Archaeopteryx had a wing that was different from that of modern birds, and, as seen here, might have been a glider more than a powered flyer. Art by Carl Buell, courtesy of Nicholas Longrich.

How did feathered dinosaurs take to the air? Paleontologists have been investigating and debating this essential aspect of avian evolution for over a century. Indeed, there have been almost as many ideas as they have been experts, envisioning scenarios of dinosaurs gliding through trees, theropods trapping insects with their feathery wings and even aquatic Iguanodon flapping primitive flippers as flight precursors (I didn’t say that all the ideas were good ones). The biomechanical abilities of bird ancestors and their natural history has always been at the center of the debate, and a new Current Biology paper adds more fuel to the long-running discussion.

At present, hypotheses for the origin of avian flight typically fall into one of two categories. Either bird ancestors accrued the adaptations necessary for flight on the ground and, through evolutionary happenstance, were eventually able to take off, or small tree-dwelling dinosaurs used their feathery coats to glide between trees and, eventually, flapped their way into a flying lifestyle. There are variations on both themes, but feathers and the characteristic avian flight stroke are at the core of any such scenario. In the case of the new paper, Yale University paleontologist Nicholas Longrich and colleagues draw from the plumage of early bird Archaeopteryx and the troodontid Anchiornis to examine how feathers changed as dinosaurs started to fly.

In modern flying birds, Longrich and coauthors point out, the wing arrangement typically consists of “long, asymmetrical flight feathers overlain by short covert feathers.” This pattern creates a stable airfoil but also lets the flight feathers separate a little during the upstroke of a wing beat, therefore reducing drag. When the paleontologists examined the fossilized wings of Archaeopteryx and Anchiornis, they found different feather arrangements that would have constrained the flight abilities of the Jurassic dinosaurs.

Both prehistoric creatures had long covert feathers layered on top of the flight feathers. Anchiornis, in particular, appeared to have an archaic wing form characterized by layers of short, symmetrical flight feathers and similarly shaped coverts. Archaeopteryx showed more specialization between the flight feathers and the coverts but still did not have a wing just like that of a modern bird. As a result, Longrich and collaborators hypothesize, both arrangements would have stabilized the wing at the cost of increased drag at low speeds, making it especially difficult for Anchiornis and Archaeopteryx to take off. As an alternative, the researchers suggest that these dinosaurs might have been parachuters who jumped into the air from trees, which might hint that “powered flight was preceded by arboreal parachuting and gliding.”

The trick is determining whether Anchiornis and Archaeopteryx actually represent the form of bird ancestors, or whether the dinosaurs, like Microraptor, were independent experiments in flight evolution. At the Society of Vertebrate Paleontology conference in Raleigh, North Carolina last month, flight expert Michael Habib quipped that all that was needed to make dromaeosaurs aerially competent was the addition of feathers. If Habib is right, and I think he is, then there could have been multiple evolutionary experiments in flying, gliding, wing-assisted-incline-running and other such activities. There’s no reason to think that flight evolved only once in a neat, clean march of ever-increasing aerodynamic perfection. Evolution is messy, and who knows how many ultimately failed variations there were among flight-capable dinosaurs?

The three-step Anchiornis-Archaeopteryx-modern bird scenario of wing evolution fits our expectations of what a stepwise evolutionary pattern would look like, but, as the authors of the new paper point out, shifting evolutionary trees currently confound our ability to know what represents the ancestral bird condition and what characterized a more distant branch of the feathered dinosaur family tree. We need more feathery fossils to further investigate and test this hypothesis, as well as additional biomechanical and paleoecological information to determine whether such dinosaurs really took off from trees. We must take great care in distinguishing between what an organism could do and what it actually did, and with so much up in the air, the debate on the origin of flight will undoubtedly continue for decades to come.

Reference:

Longrich, N., Vinther, J., Meng, Q., Li, Q., Russell, A. 2012. Primitive wing feather arrangement in Archaeopteryx lithographica and Anchiornis huxleyi. Current Biology DOI: 10.1016/j.cub.2012.09.052

Today’s turkeys are living dinosaurs, snoods and all. Photo by Yathin S Krishnappa, image from Wikipedia.

Tonight, at dinner tables all around the country, families are going to dine on dinosaur. If you dissect your holiday theropod just right, the ancient nature of the tasty avian is strikingly evident–right down to the wishbone. But what kind of dinosaur is a turkey, anyway?

Birds are dinosaurs. That’s a fact. But birds are really just one kind of dinosaur. Indeed, we call Triceratops, Euoplocephalus, Futalognkosaurus, Allosaurus and their ilk non-avian dinosaurs because these lineages fell outside the bird subgroup at greater or lesser distances. Birds are a distinct form of dinosaur, nested within a great group of fuzzy and feathery forms.

Let’s start from the bottom up. The dinosaur family tree is divided into two major branches–the ornithischians (the ceratopsids, hadrosaurs, stegosaurs and their relatives) and the saurischians. The saurischian side is made up of the long-necked, big-bodied sauropodomorphs and the bipedal, often-carnivorous theropods. The theropod subset is further subdivided into various groups, one of the major ones being the coelurosaurs. This subset includes the the famous tyrannosaurs, ostrich-like ornithimomosaurs, odd-looking oviraptorosaurs, sickle-clawed deinonychosaurs and birds, among a few others. Every lineage within this group contained at least one representative with feathers, and many of these dinosaurs were quite bird-like both anatomically and behaviorally.

Now here’s where things get tricky. For decades, numerous anatomical characteristics seemed to link the earliest birds, represented by Archaeopteryx, with deinonychosaurs similar to Velociraptor and Troodon. But some paleontologists have questioned this hypothesis. Last year, a controversial Nature paper suggested that the resemblance was because Archaeopteryx wasn’t actually a bird but a non-avian dinosaur more closely related to Deinonychus, while the first birds evolved from feathered dinosaurs akin to Oviraptor or the enigmatic Epidexipteryx. Rather than being deadly hypercarnivores, these alternative candidates for avian ancestry were oddball omnivores that often sported flashy tail feathers.

