Often, students in biology and paleontology wonder why it is that we “force” them to take physics. I ought to know — I was one of those students! It wasn’t until later in graduate school that I began to appreciate the application of physics to matters of dinosaur movement. I believe part of this reticence among many future biologists and paleontologists to embrace and understand physics is that they feel (as I once did) that it was mostly the arena of engineers and cosmologists.
Yet, the questions we are often so interested in about living organisms and those in the fossil record relate to physics. How did they move? Were they moving in water? How could their heart pump blood to their head? How did a giant sauropod move, let alone stand, without breaking its bones? So, if you are interested in dinosaurs and other magnificent animals of the past in the context of how they went about their daily lives, then you are interested in physics.
When I first began teaching vertebrate paleontology back in 2003, my goal then as now was to communicate to biology and paleontology students how modern vertebrate skeletons and body form are related to their function. Too often, in my opinion, we tend to emphasize taxonomy and relationships over how, as scientists, we reconstruct paleobiology. To be clear, taxonomy and the study of evolutionary relationships (systematics) are hugely important — they provide the context in which we test evolutionary hypotheses. However, I wanted to strike a balance in my courses of teaching how the vertebrates were related in combination with how they lived their lives and responded to the physical world.
Today in my vertebrate paleontology course at Richard Stockton College, I hope a new group of students has begun to appreciate this intersection among biology, paleontology, and physics. In the lab, students used a small wind tunnel and “smoke” from a fog machine to test how three different fossil fishes may have moved through the water. I have found it is one thing to talk about Bernoulli’s Principle or discuss friction and pressure drag. It is a whole other kettle of fish (pun intended) to see for one’s self how body shape actually changes the fluid around it.
Each group of students was assigned a fossil fish to research and model out of clay in lab. Then, after hypothesizing how they thought their particular fish would behave relative to the water current (or in this case, the air current with “smoke”), they put their models in the wind tunnel, turned on the smoke, and put their hypotheses to the test. They will later present their findings to the class. My hope in all of this is that these students appreciate that our hypotheses about past life rely heavily on our models of the present flesh, bone, and physical laws.
I want to dedicate this short post to the following people at Richard Stockton College. First, having a wind tunnel and smoke machine would not have happened at all were it not for the help of our shop staff in the Natural Sciences — Bill Harron, Mike Farrell, and Mike Santoro. They worked on this small scale wind tunnel with my input, and helped give our students a wonderful lab experience.
Second, Christine Shairer was invaluable for her help with getting me the materials my students and I needed to do this small-scale experiment.
Finally, third, Dr. Jason Shulman in physics who is a colleague, research collaborator, and one of the few physicists willing to put up with a paleontologist who is constantly asking what I can only assume are ignorant and humorously simple questions. If only I had had such an enthusiastic professor when I was questioning why I had to learn physics all those years ago!
Just a short post to introduce you to some of the “newer” students in the Bonnan Lab: Kelsey Gamble and Caleb Bayewu.
Today we were working with some Sprague-Dawley rats to track how much their forelimb is abducted at the elbow (pulled away from the side of the body) during locomotion. We use an apparatus called the OptiTrack V120 which consists of 3 integrated infrared cameras that send out rapid pulses of IR light. The rats wear a vest with two markers on the back which gives us the position of their body’s mid-line, and another small marker is affixed to their elbow (with the equivalent of eyelash glue) … with tender loving care, of course.
You know you’re a scientist when after months of trial and error and fiddling with the equipment, we literally jumped for joy today when we successfully recorded all five walking trials! Why are we doing this? Stay tuned …
This debate was apparently triggered by a video posted by Bill Nye entitled, “Creationism is Not Appropriate For Children” on YouTube. Not to be undone, Ken Ham posted his own response with embedded links to two other Ph.D.s who amplify his belief that evolution, not Creationism, is damaging to children.
If the goal is science education, then I believe this debate is a poor way to improve the reception of science education in the general public. Why do I feel this way?
There is a poor or nebulous definition of evolution and science by both parties.
In his video, Bill Nye states, “Evolution is the fundamental idea in all of biology.” I really like Bill Nye, but I’m sorry, Bill. Evolution is not an idea. It is a scientific theory. If you’re going to have a debate about science, definitions become hugely important. A scientific theory is a testable, falsifiable, and predictable explanation of natural phenomena. If you couch evolution as an idea, you open the door to a debate about ideology, not science.
