Jurassic World: Not About Science

As a dinosaur paleontologist, I was perhaps duty-bound to see Jurassic World … that and my 10-year-old daughter was keen to see it as well. I am teaching a freshman-only seminar on dinosaurs this fall, and that also made the choice to see the movie a no-brainer. I had only seen one or two brief previews of the movie and had avoided reading reviews of the plot so I could go into the movie with as few preconceptions as possible. Here are my thoughts.

Before I start, let me say that this is not a review of the story or much about the accuracy of the science. That has already been done in multiple ways by many of my colleagues in the dinosphere. There is not much new I could add there.  Therefore, there are no spoilers here unless you consider what is shown in the movie previews as spoilers.

I was not surprised and kind of disappointed by I what I saw. In a sentence: it was a monster movie and not a movie about dinosaurs or science. There were no paleontologist characters in the movie, and the dinosaurs were there to devour people and cause mayhem or serve as background. As anyone would know from the movie previews, this is again a retread of technology gone wrong and hubris. No one should be surprised by the basic plot and its outcome.

So here is my question: since this movie is clearly not about science and is, like the original Jurassic Park, yet another Frankenstein story, why should we as scientists care how accurate is? And I ask this question because we dinosaur paleontologists suffer from a public image problem. We are often considered to be kids who never grew up, but not “real” scientists. I am the first to admit that my fascination with dinosaurs started early, and that many of us have a friendly competition to see who was interested in dinosaurs the earliest. It does come with a certain badge of honor. But I think that outside of our small group, this doesn’t often help us be taken seriously.

I suppose, for example, one could point to someone like Neil DeGrasse Tyson, arguing that he engages the public with his take on science-fiction movies. But even here astronomy and physics have more science “street cred” than dinosaur paleontology. Tyson can let his nerd flag fly, so to speak, without much “damage” to the reputation of physics because his science is “the” science in the mind of the public. Nobody (sane) argues about gravity. Everyone, though, is happy to argue with dinosaur experts about what they think dinosaurs were like … perhaps in part because we all know the science is done by big kids who aren’t real scientists.

I agree and empathize with many of my colleagues that dinosaur movies often miss an opportunity to educate the public about science as a process as well as entertain. But I also think we tread a fine line here — one that may inadvertently only reinforce the stereotype of the nerdy (read “child-like” and “out-of-touch”) dinosaur paleontologist when we engage the “science” of a movie that is clearly not about science at all. This stereotype of the “big kid” dino-nerd is more damaging than just reputation. For example, the recent attempt to sell the privately-owned “Dueling Dinosaurs” was predicated on the identity of one of the dinosaurs as Nanotyrannus. Even when an expert on tyrannosaurids like Thomas Carr pointed out in great detail why Nanotyrannus is not real, it is perhaps easier to ignore his expertise in favor of profit partly because of the “big kid” stereotype.

My suggestion would be, rather than engaging the press in the predictable “this and that were wrong” conversation, why not simply say, “this is science fiction and a monster movie and it doesn’t represent paleontology.” Jurassic World is about as close to dinosaur paleontology as Star Wars is to astronomy. These movies can be inspiring to children and adults, but their main focus is a story, its plot, climax, and resolution, not scientific accuracy. And the sad part about Jurassic World is that the missed opportunity is less about the science (which is relatively non-existent) and more about the tired re-hashing of gender stereotypes and hubris/comeupance plot lines.

Dinosaur paleontology, for those of us who are experts, is a rigorous science with many insights to offer us in the present. And, yes, many of us have been enraptured with this science since childhood. There is nothing wrong with that. But understanding how stereotypes about our science and about us as scientists play in the larger world are equally important to recognize. We have an important message about the past and our future to impart to the public. Let’s not dilute our energies on the trivial details of an expensive and silly monster movie.

New interview on Prehistoric Pub

Just a brief post to point those interested to my interview with Jersey native and paleontology enthusiast Gary Vecchiarelli: http://prehistoricpub.blogspot.com/2015/05/science-sunday-with-paleontologist.html

Thanks for the interview, Gary!


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.