Not everyone agrees with the new proposal. For now, Archaeopteryx is still widely regarded to be at the base of the bird family tree, recently branched off from a deinonychosaur ancestor. Nevertheless, the argument underscores the point that many traits thought to be exclusively avian evolved much earlier in dinosaurian history than we previously expected. The more dinosaurs we find, the smaller the difference between the earliest avian dinosaurs and their non-avian ancestors. I know the pudgy kid in Jurassic Park called Velociraptor as “six foot turkey” as a put-down, but the comment isn’t too far of the mark. When you pick at the bird on your plate tonight, you’re devouring the dressed remains of a distant Deinonychus cousin.

Not only was Ornithomimus feathered, but the dinosaur’s fluffy coat changed as it aged. Lovely art by Julius Csotonyi.

Another week, another feathery dinosaur. Since the discovery of the fluffy Sinosauropteryx in 1996, paleontologists have discovered direct evidence of fuzz, feather-like bristles and complex plumage on over two dozen dinosaur genera. I love it, and I’m especially excited about a discovery announced today. In the latest issue of Science, University of Calgary paleontologist Darla Zelenitsky adds another enfluffled species to the dinosaurian ranks. Even better, the specimens raise hopes that many more dinosaurs might be preserved with their feathery coats intact.

Zelenitsky’s downy dinosaurs are not newly discovered species. Ornithomimus edmontonicus was initially described by famed bone hunter C.H. Sternberg in 1933, and it is one of the characteristic Late Cretaceous species found in Alberta, Canada’s fossil-rich Horseshoe Canyon Formation. In Sternberg’s time, these dinosaurs were thought to be scaly, but recent finds of so many feathery dinosaurs has raised the likeliehood that the “ostrich mimic” dinosaur was at least coated in some sort of dinofuzz.

A family tree of Saurischian dinosaurs, showing lineages within this group with direct evidence for feathers. From Zelenitsky et al., 2012.

The prediction of fluffy Ornithomimus came from the spread of feathers on the coelurosaur family tree. The Coelurosauria is a major dinosaur group that encompasses tyrannosaurs, compsognathids, ornithomimosaurs, alvarezsaurs, oviraptorosaurs, deinonychosaurs and birds. To date, evidence of feathers has been found in every coelurosaur lineage except one–the ornithomimosaurs. The spread of feathers hinted that some sort of plumage was present in the common ancestor of all coelurosaurs and therefore should have been inherited by the ornithomimosaurs, but, until now, no one had found direct evidence.

A trio of Ornithomimus skeletons have finally confirmed what paleontologists expected. Zelenitsky enthusiastically explained the details to me by phone earlier this week. In 1995, when Zelenitsky was a graduate student, paleontologists uncovered an articulated Ornithomimus with weird marks on its forearms. No one knew what they were. But in 2008 and 2009 a juvenile and an adult Ornithomimus turned up with preserved tufts of filamentous feathers. “When we found these specimens,” Zelenitsky said, “we made the link to the 1995 dinosaur.” All those strange marks on the arms of the previously discovered Ornithomimus, Zelenitsky and colleagues argue, are traces of longer, shafted feathers.

Even though paleontologists expected feathery Ornithomimus, the discovery was still a surprise. “I was in disbelief,” Zelenitsky said. “They’re the first feathered dinosaurs from the Americas, and the first ornithomimosaurs with feathers, as well. It was shocking to say the least.”

But there’s more to the find than simply adding another species of fluffy dinosaurs to the list. The fact that the adult and juvenile animals had different kinds of plumage adds new evidence that coelurosaurs changed their fluffy coats as they aged. “The one juvenile was completely covered in filamentous type feathers,” Zelenitsky said. What the adults looked like comes from the two other specimens. One adult skeleton, lacking forearms, preserves fuzzy feathers, and “the second adult had markings on the forearm.” Together, the specimens indicate that adult Ornithomimus were mostly covered in fuzz but developed more complex arm feathers by adulthood.

Sex is probably behind the plumage change. “We infer that because these wing feathers are not showing up until later in life, they were used for reproductive purposes,” Zelenitsky said. Perhaps adult Ornithomimus used flashy arm feathers to strut their stuff in front of potential mates. Then again, based upon the resting and brooding postures of other theropod dinosaurs, adult Ornithomimus could have used their proto-wings to cover their nests. We don’t know for sure, but the developmental change appears to be another example of dinosaurs undergoing significant changes as they approach sexual maturity. This discovery, and others like it, will undoubtedly play into the ongoing discussion about the role of sexual selection in dinosaur biology and evolution.

Best of all, the new study indicates that paleontologists may soon find more feathered dinosaurs in unexpected places. The Ornithomimus skeletons were found in prehistoric river deposits composed of sandstone. Since almost all feathered non-avian dinosaurs have been found in fine-grained sediment–such as those around Liaoning, China–paleontologists thought that coarser-grained sandstone deposits were too rough to record such fine details. Now we know better. “That’s the really exciting part of it,” Zelenitsky says. If traces of dinosaur feathers can be preserved in sandstone, the twist opens up the possibility that paleontologists might find fluff and feathers with a greater array of dinosaurs–including the tyrannosaurs, deinonychosaurs, therizinosaurs and other coelurosaurs of North America. The trick is recognizing the traces before they’re destroyed during excavation and preparation. Rock saws and airscribes can all too easily obliterate the delicate fossils. A word to researchers–keep your excavation tools sharp, and your eyes sharper.

Reference:

Zelenitsky, D., Therrien, F., Erickson, G., DeBuhr, C., Kobayashi, Y., Eberth, D., Hadfield, F. 2012. Feathered non-avian dinosaurs from North American provide insight into wing origins. Science. 338, 510-514

Pennycuick’s hypothetical Archaeopteryx ancestor, with membranes between the fingers and no feathers. From Pennycuick, 1986.

