The Bare Bones – An Unconventional Evolutionary History of the Skeleton

I am happy to announce that I will be publishing my first book, The Bare Bones: An Unconventional Evolutionary History of the Skeleton with Indiana University Press. This has been a labor of love over the past 6 years, and it is great to see it finally coming to fruition.

What is the book about? An accessible guide to the evolutionary history of the skeleton — from the Indiana University Press “blurb”:

What can we learn about the evolution of jaws from a pair of scissors? How does the flight of a tennis ball help explain how fish overcome drag? What do a spacesuit and a chicken egg have in common? Highlighting the fascinating twists and turns of evolution across more than 540 million years, paleobiologist Matthew Bonnan uses everyday objects to explain the emergence and adaptation of the vertebrate skeleton. . .What can camera lenses tell us about the eyes of marine reptiles? How does understanding what prevents a coffee mug from spilling help us understand the posture of dinosaurs?. . .The answers to these and other intriguing questions illustrate how scientists have pieced together the history of vertebrates from their bare bones. With its engaging and informative text, plus more than 200 illustrative diagrams created by the author, The Bare Bones is an unconventional and reader-friendly introduction to the skeleton as an evolving machine.
Here is an example figure:
Fig 17.4 Metronome of science

The metronome of speed. In a musical metronome, the speed of the ticking pendulum is controlled by a weight on its end. In this case, a slow tempo results from placing the metronome’s weight far away from the pivot, whereas placing the weight close to the pivot allows it to tick faster. Similarly, a hypothetical dinosaur with a long femur and short leg and foot segments would be relatively slow because the heavy muscles that move the thigh are spread far from the hip joint, much like a metronome weight displaced far from the pivot. In contrast, a hypothetical dinosaur with a short femur and long leg and foot segments would be relatively fast because now the heavy thigh muscles are bunched near the hip joint, much like a metronome weight placed close to the pivot.

Why did I write it? I was inspired to write this book when I began teaching my own vertebrate evolution and paleontology course for undergraduate students. What I found was that many of these students were fascinated by vertebrate evolution, but that few, if any, went on to careers in museums and academe. Instead, many of my students were future teachers, doctors, veterinarians, and perhaps even politicians. There are many excellent books available on vertebrate paleontology, many of which I consulted in writing this book, but their focus tends to be strongly taxonomic and linearly chronological: who is who, who is related to whom, and in what order do we find them. However, the books that had truly inspired me to become a paleontologist were those that tackled the issue of functional morphology and paleobiology: what does the skeleton tell us about how the animal moved, fed, and behaved? This is the type of questions that motivated me as a student to learn about vertebrate history.
During my undergraduate days, I stumbled upon a small book called The Evolution of Vertebrate Design by the late paleontologist Leonard Radinsky that would truly influence my approach to writing. Radinsky took a complex subject like vertebrate paleontology and, using cartoons and brief but informative language, distilled the essence of our evolutionary story into a format that was friendly and approachable. In fact, I initially used his book in my vertebrate paleontology and evolution courses because it served as a jumping-off point for exploring the rich tapestry of vertebrate life past and present.
Given that Radinsky passed away in 1985, his beautiful book was never updated. Despite its appeal to my students, with each passing year the stack of articles I was assigning to supplement the understandably dated material was becoming larger than the book itself! Simultaneously, as my research developed into understanding the evolution of dinosaur locomotion, I was beginning to question why I had never paid more attention to classical mechanics in my physics courses. When I took physics, I found the course to be absolutely dull and dry. However, if you can understand the way that the machines and tools that surround us in our daily lives work the way that they do, you can approach the skeleton the same way. And then I thought, what if I tried to write a book about the evolution of the vertebrate skeleton as if I were someone trying to teach my younger self about classical mechanics and physics? Using Radinsky’s book as an inspiration and launch point, I began writing the book now being published: what I hope is a friendly but somewhat unconventional introduction and exploration of the history of the skeleton, using machine metaphors, for those who want to learn but do not (yet) have the chops for anatomy.
Why should you buy this book? Among many reasons, the best is probably that I have included a figure of a cat overturning a Prius.
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Dr. Bonnan to give free dinosaur presentations at Southern New Jersey libraries

A short post to let all interested New Jersey parents and their children know that I will be giving a series of free dinosaur presentations at libraries throughout Atlantic County this July, 2014!  My presentations consist of fossils, bones, and dinosaur artwork featuring dinosaurs selected by audience members!

Check out the attached PDF link and poster below, and see when I’m coming to a library near you!

Atlantic County Library Presentations PDF Schedule 2014

Bonnan_Dinosaurs_July 2014

What lies beneath the cartilage just might help you become a giant dinosaur

Figure 7 from our PLOS ONE paper -- This figure conveys the essence of our conclusions: as mammals become giants, their joints become ever more congruent with thinning articular cartilage.  For dinosaurs, the cartilage remains thick and the joint region expands.

