individual ZDM T5401, dorsal vertebrae 3, 7 and 11 in left lateral view. Note postparapophyses on dorsals 7 and 11. From Zhang (1988:figs. 31-32)
Sadly, these are the only figures in the paper that show the postparapophyses (and as far as I know the only published figures anywhere). So we have them in lateral view only, and lack what would be an informative posterior view. Plate 10, part 1, supposedly shows one of the posterior dorsals in posterior view, but in my PDF at least the reproduction is so poor as to be wholly uninformative.
What makes things even worse is that the extended English-language abstract on pages 86-91 of Zhang (1988) does not mention this feature at all — in fact it occurs only in the list of anatomical abbreviations on page 6. So, to the best of my knowledge, here is the entirety of what has been published in the English language about this feature based on observation of the material:
ppp, postparapophysis
Wilson and Sereno (1998:14-15) expanded a little on this, but it’s not clear that what they wrote was based on anything more than the figure above. Here it is anyway, for completeness:
Comments–Zhang’s (1988:78-79) diagnosis listed numerous features, only a few of which appear to be autapomorphies of Shunosaurus lii. One of the more striking autapomorphies is an unusual articulation between the ribs and the posterior dorsal vertebrae. The parapophyseal articulation is split between adjacent vertebrae, with a portion of the articulation in its usual position by the prezygapophyses and an anterior extension located near the postzygapophysis on the preceding vertebra (Zhang, 1988:figs. 31, 32; “postparapophysis”).
That’s your lot.
So if we’re to make anything at all of the PPPs, it will have to be on the basis of the figure reproduced above. And I don’t really know how much we can say. The PPPs look sort of like postzygapophyses, havng a distinct ventrally oriented facet. This makes me wonder whether they are in fact lateral extensions of the postzygapohyseal facets, perhaps connected by a lamina that would be visible in posterior view.
The bottom line is, I don’t know, and I would greatly appreciate comments (or better still, photos!) from anyone who has seen the material first-hand.
I leave you with Zheng’s (1988:fig. 57) skeletal reconstruction of this distinctively dumpy-looking sauropod. Note by the way that the plantigrade manus reconstruction is almost certainly wrong: the metacarpals should be held in a more or less vertical arcade as in other sauropods.
Shunosaurus lii, referred adult individual ZDM T5402, skeletal reconstruction in left lateral view. From Zheng (1988:fig. 7). Man, that thing is ugly.
References
- Wilson, Jeffrey A. and Paul C. Sereno. 1998. Early evolution and Higher-level phylogeny of sauropod dinosaurs. Society of Vertebrate Paleontology, Memoir 5: 1-68.
- Zhang Yihong. 1988. The Middle Jurassic dinosaur fauna from Dashanpu, Zigong, Sichuam, vol. 1: sauropod dinosaur (I): Shunosaurus. Sichuan Publishing House of Science and Technology, Chengdu, China.
Update (9 March 2010)
Rob Taylor found this nice photograph of what is apparently a skeletal mount of Shunosaurus: the original is here. Any information about this mount will be gratefully received: please comment below if you know anything.
Opening today: Snakes on a ‘Pod
March 2, 2010
This is so unspeakably cool. Today in PLoS Biology (yay, free reprints for everybody!), Wilson et al. (2010) describe a new snake, Sanajeh indicus, based on multiple specimens from multiple sauropod nests where they were apparently eating baby sauropods! This is sweet for loads of reasons. There aren’t that many well-documented cases of predation in the fossil record in the first place. Predation on dinosaurs by non-dinosaurs is especially cool–you may remember the announcement of Repenomamus by Hu et al. (2005), a giant (for its time and clade) badger-sized mammal from China that was found with a gut full of baby Psittacosaurus. And as Wilson et al. note, this is only the second secure association of sauropod bones with eggs; the other is the Auca Mahuevo site in Patagonia that produced the first definitive sauropod eggs and embryos. If we learn half as much about sauropod biology from these Indian nests as we have from the Patagonian ones, it’s going to be an exciting decade.
Fossils of the new snake (left), sauropod egg (upper right), and sauropod hatchling (lower right), Wilson et al. 2010, fig 1.
The best bit, though, is the window this gives us into Mesozoic ecosystems. Dinosaurs made lots of offspring, and sauropods seem to have been particularly R-selected. With loads of multiton animals producing zillions of defenseless babies for most of the Mesozoic, it would be weird if other critters, dinosaurian and otherwise, didn’t take advantage of that seasonally abundant food source. It’s great to get some direct evidence.
This is like a swamp full of radioactive awesome. Go roll around in it and let it mutate you.
References
- Yaoming Hu, Jin Meng, Yuanqing Wang, Chuankui Li. 2005. Large Mesozoic mammals fed on young dinosaurs. Nature 433: 149–152.
- Wilson JA, Mohabey DM, Peters SE, Head JJ. 2010. Predation upon hatchling dinosaurs by a new snake from the Late Cretaceous of India. PLoS Biol 8(3): e1000322. doi:10.1371/journal.pbio.1000322
Addendum (from Mike)
Let’s not miss the opportunity to reproduce this classic, uh, life restoration, executed pre-emptively by William Stout decades before this fossil was even found! It’s from his 1981 book The Dinosaurs: a fantastic new view of a lost era.
Madtsoia crushes a young Laplatasaurus. By William Stout.
Sauropod Vertebra Picture of the Week 