Of course, Ken Ham has science wrong as well. He says, “Science means knowledge – you can divide science into historical science … and observational science.” No on both fronts. First, science as it is practiced is not a definition but a method — specifically methodological naturalism. It is the tool by which we understand the natural world — a narrow discipline, in fact, that seeks to pose answerable questions about nature. Second, science is science. All science is based on observations at some level — the dinosaur bones may not “come with labels on them,” but they are observable data that can measured, studied, and so forth. So, there is not observable versus historical science — it’s all the same thing.
A scientist works under a theory, an explanation for some type of phenomenon in the natural world, to test hypotheses. If you work on chemistry, you are working under (among other theories) the atomic theory which states that all matter is made of atoms with specific properties. Until recently, chemists have done a bang up job of testing and predicting chemical reactions and their consequences without seeing directly into atoms. That’s because the testable explanation (atomic theory) was effective for inferring what should occur. So, to say that evolution is “historical science” which is “beliefs about the past” is a gross misconstruction of how science works.
When Ken Ham says, “If evolution were true … it would be so obvious to the kids …” he is ignoring the fact that many applicable theories of science are weird and not obvious. For example, the theories of general and special relativity predict that time is experienced differently by different objects at different speeds and in different gravitational fields. If you use satellite technology, those satellites whizzing in orbit around the earth have clocks that quickly go out of synch with those on earth (which is explained by the theories of relativity) and thus we have to take special measures to synchronize them with our devices on the earth (GPS comes to mind). That is good science but not something particularly obvious to kids.
In a nutshell, science is like the honey badger of internet lore — it doesn’t care about your beliefs or opinions. Data drives what is accepted and rejected.
We are again fighting a metaphysical clash of civilizations.
Based both on what Bill Nye and Ken Ham say, this debate is not about data. A scientific debate would be about data. Instead, we have what amounts to, in my mind, another metaphysical clash of civilizations. Ken Ham and his organization are very clear on this. He is not concerned about data, but rather showing that “Creationism teaches children that they’re special, that they’re made in the image of God.” In that one statement, you have what is actually being debated spelled out: whether or not you believe in a particular deity in a particular way. This is why Ken Ham, his organizations, and others like him make the leap from teaching evolution to teaching kids they’re “just animals” to gay marriage and so forth.
However, Bill Nye is not doing anyone a favor by saying, “In a couple of centuries that world view [creationism] will not exist … there’s no evidence for it.” Nye has basically indicated that, yes, evolution is a world view, but it is supported by evidence. And if that is true, then it follows that in this metaphysical clash of civilizations you have to pick a side. At least, if you follow Ken Ham and his compatriots, that is likely what you are led to believe from such statements.
There is No Clear Distinction About Faith and Creationism
I have said this before, but it bears repeating – there is no conflict between science and faith. Yet, that is precisely what this debate is already boiling down to. Science is not faith – it is a tool for understanding the natural world. Faith is a deeply personal set of beliefs that often cannot be demonstrated scientifically, but that makes them no less valid to the individuals that hold them. This is not my idea, not by a long shot, but to rephrase the words of many who have come before me, science and faith are after separate goals. You don’t scientifically test faith, and you don’t apply faith where science works well (the natural world). This is why they can and should coexist — they serve different purposes, often to the betterment of us all by people with noble intentions.
But the Creationism of Ken Ham and the Creation Museum is not mainstream Christianity. Many Christians from many faith traditions accept science and evolutionary theory while maintaining their faith. Ken Ham wants you to conflate his narrow concept of Christianity (a fundamental, literal interpretation of a particular version of the Bible) with Christianity as it actually exists in the world. But that conflation works to his advantage, because if we are choosing camps, and you identify as a Christian, you cannot “believe” evolution because a humanist (whatever that may mean to you), Bill Nye, is coming after your faith.
A Plea and Some Thoughts
No one person holds all the keys to our problems, so I would never be so bold as to say I have the answer. Here, then, is my plea and a few thoughts.
I think what many scientists, myself included, are troubled by is hucksterism and charlatanism — snake oil salesmen dressed in religious or authoritarian garb using ignorance to fund their own ambitions and power. But it is vitally important that we do not conflate that clear and present danger with faith overall. Given that a majority of Americans identify as people of faith, broadly lumping them in with extremists serves no one and is very damaging. My plea to my scientific colleagues is, stop doing that. This is just as damaging as saying that people with no religious beliefs are evil, wrong-headed, and trying to subvert American culture.
