February 26, 2009
New hotness out today: Miragaia, a new long-necked stegosaur from the Late Jurassic of Portugal (Mateus et al. 2009). What is “long-necked” for a stegosaur? In this case, well over a meter! That may not sound too impressive for those of you who have gotten complacent about 10-meter-plus sauropod necks, but it’s a big deal. Miragaia is described as a sauropod mimic, and with good reason: its body proportions are not that different than those of a basal sauropod.
The number of ways to increase the proportional length of the neck are limited: you can add cervicals, or recruit dorsals into the neck, or make the individual vertebrae longer, or do some combination of the above. In sauropods, different clades took different routes. Brachiosaurids kept a fairly primitive cervical count of 13 but made the individual vertebrae crazy long. Diplodocids recruited dorsals into the neck, and some (like Barosaurus and Supersaurus) also made the vertebrae crazy long. Mamenchisaurids and Euhelopus added cervicals (independently), up to a total of 17 or more, and some (like Omeisaurus)–are you ready for it?–also made the vertebrae crazy long.
In general, stegosaurs took an evolutionary walk through Door Number 2: turning dorsals into cervicals. Mateus et al. (2009) show this nicely in a table; the number of presacrals (cervicals plus dorsals) in stegosaurs stays about the same, between 25 and 27, but between the basal Huayangosaurus and the derived Stegosaurus 3 or 4 dorsals go forward to play for the other team. Is dorsal recruitment sufficient to explain the long neck of Miragaia? Hard to say, since the dorsal series has not been found. But Miragaia‘s count of 17 cervicals is significantly more than Stegosaurus‘s 13. If Miragaia didn’t add any cervicals but only recruited dorsals, it would have had only 9 of the latter. That’s not impossible–Barosaurus did that very thing–but it’s weird, and extreme. As Mateus et al. (2009:p. 4) state, “Miragaia possessed more cervical vertebrae than any other non-avian archosaur, except the Chinese sauropods Mamenchisaurus, Omeisaurus and Euhelopus, also with 17″. And yet the individual vertebrae are pretty short, no longer than in your not-exactly-average Stegosaurus.
I couldn’t resist pitting Miragaia, the longest-necked stegosaur (so far!) against Brachytrachelopan, the shortest-necked sauropod (so far!). Miragaia is stolen from Mateus et al. (2009:fig. 1a), and Brachytrachelopan from Rauhut et al. (2005:fig. 1a). Both critters come with the 1 meter scale bars from their respective figures. I’m in there for scale, too, at 6’2″ or 1.88 meters. Sauroposeidon looms in the background, just to keep things in perspective. The entire neck of Miragaia might have been about as long as one of the middle cervicals of Sauroposeidon or Supersaurus.
Still, you know.
(for a stinkin’ ornithischian)
A couple more pictures here.
- Mateus, O., Maidment, S.C.R., and Christiansen, N.A. 2009. A new long-necked ‘sauropod mimic’ stegosaur and the evolution of the plated dinosaurs. Proceedings of the Royal Society of London, Series B. (doi:10.1098/rspb.2008.1909)
- Rauhut, O. W. M., Remes, K., Fechner, R., Cladera, G. & Puerta, P. 2005. Discovery of a short-necked sauropod dinosaur from the Late Jurassic period of Patagonia. Nature 435:670–672. (doi:10.1038/nature03623)
February 20, 2009
UPDATE: Oops, I’m a moron. I wrote this post at work (on my lunch hour!) and didn’t realize that I had free access to the Wiley stuff because I was at work. I can’t get them from home either. But as a public service to disappointed readers, I will send PDFs of the three Wiley articles to anyone who e-mails me: email@example.com (spam bots can suck on Google’s filters, which are teh awesome).
Apologies to Jerry for the title (you DMLers know what I’m talking about). In case no one has drawn your attention to it, the rate of arrival of hot new SV-POW!-revelant papers has gone near-exponential lately. Here’s a short hit list, all a few of which are currently free downloads!