Sauropod forelimbs -or- why I was wrong -or- why I do research

An in-press, open access paper by Joel Hutson extensively cites my Bonnan (2003) paper while developing a hypothesis that quadrupedal dinosaurs did not evolve fully pronated forearms.  Hutson suggests, correctly, that the hypothesis linking hand morphology and pronation in Bonnan (2003) is falsified.  I agree.  I also agree with Hutson that dinosaur forearms are best understood in the context of other non-mammal tetrapods, and I agree that mammalian-style (and chameleon-style) pronation of the hand was not possible in known quadrupedal dinosaurs.  But I take issue with the tone of Hutson’s paper, and for what I think he misses about the process of science.  To put this in context, first a little history:

As odd as it may seem, the forelimb posture of quadruepdal dinosaurs is anything but settled.  This is due to several reasons, chief among them being that a large amount of articular cartilage encapsulated the ends of the long bones (see here and here, for example).  Since this tissue is rarely preserved, determining how the elbows and shoulders of dinosaurs went together, let alone their possible ranges of movement, is difficult to determine at best.  This makes determining how the bones were oriented in life difficult to resolve.  Regardless of how much cartilage was or was not there, a dinosaur forearm and that of a large, quadrupedal mammal are different.  Without going into a long, drawn-out discussion on the subject, suffice it to say that, like other archosaurs, the radius and ulna of most quadrupedal dinosaurs lie parallel to one another.  If the forearm was held as a relatively vertical support structure, it is difficult to envision how the hand would be pronated so that it moved in synchrony with the foot.  Large mammals accomplish this by significant crossing of the radius over the ulna: this turns the hand palm-side down (pronation) and essentially allows it to work effectively in tandem with the foot to push the animal forwards.  In other words, an elephant hand and foot push in the same direction.

In graduate school (mid-to-late 1990s), I noted what I believed were inconsistencies: 1) sauropod trackways show that the manus is often pronated (although not quite as much as mammals and certainly the palm did not face directly backwards); 2) the forearm bones articulated like they do in other archosaurs, like alligators, that cannot assume an upright, columnar forelimb posture with a pronated hand; 3) quadrupedal dinosaur forelimbs were often restored with the radius crossing the ulna to some degree, which cannot occur when you articulate the bones together.  In essence, there appeared to be a mismatch between trackways and bone morphology.

It had been well-known that the hands of most sauropods were a vertically-oriented, tubular metacarpus (palm) with stubby fingers and sometimes a large thumb claw, whereas the hind feet were more what you might expect in a big animal: a large foot spread across a fat pad.  Why the difference?  I began to notice that when the radius was articulated with the ulna, it was cradled on either side by ulnar processes at the elbow.  One of these processes was not present in “prosauropods,” theropods (including birds), and crocs.  It occurred to me that, perhaps, the radius had shifted internally in the forearm relative to the ulna, and this “new” process (the craniolateral process) evolved to buttress the humerus where the radius once resided ancestrally.  If the radius had shifted medially, this would further “drag” the hand into pronation.  There was also a lot of cool Evo-Devo stuff going on at the time, and I was absolutely enraptured with the concept of the digital arch that forms the hand in embryos.  Since this arch forms from the ulna side and spreads to the radius side, I hypothesized that a shift in radius position internally could bend the hand into a U-shaped structure.

I published on this in the Journal of Vertebrate Paleontology in 2003, and it is one of my most cited papers.  It was, to the best of my knowledge at that time, the simplest “solution” to two “problems” — pronation of sauropod hands and their U-shape.

Needless to say, a lot has happened since 2003.  Many, many more sauropods and “prosauropods” have been discovered, and other well-known species have been re-described.  In my 2003 paper, I predicted that when the earliest sauropods were found, if they had an ulna with a craniolateral process that hugged the radius, they should also have a U-shaped hand.  You know what?  I was wrong.  My first excursion out to South Africa cinched it for me — I got to examine the forelimb of Melanorosaurus, either an almost-sauropod or a basal sauropod.  That one animal blew up my hypothesis — it had a craniolateral process on the ulna, but a flattened hand.  End of story. Done.