As I have said before, fear, not data, is the bottom line here. People are afraid that their faith is being attacked — once you are afraid, data (the currency of scientists) doesn’t really matter. What scares people about science? What scares them about evolution? How, as scientists, do we work with the majority of people who can see the benefits of science as a tool but are afraid to compromise their spirituality? That, to me, is the challenge of our time.
You will not convince those with extreme convictions to self-reflect and re-evaluate. You can bring oceans of data and heaps of observations, but it will do you no good, because the debate is not really about science but about fear and emotion. So, if Ken Ham and his followers are convinced they are right, having a debate only ever further convinces them that they are. Do you really think Ken Ham would ever take the results of the debate as anything but a win if not just great publicity?
My last thought or plea: don’t debate Ken Ham and other so-called Creationists. There are people convinced to their core that the world is flat – no amount of data and debate will sway them, and nothing much will be accomplished. But they, like Ken Ham, do not represent the majority. The majority is who we desperately need to reach. Certainly, when such extremist views threaten to undermine science education, we should and must push back as the National Center for Science Education has admirably done. That is very different, however, from going out of one’s way to have what will amount mostly to spectacle and the reinforcing of deeply held convictions on both sides.
Again, I like and respect Bill Nye a lot, and I think he has done wonders for science education in the United States. To Bill Nye and any other well-meaning scientists out there who want to improve science education, please do not debate Creationists — this is not the way to accomplish what we all want.
The 6th-8th grade was a special time in my development as a budding scientist. No, I would never say Junior High was my favorite time or that I was popular (ha, it is to laugh). However, it was during this time that I began to devour my first “young adult” and adult books on dinosaurs and zoology. Among them were two by Dougal Dixon, Time Exposure and After Man: A Zoology of the Future. I loved the latter book – for those who don’t know, it is the “journal” of scientist from the future Earth 50 million years from now. As a kid, that book was amazing to me, because it linked together evolution, natural selection, and plate tectonics in ways that were inspiring and downright weird. For example, bats that had become terrifying terrestrial carnivores or rabbit descendants taking the place of modern ungulates! It was one of the first books that taught me that evolution was not directed but subject to the vagaries of the environment and the anatomical baggage of past generations. This had been an unexpected Christmas gift from my Aunt Ramona and Uncle Joel — and it has made that kind of lasting impression!
But I had a serious issue as a 13-year-old with Dr. Dixon’s Tyrannosaurus in the other book, Time Exposure. He called it a scavenger! This could not stand. And so, back in the days before internet or e-mails, I typed up a message to him on my mom’s old typewriter informing him of why Tyrannosaurus must, of course, be a top predator. My evidence? Legs built for fast speed, a heavy head with big teeth, and who had ever seen lions taking the kill away from jackals? (I laugh at this last bit now a lot.) My mom (bless her heart) dutifully sent this letter out to a scientist in the UK (postage? $$$) and I waited for a reply.
And a very nice reply did I receive from the desk of a Dougal Dixon a few weeks later. Whereas he disagreed with some of my headstrong assertions about the lifestyle of Tyrannosaurus, he sent a kind and encouraging letter that meant probably more than he will ever know to me and my career. On the rare occasion I have now crossed paths with him at the Society of Vertebrate Paleontology meetings, I have always let him know how much that simple, kind gesture meant to me.
Then this Spring, I was contacted by Highlights Magazine for Children, a magazine I used to get and to which I drew dinosaur pictures for back in the day. They were doing an illustration of the dinosaur I helped to discover and describe, Aardonyx, in, of all things, Dougal Dixon’s Dinosaurs! They showed me a preliminary illustration and the anatomical “bits” they were going to label. I was flattered and a bit emotional, to be quite honest. Here, I was being asked to comment on a dinosaur I helped discover for a page in a kid’s magazine by one of the paleontologists who had encouraged me all those years ago. The circle was complete.
In the past month, the publisher contacted me with the final illustration as it appeared in this summer’s (2013) Highlights for Children Magazine:
This serves as a reminder to me that the power of being a scientist who studies dinosaurs and other prehistoric life is that our work directly touches and inspires children to think about science and to wonder about the world beyond their own backyards. So this was my belated Christmas gift this year. And a belated post!
