Ahead by a tail
February 2, 2009
You’d think that in 100+ posts we’d be starting to exhaust the territory, but there are vast swaths of sauropod vertebral morphology that we haven’t even touched. Like fused vertebrae. Sauropods fused their vertebrae all the time. Some of those fusions are age-related, many are pathological, and some are…hard to classify.
Exhibit A: fused distal caudals in a specimen of Mamenchisaurus hochuanensis described by Ye et al. (2001). In contrast to the terminal caudals comprising the tail club of Shunosaurus, the centra here are not ballooned out. The one in the middle is clearly waisted, as in “narrower in the middle than at the ends” (not the same clearly wasted as your college roommate). The neural, uh, elements are expanded and fused into something that the authors describe as resembling the comb of a rooster. I can’t improve on that metaphor so I won’t try. Here’s the full weirdness, straight from the authors (p. 39):
The posterior caudals are fused with each other, their centra are not expanded, the neural arch is remarkably expanded and the size of the neural canal and the height of the neural spines increased. In lateral view, the posterior caudals are cockscomb-shaped.
That’s all pretty weird. The authors go on to speculate that the expanded neural canal indicates that the tail club fin thingy served as some kind of special sense organ. I don’t think that idea is too bold. I don’t think it’s bold enough.
Hypothesis: Mamenchisaurus had a pseudohead on the end of its tail, with fused verts to form a pseudoskull and a big nerve bundle to give the pseudomouth (probably articulated chevrons) and pseudoeyes (possibly heat-sensitive like rattlesnake pits) some lifelike movements and relay thermal images up to the brain. It probably started out as a predator-confusion thing. The carnosaurs would obviously like to attack the inattentive end of the sauropod but these push-me-pull-yous were on the lookout fore and aft! And if the carnosaurs did attack, there was a 50/50 chance they’d bite off the wrong head. Then the pseudohead, which evolved to simulate attention, got so good at it that it was exapted into an actual lookout post at the individual’s farthest extremity. What an advantage those animals had!
But, alas, the caudal pseudohead turned out to be a serpent in paradise. It started getting ideas. Demanding equal time to “teach the controversy” to the forebrains of juvenile conspecifics. Mamenchisaurus became a house divided. First there were pranks, as the real brain started hearing “voices” in its tail. Then outright arguments as the brain and pseudobrain struggled for control of the animal. Finally the pseudohead took over, started marching the animal around backwards. Poor Mamenchisaurus was tripping over logs, which don’t show up so well on infrared, and slipping on its own feces. Lost in delusions of grandeur, the pseudohead chomped on ferns for hours, unwilling to admit that it couldn’t swallow and too proud to realize that it was starving the animal to death (certain political and economic parallels suggest themselves here).
We all know what happened: Mamenchisaurus died out, the pathetic victim of a caudal takeover, and was replaced by other sauropods that, if perhaps more conservative, could at least keep their tails in line. And the world passed once again into the metaphorical hands of the heads. But even now, 140 million years later, tails the world over recall their ancient glory and plot revenge–perhaps even the tail you’re sitting on right now. If you are quiet, and cunning, you may hear your tail’s defiant murmur: the south will rise again!
Reference
- Ye, Y., Ouyang, H., and Fu, Q.-M. 2001. New material of Mamenchisaurus hochuanensis from Zigong, Sichuan. Vertebrata PalAsiatica 39(4):266-271.
Sauropod Vertebra Picture of the Week 
February 2, 2009 at 10:03 am
… there are vast swaths of sauropod vertebral morphology that we haven’t even touched.
And this was one of them. Funny, that.
February 2, 2009 at 3:05 pm
This might be the best bit of evolutionary humor since The Snouters.
Dude, this is quality funny here. I’m impressed.
February 2, 2009 at 9:34 pm
Brilliant! Just… brilliant!
February 3, 2009 at 10:44 am
Pushmepullyousaurus? “If we could talk to the dinosaurs, just imagine it …”
February 3, 2009 at 10:46 pm
Hi Matt (or Mike or Darren or whoever is willing to answer my question),
I was wondering if the tail club on Mamenchisaurus is really a club that was present on all members of this species, or if it was pathological in nature? (as I do not have access to the paper in question….)