First, three hotties from the all-open-access, all-the-time PLoS ONE:
- Claessens, L. P. A. M., O’Connor, P. M. & Unwin, D. M. 2009. Respiratory evolution facilitated the origin of pterosaur flight and aerial gigantism. PLoS ONE 4 (2): e4497. doi:10.1371/journal.pone.0004497. This one is about pterosaurs, but it is also about pneumaticity and air sacs. The case for a bird-like air sac system in the ancestral ornithodiran is getting stronger…
- Martinez, R. N. & Alcober, O. A. 2009. A basal sauropodomorph (Dinosauria: Saurischia) from the Ischigualasto Formation (Triassic, Carnian) and the early evolution of Sauropodomorpha. PLoS ONE 4 (2): e4397. doi:10.1371/journal.pone.0004397. Explore the humble roots of sauroponderous vertebrawesome with Panphagia, a new basalmost sauropodomorph from Argentina.
- Bates, K.T., Manning, P.L., Hodgetts, D., Sellers, W.I. 2009. Estimating mass properties of dinosaurs using laser imaging and 3D computer modelling. PLoS ONE 4(2): e4532. doi:10.1371/journal.pone.0004532. We haven’t talked enough about mass estimates here (yet), and this paper unfortunately only features stinkin’ theropods and a stinkin’ ornithischian, but I’m sure it will be discussed here a lot in the future. A little bird told me…and by “little bird” I mean “huge bird-lunged sauropod”.
As long as you’re over at PLoS ONE, you might as well read up on fighting ceratopsians and pregnant land whales (be careful how you use that last phrase, too–we don’t want to lose any readers to domestic violence).
Next, two important recent papers from the Journal of Experimental Zoology (other than my own). These are free right now but who knows for how long, so download them pronto before they go behind a paywall to anyone who e-mails me for them.
- Claessens, L.P.A.M. 2008. The skeletal kinematics of lung ventilation in three basal bird taxa (emu, tinamou, and guinea fowl). Journal of Experimental Zoology 309A. Leon has been busy. This paper is all stinkin’ theropods of the stinkin’ present (i.e., birds), but it is the new state of the art for understanding how birds breathe, and therefore worthy of mention in these hallowed electronic halls. If we ever figure out the actual mechanics of sauropod breathing, it will be because of work like this.
- Perry, S.F., Christian, A., Breuer, T., Pajor, N., Codd, J.R. 2009. Implications of an avian-style respiratory system for gigantism in sauropod dinosaurs. Journal of Experimental Zoology 311A. Everyone’s favorite topic (or mine, anyway): sauropod air sacs. Includes some new physiological calculations and some novel ideas on the link between air sacs and giant body size in sauropods.
Continuing with another sauropod paper from Germany, this time in the journal of the Museum fur Naturkunde in Berlin. This one is also currently free but may not be forever. Don’t tarry. You know the drill.
- Remes, K. 2009. Taxonomy of Late Jurassic diplodocid sauropods from Tendaguru (Tanzania). Fossil Record 12(1):23-46. A very useful rundown of Tendaguru diplodocid material, including Tornieria africana (formerly “Barosaurus” africanus), Australodocus bohetti, and some bits that might belong to either or neither.
Finally, the redescription of Euhelopus by Jeff Wilson and Paul Upchurch is in press, and hopefully we will have a URL to add here soon (and hopefull it will also be free, at least for a while).
At least some segments of the music industry are getting used to the idea that file-sharing can be piracy, but it can also be free distribution and publicity. The new trend of corporate journals offering free downloads on current articles makes me wonder if they’re starting to think the same way [or not]. I’m reminded of John Gilmore’s famous line, “The net interprets censorship as damage and routes around it.” [like me] Authors are going to keep e-mailing PDFs to all of their friends and colleagues anyway; why not go with the flow? If everyone else’s stuff is being traded and read (and cited!) while yours is sitting behind a paywall, you lose; the “you” applies to both authors and publishers [unless some idiot volunteers to send your stuff around, in which case you only lose if you are the publisher]. End of rant.
Enjoy the new goods!