Thanks and gratitude go out to Adam Yates for involving me in the research that led to the discovery of Aardonyx, to Celeste Yates for the beautiful preparation of the beast that allowed us to describe it and now Highlights for Children to illustrate it. And of course, thanks and gratitude to Dougal Dixon.
Happy holidays and peace to all.
As I recently learned from a fall in which I broke one of my ribs, gravity is an irresistible force.
Gravity’s relentless pull has shaped the evolution of the skeleton in land vertebrates who have had to stand tall or be crushed. Trees have it easy in that they only have to stand and sway (Vogel, 2003) – our skeletons have to resist gravity while on the move (McGowan, 1999; Carter and Beaupré, 2001). If force equals mass times acceleration, then every time you walk, jog, or climb a flight of stairs, you are pummeling your limb skeleton with forces greater than your body weight! But your bones are alive and they adapt to this daily abuse by changing their shapes to best resist those forces. Therefore, paleontologists, like my colleagues and I, are obsessed with bone shape because it is a proxy record of how the limb skeleton adapted to support and move a fossil animal like a dinosaur. Until we recreate living dinosaurs ala Jurassic Park, limb shape is the next best thing to putting a dinosaur or mastodon on a treadmill.
Many dinosaurs were successful in becoming land giants, whereas a comparative handful of land mammals have ever crossed the 1,000 kg mark (Farlow et al., 1995, 2010; Prothero and Schoch, 2002; Prothero, 2013).
Therefore, you might predict to see stark differences in limb skeleton shape between dinosaurs and land mammals … and yet you don’t! In fact, getting big on land as a dinosaur or mammal usually results in stout columnar limb bones which resist weight combined with a decrease in activities like running or jumping (Christiansen, 1997, 2007; Carrano, 2001; Biewener, 2005; Bonnan, 2007). In essence, you get an interesting but ultimately boring pattern that shows us there are only so many solutions to fighting gravity.
In a recently published open-access, peer-reviewed article in PLOS ONE, my colleagues and I have shown that there is one area of a limb bone that does change in different ways with increasing size between land mammals and dinosaurs: the joint-bearing region.
Called the sub-articular surface, this zone supports the slippery and pliable articular cartilage that makes movement possible at joints by decreasing friction and absorbing stress. We focused on this region because: 1) its shape should reflect how the bone beneath the cartilage was reacting to stress; and 2) recent work has shown that articular cartilage thickness in dinosaurs and land mammals differs, being very thick (several centimeters in some cases) in the former and very thin (only a few millimeters) in the latter (Graf et al., 1993; Egger et al., 2008; Bonnan et al., 2010; Holliday et al., 2010; Malda et al., 2013).
What we found surprised us. As land mammals become giants, their sub-articular regions become narrow with well-defined surface features. In contrast, becoming a giant sauropod involves an increase in the sub-articular region combined with a subdued, gently convex profile.
Why this difference? Our results suggest two interrelated relationships. First, sub-articular bone profile and cartilage thickness go hand-in-hand. In living animals, those with thick articular cartilage (alligators and guinea fowl birds in our sample) have expanded sub-articular regions with gentle convexity, whereas those with thin articular cartilage (the living mammals in our sample) retain narrow and increasingly well-defined sub-articular regions. Hence, seeing the narrow and well-developed sub-articular regions in fossil elephants and Paraceratherium show convincingly that they had very thin articular cartilage. In contrast, the expanded and gently convex ends of the limb bones in sauropods appear to be well-correlated with thick articular cartilage.
Second, and more intriguing, these differences suggest different adaptations to becoming a giant constrained by cartilage thickness. In mammals, it has been well-documented that the best way to disperse stress through thin cartilage is to increase the surface contact area (Simon et al., 1973; Egger et al., 2008). In other words, mammals spread the load by narrowing their joints and increasing surface complexity, allowing the bones to articulate closely. As we say in the paper, becoming a giant mammal means developing highly congruent joints. In contrast, becoming a giant sauropod dinosaur involves retaining thick articular cartilage that presumably deforms under pressure. This would go a long way to explaining the expanded sub-articular surfaces we see in sauropods: deforming a thick block of cartilage safely likely requires enough space over which to spread the load.