How dinosaurs took to the air is one of the longest-running debates in paleontology. Ever since the first skeleton of Archaeopteryx was discovered in 1861, researchers have wondered what the archaic bird might tell us about how flight evolved and how the feathery creature connected its reptilian ancestors with modern birds. Even now, when we know that birds are a feathered dinosaur lineage, the origins of flight remain a contentious issue constrained by the available fossil evidence and our ability to reconstruct how prehistoric creatures moved.

Before paleontologists confirmed that birds are dinosaurs, though, various researchers came up with speculative schemes to explain how birds originated. Naturalist William Beebe, for one, proposed that bird ancestors started off as parachuting reptiles that benefited from expanded scales (his conception of protofeathers). Other scientists came up with their own ideas, imagining everything from seagoing protobirds to gliding reptiles.

When ornithologist Colin Pennycuick wrote his paper “Mechanical Constraints on the Evolution of Flight” in 1986, however, paleontologists were warming to the idea that Archaeopteryx spanned the evolutionary space between living birds and dinosaurs like Deinonychus. This narrowed down the list of early flight scenarios to hotly debated “ground up” or “trees down” hypotheses for the origin of flight, and raised the possibility that feathers evolved among non-avian dinosaurs first. Within these debates, Pennycuick put forward his own idiosyncratic proposal.

Pennycuick believed that birds took to the air by way of the trees. Bird ancestors progressively shrunk in size over time, he believed, and started gliding before they could actually fly. He couldn’t envision that birds evolved from a running, leaping ancestor, as other researchers suggested. For Pennycuick, flight was a gradual extension of gliding.

But what did the ancestor of Archaeopteryx look like? Pennycuick assumed that feathers and flight were closely tied together–something that is not true at all and had already been pointed out by paleontologist John Ostrom in his work on bird origins. Feathers are important for display and insulation and were only later co-opted for flight. All the same, Pennycuick needed a gliding–but featherless–ancestor for Archaeopteryx to make his idea work. So he conjured something really weird.

Pennycuick was puzzled by the clawed fingers of Archaeopteryx. Why would a bird have differentiated fingers? Rather than look at the fingers as just a holdover from dinosaurian ancestry, Pennycuick assumed that they had some kind of flight function. The fingers of Archaeopteryx, he proposed, “could have supported a small, batlike hand-wing.” Such a structure would have been inherited from the featherless ancestor of Archaeopteryx, he proposed, “constituting the main wing area in the stage before feathers were developed.”

Where the feathers of Archaeopteryx came from, Pennycuick couldn’t say. He mused on the need for feathers in the transition from gliding to flight, but he didn’t offer an explanation for how feathers evolved. He only mentioned that “The development of down feathers as thermal insulation is a separate process that may or may not have preceded the development of flight feathers.”

The fuzzy dinosaur Sinosauropteryx proved Pennycuick wrong a decade later. Paleontologists like Ostrom and artists such as Gregory S. Paul had long suspected that feathers were a widespread trait among bird-like theropod dinosaurs, and a flood of exceptional fossils has shown that feathers and their precursors have a deep, deep history. Dinofuzz, or structurally similar body coverings, might even go back to the root of the Dinosauria. How evolutionary forces molded those adornments, however, and what drove the evolution of flight feathers, remain as aggravatingly contentious as ever.

[Hat-tip to paleontologist Victoria Arbour for bringing this paper to my attention]

Reference:

Pennycuick, C. 1986. Mechanical Constraints on the Evolution of Flight. Memoirs of the California Academy of Sciences. 8, 83-98

“Feathers” by Randall Munroe, from http://xkcd.com/

Anyone who regularly reads this blog knows that there’s a very easy way to make me annoyed–all you have to do is start whining about how dinosaurs are less cool since paleontologists discovered that many non-avian species sported tufts and coats of fluff, fuzz, bristles and feathers. My reaction is usually along the lines of “Brian SMASH!” Even though I understand that some people find scaly, monstrous dinosaurs aesthetically appealing, I have no patience for the callow assertion that science has somehow ruined dinosaurs through the addition of plumage.

Cartoonist Randall Munroe summed up my feelings–albeit in a more concise and positive way–this week at XKCD. Restoring dinosaurs with protofuzz and feathers isn’t just about giving Tyrannosaurus, Velociraptor and company a new look. Dinosaur feathers, and feather-like structures, are allowing paleontologists to think of dinosaurs in new ways. In particular, Munroe cites a PLoS One study about how feathers may have played into the predatory behavior of sickle-clawed dromaeosaurs  such as Deinonychus. According to paleontologist Denver Fowler and co-authors, Deinonychus may have used its famous “killing claw” to pin down small prey just like modern hawks and eagles do. More than that, the avian raptors flap to help stabilize themselves while immobilizing their prey, and Deinonychus–almost certainly a feathered dinosaur–may have done the same.

Deinonychus might have flapped its arms to help restrain prey. Art by Emily Willoughby, image from Wikipedia.

We can’t know for sure whether Deinonychus killed prey like a big, grounded version of a hawk. But it’s possible. Either way, though, studies like these show that prehistoric dinosaur feathers are allowing paleontologists to look to modern birds to generate new hypotheses and tease out previously-unknown aspects of dinosaur lives. As I’ve mentioned before, feathers are the key to figuring out dinosaur colors. How wonderful is that? Again, Munroe says it better than I can: “The past keeps getting cooler!”

Post script: Munroe isn’t the only cartoonist to take on dinosaurs this week. FoxTrot’s Bill Amend had a few suggestions for the Smithsonian National Museum of Natural History’s dinosaur hall renovation. Paleontology curator Matt Carrano responded to the idea of installing a “Tourist Chompsognathus” at our Around the Mall blog.

I adore feathered dinosaurs. It feels a little strange to say that, but it’s true. Few things make me happier than seeing delicately-rendered restorations of theropods covered in fuzz and ceratopsians with some accessory bristles. The various bits of plumage–from quill-like structures to true feathers–make dinosaurs look even more wonderful and fantastic than the drab, scaly monsters I grew up with. And who wouldn’t love a fluffy like dinosaur like Sciurumimus, perhaps the cutest dinosaur of all time?