February 19, 2009
Here are the first two cervical vertebrae of the Carnegie Apatosaurus, from Gilmore’s 1936 monograph. As you can see, they are fused together. It is a bit weird that we haven’t covered the morphology of the atlas-axis complex here before. And sadly we’re not going to cover it now. I needed to get an image of these verts to a group working on…something secret…and this turned out to be the fastest way to get them the information in a format that would be easy to find for future reference. Hope you don’t feel used.
UPDATE: Here’s something weird: the both verts have facets for cervical ribs, but the cervical ribs had not fused to the vertebrae, even though they normally do, and despite the fact that the vertebrae had fused to each other, even though they normally don’t.
February 17, 2009
It’s been a while since we looked at everybody’s favourite partial dorsal vertebra, and there may be those who feel we’ve said all that can be said about it, but there is one feature of Xenoposeidon that we’ve never really highlighted here and which is well worth a look.
For anyone who’s not up to speed, a super-brief resumé: Xeno is an indeterminate neosauropod which Darren and I named in 2007 on the basis of a single element, a superbly preserved partial dorsal vertebra loaded with distinctive features that make it very clearly distinct from any other named taxon. For anyone who wants more background, the original paper is freely available, as is a page summarising the story for the media, some unnofficial supplementary information, and a whole week’s worth of SV-POW! posts.
Here is the canoncial Xenoposeidon photo: the specimen in left lateral view. (Don’t worry, this old chestnut is not your Picture of the Week — it’s just setting the scene.)
Up near the top of the preserved part of the vertebra, where the neural arch is broken off, there is a distinctive “V”-shaped pair of laminae, which we identified as accessory infraparapophyseal and infrapostzygapophyseal laminae. The more posterior of the two (on the right as we look at at it here) has a very distinctive wrinkled texture, and that’s what I want to show you today:
Now I’ve heard different things said of those wrinkles: I’ve never seen them on any other specimen of anything before, but then I’ve not seen a whole lot of material. Other people have told me that this kind of thing is pretty common, though I don’t recall anyone ever having told me a specific other specimen that has it. What is completely clear is that no-one seems to know what it is or what it means. It’s very hard to see how this could be the result of any kind of post-mortem distortion, so this must be what the bone was like when the animal was alive. What are the possibilities?
- I wondered whether it could be some kind of pneumatic feature, perhaps the trace left by a diverticulum or set of diverticula; but IIRC Matt doesn’t think that’s likely.
- Could it be the result of some sort of infection? Maybe neontologists, or for that matter doctors, see this kind of thing all the time but we poor palaeontologists are ignorant.
- Er … what else? Seriously, I am out of ideas here.
So, comments are open. Enlighten me. What is the cause of this distinctive texture?
Oh, and finally — for some reason, I don’t think I’ve ever mentioned that I uploaded most of the Xenoposeidon news spots onto Youtube a while back. So if anyone wants to hear me talking about my favourite subject, and arguing with the Channel 4 News guy, or indeed just wants to see how mainstream media can get a science story completely right when we trouble to give them good information, get over to http://www.youtube.com/user/Mirk101
February 11, 2009
I had a new paper come out today. Unofficial supplementary info here, PDF here. I would have had all this ready to go sooner, but the paper came out sooner than I expected. In fact, I didn’t even know that it had been published until Andy Farke (aka the Open Source Paleontologist) wrote me for a PDF. Turnabout’s fair play, I suppose, because last year I congratulated Stuart Sumida on his Gerobatrachus paper before he knew it was out. I guess letting the authors find out through the grapevine that their stuff has been published is part of the “value added” that commercial journals provide. ;-)
Anyway, I’m happy the paper is out, finally. It’s the third chapter of my dissertation, but with teaching and traveling to Spain and such I didn’t get it submitted until last January. I had to forcibly bite my tongue during the Aerosteon saga last fall, when such a big deal was made about the absence of pneumatic hiatuses in non-avian dinosaurs. This despite the facts that there are several good reasons to expect pneumatic hiatuses to be rare, and that pneumatic hiatuses are not the Rosetta Stone or magic bullet for air sacs in saurischian dinosaurs. They’re more like the cinderblock that broke the camel’s back, given all the other evidence for air sacs.