What does this all have to do with the frequency of gigantism? We speculate that articular cartilage thickness may have a limiting effect on size. If in mammals the best way to spread stress through a joint is by thinning the cartilage and increasing congruence, you are going to get to a point where the joints are as congruent as possible and the cartilage cannot get any thinner. In contrast, retaining thick articular cartilage at large size might have been one factor that contributed to the frequent evolution of so many dinosaur giants. Therefore, our data suggest that the rarity of large land mammals may be due, in part, to their highly congruent limb joints with thin articular cartilage, whereas the success of sauropod dinosaurs as giants may be tied, in part, to their retention of thick articular cartilage.
As we say in the article, we in no way intend this to be the last word on dinosaur gigantism or imply that this was the only explanation for their success as land giants. In fact, we hope our work, which was limited to 2-D profiles of the sub-articular surfaces, will be expanded upon using newer, 3-D technology by future researchers (see for example recent work by Tsai and Holliday ). So the next time you take a walk, think about and appreciate how a narrow slice of cartilage helps ensure your bones glide past one another and don’t smack together. I only wish thick, pliable cartilage was in my poor rib, which deformed and snapped under stresses far, far less than those which pummeled the limbs of giant mammals and dinosaurs.
This study would not have been published without the help and perseverance of my co-authors.
Ray Wilhite is a kindred sauropod spirit, and an associate professor of veterinary anatomy at Auburn College who knows far more about alligator anatomy than I can ever hope to amass. His assistance in helping me twice procure, dissect, and prepare alligators from the Louisiana Rockefeller Wildlife Refuge was invaluable. He also introduced me to Ruth Elsey, the goddess of alligators, whom ended up as an author on one of our previous forays into the relationship between cartilage thickness and shape (Bonnan et al., 2010).
Ray comments on our paper: “For most of the history of vertebrate paleontology scientists and explorers focused on finding new fossils and organizing them into meaningful taxonomic groups. Recently, however, many paleontologists have shifted their focus to trying to understand the biology and functional morphology of extinct species. I believe our study has moved the discussion forward regarding the morphological adaptations of sauropods that allowed the to grow to such gigantic proportions. Our study provides a possible clue about why sauropod humeri and femora have expanded ends and large terrestrial mammals do not. The revelation in recent years that there is most likely a significant portion of the articular surface missing in preserved sauropod limb bones is supported by this study. Slowly but surely we are beginning to not just put flesh on the bones, but put the bones on the bones and see what lay between.”
Simon L. Masters was a former graduate student of mine, and his thesis on the ontogeny of the forelimb in Allosaurus was to form the basis of the theropod dinosaur set in our paper. Simon, along with Jim Farlow, previously helped with the writing and analysis of using shape-based statistics for determining sex from the alligator femur (Bonnan et al., 2008). Simon has done well for himself and I’m happy to say he is inspiring a new crop of STEM students as a high school teacher at the all-girls Beaumont School in Cleveland Heights, Ohio.
Adam M. Yates has been an invaluable friend and colleague, and his contribution to this paper allowed us to compile a great deal of morphometric data on “prosauropods.” More specifically, when he, Johann Neveling, and I were working up a different paper on what would become our new dinosaur, Arcusaurus (Yates et al., 2011), I began running morphometric analyses of the distal ends of dinosaur and archosaur humeri because we had only the distal end of that animal’s humerus. That figure never made the final paper but it was my first hint that something interesting was going on in dinosaurs: as I plotted “prosauropod” and sauropod humeri, I could see that there was this trend towards expansion and slight convexity. I wanted to note that in our Arcusaurus paper, but Adam encouraged me to save the data for a later time … and that time is now.
Christine Gardner was one of my many successful undergraduate honors students. While working with me, she measured nearly all of the Afrotherian mammals in our paper for her undergraduate thesis on long bone scaling in these mammals. Her hard work at collecting and analyzing her dataset not only gave her honors in finishing her undergraduate work, but contributed in a substantial way to our paper. She has also journeyed with me out to the field a number of times, and has successfully landed herself in the graduate program at the South Dakota School of Mines.
Christine had this to say about our study: “It was the summer between my junior and senior years when I officially began my undergraduate thesis project. Obviously a new experience for me, I didn’t entirely know what to expect. Little did I know I’d watch my raw data not only yield my honors thesis, but eventually become part of much bigger research which has ended with my name being published. Not many students get to share this privilege before finishing their Master’s thesis.”
