Dead dinosaurs and reasons for hope

“Time will turn us into statues, eventually.”

– Saint David Grohl, a fighter of foo

As we enter this time of the holidays in the United States, many of us become reflective on the year and take stock of our lives.  For my family and I, this year has been absolutely wonderful, dreadful, fantastic, unnerving, scary, and hopeful.  Why?  There has been a lot of change in our lives: see my lonely post from September for more details and my farewell to my previous institution.  This would also explain my dearth of blog posts, although a weird and interesting topic snuck in this November.

I am also finishing my dinosaur course here at Stockton, and that means I give my final lecture on “What I hope you have learned from dinosaurs.”  It struck me today that this would make an excellent little blog post as well.

One of my grandfathers was fond of asking me, “Why study dinosaurs?  What’s the point?” When you are asked that question enough times, you eventually develop a repertoire of answers.  I don’t know if these ever satisfied him, but I do hope they satisfy those willing to listen:

There are the Big Picture Reasons:

• First off, dinosaurs are just so damn cool.  Those who need convincing haven’t been paying much attention to the plethora of amazing discoveries that have continued at an ever-accelerating pace since the late 1800s.
• Dinosaurs put our place in the world into perspective – this is not a world meant for us, but one we have had the happy fortune to inherit from previous generations of life.
• Dinosaurs were the most successful group of terrestrial vertebrates the world has seen … and they are still among us as beautiful, feathered treasures.  Oh, birds are not dinosaurs?  Like the Honey Badger, the data don’t care … and the support for birds as dinosaurs is as overwhelming as the data for humans as mammals.

And then there are the Practical Reasons:

• Dinosaurs are the perfect ambassadors for science – they bring scientific concepts and the nature of science to children and the public like nothing else I know.
• While the doctors and veterinarians of the world are busy saving those people and pets you love, the vertebrate paleontologists are in the trenches at the universities and colleges, teaching the next group of practitioners their anatomy.  That’s right – most vertebrate paleontologists are excellent anatomists.  A certain Larry Witmer comes to mind …
• Want to understand why vertebrate anatomy is the way it is?  Ask a vertebrate paleontologist – we have to know all that embryology and evolution stuff to inform our research and to blow your mind. =)  The bottom line has always been the anatomy is the result of embryology and evolution … who better to teach that we dinosaur-o-philes?  And so that I’m being fair – all vertebrate paleontologists are this excellent, not just the dinosaur ones!

Yes, you say, but we’ve heard these platitudes before.  You spoke of hope … where is that?  If dinosaurs have taught me nothing else, it is an appreciation for human life.  As successful as dinosaurs were, their Encephalization Quotient (their EQ, or brain size) was never too generous.  We mammals, on the other hand, have had the evolutionary fortune of inheriting a rather different brain with a typically much higher EQ.  To be fair, the birdy dinosaurs around us have enlarged brains compared to their predecessors.

Why is EQ size a reason for hope?  Well, EQ by itself is not, but it is what we Homo sapiens do with it that is.  I am no anthropologist, but speaking in general terms, here are two things one can say about humans that cannot, so far as I know, be applied to other vertebrate animals:

1. We can both anticipate the future and act on it.
2. We can use imagination to bring positive things into concrete existence.

For all of their significance and success, the non-avian dinosaurs could not have anticipated their demise, nor could they have done anything to act on it.  Apart from ancient aliens imbuing dinosaurs with a sense of imagination (I can imagine a particular channel of history losing all its credibility), these mighty animals could not have brought forth everything from medicine to concepts of social justice.  As a species, we are certainly still working on a lot and have a long, long way to go, but have you ever stopped to think of how unbelievably special and unique it is that we can act on knowledge and create our future?

So this holiday season, and throughout the year, I hope you may reflect on the fact that whereas for non-avian dinosaurs history’s lessons were inaccessible, they are very much an open book for us.  If we can anticipate what the future will bring, we can act on it.  If we decide to put our imagination to good use, we can create positive change in the world.

The non-avian dinosaurs could not learn from their past, but perhaps we can learn from them … and from our own ancestors.

“So have a toast and down the cup, and drink to bones that turn to dust.” — Oingo Boingo (Danny Elfman’s rock band)

Danny Elfman, creator of the Simpson’s Theme Song, can’t be wrong …

References

Fastovsky, D. and Weishampel, D. 2009. Dinosaurs: A Concise Natural History. Cambridge University Press. 379 pp.

Let’s face it: birds are dinosaurs -Part 3-

In the last two posts, I outlined many of the reasons why birds and dinosaurs have been “estranged” and are now being reunited as members of the same clade: Dinosauria.  If you haven’t read these first two posts, check them out:

• Part 1
• Part 2

So, at this point if you’re still not convinced that birds are indeed the living dinosaurs among us, here is one more thing to consider.  Let me take you by the hand …

Embryologists who have studied the development of bird embryos for decades have always come away from studies of their hands with the following conclusion: five initial digits form in cartilage (technically called anlagen), but after awhile, only the three middle digits remain.  Technically, we number digits from the thumb out to the little finger.  So, your thumb would be digit I and your little finger would be digit V.  In birds, the three remaining digits that fuse into the hand are II, III, and IV.  Okay, great, so what?