Of course, not everyone feels the same way. There are some people who want their dinosaurs to be scaly, scaly, scaly, science be damned. They weep, wail and gnash their teeth whenever a new study suggests that another branch of the dinosaur family tree might have been adorned with plumage. It’s as if they expect the Dinosauria to be consistent with an unchanging canon–sci-fi and comic fans suffer a similar apoplexy when one of their favorite characters deviates from their most cherished storyline.

io9′s “We Come From the Future” show recently debated whether science had “ruined” dinosaurs by decorating so many non-avian species with feathers. (Remember–birds are dinosaurs, too, and there have been some very scary birds in the history of life on earth). Granted, some restorations of feathery dinosaurs really do look stupid, and the minor plumes on the heads of Jurassic Park III‘s Velociraptor didn’t really help.

The show’s point-counterpoint debate on the matter isn’t totally serious, and it’s a way to get a tidbit of science out to a wider audience. That’s a good thing. All the same, I’m pretty sick of people who complain that feathers somehow detract from dinosaurian magnificence. How immature can you get? We all love the dinosaurs we first meet as kids, and, for many of us, those leviathans were drab and scaly. But those earlier versions have been slit from stem to stern by more active, colorful and complex dinosaurs, many of which had some kind of feather-like body covering. Which would you prefer? The scaly, sluggish pot-bellied Tyrannosaurus of the mid-20th century, or a svelte, agile predator that has a few patches of fuzz?

Don’t misunderstand me here. I’m not saying that all dinosaurs looked like big chickens. Dinosaurs exhibited an array of body structures–from simple, fuzzy tubes to bristles and full-on flight feathers. Some species, like modern birds, even exhibited several different types of feathers. The weird Beipiaosaurus, for one, had fuzzy protofeathers on much of its body but also had a sort of tail fan created by a different feather type. And “feathered dinosaur” doesn’t mean that the animal was entirely cloaked in plumage. Take Psittacosaurus, for example–this little ceratopsian was a very, very distant relative of birds and had a row of bristles along its tail. The structures were probably visual signals, and I have no doubt that same was true among other dinosaurs. Feathers aren’t just about flight or insulation, but they’re also important in display and communication.

And feathers are the key to dinosaur color. I’m still awestruck that we can recreate the colors of creatures that have been extinct for tens of millions of years. By comparing the microscopic details of prehistoric dinosaur feathers to the feathers of modern birds, we can finally answer that most persistent of paleo questions. That fact, alone, makes feathered dinosaurs especially magnificent.

I’m weary of this Portlandia-esque attitude that dinosaurs are over if they’re feathered. Please. New scientific discoveries are allowing us to gain unprecedented insights into the biology of dinosaurs, including the lives of the fluffy species. Feathers are just part of that bigger picture, and I’m ecstatic that paleontologists are reconstructing dinosaurs in ever-greater detail. The point is this. Feathered dinosaurs are awesome. Deal with it.

The skeleton of Sciurumimus, seen under UV light. You can see traces of protofeathers alon the dinosaur’s tail. Photo by Helmut Tischlinger.

On Monday, the world met yet another fuzzy dinosaur. The little theropod – named Sciurumimus albersdoerferi – is beautifully preserved in a slab of roughly 150 million year old limestone found in Germany. (These deposits have also brought us Archaeopteryx and the also-fluffy Juravenator.) And, with a little evolutionary context, Sciurumimus hints that filament-like protofeathers were more common among dinosaurs than we previously expected.

Birds – the only surviving lineage of dinosaurs – are covered in plumage. No surprise there. But since 1996, paleontologists have identified about 30 genera of non-avian dinosaurs with feathers. Most of these dinosaurs are coelurosaurs – the major group of theropod dinosaurs that contains tyrannosaurs, the switchblade-clawed deinonychosaurs, the truly weird therizinosaurs, and, among others, birds. As the discoveries accumulated, it seemed that feathers originated at the base of this group, and were inherited by birds. And feathers were not only present an small, especially bird-like dinosaurs. As the recently-described Yutyrannus shows, even 30-foot-long tyrannosaurs were fluffy.

Up until a few years ago, birds and their closest non-avian relatives were the only dinosaurs known to have feathers. Simple enough. But then two ornithischians crashed the party.You see, the dinosaur family tree is split into two halves – the saurischians on one side, and the ornithischians on the other. The split goes back about 230 million years or so, nearly to the origin of the very first dinosaurs.

The feathery coelurosaurs belong to the saurischian side of the tree, but paleontologists have also discovered dinosaurs on the other side – on the ornithischian branches – with feather-like structures. In 2002, paleontologists discovered that the archaic ceratopsian dinosaur Psittacosaurus had a brush of bristle-like structures jutting from its tail. And in 2009, another team discovered Tianyulong – another ornithischian dinosaur with a row of similar filaments running down its back. The bristles were not just like the fuzz and feathers seen among the coelurosaurs, but they were structurally similar.

Paleontologists were left with two possibilities. Either protofeathers evolved multiple times in different dinosaur lineages, or simple “dinofuzz” was an ancestral dinosaur feature that was later lost in some lineages. We don’t have enough fossils yet to know for sure, but the discovery of Sciurumimus is a significant clue that most, if not all, dinosaur lineages were at least partially decorated with protofeathers.

Even though Sciurumimus is a theropod dinosaur – part of the saurischian side of the family – it isn’t a coelurosaur. Sciurumimus is a megalosauroid, which is a lineage of dinosaurs that’s closer to the base of the theropod group. In other words, Sciurumimus is a relatively archaic theropod that isn’t very closely related to birds, yet it still has dinofuzz.

Paleontologist Thomas Holtz helped provide some context on Twitter shortly after the new dinosaur was announced. Before Sciurumimus, only coelurosaurs were known to have fuzz. (What the bristles on Psittacosaurus and Tianyulong actually are is still unclear, but no one calls their filaments “fuzz.”) After Sciurumimus, fuzz has been moved down a branch to a group called the Carnosauria.