In fact, the structure of the new paper is built around the idea that there are several tiers of evidence for bird-like air sacs in saurischians. Those tiers are:
- The presence of postcranial pneumaticity at all. Some of the first authors to get interested in the implications of pneumaticity for dinosaurs argued that pneumaticity probably implies an air sac system, and left it at that. Later workers have tended to denigrate this argument as overly simplistic–just because some of the postcranial skeleton is pneumatic does not mean that the animal’s air sac system was necessarily like that of birds–but it’s not actually a bad argument. We can imagine lots of ways to get air into the postcranial skeleton, but for tetrapods the only system that we have any evidence for is diverticula of a lung/air sac system like we see in birds.
- The distribution of pneumaticity in the skeletons of most saurischians and pterosaurs is diagnostic for specific air sacs, namely the cervical, clavicular, and abdominal air sacs that we see in birds. This is what Pat O’Connor and Leon Claessens established so firmly with their work on mapping parts of the respiratory system to skeletal domains in birds.
- The evolutionary patterns of pneumatization in sauropods and theropods parallel the development of pneumatization during ontogeny in birds. Or, more economically, ontogeny recapitulates phylogeny in this system. This is more evidence that the observed patterns of pneumaticity in the skeletons of birds and non-avian saurischians are produced by the same underlying process of diverticula developing from different air sacs in a highly conserved order–even if we don’t know why things evolved, and continue to develop, in the order that they do. And it’s better evidence, because it accounts for more observations (points 1 and 2 can be established from single specimens) and ties postcranial pneumaticity in all saurischians, living and extinct, into a more coherent picture.
- Pneumatic hiatuses are more evidence that the postcranial skeleton is pneumatized by diverticula from more than one part of the respiratory system. Not the only evidence–we already suspect this quite strongly based on points 2 and 3–but more evidence. It is possible that the diverticula of extinct animals behaved differently than those of all extant birds, and diverticula from a single source could conceivably pneumatize the whole vertebral column. Possible. Conceivably. How likely? Dunno–our n on this is either 1 (if you count all living birds as a batch) or several hundred (if you count each of the species that Pat O’Connor has dissected and injected). Pneumatic hiatuses offer another level of evidence, because they can potentially show that the patterns of pneumaticity in fossil taxa are inconsistent with pneumatization from a single point. That’s how they work in chickens, and that’s how they may work in non-avian dinosaurs, as long as diverticula don’t leapfrog over some bones without leaving any traces, or at least don’t do that very often.
For the record, I don’t think that pneumatic hiatuses are stronger evidence than point 3; if I was ranking the tiers based on importance I would put 3 at the top. Pneumatic hiatuses ended up being last in the paper because 1-3 were basically review material, and it made sense to group them together before the big bolus of description.
[UPDATE the next day: also, I just realized that those 4 are not the same as I used in the paper! In the paper I left out 1, advanced 2 and 3, and added a different number 3, which is pneumatization of the pelvic girdle and hindlimb. I tend to forget about that one because the evidence in sauropods is underwhelming so far. And arguably this is just another aspect of 2 (above), or if you like you can think of 5 tiers. They say consistency is the hobgoblin of small minds!]
The importance of pneumatic hiatuses remains to be seen; there might not be enough of them to tell us very much, or we might find that leapfrogging diverticula exist and are common (we’d then need a way to sort hiatuses caused by multiple sources of diverticula from those caused by leapfrogging diverticula). But they’re important to me, for a couple of reasons.
First, they’re probably one of the two or three best ideas that I’ve had in my life. When I realized that pneumatic hiatuses could potentially indicate pneumatization from multiple sources it really was like a light going on in my head. I walked around seeing stars all week.
I got the idea from this figure, from King (1957):
On the left King has drawn the vertebral columns of several chickens, and shaded in the pneumatic regions. Blocks of pneumatic verts separated by apneumatic gaps represent pneumatization from different sets of diverticula. I remember very vividly sitting in the Padian lab reading this paper and thinking, “if we found one of those in a dinosaur it would be the money.” Then I suddenly sat up straight, then stood up, then paced around the room a few times to burn off the discovery energy. I had a very profound need to tell someone. I don’t remember who I told, but it was probably Mike.
