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.
Biewener, A. A. 2005. Biomechanical consequences of scaling. The Journal of Experimental Biology 208:1665–76.
Bonnan, M. F. 2004. Morphometric analysis of humerus and femur shape in Morrison sauropods: implications for functional morphology and paleobiology. Paleobiology 30:444–470.
Bonnan, M. F. 2007. Linear and geometric morphometric analysis of long bone scaling patterns in Jurassic neosauropod dinosaurs: their functional and paleobiological implications. Anatomical Record (Hoboken, N.J. : 2007) 290:1089–111.
Bonnan, M. F., J. O. Farlow, and S. L. Masters. 2008. Using linear and geometric morphometrics to detect intraspecific variability and sexual dimorphism in femoral shape in Alligator mississippiensis and its implications for sexing fossil archosaurs. Journal of Vertebrate Paleontology 28:422–431.
Bonnan, M. F., J. L. Sandrik, T. Nishiwaki, D. R. Wilhite, R. M. Elsey, and C. Vittore. 2010. Calcified cartilage shape in archosaur long bones reflects overlying joint shape in stress-bearing elements: Implications for nonavian dinosaur locomotion. Anatomical Record (Hoboken, N.J. : 2007) 293:2044–55.
Carrano, M. T. 2001. Implications of limb bone scaling, curvature and eccentricity in mammals and non-avian dinosaurs. Journal of Zoology 254:41–55.
Carter, D. R., and G. S. Beaupré. 2001. Skeletal Function and Form : Mechanobiology of Skeletal Development, Aging, and Regeneration. Cambridge University Press, Cambridge; New York, pp.
Christiansen, P. 1997. Sauropod locomotion. Gaia 14:45–75.
Christiansen, P. 2007. Long bone geometry in columnar-limbed animals: allometry of the proboscidean appendicular skeleton. Zoological Journal of the Linnean Society 149:423–436.
Egger, G. F., K. Witter, G. Weissengruber, and G. Forstenpointner. 2008. Articular cartilage in the knee joint of the African elephant, Loxodonta africana, Blumenbach 1797. Journal of Morphology 269:118–127.
Farlow, J., P. Dodson, and A. Chinsamy. 1995. Dinosaur biology. Annual Review of Ecology and \ldots 193:44.
Farlow, J., I. D. Coroian, and J. Foster. 2010. Giants on the landscape: modelling the abundance of megaherbivorous dinosaurs of the Morrison Formation (Late Jurassic, western USA). Historical Biology 22:403–429.
Graf, J., E. Stofft, U. Freese, and F. U. Niethard. 1993. The ultrastructure of articular cartilage of the chicken’s knee joint. Internationl Orthopaedics (SICOT) 17:113–119.
Holliday, C. M., R. C. Ridgely, J. C. Sedlmayr, and L. M. Witmer. 2010. Cartilaginous Epiphyses in Extant Archosaurs and Their Implications for Reconstructing Limb Function in Dinosaurs. PLoS ONE 5:e13120.
Malda, J., J. C. de Grauw, K. E. M. Benders, M. J. L. Kik, C. H. A. van de Lest, L. B. Creemers, W. J. A. Dhert, and P. R. van Weeren. 2013. Of Mice, Men and Elephants: The Relation between Articular Cartilage Thickness and Body Mass. PLoS ONE 8:e57683.
McGowan, C. 1999. A Practical Guide to Vertebrate Mechanics. Cambridge University Press, New York, 316 pp.
Prothero, D. R. 2013. Rhinoceros Giants: The Paleobiology of Indricotheres. Indiana University Press, Bloomington, IN, 160 pp.
Prothero, D., and R. Schoch. 2002. Horns, Tusks, and Flippers: The Evolution of Hoofed Mammals. Johns Hopkins University Press, Baltimore, 315 pp.
Simon, W. H., S. Friedenberg, and S. Richardson. 1973. Joint congruence: a correlation of joint congruence and thickness of articular cartilage in dogs. The Journal of Bone and Joint Surgery (American) 55:1614–1620.
Tsai, H., and C. M. Holliday. 2012. Anatomy of archosaur pelvic soft tissues and its significance for interpreting hindlimb function. Journal of Vertebrate Paleontology Program and Abstracts:184.
Vogel, S. 2003. Comparative Biomechanics: Life’s Physical World. Princeton University Press, 580 pp.