We are still left with two possibilities. The fuzz on Sciurumimus could have originated independently. But as paleontologists add fuzz to lineages of dinosaurs only distantly-related to birds, it seems less and less likely that protofeathers evolved from scratch in each and every lineage. It’s looking more and more like feathers were a common, ancestral feature of dinosaurs. In this case, Sciurumimus indicates that simple feathers were an early, common theropod trait that evolved close to the origin of the group. The diminutive dinosaur also fits in the wide gap between coelurosaurs and their very distant ornithischian dinosaurs, bringing us a little closer to the idea that dinofuzz was an early, widely-shared dinosaur feature.

And there’s something else. Pterosaurs – the flying archosaurs with leathery wings stretched over elongated wing fingers – were the closest relatives to the Dinosauria as a whole. They had fuzzy body coverings, too. No one knows for sure, but this might mean that wispy plumage was present in the last common ancestor of dinosaurs and pterosaurs, and those simple body coverings were subsequently modified or lost in different lineages as both groups evolved.

We need more fossils to test the idea that dinosaurs started out feathery. Additional fossils preserving fuzz – fluffy baby sauropods, maybe? – would help us understand the spread of feathers and their precursors among dinosaurs. And, even then, we’d still need to find exceptionally-preserved specimens of the earliest dinosaurs to see if they had any kind of filament-like body covering. The trouble is that the high-definition deposits that would even have a chance of preserving feathers are rare. It may be a very long time before we ever know for sure.

Nevertheless, there’s still a possibility that all dinosaur lineages had some kind of bristly or feathery body covering. It’s a hypothesis that needs testing, but not an unreasonable one. Think about this for a moment. Imagine a Stegosaurus with patches of long, stiff filaments covering its body, or a Ceratosaurus with a little splash of brightly-covered fuzz on its already well-decorated head. And I think a huge sauropod – like Apatosaurus – with a partial covering of dinofuzz would look absolutely spectacular. These visions are wholly different than the scaly dinosaurs I grew up with, but they are not so fantastic as to be fiction. We are only just beginning to understand how fuzzy dinosaurs were.

For more on Sciurumimus, see my Nature News article and paleontologist Oliver Rauhut’s blog post about the discovery.

Last week, paleontologists at the Argentine Museum of Natural Science in Buenos Aires literally unveiled a new dinosaur. Named Bicentenaria argentina to celebrate the museum’s 200th anniversary and just over two centuries of Argentine independence, the dinosaur was presented in a dramatic mount in which two of the predatory dinosaurs face off against each other.

As yet, there’s not very much to say about the dinosaur. The paper officially describing Bicentenaria has yet to be published. Based on various news reports, though, Bicentenaria appears to be a 90 million year old coelurosaur. This is the major group of theropod dinosaurs that contains tyrannosaurs, deinonychosaurs, therizinosaurs, and birds, among others, and Bicentenaria is reportedly an archaic member of this group that represents what the earliest coelurosaurs might have looked like. It wouldn’t be an ancestor of birds or other coelurosaur groups – by 90 million years ago, birds and other coelurosaurs had already been around for tens of millions of years – but Bicentenaria may have had a conservative body plan that preserved the form of the dinosaurs that set the stage for other coelurosaurs. For now, though, we’re left to admire the impressive skeletal mount until the paper comes out.

A feathery Troodon on the Museum of Life and Science Dinosaur Trail, in Durham, North Carolina. Photo by Flickr user Cryptonaut.

Every kid knows how Easter eggs wind up in their yard. According to the canonical weirdness that is the holiday tradition, the Easter bunny delivers the colorful eggs overnight. But the origin of the eggs themselves is hardly ever mentioned. According to a well-timed press release from the University of Leicester, non-avian dinosaurs are the best candidates for some of the candy eggs hidden away on lawns.

There is some real science behind the silliness. In the latest issue of Palaeontology, researchers Nieves López-Martínez and Enric Vicens described a new type of dinosaur egg discovered in the Cretaceous strata of northeastern Spain. The roughly 70-million-year-old eggs, given the name Sankofa pyrenaica to distinguish them from other egg forms previously found, exhibited a strange combination of features.

A chart showing dinosaur egg shapes (dark grey), bird egg shapes (light grey), and Easter eggs found in English shops. Image from the University of Leicester press release.

Many non-avian dinosaur eggs are more or less symmetrical in shape, regardless of whether they are spherical or elongated. Bird eggs, such as those from hens, often have an asymmetrical, tear-drop shape in which one end of the egg is more pointed and the other more rounded. There is some overlap in form, though. Eggs attributed to the small, sickle-clawed dinosaur Troodon and to the beaked oviraptorosaur Citipati are both elongated and taper to one end, and so seem similar to bird eggs.

The profile of the newly described egg type is most similar to that of archaic birds. But, according to López-Martínez and Vicens, the microscopic structure of the Sankofa eggs shares more in common with those laid by non-avian dinosaurs such as Troodon than with birds. The Sankofa eggs exhibit a mix of characteristics seen in both non-avian dinosaurs and archaic birds. Without fossils of the chicks developing inside the eggs, or even associated bones of adult animals, exactly what sort of creature laid this egg is ambiguous.

As part of the study, López-Martínez and Vicens created a chart of non-avian and avian dinosaur egg shapes. And, while it didn’t resolve the true identity of Sankofa, University of Leicester paleontologist Mark Purnell employed the comparative diagram in an attempt to track what sorts of dinosaur—avian or otherwise—could have laid the colorful eggs offered in England’s shopping districts. While many treats had the traditional hen egg shape, Purnell found, at least one resembled the Sankofa egg shape. I have to wonder if other Easter egg variations fit within the non-avian dinosaur range. Perhaps an expedition to the supermarket is in order.

References:

LÓPEZ-MARTÍNEZ, N., & VICENS, E. (2012). A new peculiar dinosaur egg, Sankofa pyrenaica oogen. nov. oosp. nov. from the Upper Cretaceous coastal deposits of the Aren Formation, south-central Pyrenees, Lleida, Catalonia, Spain Palaeontology, 55 (2), 325-339 DOI: 10.1111/j.1475-4983.2011.01114.x

Microraptor, covered in iridescent plumage. Art courtesy of Jason Brougham/University of Texas.

