Dinosaur hand and forelimb posture might have been more diverse than previously hypothesized

Turn a doorknob and you are taking advantage of what anatomists call pronation and supination: the ability to rotate your hand palm-side down (pronation) or palm-side up (supination).  This ability stems from your bone geometry: the radius bone in your forearm is curved can pivot around your ulna, rotating your hand in the process.  Drop to the floor and crawl, and your hand is pronated by crossing the radius over the ulna just as it is for mammals which walk on all-fours like elephants, dogs, and cats.

Pronation and supination of the hand by rotating the radius bone over the ulna in humans. (c) 2013 M.F. Bonnan.

Pronation and supination of the hand by rotating the radius bone over the ulna in humans. (c) 2013 M.F. Bonnan.

In our paper published this week in PLOS ONE, my former student, Collin VanBuren (now a Ph.D. fellow at the University of Cambridge, UK) and myself suggest that most dinosaurs could not actively pronate their hands (that is, turn doorknobs) because their radius could not cross their ulna. Our conclusions were reached after analyzing the bones of nearly 300 specimens representing living birds, reptiles, mammals, and dinosaurs like Tyrannosaurus, Apatosaurus, and Triceratops.

Difference in radius bone geometry are correlated to some degree with forelimb posture.

Difference in radius bone geometry are correlated to some degree with forelimb posture.

Statistical analysis of radius geometry shows that dinosaurs most often have a straight radius bone with a non-circular head (the part that allows movement at the elbow), a shape similar to those of lizards, crocodiles, and birds.  These animals cannot actively pronate their hands, and in lizards and crocodiles this radius geometry is correlated with a non-erect forelimb posture.  In contrast, most land mammals show a curved radius geometry that enables the forelimb to be held erect and the hand to be pronated.  Mammals like ourselves have a well-rounded radial head that allows the radius to actively swivel around the ulna.  Tellingly, the only mammals in our sample that resembled reptiles, birds, and dinosaurs were the primitive, sprawling egg-laying duck-billed platypus and spiny echidna.

Our findings are significant in that they show dinosaur forelimb posture was not mammal-like and, possibly most importantly, more diverse than previously appreciated.  For example, radius shape suggests the forelimb posture and range of pronation in horned dinosaurs like Triceratops was more like those of a crocodile than a rhino.  In another example, the radius geometry of the giant, long-necked sauropods such as Apatosaurus don’t comfortably group with living reptiles, birds, or mammals, suggesting that their forelimb postures were achieved in anatomically novel ways.  Ultimately, our data strongly suggest that we must re-evaluate our conceptions of how dinosaurs could and could not use their forelimbs.

We can also breathe a sigh of relief: most predatory dinosaurs could not open our doors.

I  must give a big shout out and expression of gratitude to Collin — his dedication to this project, through several starts and stops, is what finally saw it through.  That we landed this research in a venue like PLOS ONE is that much more of a testament to his perseverance to get this science out there.  It means a lot to me that we got this out and into open-access: this represents the accumulation of some of my inferences and hypotheses on dinosaur forelimb posture since my graduate school days.  I also want to acknowledge the influence and inspiration of some fellow dinosaur forelimb fanatics, namely Ray Wilhite, Phil Senter and Heinrich Mallison.  All are colleagues and friends, and all have also in their own unique ways put dinosaur forepaws front and center — I encourage you to check out their research!

Read our paper, which is open access: http://dx.plos.org/10.1371/journal.pone.0074842


Academic “evolution”

Recently, one of my former undergraduate honors students, Collin VanBuren, did something remarkable: he not only was accepted into Cambridge University, but was also the recipient of the Gates Cambridge Scholarship!  What is the Gates Cambridge Scholarship?  It is a prestigious award for outstanding applicants from countries outside the U.K. to pursue full-time postgraduate work in any subject available at the university. For Collin VanBuren, this is well-deserved indeed.

Collin, like many of my students, came to me as an eager undergrad with an interest in zoology, and in particular he was interested in marine mammals.  So, I put him to task studying the morphology of the cetacean radius bone (a bone in the forearm) because of my broader interests in forelimb posture among mammals and dinosaurs.  Collin, like many of my students, far exceeded my expectations: he not only collected a lot of data on cetaceans and other mammals, but he desperately wanted to pursue reptile and dinosaur radius morphology.  I warned him it would not be easy and that he was under a short time constraint.  Collin assured me it could be done, and over 400 bones later, he was correct!  He presented his undergraduate work at the Society of Vertebrate Paleontology (as an oral talk, no less — and it was his first ever SVP presentation!) and he and I are now revising what I expect will be a well-received paper … and very much due to his diligence!

During all of this research, Collin headed the Zoology Club at WIU, he participated on several digs in the Late Jurassic Morrison Formation of Utah with me, other eager students, and the Burpee Museum, and was one of many active members of our Functional Morphology and Evolutionary Anatomy (FMEA) Lab, co-directed by Dr. Jess White.  Collin then was accepted into Dr. David Evans’s M.S. program at the University of Toronto, where he has continued to excel, before this latest award.

Seeing my former WIU students succeed always makes me smile and remember the many fun dissections, interesting discussions, and sense of a cohort we often had.  I am singling out Collin now, of course, but I could and will write updates about my other students, including among many others: Ashley Morhardt, now a successful Ph.D. student in Dr. Larry Witmer’s lab; Hillary Parks, who successfully defended her M.S. at WIU and went on to be a key member of the Burpee Museum; Kristy Tuttle who did an M.S. at WIU on rodents and will now be working with Dr. Virginia Naples at Northern Illinois University on her Ph.D.; Simon Masters, one of my first M.S. students at WIU, who is currently one of the best dinosaur paleontology field hands out there; Katie Reiss who did an excellent undergraduate project on shark tail morphology and has gone on to earn her M.S. in shark toxicology; and many more I could and need to mention in the near future.

It is often remarked in academic circles that we have our own academic family as well as our biological one.  In other words, we are “descendants” of our advisors, who are descendants of theirs, and so on, and we can trace back our scientific roots, if you like.  For me, my academic “ancestor” is J. Michael Parrish, and I believe that his encouragement and support of me during my formative years as a scientist have now been passed to another generation. As a scientist or other academic, your students are your “children,” and I hope that, like a “parent,” these students succeed and stand on their own two feet.  I cannot take but a shred of credit for them, because they were all self-motivated, but I am glad to know them and especially glad to hear when they do well.

Again, many congratulations to Collin, and, as I begin to advise a new and eager crop of students here at Stockton, I hope they get to meet and be inspired by my former WIU students.  Would that be cross-pollination or interbreeding?