Friday, January 20, 2012

Plateosaurus didn't gallop

Recently, I finally read a paper by Heinrich Mallison entitled 'The digital Plateosaurus II: an assessment of the range of motion of the limbs and vertebral column and of previous reconstructions using a digital skeletal mount'. Yes, it's from 2010, and I should hang my head in shame for not having read it before etc. etc. But bear with me. Reading Heinrich's paper, I was reminded of an e-mail sent to us some time back by Jay Epperhart, one that I referenced in a previous post. As a reminder, it read:
"So occasionally you will make a quip along the line of 'can you believe they ['80s and '90s authors/artists] thought dromaeosaurid theropods had non-feathered pronated hands *snicker*" and I'm like 'wait, what?!' since that it what my 10-year-old self memorized."
It's all about preconceptions, you see. In case you haven't read it (in which case, shame on you, too!), in 'The digital Plateosaurus II', Mallison - utilising a painstakingly-created digital Plateosaurus skeleton - looked at (perhaps predictably, given the title) the possible range of motion of Plateosaurus' spine and limbs, and the implications for a range of reconstructions.

Photo of SMNS wrong-o-mount by Ra'ike, via Wikipedia.















In the past, Plateosaurus was often presumed to be a quadruped - or at least, capable of switching between quadrupedalism and bipedalism, but tending towards the former. Looking at it, it's quite easy to see why - with its long neck and reasonably robust forelimbs, it looks a little front heavy. Furthermore, the more derived sauropodomorphs - the sauropods - were all resolutely quadrupedal, and so it made sense for the lineage to be heading in that direction, evolutionarily speaking. In addition, trackway evidence appeared to show 'prosauropods' walking on all fours.

However, Mallison discovered that far from being a habitual quadruped, Plateosaurus was not even able to rotate its forearm so that the palms of its hands faced the ground (pronation) - in fact, the range of motion was comparable with that of the short-armed allosauroid Acrocanthosaurus. In other words, Plateosaurus was a biped whether it liked it or not.

In fact, Mallison's work had independently confirmed the conclusions of an earlier study, by Matthew Bonnan and Phil Senter, in 2007 ('Were the basal sauropodomorph dinosaurs Plateosaurus and Massospondylus habitual quadrupeds?'). Bonnan and Senter also found Plateosaurus to be an obligate biped, in spite of the great number of quadrupedal Plateosaurus reconstructions that had popped up in the many decades since the animal's discovery.

Plateosaurus gracilis correctly restored as a biped, by Nobu Tamura via Wikipedia.
Note that this species has sometimes been placed in its own genus, Sellosaurus -
Mallison's paper deals only with P. engelhardti.














In his study, Mallison found that some of said reconstructions didn't just snap the forelimbs into an impossible position, but warped much of the rest of the body as well. A quadrupedal mount in the Staatliches Museum für Naturkunde Stuttgart (SMNS) is of sufficient sprawling-limbed wrongness that, if the animal were alive "compressive forces on the forelimbs would shear the humerus from the glenoid" (p. 449). Mallison goes on to comment that
"The...overall proportions and limb positions are in direct contradiction to the adaptations to cursoriality visible in Plateosaurus, and require significant disarticulation in several parts of the skeleton."
Mallison ultimately attributes such mistakes to the need for the reconstruction to fit a preconceived notion that Plateosaurus was highly reptilian and lizard-like, with sprawling limbs and a wide ribcage.

In addition, quadrupedal reconstructions by Gregory S Paul were found to feature very significant inaccuracies, and this was especially true of a muscular reconstruction that depicted Plateosaurus in a galloping pose (if you have the 2010 Field Guide it is on page 162). The errors - including limbs in impossible positions and huge gaps in the skeleton - were inconsistent with a reliance on data provided by Friedrich von Huene (Paul had not examined the fossils). Rather, Mallison claimed that
"...the errors seem to result from a preconceived notion that prosauropods were quadrupedal, that their manual digits I were raised off the ground during locomotion...and a desire to depict the animal in as dynamic a pose as possible." (p. 455)
(An important note before I continue: I in no way wish to join in what seems like a bit of a trend for Greg Paul-bashing after his comments pertaining to copyright and skeletals. It just happens to be Paul's work that is described in this way in Mallison's paper.)

How is this relevant to Jay Epperhart's comments about dromaeosaurs? Well, just like Plateosaurus, reconstructions of these animals were long influenced by preconceived notions, leading to the reconstructions we all remember from the '90s that often flew in the face of anatomical evidence and common sense. In fact, people's notions of what these animals looked like continue to be influenced by preconceptions based on what said people think they should look like.

Pronated theropod forearms would be an obvious reference point here. They still appear regularly in art - often commercial art - but are always based on someone's preconceived notion of how a theropod should look. The same is true of scaly or near-bald dromaeosaurs; hopefully I needn't go over the evidence yet again as to why it's far, far more likely that any given dromaeosaur was feathered than not. Those who dream of scaly Deinonychus often seem to resort to the argument that 'it looks like a chicken' when (accurately) depicted with feathers - as if looking like a plucked chicken is less absurd. And let's be quite honest - an anatomically correct, naked dromaeosaur will inevitably look like it's been prepared for the dinner table.