So this: the earliest predatory dinosaurs had five digits, but the main three digits were I, II, and III, not II, III, and IV.  In fact, during predatory dinosaur evolution, digits IV and V decrease in size until all that is left are I, II, and III.  This contradiction between the digit identities of bird hands and predatory dinosaur hands has been held up as the ultimate “proof” that all the amazing similarities between birds and dinosaurs are just that: amazing convergence.

Enter the past two decades of embryonic science, studies of evo-devo (evolutionary development), and a proliferation of studies combining old-school developmental anatomy with new-school gene studies.  It turns out that the digit identities in the hand are not set like permanent blueprints, but develop from the expression of various developmental genes to concentrations of various proteins.  Without going into great detail, we now know that the identity that digits assume (that is, whether they become I or V or something else) depends on how much of a concentration of particular proteins these regions of the hand were exposed to during development.  Simply put, higher concentrations of certain proteins trigger genes that, when transcribed and translated (i.e., expressed), ultimately create proteins that form digit I, II, III, IV, or V.

Intriguingly, this means that the relative position of a digit in the embryo’s hand and what that digit actually becomes are different.  In other words, a digit in position II could become a digit I if the concentration of various proteins and the expression of certain genes are changed.  This has been called the Frame-shift Hypothesis.  In this case, the “frame” is the region of gene expression that gives digits their identities, whereas the how this gradient moves in the developing hand is the “shift.”  What this all means is that just because you develop a digit in your hand where digit II should be doesn’t at all guarantee that it will become digit II.  It might become digit I, for example, depending on the frameshift.

What this all means is that, hypothetically, at some point during predatory dinosaur evolution, the anlagens that were in positions II, III, and IV frame-shfited to I, II, and III.  This frameshift would, of course, “solve” the digital confusion between birds and dinosaurs, but of course this hypothesis has been questioned and there was no fossil evidence of it occurring in dinosaurs … until recently.

A new Jurassic ceratosaur (a primitive type of predatory dinosaur) from China called Limusaurus preserved a complete hand that looks like an embryonic bird hand!  See for yourself: Figure 2 in their paper.  Now, compare that figure of the ceratosaur hand back to the ostrich hand.  I find this absolutely fascinating and was floored to see a dinosaur hand that looked like something undergoing the hypothesized frameshift.  Here, captured in stone for millions of years, is what you would predict to see in a transitional form going from the primitive predatory dinosaur digit arrangement to the birdy one.  Note in the Limusaurus hand figure that where the first digit is is a splint, like in a bird embryo, and next to that, the digit in the typical place of digit II, is something that looks an awful lot like digit I.

So, to conclude my thread, let me say that it is not at all parsimonious at this point in time to separate birds from dinosaurs.  That is equivalent to separating you from mammals.  It is no longer enough to argue that all the similarities between dinosaurs and birds are due strictly to an amazing amount of convergent evolution.  We have unique skeletal features only birds and dinosaurs share, we have dinosaurs that could not possibly fly possessing feathers, and we even have fossil support to explain why bird and dinosaur hands match up after all.

And finally back to the recent paper that inspired this thread in the first place: Birds have paedomorphic dinosaur skulls.  Paedomorphosis is the retention of juvenilized features into adulthood.  In other words, the proportions of the larva, infant, or juvenile remain relatively unaltered as adults.  This occurs a lot more often in nature than you may realize.  Essentially, the scientists Bhullar and colleagues used a shape analysis technique I have used myself: geometric morphometrics.  This technique analyzes changes in bony landmarks across numerous specimens and provides a mathematical test to see whether the changes predicted are actually significant.  What Bhullar and colleagues discovered was that bird skulls grow as if they were juvenilized dinosaur skulls!  Yet another nail in the coffin (scientifically) for the vague claim that birds cannot be dinosaurs.

Let’s face it: birds are dinosaurs.  I emphasize that I say this in the scientific sense of “certainty.”  Although we can’t be 100% certain in science, these data show overwhelmingly that birds are part of the dinosaur family tree.  When you realize that there are over 10,000 species of living birds but only 4600 or so species of living mammals, you realize it is still the Age of Dinosaurs after all.

Let’s face it: birds are dinosaurs – Part 2 -

To continue from the last post, where were the feathered dinosaurs?  And how did paleontologists begin to reconcile that birds and dinosaurs should start to come together again in their family tree?

Throughout the 1970s and 1980s, the hypothesis of a dinosaur-bird relationship was revived in part because of re-study of the Archaeopteryx specimens, the discovery of the “raptor” known as Deinonychus, and a new approach to understanding evolutionary relationships called cladistics.