Yates, A. M., M. F. Bonnan, and J. Neveling. 2011. A new basal sauropodomorph dinosaur from the Early Jurassic of South Africa. Journal of Vertebrate Paleontology 31:610–625.
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
I came back from teaching an introductory biology course yesterday (Friday, Sept 13, 2013), to find a whole lot of messages from friends and family waiting for me on Facebook. It turns out, unbeknownst to me, that my stick figure evolution cartoon was picked up by I F**king Love Science and went viral!
First, I am honored — honored that anything I did would even remotely reach this kind of an audience, and honored that IFLS found it worthy.
Second, please keep in mind this is intended to be fun, simple, and, above all, a diagram. I submitted it for a Stick Figure Science contest back in 2010 for Florida Citizens for Science: http://www.flascience.org/ss2010top10.html I was pleased at that time that it made the top 10. So, this cartoon of mine has been out and about for a while. It was quite surprising to see it “discovered” and shared so rapidly just now.
Third, the comments section under this cartoon has been interesting to read. I wanted to tackle some of the recurrent themes here and put to rest any misunderstandings.
First, I will tackle the whole relationship aspect of the questions:
- There a lot of comments that suggest the human family tree is wrong — that I should have aunts and uncles where I have cousins. The confusion here seems to be the conflating of “relatives” in a general sense and common ancestry. Certainly, you share DNA with your aunts and uncles, and no doubt they descended from your grandparents. But remember – your have aunts and uncles on your mom’s side and on your dad’s side. Therefore, they are related to your parents and to you, but they are not your direct common ancestors.
- Regarding your relationship with your cousins – the only direct common ancestor you have with your cousins are your maternal and paternal grandparents. Why? This is because, unless there is a lot of close family intermarriages, your aunts and uncles, from which your cousins are descended, likely married someone not related to them. So your cousins share some but not all of their DNA with you and your parents. To find a common ancestor – a group of people whom you and your cousins could all call blood relatives – we have to look to your grandparents.
- Regarding second-cousins — as it turns out, there are many colloquial and law-based ways in which this word is used. When I made the cartoon, I was simply thinking of the children of your great aunts and uncles, to which you would share a last common ancestor with your great grandparents.
Now, I want to clear up biological evolution and comments related to how I drew the “family tree”:
- The point I am making with the cartoon is that if you can appreciate that you have descended from common ancestors you call your parents, grandparents, and so on, you can understand biological evolution at it’s most basic level. Darwin said that biological evolution is a theory that explained the diversity of life because of “Descent with modification” from a single, common ancestor. All living things on earth, and all those we find as fossils, are/were part of a great family tree of life. That is the sum total of what biological evolution means to a scientist.
- Saying you “evolved” from a cat or chimp or whatever else is as incorrect and ridiculous as saying your morphed from your dad to you. No serious scientist would accept that. But saying that we have a closer common ancestor with other mammals, like a cat, than we do with a salamander is what the data support. As an example, the theory of biological evolution predicts there would be a common ancestral population of mammals from which all of we milk-giving fur balls have descended. But no monkeys are mutating into humans, I promise.
- I stress BIOLOGICAL EVOLUTION – that is because the word “evolution” means a lot of things and is used in various ways to describe change over time, star development, the development of cultural ideas, etc. BIOLOGICAL EVOLUTION strictly means “Descent with modification from a single, common ancestor.”
Finally, there has been a “fishes” controversy:
- Please keep in mind that our common use of words doesn’t always apply in science. Theory is a great word that outside of science means a guess or hunch, but in science a theory is a powerful tool – an over-arching explanation of laws, hypotheses, and observations that can be tested, falsified, and has predictive power.
- Yes, yes, I know — we were all scolded by our English teachers that “fish” is singular and plural. Except that in biological and paleontological science, “fish” is, well, “fishy.” Based on common ancestry, for example, we humans are highly derived bony fish! Why? Because we share homologies with everything that has an internal bony skeleton that set us apart from non-bony backboned (vertebrate) animals. Sharks are a type of “fish,” technically called chondrichthyans; the fish we consume tend to be ray-finned bony fishes or actinopterygians, etc. In science, it is perfectly acceptable to use the term “Fishes” to acknowledge that “Fish” is not a catch-all for everything with fins, scales, and gills. Don’t believe me? Fine, see Berkeley’s evolution website right here: http://evolution.berkeley.edu/evolibrary/article/fishtree_01
Still confused? Please remember that what you were taught in high school for biology is often simply a list of beasties with name tags — the good old Linnean classification system: Kingdom, Phylum, Class, and so on. The Linnean system is fantastic for being a universal labeling system, but it does not often reflect evolutionary relationships, just as your name and family name don’t always accurately reflect your DNA and actual ancestry. Why else would National Geographic and other entities be so popular at tracing people’s lineages through DNA? Modern biology and paleontology use a tool called cladistics which focuses on unraveling relationships through special, shared traits called homologies — however, most of the non-career-science public is not familiar with this science, and that understandably causes confusion.