Microraptor was an exquisitely feathered dinosaur. The small, sickle-clawed predator, which lived about 120 million years ago, was covered in well-developed plumage, including long feathers on its arms and legs. But we now know that Microraptor was not only beautiful in an anatomical structure sense. A detailed new study has painted this dinosaur in a glossy black sheen.

The range of the dinosaur palette has been one of the most mysterious aspects of dinosaur biology. For most species, we just don’t know—bones and teeth can’t tell us anything about skin color. But feathered dinosaurs contain evidence of their hues within their feathers. Microscopic organelles called melanosomes are the key. In fossil creatures—just as in living ones—the size, shape, density and distribution of these tiny, pigment-filled blobs created different colors. By studying the characteristics of melanosomes in feathered dinosaurs and comparing the patterns with those that create the colors of modern birds, paleontologists can reconstruct dinosaur feather colors.

Several dinosaurs have already received a color treatment. After establishing that fossil melanosomes are faithful indicators of prehistoric color in ancient birds, paleontologist Jakob Vinther and colleagues restored the full-body coloring of the feathered, non-avian dinosaur Anchiornis. This small dinosaur looked something like a magpie with a bright red splash of feathers on top of its head. Earlier this year, Vinther, Ryan Carney and co-authors determined that the famous feather used to name the earliest known bird—Archaeopteryx—was black. And a different team of researchers, led by paleontologist Fucheng Zhang, hypothesized that the fuzzy Sinosauropteryx had a candy-cane tail ringed in white and rusty red. Paper by paper, dinosaurs are being colored in.

In the case of Microraptor, the dinosaur did not turn out quite like any of the restorations that artists had previously composed. Many Microraptor illustrations envisioned the dinosaur in shades of brown, white and blue. But when Vinther, Quanguo Li and collaborators studied the melanosomes sampled from 26 different locations on a Microraptor specimen designated BMNHC PH881, they didn’t find those colors. Microraptor feathers were iridescent blue-black. In appearance, Vinther said via email, Microraptor would have looked similar to “grackles or a magpie, or indeed a crow.”

Black was apparently quite fashionable among feathered dinosaurs. Anchiornis, while overall more colorful, was also predominantly black, and the lone Archaeopteryx feather was also black. Why black was so common for dinosaurs with complex, specialized feathers isn’t clear. Vinther pointed out that the small sample size might be creating this pattern, especially since other, unpublished specimens show different colors. Then again, black and other dark shades might have had something to do with where the animals lived. Citing a phenomenon called Gloger’s rule, Vinther explained that mammals and birds that live in hot, humid environments near the equator have more of the pigment melanin, and therefore appear darker, than those living closer to the poles, though “sample size needs to be increased to make any generalizations like these,” he cautioned.

Vinther is confident that further studies will increase the number of dinosaurs for comparison. “The material is clearly there,” he said. It is only a matter of time before paleontologists can start to understand how color varied between individuals, and possibly even between the sexes. For the moment, though, the handful of dinosaurs that have been restored in color have shown that intricate avian traits existed far back in the past. “We were speculating about how deep iridescent colors might be and we were pretty excited when we realized that Microraptor indeed is iridescent,” Vinther said, and this discovery can tell us something about how feathers and even behaviors evolved among early birds and their dinosaurian kin.

“We can see that the paravian clade,” the group that contains birds and non-avian dinosaurs more closely related to birds than dinosaurs , “has complex feather morphologies and exhibit colors and color patterns for display and even iridescence like in modern birds, so these features are ancient and indeed suggest that at least the derived theropod dinosaurs were more similar in ecology and behavior to birds,” Vinther said. And, as research continues on feathered dinosaurs more distantly related to birds, Vinther suspects that many characteristics of modern birds will be pulled “deep down” the dinosaurian tree. The more we learn about feathered dinosaurs, the further back we can draw traits seen among birds today.

And there are still things to learn about the anatomy of feathered dinosaur plumage. While the iridescent hues of Microraptor are the major finding of the new paper, the study also pointed out that specimen BMNHC PH881 had a specialized set of paired feathers at the end of the tail. Similar feathers had been noted in other Microraptor specimens before, but this fossil had an especially lovely set. The structures are “simply too small and the feathers too spaced to create any lift,” Vinther said, so it’s unlikely that they aided the dinosaur in gliding or flying. Instead, citing the assessment of co-author Julia Clarke, Vinther said that the feathers might have been a display structure. Combined with the flashy feathers, these structures might be another clue that display and visual communication were very important factors in the early evolution of feather anatomy and color.

For most of my life, I was told that we would never know what colors dinosaurs were. Now, amazingly, there is a way to restore the appearances of some dinosaurs with a fidelity never thought possible. But I had to wonder if paleo-artists have felt any aggravation about such discoveries. As new studies establish feather colors for dinosaurs, the realistic palettes for those dinosaurs are constrained. I asked Vinther if he has received any irritated comments from artists about his work. He replied that, to the contrary, his research has been greeted with excitement. And while defining dinosaur colors “might take some of the imagination from the artists,” Vinther said, “I think that their fascination with these beasts gives them a desire to make them more scientifically correct.” The colorfully restored dinosaurs seem to be a hit. “I am struck by awe when I google-image Anchiornis and see forty plus versions of Anchiornis by various artists all over the world and even tattoos of it,” Vinther said. With any luck, the new glossy Microraptor will be just as popular.

References:

Carney, R., Vinther, J., Shawkey, M., D’Alba, L., & Ackermann, J. (2012). New evidence on the colour and nature of the isolated Archaeopteryx feather Nature Communications, 3 DOI: 10.1038/ncomms1642

Li, Q., Gao, K., Vinther, J., Shawkey, M., Clarke, J., D’Alba, L., Meng, Q., Briggs, D., & Prum, R. (2010). Plumage Color Patterns of an Extinct Dinosaur Science, 327 (5971), 1369-1372 DOI: 10.1126/science.1186290

Li, Q., Gao, K., Meng, Q., Clarke, J., Shawkey, M., D’Alba, L., Pei, R., Ellison, M., Norell, M., & Vinther, J. (2012). Reconstruction of Microraptor and the Evolution of Iridescent Plumage Science, 335 (6073), 1215-1219 DOI: 10.1126/science.1213780

Zhang, F., Kearns, S., Orr, P., Benton, M., Zhou, Z., Johnson, D., Xu, X., & Wang, X. (2010). Fossilized melanosomes and the colour of Cretaceous dinosaurs and birds Nature, 463 (7284), 1075-1078 DOI: 10.1038/nature08740

A specimen of the non-avian dinosaur Sinosauropteryx, showing the ruff of simple protofeathers along the back and tail. Image from Wikipedia.

