"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.|