Finally — yes, technically what I have drawn in the cartoon are over-simplified cladograms. They still reflect the fundamental principle of BIOLOGICAL EVOLUTION — a family tree of life, descent with modification from a single, common ancestor. If you can communicate this family tree concept to a lay audience with stick figures even more elegantly in a single panel, I would love to see it and cherish using it in my teaching and outreach.
As the National Center For Science Education has been demonstrating for some time now, denying biological evolution and denying climate change are part of a larger phenomenon related to science illiteracy. But I think we often tend to conflate the knowing of scientific data with knowing the process of science itself. As a college professor, I can tell you that smart students who know a lot about the natural world don’t always actually know the process of science. In one of my first lectures to undergraduates in the introductory biology majors course, when I press them to define science, hypothesis, and so on, very few can. And I have come to believe that our current societal issue with accepting science is a fundamental misunderstanding of the process, not simply a dearth of facts.
In my undergraduate days, I was a climate change denier. That’s correct — I felt that the evidence was at best equivocal for global warming. If you couldn’t prove it directly, how confident could we be? In fact, I felt a good amount of the environmental “science” out there was nothing more than misplaced hysteria or political propaganda. For those who do know me and my political leanings, you are probably surprised.
So I speak from experience when I say that I understand the reservations among many people when it comes to climate change. Ask any climate scientist, and they will never tell you with 100% certainty that their predictions will come to pass. In fact, these scientists rely on models of climate, and those models are a hypothesis of reality, not reality itself. Remember, I was a science major with aspirations of becoming a paleontologist, so my undergraduate self decided that if we couldn’t be certain, we shouldn’t go around broadcasting that it was the end of the world. In my undergraduate head, the best science was certain, and that was why paleontology was so difficult — a lot of uncertainty.
So here’s the thing — a climate scientist can show you a lot of data (see below), and can tell you based on their expertise which are the most probable outcomes of current trends, but if you were my undergraduate self, you would not be convinced.
Whether or not my younger self (let alone my older self) was stubborn or simply a bit daft (probably both), I again point out a key feature in the thought process: if it isn’t certain, it’s not good science.
So, the assumption or implication that good science is certain is the first part of the puzzle. The second part of the stubbornness by many of us to accept climate change or perhaps biological evolution is that we want evidence presented in a court room. We want the TV show Law & Order, and we want the good lawyer to give us an iron-clad argument, or to show that our opponent is a lesser person, or to literally give us a smoking gun. We are convinced that science works like this, and that the person with the best argument and evidence wins. And most importantly, that the winner stays the winner. Nothing can ever overturn the win. Good science should be certain and win the day’s argument, for now and forever.
But of course, science has little or nothing to do with certainty and court room drama. There is no certainty in science — there is simply probability. Because a good scientist recognizes that we are only human, and we can only realistically deal in samples, we can’t measure every aspect of the known universe, and we certainly can’t have all the data on all the clouds, carbon dioxide, and local temperatures. Therefore, a good scientist will never say they have “proved” something — rather, they will indicate that their data suggest certain scenarios are more probable than others. The higher the probability, the more confident one can be that the predictions may come to pass.
It took a while for this concept to sink in with me. It took graduate school and having to do science, and taking an excellent seminar from Professor Emeritus Ronald Toth at Northern Illinois University, that finally made science as a process click.
(As an important aside, much of my thinking as a scientist I owe to Ron — so the “smart” stuff I say about evolution and science are me emulating him. My evolution podcasts and understanding evolution website are extensions [and I hope a sincere form of flattery] of Ron’s approach. Thank you, Ron!)
That means, as someone who earned a B.S. in Geology with a Biology major, I had no real concrete idea about science as a process! I am not surprised nor judgmental that many of our undergraduates, let alone the larger public, don’t understand this either — but this I believe is what needs to be most addressed.