Poet Emily Dickinson once wrote, “Hope is the thing with feathers.” To fossil bird expert Alan Feduccia, however, anything with feathers is a bird and emphatically not a feathered dinosaur.

For decades Feduccia has been one of the most prominent members of a small and steadfast group of researchers who reject the growing body of evidence that birds are the descendants of one lineage of feather-covered coelurosaurian dinosaurs (the large and varied group which included tyrannosaurs, oviraptorosaurs, deinonychosaurs, therizinosaurs and others). Feduccia and like-minded peers have been provided no solid alternate hypotheses about where, when, why and how birds originated—they point to some yet-unknown lineage of creatures that might have lived more than 200 million years ago—but they insist that birds cannot be dinosaurs. Yet Feduccia’s argument in his new book Riddle of the Feathered Dragons is not quite that simple. Near the book’s conclusion, Feduccia writes “if [a creature] has avian feathers, it is a bird”—a view popular among dinobird denialists that some dinosaurs were, in fact, “hidden birds.”

Non-avian, feathered dinosaurs have been known to paleontologists since 1996. In the 16 years since the first such creature was found—a small theropod dinosaur preserved with fuzzy protofeathers and named Sinosauropteryx—scores of plumage-bearing dinosaur specimens have been discovered. These creatures exhibit a variety of different feather types, which has helped paleontologists, ornithologists and developmental biologists understand how feathers went from simple, wispy structures to complex, asymmetrical feathers that allow birds to fly.

Feduccia disagrees. He says that the protofeathers on Sinosauropteryx and other dinosaurs are, instead, collagen fibers from inside the animal’s body. This would keep dinosaurs comfortably scaly for those who don’t like the idea that birds are derived dinosaurs. But a number of coelurosaurian dinosaurs, such as Anchironis, Microraptor and others, have been preserved with more complex feathers that more closely approximate those seen on living birds. These structures cannot be simply cast off as collagen fibers or other quirks of preservation, and so Feduccia makes a strange argument. Microraptor and kin are not dinosaurs, Feduccia argues, but are instead birds that lost the ability to fly and were molded into the form of dinosaurs through a circuitous evolutionary pathway. By employing a very narrow definition of what a feather is, and by asserting that only birds can have feathers, Feduccia tries to rearrange evolutionary relationships through semantics.

When Sinosauropteryx was discovered, the dinosaur seemed to be an enigma. Paleontologists were not optimistic about the prospect of finding dinosaurs with feathers. Such intricate structures would only be recovered in instances of exceptional preservation. But additional discoveries since 1996 have confirmed that the find was not a fluke. And the fuzzy structures preserved along the backs of these dinosaurs contain an important clue that they are, in fact, protofeathers. In 2010 a pair of papers was published regarding the reconstructed feather colors of dinosaurs. These findings were based on melanosomes—microscopic organelles found in feathers that, depending on their shape and distribution, create different colors and sheens. Such structures would be expected in feathers, but not collagen, and so when paleontologists were able to identify melanosomes in the fuzz of Sinosauropteryx, they provided new evidence that the dinosaur carried protofeathers.

Perhaps more importantly, however, there is no indication that creatures such as Oviraptor and Velociraptor were birds. Analysis after analysis has found them to be unequivocal, non-avian dinosaurs within the coelurosaur subgroup. Although Feduccia hypothesizes that birds originated from some mysterious Triassic ancestor, and then bird-like dinosaurs evolved from early birds, there is not a shred of evidence that such an evolutionary repeat ever took place. The idea is an attempt to remove uncomfortable facts in the way of a preconceived view.

Many of the book’s arguments take on a “because I said so” tone. Feduccia states that dinosaurs could not have been covered in protofeathers at any point because their archaic plumage would have gotten wet and mucky in the rain. Likewise, Feduccia argues that dinosaurs could not have evolved the long arms necessary for flight, and he casts dinosaurs as relatively sluggish ectotherms that had more in common with lizards and crocodiles than birds. None of these points are discussed in detail or backed up with sufficient evidence. Readers are left to take Feduccia at his word.

Ultimately, though, many of Feduccia’s objections boil down to a rejection of a methodology known as cladistics. This method of determining relationships among organisms is based on the analysis of shared derived characteristics—specialized features found in two organisms or lineages and their most recent common ancestor. Researchers look for numerous traits, record whether the traits in question are present or absent, and then insert that mass of data into a computer program that produces a hypothesis about the relationships among the various organisms included in the study. The point is not to find direct ancestors and descendants, but to figure out who is most closely related to whom. The method is not perfect—which organisms are included, the choice of traits for comparison and the way those traits are scored all affect the outcome. Still, this process has the benefit of requiring researchers to show their work. Each evolutionary tree resulting from such methods is a hypothesis that will be tested according to new evidence and analyses. If someone disagrees with a particular result, they can sift through the collected data to see if an inappropriate trait was included, an essential organism was left out, or if there was some other problem. Cladistics is useful not because it results in a perfect reflection of nature each time, but because it allows researchers to effectively examine, test and improve ideas about relationships.