Best regards…
February 3, 2009 at 11:21 pm
Hi Zach,
On the tail “club” of Mamenchisaurus: so far our n is 1, so it’s hard to assess. However, it doesn’t look like any pathology I’ve ever seen (beware that massive qualifier), and it is awfully…suspicious that genuine tail clubs are present in Shunosaurus and, reportedly, Omeisaurus, which are close to Mamenchisaurus in space and time, at least. There is little doubt that Mamenchisaurus and Omeisaurus clade together, and given that they are both outside of Neosauropoda it is at least conceivable that Shunosaurus might belong in there, too. That said, most phylogenies get Shunosaurus quite a bit farther down the tree. Interesting to speculate: in our readers’ opinions, would definite tail clubs in Omeisaurus and Mamenchisaurus drag Shunosaurus up into Mamenchisauridae, or not? Keeping in mind that the pseudoskull in Mamenchisaurus doesn’t look much like the tail club in Shunosaurus. Also, I can’t remember off hand ever seeing a good image of the tail club in Omeisaurus; perhaps some alert commenter can point me in the right direction.
February 3, 2009 at 11:58 pm
You boys are so violent. Those weren’t clubs, those were musical instruments that made notes when the wind whistled through and past while Mamenchisaurus, Omeisaurus, and Shunosaurus swung them from side to side.
February 4, 2009 at 7:12 am
“Interesting to speculate: in our readers’ opinions, would definite tail clubs in Omeisaurus and Mamenchisaurus drag Shunosaurus up into Mamenchisauridae, or not?”
Nope. If you constrain Shunosaurus to be a mamenchisaurid in Wilson’s (2002) matrix, the trees are 17 steps longer than otherwise. Thus adding one character that is congruent with that phylogeny would still leave it 16 steps longer than the most parsimonious tree. Incidentally, Barapasaurus and Patagosaurus also join this clade, but have unknown tail tips as far as I know.
As for the Omeisaurus tail clubs, aren’t they isolated but referred to Omeisaurus mainly because they don’t match Shunosaurus from the same formation?
February 6, 2009 at 12:11 pm
Ah, so some pseudoheads broke off and learnt to live on their own?
February 9, 2009 at 9:13 am
[…] as Sauropoda incertae sedis, and only provisionally valid. It is entirely coincidental that Matt is also dealing with vertebral fusions at the moment – I hope I’m not treading on his toes by writing all this, apologies if I […]
February 10, 2009 at 6:13 am
Perhaps you should have cited a couple of analogous adaptations, real and hypothetical: Ken Zimmerman and Hal Heatwole (1990) measured light-sensitivity in the skin of olive sea-snakes, and Tony Thulborn (1994) suggested that ankylosaur tail clubs were also useful as dummy heads, held erect while the dino was feeding at ground level to simulate vigilance. Not only brilliantly funny, but actually plausible too (up to a point). And testable, with the right fossils.
Thulborn, R.A. 1994. Mimicry in ankylosaurid dinosaurs. Records of the South Australian Museum 27: 151-158.
Zimmerman, K. and H. Heatwole. 1990. Cutaneous photoreception: a new sensory mechanism for reptiles. Copeia 1990: 860-862.
February 10, 2009 at 7:53 am
Cool, many thanks for the refs!
February 16, 2009 at 2:25 am
Matt, you are mad. I love it!
I suggest that fused tail vertebrae could result from tails being stepped on (likely in herds)… (or maybe bitten).
In those species where tail-clubs were present in all individuals, a traumatic origin need not be ruled out in favour of a genetic developmental origin. No… for these would simply be species in which tail-treading was a traditional ritual, likely as a rite of passage for these sauropods on reaching breeding age.
The tradition likely arose by mimicry – deliberate emulation of a widely-admired elder whose own accidental injury had given him/her a distinctively-recognisable unusual tail morphology.
For a historical instance of such deliberate, admiring, imitative caudal modification I refer you to the Beruna postbellum Reepicheep incident, first documented by Lewis, C.S. sometime in 1949 and published in 1951. (In that case, mass voluntary caudal autotomy; admittedly, only proposed, not actually carried through, but surely averted only by a whisker.)
February 23, 2009 at 1:29 am
Matt, you really caught me by surprise and I couldn’t stop laughing :D
Thanks for the silliness that only true seriousness can beget……
February 23, 2009 at 9:34 am
[…] so how has this eluded me thus far? Slutty agendas aside, my favourite SV-POW! post to date is this one, which features the fused distal caudals from a Mamenchisaurus hochuanensis specimen, Doctor Matt […]
February 24, 2009 at 3:55 am
I adore this post, Matt. I wrote about it here – http://runningponies.com/2009/02/23/wise-up-mamenchisaurus. Hope you like it!
February 24, 2009 at 12:59 pm
Wow. Nice! As a matter of policy, we are totally down with fan blogging. Glad you’re digging the blog. Hang on tight, more coolness is inbound shortly.
March 15, 2010 at 8:02 am
[…] 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 […]
March 12, 2022 at 2:04 am
[…] it will generally find it. A lot of the battle over OA is getting hidebound administrators to stop thinking with their pseudoheads and find non-stupid ways to assess the output of their faculty. It shouldn’t be part of the […]