Well, sort of.  Adam Yates and I published on the forelimb of Melanorosaurus in 2007, and we drew attention to this issue.  We suggested that the radius might still have shifted proximally at the elbow, but that it did not directly and radically effect the hand.  We suggested that the U-shaped hand seen in most “classic” sauropods evolved after this shift and may have enhanced pronation by assuming a U-shape.  But we definitely stated that the Bonnan (2003) hypothesis linking the possible shift in the radius and the U-shaped hand was falsified.  As we stated in the abstract for that paper:

The forelimb morphology of Melanorosaurus suggests that pronation of the manus occurred early in basal sauropods through a change in antebrachial morphology, but that changes to the morphology of the manus followed later in eusauropods, perhaps related to further manus pronation and improved stress absorption in the metacarpus. Thus, we conclude that changes to antebrachial morphology and manus morphology were not temporally linked in sauropods and constitute separate phylogenetic events.

So, to return to Hutson’s paper, I was surprised that he is apparently unaware of the Bonnan and Yates (2007) paper on Melanorosaurus where we clearly say, yes, there probably was no direct link between pronation and U-shaped hands.  Again — the hypothesis put forward in Bonnan (2003), based on what was available and known at the time, is falsified, so far as the U-shaped hand and radius-shift are concerned.

I was also surprised that Hutson claims, for example, that I formulated my original hypothesis within a restricted phylogenetic context.  At the time, I had dissected and studied bird and reptile forelimbs, and also examined and articulated where possible the forelimbs of “prosauropods” and theropods, and had examined a variety of mammalian forelimbs — keep in mind, this is all before it was feasible to easily digitize and manipulate sauropod dinosaur skeletons.  I reference all of these taxa in additional to numerous sauropods in my study.  To suggest my hypothesis was developed within a restricted phylogenetic context is specious.  Hutson also suggests that I was unaware of the plesiomorphic condition for pronation in tetrapod forelimbs.  I will leave that to my readers and to the scientific community to judge.

Throughout the paper, Hutson uses phrases like “Bonnan reasoned …,” “Bonnan relied upon a suggestion …,” and so forth that imply I did not examine material first-hand.  I did, and spent many many months and years agonizing over what I had examined, articulated, and dissected.

I could go on, but my point is this.  Science proceeds by making hypotheses, testing them, putting that through the process of peer-review, and the allowing the scientific world community to continue to test and modify those hypotheses.  As a scientist, you are going to be wrong, and wrong a lot.  Over time, new data are going to emerge, new approaches will crop up, and new eyes will look at old bones.  You do the best you can with what you have, but you can’t let perfection be the enemy of progress.  No paper and no study is perfect — hypotheses will be overturned.  If we waited to publish when everything was perfect, nothing would be.

When your hypotheses have been falsified, it is okay to admit that.  In 2007, that is precisely what Adam Yates and I did — we said, yep, Bonnan (2003) got some things wrong because we now have better data, and the data don’t agree with that hypothesis anymore.  And you know what?  That is going to keep happening — scientists evolve past their older papers, and science is self-correcting.  If I were still trumpeting from the hills that my Bonnan (2003) article was totally correct and unassailable, the scientific community would be right to castigate me in light of all the new data.

So I think Hutson misses the point.  There are statements in his paper such as, “Unfortunately, pronation research has suffered from a lack of awareness that semi-pronated forearm anatomy is plesiomorphic to Archosauria, and indeed all tetrapods.”  I know many colleagues who spend an inordinate amount of time carefully collecting and examining data from fossils and living animals.  The issue is not one of ignorance or lack of awareness, but one of difficulty — it is damn hard to elucidate evolutionary patterns of forelimb posture because of so many contingencies.  I have grown to appreciate these even more as I’ve ventured into collecting kinematic data on live animals.  It ain’t easy, and it never will be perfect.

I wish nothing but the best for Hutson and his future studies on what is admittedly an intriguing evolutionary history among the archosaurs. I do hope that he remembers, when his hypotheses are ultimately changed or falsified, that this is the process of science — and that that’s okay.

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

Now the circle is complete -or- a belated dinosaur Christmas gift

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:

Aardonyx in Highlights Magazine

Aardonyx in this year’s Highlights for Children Magazine (summer of 2013) – artwork by Robert Squire. Kindly sent by Andy Boyles. Published with permission of Highlights for Children, Inc.  Any formatting anomalies are due to converting a PDF to a JPEG — i.e., they’re my fault.