The other reason that pneumatic hiatuses are important to me: they are now one of those cool little cases that show that paleontology can be a predictive science. If you want to test a hypothesis in the experimental sciences you manipulate the conditions and see what happens. Historical sciences don’t usually give you that option. But you can play What If? As in, “If hypothesis A is true then we ought to see such-and-such evidence.” In 2003, I predicted that if sauropods had abdominal air sacs we ought to see pneumatic hiatuses once in a while. Finding the evidence that validated the prediction was almost as much of a rush as having the idea in the first place.
The owner of Sauropod Pneumatic Hiatus #1 is Haplocanthosaurus CM 879, which is a cool animal but fairly pathetic as sauropods go. In my dissertation/job talks I would show the above picture and joke that I could probably beat up that animal on a good day. I found out about the pneumatic hiatus by accident, when I was poring over Hatcher (1903). In one of the figures near the end of the paper, Hatcher shows the centra of the fourth and fifth sacral vertebrae. I noticed that sacral 4 had a pneumatic chamber of some sort but sacral 5 did not. Then a few minutes later I had gotten to the plates at the back of the paper, and saw what looked like a pneumatic chamber on the first caudal. Somewhere in the dank, beer-flooded grottoes of my skull, the neuron fired.
This is the figure I put together, using images from Hatcher (1903), for a Jurassic Foundation grant to go see the material in the Carnegie Museum in 2005. It worked; they came through with $1500 for that trip and a week at BYU the same fall (to my immense shame, although the Jurassic Foundation is credited for funding on the first page, I see that I forgot to thank them in the acknowledgments. Belatedly: thanks, you guys rock, I suck). The pneumatic cavities are labeled as foramina because that’s what they look like in the drawing, and not having seen them I didn’t know any better. In fact they are fossae, but they are deep, invasive fossae and their morphology is not consistent with anything other than pneumatic invasion. (Pneumatic invasion!? Flee for your lives!!) See the paper for all the excruciating details. Note that the sacrals have unfused neurocentral sutures, so the animal was not fully mature when it died (there is probably a whole post ahead just on the neurocentral weirdness in this animal).
So that’s the story, for now at least. There are more pneumatic hiatuses coming, but those papers are still in the pipe so I can say no more for now. I’m sure when they come out some alert blogger will notice and e-mail me for a PDF, and then you’ll get the news here.
The moral of the story is that you can make real progress by reading lots of old, obscure stuff. Support–and abuse–your local academic library!
- Hatcher JB. 1903. Osteology of Haplocanthosaurus, with a description of a new species, and remarks on the probable habits of the Sauropoda, and the age and origin of Atlantosaurus beds. Memoirs of the Carnegie Museum 2:1–72.
- King AS. 1957. The aerated bones of Gallus domesticus. Acta Anatomica 31:220–230.
- Wedel, M.J. 2009. Evidence for bird-like air sacs in saurischian dinosaurs. Journal of Experimental Zoology 311A.