In truth, I think it's down to the '10 year old self' coming through with preconceived notions, borne of nostalgia and a belief in what a dinosaur should look like, contrary to the evidence. But it's not the 1990s anymore, Plateosaurus didn't gallop, and Deinonychus had feathers.

And if you're angry at me now, please placate yourself with this photo of me being a dork (also featuring Plateosaurus).


Photo by Nicole Heins.





24 comments:

  1. Hate to drop two f-bombs in the span of a week here... but fuckin' excellent post, Marc.

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  2. I hate you.. And since when was the last time you saw a 'scaly' chicken?

    Nice post though! :)

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  3. Thank you for this series, Marc! While I was well aware of theropod hands, I had somehow completely missed the news about Plateosaurus.

    Also, I'm aware I am obsessed, but I can't help but notice the visual similarity between bipedal Plateosaurus and Therizinosaurus.

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  4. Talcott - I think you can be forgiven for missing this. Early sauropodomorphs, for as many fascinating things as they can teach us, somehow don't seem sexy to the media.

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  5. David & Talcott: I'm especially fond of sauropods, but to my shame, early sauropodomorphs are still darkness to me.

    And thanks for making me feel worse about my already lamentable ignorance, Marc. :P

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  6. I have been trying to read Mallison's posts about his paper on his blog since I don't know how long but I never found myself sitting at the desk with time to read them. So thank you for this summary.

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  7. @Talcott: and then look at Tenontosaurus. Again a very similar body shape.

    @Marc, thanks! I love getting good write-ups!

    @all: I ma bashing a lot of reconstructions, not just Paul - his was just the juiciest one.

    @ Henrique Niza: the posts are not on my blog, but on the Palaeontologia Electronica one:
    http://www.palaeo-electronica.org/blog/?p=35
    http://www.palaeo-electronica.org/blog/?p=61

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  8. Makes you wonder when exactly quadrupedalism started in sauropods, and why...

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  9. @David: That's only because the articles aren't being framed correctly. "T-Rex Cousin Walked Like Humans." There, now it will get attention.

    @Heinrich: I've always been fond of Tenontosaurus, but I never made that connection. I tend to think of it as Iguanodon with a better tail.

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  10. @Durbed: Good question.

    @Talcott: I'd always thought that of Tenontosaurus too.

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  11. @David: I guess the early sauropodomorphs are the ugly, awkward cousins of the more fashionable brachiosaurus.

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  12. Thanks for all the comments so far. I'm glad you approve, Heinrich. And nothing personal, Jon...

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  13. @Mallison: you're right, indeed. I was thinking about your SVP talk "Fast Forward Dinosaurs". Thank you.

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  14. This made it onto that Ryan Gosling meme blog... http://paleontologistryangosling.tumblr.com/post/16192846411

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  15. @Mallison

    "and then look at Tenontosaurus. Again a very similar body shape."

    That makes me wonder: Any idea whether it was bipedal, quadrupedal or both? I usually see it portrayed as both.

    @Durbed

    "Makes you wonder when exactly quadrupedalism started in sauropods, and why..."

    Not necessarily: Plateosaurus was unique among "early sauropodomorphs" (See the highlighted sentence: http://books.google.com/books?id=1GOYYwqctxMC&pg=PA232&dq=%22considering+the+varying+adaptations%22&hl=en&sa=X&ei=akUaT5SgIMr50gH53OCeCw&ved=0CDIQ6AEwAA#v=onepage&q=%22considering%20the%20varying%20adaptations%22&f=false ).

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  16. I've always assumed that Tenontosaurus was probably an obligate quadruped on account of it having to support the weight of all those Deinonychus.

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  17. In the past, Plateosaurus was often presumed to be a quadruped

    Back in the 1950s I had a dinosaur book which featured a determinedly bipedal prosauropod, Anchisaurus, I think, probably based on whatever this is based on, if memory serves me. So the quadrupedal assumption must have come later. I wonder why.

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    1. Often, but not always. Von Huene thought Plateosaurus to be a biped much earlier than the 1950s, while others thought it to be a quadruped (sometimes with sprawling limbs).

      I should probably also mention, re my inclusion of Nobu Tamura's Plateosaurus gracilis illustration, that that animal's inclusion in the genus Plateosaurus is controversial. Heinrich's paper deals only with Plateosaurus engelhardti.

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    2. I've amended the caption now to point that out. Seemed a bit misleading otherwise.

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  18. Jaekel also thought P. was bipedal, but suggested a clumsy hopping gait LOL
    Tenontosaurus I am not so sure about, but I believe that it was at least capable of a quadrupedal gait, when feeding on the ground for example. The arms looks that tiny bit different.....

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  19. Great, another new discovery making Walking With Dinosaurs even more obsolete...

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