Archaeopteryx and Deinonychus are known and discussed in great detail in many sources.  Suffice it to say John Ostrom, among others, began to notice striking skeletal similarities between Archaeopteryx,Deinonychus, and dinosaurs generally.  It was eventually recognized that there are a number of special, shared traits that only seem to occur together in birds and dinosaurs, and especially among predatory dinosaurs and birds.  I could provide a substantial list, but here are a few, selected key features:

• A fully erect stance where the shaft of the femur (thigh bone) is perpendicular to the femoral head. (Incidentally, the femoral head points inwards towards the pelvis, and this allows the femur to be held vertically.)
• The ankle is a modified mesotarsal ankle joint.  What this means is that the proximal and distal ankle bones form a cylinder-like roller joint between themselves.  You can see the upper part of this roller joint at the end of a chicken or turkey drumstick, and you also see it in dinosaurs.
• Predatory dinosaurs and birds have specialized, hollow bones.
• Predatory dinosaurs and birds have a three-fingered hand, and Archaeopteryx has a clawed, three-fingered hand with deep ligament pits, just like other predatory dinosaurs.
• A large majority of predatory dinosaurs are classified as tetanurans, and it has been discovered that the tetanuran predators and birds have a furcula.  Despite earlier suggestions to the contrary, many dinosaurs have clavicles and furcula.
• Coelurosaurs are predatory dinosaurs with specialized wrist bones that allow the hand to swivel sideways.  In other words, the hand doesn’t flex and extend, it rotates sideways towards the ulna.  Guess what other group of vertebrates has this specialized wrist? Birds!
• Within coelurosaurs are the maniraptorans, the predatory dinosaurs that include Deinonychus and the now universally-knownVelociraptor.  These dinosaurs have highly flexible necks, elongate forelimbs, and the ulna is bowed outwards — the only other vertebrates with these features? Birds.

These observations, while powerful on their own, really started to hit home when placed within a scientifically-testable framework called cladistics.  In a nutshell, cladistics relies on special, shared traits rather than overall similarities to determine common ancestry.  In extremely simplified form, cladistics attempts to do what your family tree does: group everyone together who is related by common ancestry.  Yes, we all have an uncle or group of relatives we wish were not part of our family, but our shared genetic traits still show our close relationships.

Cladistic analyses of dinosaurs among the vertebrates revealed what Huxley had hypothesized all those years ago: birds were not just relatives of dinosaurs, they were a branch of the predatory dinosaur family tree!  Birds were dinosaurs just like humans are mammals.

But where were the feathered dinosaurs?  Until the 1990s, all paleontologists could do is point to the special, shared traits of Archaeopteryx, predatory dinosaurs, and birds and infer that maybe some dinosaurs had feathers.  This ambiguity was seized on by opponents of the birds-as-dinosaurs hypothesis to again suggest all the features (and more) that we have listed here were simply due to an amazing amount of convergent evolution.

Enter the Cretaceous Chinese predatory dinosaur discoveries of the 1990s in the Liaoning Province.  Unprecedented soft-tissue preservation in these fossils showed what was predicted by cladistics, Archaeopteryx, the suite of features shared between dinosaurs and birds only, and even back to Huxley’s observations: unmistakable dinosaurs with unmistakable feathers*.  And not flight feathers, either.  Barb-like and downy-like feathers that ran along the lengths of dinosaurs that could not have flown.  These animals would have used the feathers for insulation and perhaps display, but many could not have flown.  To tick off a few on the list of feathered dinosaurs discovered since the 1990s:

• Sinosauropteryx
• Caudipteryx
• Beipiaosaurus
• Sinornithosaurus
• Microraptor

And in the past few years, non-predatory dinosaurs and large predatory dinosaurs with feathers have appeared.  Among them:

• Dilong, a distant relative of Tyrannosaurus rex, showing feather impression along the jaw and tail.
• Tianyulong, a heterodontosaurid dinosaur in the same major group as the so-called “duck-billed” dinosaurs, sporting feathers on neck, back, and tail
• Yutyrannus, a 30-foot long predator weighing over 1 metric ton, and displaying elongate feathers along its belly, foot, and even projecting from its arms.

This many dinosaurs with feathers, some nowhere near the bird-line let alone among the predatory dinosaurs at all, leads to what we call in science robust evidence.

*Now, the reason for the asterisk — to be absolutely clear and fair, “feather” can be a rather broad term.  Some of these dinosaur feathers are long, hollow barbs, and some don’t branch like modern feathers.  However, Richard Prum and Jan Dyck have demonstrated through detailed studies of feather development in modern birds how feathers begin and diversify.  They have “staged” feathers, meaning that he has hypothesized what the earliest types of feathers should be and so on.  Interestingly enough, the variety of filamentous structures found in the many so-called feathered dinosaur fossils fit these predictions very, very well.

But perhaps you’re still not satisfied that birds are indeed dinosaurs?  Okay, stay tuned …