You can read the paper for free by clicking here.

As I recently learned from a fall in which I broke one of my ribs, gravity is an irresistible force.

My poor broken rib.

My poor broken rib.

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).

The average dinosaur (excluding birds) weighed in at over 1 ton, whereas the average land mammal barely tips the scales at 1 kilogram. (c) 2013 M.F. Bonnan.

The average dinosaur (excluding birds) weighed in at over 1 ton, whereas the average land mammal barely tips the scales at 1 kilogram. (c) 2013 M.F. Bonnan.

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.

By Bonnan after Carter & Beaupre (2001) and Holliday et al. (2010).

Dinosaurs share the primitive tetrapod condition of retaining thick cartilaginous joints.  Diagram by Bonnan after Carter & Beaupre (2001) and Holliday et al. (2010).

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.

Figure 3 from our PLOS ONE paper -- On the X-axis, the sub-articular bone region narrows significantly with increasing size, and the shapes of these regions become more convex and/or distinct.

Figure 3 from our PLOS ONE paper — On the X-axis, the sub-articular bone region narrows significantly with increasing size, and the shapes of these regions become more convex and/or distinct.

Figure 5 of our PLOS ONE paper -- .  In particular, the sub-articular region expands tremendously whereas its overall shape remains gently convex.

Figure 5 of our PLOS ONE paper — . Along the X-axis, the sub-articular region of the humerus expands tremendously whereas its overall shape remains gently convex.

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.

Figure 7 from our PLOS ONE paper -- This figure conveys the essence of our conclusions: as mammals become giants, their joints become ever more congruent with thinning articular cartilage.  For dinosaurs, the cartilage remains thick and the joint region expands.

Figure 7 from our PLOS ONE paper — This figure conveys the essence of our conclusions: as mammals become giants, their joints become ever more congruent with thinning articular cartilage. For dinosaurs, the cartilage remains thick and the joint region expands.

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 [2012]).  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.

My poor broken rib revisited.

My poor broken rib revisited.

You can read the paper, for free, here.

My Co-authors

This study would not have been published without the help and perseverance of my co-authors.

RayWRay 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 SimonMform 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.

AdamYAdam 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.

ChristineGChristine 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.”

AdamAAdam 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.

Acknowledgments

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.

References

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.

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

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

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

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

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

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

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

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

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

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

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

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

The Visit to Brown University

Radha Varadharajan at Brown with Beth Brainerd.

Radha Varadharajan at Brown with Beth Brainerd.

After spending five valuable days at Brown University, Dr. Matthew Bonnan and I learned a great deal about C-arm fluoroscopes and with XROMM technology. The early stages involved getting accustomed to the protocols of working with the fluoroscopes. This step was pivotal for the machines emit an innocuous but not neglible amount of radiation to capture the motions of our rats: Pink, Floyd, Evan, Rudy, Harry, and Taylor.  Personally, the pinnacle of the visit to Brown can be identified as the days the rats walked across the beam. With much guidance from both me and Dr. Bonnan, our furry test subjects were cajoled across the plank or dowel. Although Dr. Bonnan was the primary coaxer of our scampering participants, I was also able to give a hand in guiding them.

Within a few days into the visit, I was amazed with the advanced technologies at Brown. Comprehending the process of how the fluoroscopes operated was especially intriguing. Because I was able to accompany Dr. Bonnan on this trip to Brown University, not only did I understand the innovational technology that is XROMM, but I was also able to contribute in the smallest way possible in understanding the evolution of forelimb posture.

Here is Radha coaxing Pink the Rat through the X-ray beams.

Here is Radha coaxing Pink the Rat through the X-ray beams.

I would like to conclude this post by expressing my utmost gratitude to numerous individuals that allowed for my collaboration. My involvement in this educational visit would not have been feasible without the generous contribution of Dr. Robert Fine; Dr. Fine’s munificent gesture solely funded my trip. I would also like to thank Dr. Elizabeth Brainerd and Dr. Angela Horner for their guidance. Finally, I would like acknowledge Dr. Bonnan for his unceasing support.  Without his patience, I would not have been able to discover the numerous benefits of researching in such a compelling field.

Rodents of usual size and their moving skeletons

Harry, one of the rats in our trials, walking through the X-ray beams.

Harry, one of the rats in our trials, walking through the X-ray beams.

The past week at Brown University’s C-arms XROMM lab was so busy I haven’t had a moment to post about our research experiences until now.  If you’re just catching up, please see my previous post on our setup.

This was certainly a new but fascinating experience both for me and my student, Radha.  With help from Dr. Beth Brainerd and Dr. Angela Horner, we learned how to coax the rats to walk a plank of wood between the two X-ray emitting “cans” of the positioned C-arm fluoroscopes.  At one end of the room is a bank of two computers connected to each high-speed camera and C-arm.  When the rats were doing what we were interested in, a push of a floor pedal turned on the X-rays and recorded the ensuing stream of images which were then converted into standard computer movies.