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.

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.


We thank the many institutions and individuals that provided us with access to specimens for this study.  I cannot possibly list all of them here: much of the archosaur data was collected for previous studies (Bonnan, 2004, 2007; Bonnan et al., 2008, 2010)  and the heartfelt thanks and appreciation expressed in those references continues more strongly than ever here.  For the present study, we wish to thank the following institutions and staff: AMNH: N. B. Simmons and staff (Mammalogy), J. Meng, J. Galkin, and staff (Fossil Mammals); FMNH: W. Stanley and staff (Mammalogy), K. D. Angielczyk, W. Simpson, and staff (Fossil Mammals); UNMH: R. Irmis, M. Getty, and staff; CLQ: M. Leschin; SAM: A. Chinsamy-Turan and staff; BPI: B. Rubidge and staff.  We thank Kimberley Schuenman at WIU for collecting data on felids used in this study.  Feedback from Gregory S. Paul, Henry Tsai, and Stephen Gatesy at the 2012 Society of Vertebrate Paleontology meeting further improved our manuscript.  Discussions with Jason Shulman at the Richard Stockton College of New Jersey on static physics were helpful.  Donald Henderson and an anonymous reviewer provided useful comments, critiques, and suggestions on a first draft of this manuscript.  We are also indebted to PLOS ONE editor Peter Dodson for shepherding our manuscript through the PLoS system, and his feedback, comments, and suggestions.

Last but not least – a great big thank you to my new employer, the Richard Stockton College of New Jersey, for helping with publication costs!  Thank you Stockton and the Grants Office, particularly Beth Olsen!

 An Important Aside on Methods and Why We Did What We Did

  • We chose to focus on evolutionary lines of mammals and dinosaurs that gave rise to the very largest land species.  For mammals, we focused on the placental (eutherian) lines called Afrotheria and Laurasiatheria because elephants and Paraceratherium, the giant rhino relative, descended from these.  For dinosaurs, we focused on the Saurischians because the giant, long-necked “brontosaurs” called sauropods were members. We also selected smaller-bodied relatives of these giants in their family trees to examine how similar or different the sub-articular zones of these giants were to their smaller relatives.  To analyze shape, we used a computer program called Thin-Plate Splines that tracks and compares landmark coordinates on bones.
  • Because bony landmarks and sub-articular surfaces were not always anatomically homologous between archosaurs and mammals, we avoided issues of mixing non-homologous areas in our data by running the analyses on these two groups separately.
  • Why did we use a two-dimensional analysis instead of a three-dimensional analysis?  Undoubtedly, three-dimensional shape analysis would have further enhanced our interpretation of sub-articular shape patterns.  However, a number of challenges prevented such an approach:
    • First and most significantly, the data collected in this study span a period of over 10 years during which time cost-effective and portable three-dimensional scanning technologies for acquiring large bone geometries have only recently started to become available.  Had we access to these technologies ten years prior, we would have utilized them, as we plan to utilize such approaches in future studies.
    • Second, our main goal in this study was to quantify whether or not there were significant differences in the scaling patterns of surface morphology between eutherian mammal and saurischian dinosaur long bones, and whether such differences were correlated with known differences in articular cartilage properties.  We emphasize that our goal was not to realistically recreate joint surfaces or establish precise measures of joint articulation, nor do we propose how the three-dimensional shape of the subchondral bone is used to reconstruct joint geometry.  Our selection of the humerus and femur furthers our goal: these are long bones in which a significant portion of the subarticular surfaces can be reliably captured and interpreted in two dimensions.
    • Finally, third, two-dimensional data is valuable, comparable to previous studies, and provides a good first-level approximation of scaling patterns.  Just as linear morphometrics informed and directed the study of two-dimensional geometric morphometrics (GM) of long bones, so, too, can two-dimensional GM illuminate where future three-dimensional GM studies can make the best impact.  Our study is certainly not the last word on long-bone scaling and subarticular patterns in non-avian dinosaurs.  Rather, we hope it inspires and provides the basis for research incorporating three-dimensional technologies in years to come.


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