Adam Aguiar is one of my new colleagues at the Richard Stockton College of New Jersey who specializes is understanding the molecular-level details of bone and cartilage biology. After the first draft of the paper, he was invaluable at providing insight into thinking about articular cartilage and its responses to shock and stress. This gave the paper a new lease on life, and I doubt we would have been successful on our next submission had it not been for his encouragement and contribution.
We thank the many institutions and individuals that provided us with access to specimens for this study. I cannot possibly list all of them here: much of the archosaur data was collected for previous studies (Bonnan, 2004, 2007; Bonnan et al., 2008, 2010) and the heartfelt thanks and appreciation expressed in those references continues more strongly than ever here. For the present study, we wish to thank the following institutions and staff: AMNH: N. B. Simmons and staff (Mammalogy), J. Meng, J. Galkin, and staff (Fossil Mammals); FMNH: W. Stanley and staff (Mammalogy), K. D. Angielczyk, W. Simpson, and staff (Fossil Mammals); UNMH: R. Irmis, M. Getty, and staff; CLQ: M. Leschin; SAM: A. Chinsamy-Turan and staff; BPI: B. Rubidge and staff. We thank Kimberley Schuenman at WIU for collecting data on felids used in this study. Feedback from Gregory S. Paul, Henry Tsai, and Stephen Gatesy at the 2012 Society of Vertebrate Paleontology meeting further improved our manuscript. Discussions with Jason Shulman at the Richard Stockton College of New Jersey on static physics were helpful. Donald Henderson and an anonymous reviewer provided useful comments, critiques, and suggestions on a first draft of this manuscript. We are also indebted to PLOS ONE editor Peter Dodson for shepherding our manuscript through the PLoS system, and his feedback, comments, and suggestions.
Last but not least – a great big thank you to my new employer, the Richard Stockton College of New Jersey, for helping with publication costs! Thank you Stockton and the Grants Office, particularly Beth Olsen!
An Important Aside on Methods and Why We Did What We Did
- We chose to focus on evolutionary lines of mammals and dinosaurs that gave rise to the very largest land species. For mammals, we focused on the placental (eutherian) lines called Afrotheria and Laurasiatheria because elephants and Paraceratherium, the giant rhino relative, descended from these. For dinosaurs, we focused on the Saurischians because the giant, long-necked “brontosaurs” called sauropods were members. We also selected smaller-bodied relatives of these giants in their family trees to examine how similar or different the sub-articular zones of these giants were to their smaller relatives. To analyze shape, we used a computer program called Thin-Plate Splines that tracks and compares landmark coordinates on bones.
- Because bony landmarks and sub-articular surfaces were not always anatomically homologous between archosaurs and mammals, we avoided issues of mixing non-homologous areas in our data by running the analyses on these two groups separately.
- Why did we use a two-dimensional analysis instead of a three-dimensional analysis? Undoubtedly, three-dimensional shape analysis would have further enhanced our interpretation of sub-articular shape patterns. However, a number of challenges prevented such an approach:
- First and most significantly, the data collected in this study span a period of over 10 years during which time cost-effective and portable three-dimensional scanning technologies for acquiring large bone geometries have only recently started to become available. Had we access to these technologies ten years prior, we would have utilized them, as we plan to utilize such approaches in future studies.
- Second, our main goal in this study was to quantify whether or not there were significant differences in the scaling patterns of surface morphology between eutherian mammal and saurischian dinosaur long bones, and whether such differences were correlated with known differences in articular cartilage properties. We emphasize that our goal was not to realistically recreate joint surfaces or establish precise measures of joint articulation, nor do we propose how the three-dimensional shape of the subchondral bone is used to reconstruct joint geometry. Our selection of the humerus and femur furthers our goal: these are long bones in which a significant portion of the subarticular surfaces can be reliably captured and interpreted in two dimensions.
- Finally, third, two-dimensional data is valuable, comparable to previous studies, and provides a good first-level approximation of scaling patterns. Just as linear morphometrics informed and directed the study of two-dimensional geometric morphometrics (GM) of long bones, so, too, can two-dimensional GM illuminate where future three-dimensional GM studies can make the best impact. Our study is certainly not the last word on long-bone scaling and subarticular patterns in non-avian dinosaurs. Rather, we hope it inspires and provides the basis for research incorporating three-dimensional technologies in years to come.
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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.
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.
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