Walk the plank - each rat walked across this plan between the C-arm fluoroscopes to a hidey-hole box we nick-named the Rat Haven.

Walk the plank – each rat walked across this plank between the C-arm fluoroscopes to a hidey-hole box we nick-named the Rat Haven.

Dr. Brainerd helping Radha and I to capture the X-ray data.

Dr. Brainerd helping Radha and I to capture the X-ray data.

Radha Varadharajan at C-arms lab

Here is Radha Varadharajan capturing and recording the X-ray movies that will be the foundation of our study.

Angela Horner has been working with rats for years, and her experience in motivating these little mammals was a godsend — from Wednesday to Thursday, Radha and I learned from her experience and were able to collect loads of data that will allow us to begin reconstructing their locomotor and postural movements in 3-D.

Here, Dr. Angela Horner is motivating the rat Harry to walk the plank through the X-ray beams.

Here, Dr. Angela Horner is motivating the rat Harry to walk the plank through the X-ray beams.

Radha and I both had opportunities to coax the rats across the plank to the Rat Haven as well.  You will notice we named our rats.  Two of them were dubbed Pink and Floyd as a nod to one of my favorite bands who also featured cartoon rats in their backdrop movie for “Welcome to the Machine.”  Yeah, we’re geeky like that.

Here I am holding one of the rats we named Evan.  Evan was a bit "lazy," but ended up being great at walking a narrow dowel, helping us to see forearm movements in detail.

Here I am holding one of the rats we named Evan. Evan was a bit “lazy,” but ended up being great at walking a narrow dowel, helping us to see forearm movements in detail.

Here is Radha coaxing Pink the Rat through the X-ray beams.

Here, Radha is coaxing Pink the Rat through the X-ray beams.

Want to see a sneak-peak of the end result of our labors?  Here is one clip of Harry the Rat.

We are especially grateful for all the help we had this past week, and among many others Erika Giblin and Ariel Camp were invaluable in providing access and assistance with all of our XROMM issues.  Thank you everyone!

An old dinosaur learning new tricks

Okay, so I’m the “old dinosaur” here, although I was informed recently that I could still pass as a graduate student.

I am happy to report that I am back on the campus of Brown University this week with one of my undergraduates, Radha Varadharajan, to begin what I hope to be the first in a long series of studies on the evolution of amniote (reptile, bird, mammal) forelimb posture.  We (my “rat pack” students and I) are using the XROMM technology I have detailed here on this blog to understand how the three-dimensional movements of the forelimb bones of rats actually occur.  The long-term goal of this initial study is to document how these movements facilitate hand placement and posture, and how these details of locomotion are related to bone shape.  My ultimate goal is to use the somewhat primitive forelimb posture of rats as a template to understand how some early fossil mammals may have moved.

Today, Radha and I, under the tutelage of Dr. Elizabeth Brainerd, began the process of setting up the so-called C-arm fluoroscopes that will allow us to take calibrated X-ray movies of a number of rats as they walk, run, and perhaps do other activities that we happen to capture.  This was especially exciting and informative for me, because these are the “new tricks” this “old dinosaur” wants to learn.  Tomorrow, we begin in earnest filming the skeletal movements of the rats.

You will notice in the pictures posted here that Radha and I are suited up in lead aprons and thyroid collars because, as you might anticipate, we do not want to expose ourselves to X-ray radiation during the data capture.  In fact, she and I have participated in numerous safety trainings and tests to ensure we stay safe.

Here I am behind the two C-arm fluoroscopes.  In front of the scopes, you can spy the wooden plank walk-way for the rats, and an acrylic box that the rats will walk or run through in the vicinity of the X-ray fields.

Here I am behind the two C-arm fluoroscopes. In front of the scopes, you can spy the wooden plank walk-way for the rats, and an acrylic box that the rats will walk or run through in the vicinity of the X-ray fields.

Here is Radha learning x-ray capture at the Brown C-arms lab.

Here is Radha learning x-ray capture at the Brown C-arms lab.

We also spent time today with Dr. David Baier learning how to set up what is called a rig in the MAYA software program that will later animate the skeletons of the rats we film.  Essentially, a rig in this case means creating a joint system that can be calibrated with the X-ray films and “attached” to the 3-D bone geometry from CT-scans of the rats used in the study.  I further shook some of the rust out of my head reviewing and practicing how to import calibrated data from X-ray digital movies and syncing them with 3-D bone geometry — skills I first acquired almost one year ago during Brown’s 2012 XROMM course.

All of this setup and learning is key for me and my students, not only because we want to do the science right, but also for other reasons I shall divulge in future posts.

Everyone at Brown has once again been incredibly helpful, and I am especially indebted to Dr. Brainerd for her encouragement and help over the past year with XROMM.

Please stay tuned … this week promises to get more interesting …