February 9, 2009
Thanks to all for congrats regarding the baby news. Will this mean a short-term break from blogging? In part, yes, but luckily I’ve had the opportunity lately to prepare quite a lot of stuff in advance, so fear ye not oh fans of SV-POW! and Tet Zoo. And to demonstrate that point: welcome to another article in the ‘sauropods of 2008’ series. In the previous entry we looked at the Chinese titanosauriform Dongyangosaurus sinensis. Now for something completely different…
Potentially one of the most interesting of recently named sauropods is Eomamenchisaurus yuanmouensis Lü et al., 2008 from the Middle Jurassic Zhanghe Formation of Yuanmou County, Yunnan Province, China. Yuanmou is already known in the world of sauropod research for yielding Yuanmousaurus [reconstruction above, from Lü et al. (2006)], a possible relative of Euhelopus named in 2006. The only known Eomamenchisaurus specimen consists of dorsal and sacral vertebrae, a partial pelvis, and hindlimb elements: unfortunately, however, the material isn’t fantastic and at least some of the diagnostic characters identified for the taxon are not entirely convincing and mostly look like widespread, primitive features. In the dorsal vertebrae, for example, the absence of pneumatic foramina is listed as a diagnostic feature, but if this animal really is a member of Mamenchisauridae as claimed, then absence of foramina doesn’t work as an autapomophy because other members of the group (e.g., Mamenchisaurus hochuanesis) are also reported to lack foramina on their dorsal centra (as are many other non-neosauropodan sauropods). Pneumatic foramina are indeed absent in Eomamenchisaurus, but note from the image below that pneumatic fossae are present (actually… I assume those lateral cavities are pneumatic fossae, but have just realised that they might not be. Let me know what you think). As is – I hope – well known by now, we’ve found it useful to distinguish ‘pneumatic foramina’ from ‘pneumatic fossae’: gone are the days when all pneumatic holes or cavities could simply be referred to as ‘pleurocoels’ or ‘pneumatopores’.
In the image shown here [from Plate II of Lü et al. (2008)], the ninth and tenth dorsals are shown in (A) ventral and (B) lateral views. See below for discussion. Note the pneumatic fossae. Scale bar = 10 cm.
As indicated by its name, Lü et al. regarded Eomamenchisaurus as an early relative of the famously long-necked mamenchisaurid Mamenchisaurus. Are there any characters that support this assignment? There are, but they aren’t very convincing either: three concern the anatomy and degree of fusion in the sacrals, and that’s always a problematic area because sacral fusion varies with age and, in some taxa, with sex. The fusion of two posterior dorsals (probably the ninth and tenth) is used as a fourth character. According to Lü et al., this fusion is also present in M. hochuanensis, M. youngi and in Chuanjiesaurus anaensis. The last taxon listed there was regarded by Lü et al. as a mamenchisaurid, but the original description provides little information and Upchurch et al. (2004) treated this form 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 am.
A full evaluation of Eomamenchisaurus is needed to further determine its affinities: it might be a mamenchisaurid, but we need more data. In fact it’s worth saying at this point that mamenchisaurids as a whole need a thorough revision: as is widely recognised among sauropod workers, Mamenchisaurus (currently containing seven species) now seems to be a waste-basket genus housing disparate animals that are probably not all close relatives.
Lü, J., Li, T., Zhong, S., Ji, Q. & Li, S. 2008. A new mamenchisaurid dinosaur from the Middle Jurassic of Yuanmou, Yunnan Province, China. Acta Geologica Sinica 82, 17-26.
Lü, J., Li, S., Ji, Q., Wang, G., Zhang, J. & Dong, Z. 2006. New eusauropod dinosaur from Yuanmou of Yunnan Province, China. Acta Geologica Sinica 80, 1-10.
Upchurch, P., Barrett, P. M. & Dodson, P. 2004. Sauropoda. In Weishampel, D. B., Dodson, P. & Osmólska, H. (eds) The Dinosauria, Second Edition. University of California Press (Berkeley), pp. 259-322.
February 8, 2009
At 9:43 this morning, Darren’s wife Toni gave birth to their daughter Emma. I don’t know much more than that except that everyone is well. Join me in offering Darren, Toni and Emma your congratulations!
UPDATE: Not to detract at all from the momentous news at the Naish house, but we have a policy around here of not posting anything without a picture of a sauropod vertebra, so here’s the holotype of Dystylosaurus (= Supersaurus) with a pen for scale. I reckon if we flipped that thing over and put a blanket in the cotyle, it would make a roomy and entirely appropriate bassinet for baby Emma. Congratulations again to the Naishes, especially the as-yet-uncongratulated Wil, who now has a baby sister to torment.
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!
- Ye, Y., Ouyang, H., and Fu, Q.-M. 2001. New material of Mamenchisaurus hochuanensis from Zigong, Sichuan. Vertebrata PalAsiatica 39(4):266-271.