Even if you do succeed in uncovering something new or accurately predicting a trend, there will always be new data. The complaint you often hear about science is how we keep changing our damn minds — we knew Pluto was a planet, or we knew that birds were not dinosaurs, or we knew that cholesterol was bad, and so on. But the process of science requires that one keep testing the hypothesis, and to incorporate new data as it comes in. So we’re not changing our minds to tick you off — we adapting our models and our understanding of the natural world as more data come rolling in.
What I realized at long last in graduate school was that scientists speak in probabilities. And when you think about it, we deal in probabilities all the time, and we make decisions based on those probabilities, and we are okay with that. Every time you get in a car, there is a probability you will be in an accident … but you probably still get in that car. Imagine if someone told you that unless you could 100% guarantee that no accidents would ever occur, it was pointless to drive.
Okay, but now for something more ominous: what about the probability that you will get sick if you ingest salmonella bacteria. I have been sickened myself by this nasty “bug,” and many people have died from salmonella poisoning. But there will always be cases where someone ingests salmonella or another pathogen and doesn’t become sick. Now imagine a friend tells you that since every time a person has ingested salmonella they haven’t always become ill or died, we don’t have enough data to know whether or not it is truly deadly. Therefore, wasting money and resources on preventing the spread of salmonella is not advisable because we can’t know with 100% certainty that everyone who ingests it will get sick or die. This person would probably not remain your friend for long.
Probability in science works along this spectrum — from low to high odds. Low odds: you will be hit in the head and killed by a rouge meteorite tomorrow. High odds: the climate will continue to change, with an overall trend toward higher global temperatures. Can we be certain climate will change in these ways? Not 100%. But the probabilities are high … and that’s why we should be concerned: the scientific predictions of increasing global temperatures suggest our world will change in ways that, if we are not prepared, will be devastating. Of course, we could wait until we’re certain, and we could wait for the ultimate court room battle of the sciences … but if the probabilities are high, why wait? What are waiting for? Waiting for all the data to come in (which will never happen) and waiting for 100% certainty (which will never happen) is simply another way of doing nothing in the face of probable danger.
If you understand that the process of science is by its very nature is one based on probability, not certainty, I think we begin to get to the heart of the scientific illiteracy problem. Giving people more and more data won’t help if they sincerely believe that uncertainty means no one knows anything. This is, I believe, the core issue with science literacy — and why our politicians, our media, and our public are so often mislead to disregard good science and its important predictions that effect us all.
The Discovery Channel is a commercial network that, like all networks, functions to make money. It does this, like all commercial networks, by selling airtime to advertisers who hope you will watch the shows and, as a consequence, have a seed planted in your head to buy their products. There is nothing necessarily “evil” or “wrong” about this — this is capitalism, and this is the mechanism by which we have been getting our TV shows for a very long time.
Shark Week is perhaps the most famous and certainly biggest money maker for Discovery that continues to draw many, many viewers that advertisers hope will come in droves to buy whatever it is they make and sell. People like sharks. I like sharks — they are so fascinating that I actually published a paper with a former undergraduate on tail growth in spiny dogfish!
And I have to believe that at some level or another, one of the positive byproducts of Shark Week and many of Discovery’s shows (including Mythbusters, which I simply can’t get enough of) has been to get the lay public and children interested in the natural world and the role that science plays in helping us understand that world. I also believe many of the people who work for and create programs for Discovery have education as a goal in mind, if not just the bottom line.
This said, I, like many of my colleagues who are biologists and paleontologists, were disappointed and disheartened to see the new “mockumentary” Megalodon: The Monster Shark Lives. In some ways this is not a surprising development for Discovery, because it has previously aired the ridiculous but equally “convincing” Mermaids: The Body Found. But this is all good fun, right? It’s all entertainment, what’s the harm?
When Fonzie literally jumped a shark on the classic television program Happy Days, that was when the audience knew the producers were out of ideas and were getting desperate for ratings. Many have now made that same comparison with Discovery’s Shark Week — except this time they “jumped” a prehistoric shark but probably for similar reasons. But again, so what, the Discovery network can do what it wants — it’s commercial and you tune in to tune out, so to speak.
I wish it were that simple. I wish I could simply shrug this off as “edutainment,” but the sad part is that I cannot. Because what Discovery has basically done is told us that profits can only be made by selling to the least common denominator, and that the real world is too “boring” for anyone to care. In essence, despite the always heightened interest and excitement that the public and children have for these magnificent ocean predators, that just isn’t enough. It’s not enough that sharks rank among the most intelligent of the “fishes,” or that their lineage goes back over 400 million years, or that many of their prehistoric ancestors were unbelievably beautiful, interesting, and, most of all, real. Nope. None of that is enough to draw viewers and make a profit. Only by making up fake stories about sharks will anyone pay attention. Their fake, still-living Megalodon is better than real natural history and real sharks.
Discovery, by airing this show, not only has suggested as a network that its watchers are too ignorant to want real information, but has denigrated the process of real science. Paleontology in particular is presented as an almost purely speculative, armchair discipline. In essence, Discovery is telling its audience, “Hey, you know those stuffy ivory tower Ph.D.s, they’re no fun, and anyways paleontology involves looking at fragments of dead things and making up what sounds best.” As my colleagues and I can attest, if this is what paleontology were, none of us would be the least bit interested in doing it. Paleontology is as much a science as physics, involving the testing of hypotheses against real-world data and admitting where we don’t have all the answers.
Here is how sad this whole thing is for scientists like myself. We know the fossil record, we know our biology, and we know this “stuff” because we have special training. That Ph.D. we have? Yeah, it means we’re experts. Not geniuses, not the all-knowing-all-powerful Oz, but experts in what we do. If you are going into heart surgery, you want the heart surgeon expert — you don’t want some guy or gal who happens to have seen lots of pretty heart pictures and says, “Psh, this supposed doctor of yours says this is risky — not if I did it!” or “But what do they really know? Stuffy doctors haven’t seen this really cool heart picture.” That would be downright ludicrous, and yet my colleagues and I are as qualified to tell you about fossils and their biological implications as that medical doctor is to fix your heart. Because we are experts — we took the time and discipline to get specialized training that you don’t have.
So, you have a paleontologist with a Ph.D., and they say, “Based on all available sources of data, there is good reason to doubt that Megalodon is still swimming in our modern oceans.” And then typically data follow — pieces of real information based on fossils, biology, oceanography, and so forth. To suggest instead that an appropriate and equally valid response to this is, “You know, the ocean is really freakin’ big and who knows what’s really still out there?” is disheartening and a sad commentary on what Discovery thinks of its viewers … let alone the scientists!
What to do? Well, since Discovery is a commercial network, if one were seriously angry they could speak with their wallet. That is, you stop watching that network but more importantly stop buying products sold on that channel. Any business wants the money to keep flowing in … if you hit them in their wallet, they are sometimes more willing to listen. You could contact as many of the makers of the product that is being sold on Discovery and tell them you refuse to buy their product unless they pull advertising from the Discovery channel.
Am I going to forgo watching Discovery and stop buying what is sold on that channel? No. Part of the reason I will continue to watch Discovery is that my students, my family, and my friends watch it, and since it is a popular medium for science, it’s good for me to remain aware of what is airing to at least field questions. And I will admit, I love Mythbusters, and I selfishly want to keep watching that.
But perhaps the better approach is to show Discovery how much more money they stand to make if they air real, intelligent science shows and documentaries. I don’t tune in to the Daily Show to get my news, nor do I expect that I get it unbiased. I tune in for laughs. Discovery, if that’s what you want, if you want to go the way of the History Channel and give us Ancient Aliens, then by all means keep making “mockumentaries” about mermaids, sharks, and whatever else. Even we “elite” academics will tune and laugh at how thoroughly terrible those shows are. But we won’t tune in as often. And we’ll tell our students your network is not to be trusted. In fact, I would even point out that Wikipedia science entries often have more to offer than shows like your fake shark.
But I promise, if you make good, quality programming, people pay for that. Well-produced science programs are purchased by libraries, are shown in classrooms where students say, “hmm, I might check out this channel some more,” and you get a more sophisticated audience … many of which will purchase sophisticated goods sold by your advertisers. And it’s easier to make this kind of money, I would suspect, than making up dumb stuff like “found footage” of an imagined mega-shark. Think about it — like reality shows, the scientific reality and the scientists are already there! It writes itself! And people will watch, and become more educated in the process.
If you stop pandering to the lowest common denominator and instead focus on making quality science programs, I suspect your bottom line will do very, very well. Ultimately, Discovery, you and your producers are experts at making what can be quite interesting, educational, and entertaining, high-quality programming. Imagine putting that creativity together with other experts who know what they’re talking about and with all the amazing nature our planet has to offer.