Cladistic analyses have repeatedly found that birds are nested within a subgroup of coelurosaurian dinosaurs called maniraptorans. The result has only become more robust as additional archaic birds and non-avian feathered dinosaurs have been found. Feduccia argues that such results are deeply flawed, but he does not provide a viable alternative for how we should identify the relationship of birds to other organisms (an essential task if we are to figure out how birds originated). Categorizing organisms on general appearances, or making feathers synonymous with birds alone, will only confuse our understanding of prehistoric life. And, contrary to his protests, Feduccia seems to welcome cladistic results that support his own views. In a section of the book on the weird oviraptorosaurs, Feduccia plays up the importance of a 2002 paper that used a cladistic analysis to support the conclusion that these creatures were archaic, secondarily-flightless birds, even though additional studies have not supported this interpretation.

Riddle of the Feathered Dragons is an intensely frustrating read. The tome is a 290-page position piece that ultimately leaves the reader stranded. Feduccia is so concerned with turning feathered dinosaurs into birds that he ultimately neglects to present any reasonable hypothesis for where birds came from. The poor production of the volume only makes things worse (the illustrations are so tightly packed in places that they make it difficult to find where the captions end and the regular flow of the chapter picks up again.)

Although I wholly disagree with Feduccia, I had hoped that Riddle of the Feathered Dragons would explicate what opponents of the dinosaurian origin of birds believe about where avians came from. Simply repeating “birds are not dinosaurs” is not enough—positive evidence must play a role in forming an alternative hypothesis. The riddle of the “feathered dragons” is not where birds came from. The puzzle is why some scientists continue to insist that birds cannot be dinosaurs.

Since Jack Horner and James Gorman’s book How to Build a Dinosaur debuted almost three years ago, periodic lectures, interviews and articles have piqued the public’s curiosity about reverse-engineering a non-avian dinosaur from an avian one. Perhaps a “chickenosaurus” isn’t as outlandish as it sounds.

The possibility of creating a long-tailed chicken with teeth and claws is based on the fact that birds are living dinosaurs. A relatively minimal amount of tinkering could turn a bird into something like its non-avian ancestors. But, during the dinomania of the late 1980s and early 1990s, the idea that birds were derived from dinosaurs was still something that made people tilt their heads and say “What?” Rather than focus on efforts to turn birds into something akin to a dromaeosaur, dinosaur documentaries envisioned the real evolutionary changes by which one lineage of non-avian dinosaurs were adapted into early birds. Even better, two shows animated this change.

Within the array of Mesozoic programming from the early 1990s, one of my favorite shows was The Dinosaurs! This four-part PBS miniseries featured scientists investigating the details of dinosaur lives, and different prehistoric vignettes were presented in colorful animated sequences. The one that stuck with me most powerfully was a short scene about the origin of birds. A small, green dinosaur akin to Compsognathus runs through a forest, but when the theropod pauses on a branch it rapidly grows feathers. In an instant the small coelurosaur changed into Archaeopteryx. The 19th century naturalist Thomas Henry Huxley was absolutely right when he imagined that, when clothed in feathers, a dinosaur like Compsognathus would look little different from archaic birds.

But a similar clip from an earlier, 1989 episode of the series The Infinite Voyage is even better. The episode, “The Great Dinosaur Hunt,” is an excellent snapshot of how perspectives on dinosaurs were changing in the wake of the “Dinosaur Renaissance,” and the program included a similar coelurosaur-to-bird transformation. This time, though, the change starts with a fuzzy, feather-covered dromaeosaurid similar to the sickle-clawed Deinonychus. Rather than focus on the outside of the dinosaur, though, the show gives viewers an animated X-ray view as the skull, arms, shoulders, legs and hips are gradually modified in a transition through Archaeopteryx and modern birds. The change didn’t happen exactly like this—Deinonychus was a larger dinosaur that lived millions of years after Archaeopteryx—but different anatomies represent the general pattern of the evolutionary change.

I still have a fondness for those animations. Part of that affinity is probably due to nostalgia, but I also think that they beautifully illustrate a point that is often taken for granted now. The fact that birds are modern dinosaurs is reiterated in books, museum displays, CGI-ridden documentaries and blogs, but rarely do we see the transitional changes actually laid out in front of us. Both animations could use some updates, but they still vibrantly encapsulate one of the most fantastic transitions in the history of life on earth.

An early 19th century representation of Megalosaurus at the Crystal Palace gardens. Thomas Henry Huxley's work gave dinosaurs a much more bird-like look. Image by Flickr user Loz Flowers.

Winter is the season for dinosaur dinners. Both Thanksgiving and Christmas traditionally feature avian dinosaurs as the main gustatory event, and according to paleontological legend, it was this custom that inspired one 19th century naturalist to realize the connection between roasted birds and Jurassic dinosaurs.

Mark Norell, Lowell Dingus and Eugene Gaffney recounted the story in their book Discovering Dinosaurs. “One Christmas Day,” they wrote, “[Thomas Henry] Huxley was carving a turkey for his annual feast. As he dissected the drumstick he was struck by an unmistakable similarity between his Christmas dinner and the fossils of the theropod Megalosaurus back in his office.” From that day on, the story goes, Huxley was convinced that there was a deep genetic connection between dinosaurs and birds. I heard to same story from my Paleontology 101 professor at Rutgers University. It is a charming bit of lore. And it’s also wrong.

I don’t know where the story about Huxley and the Christmas turkey came from. It is one of those stories that seems simply to exist in the academic ether. (Even the Discovering Dinosaurs authors voiced their uncertainty about the tale in their book.) Fortunately for us, though, Huxley’s many scientific papers trace the development of his thoughts about birds and dinosaurs.

Huxley began associating reptiles—including dinosaurs—with birds on the basis of their anatomy in the early 1860s. Both groups appeared to be different variations of a common skeletal blueprint. But Huxley wasn’t thinking about this in evolutionary terms yet. He was primarily interested in the commonalities of structure and did not immediately start drawing evolutionary implications from the anatomical correspondences he recorded. That changed in 1866, when Huxley read the German naturalist Ernst Haeckel’s book Generelle Morphologie, an influential volume that connected organisms in a tangled “tree of life.” In regard to birds and reptiles, at least, Huxley realized that he had already established the basic outline of an evolutionary transition from a dinosaur-like creature—something resembling Compsognathus—to flightless birds and culminating in flying birds.

Huxley did not suggest that birds were the direct descendants of dinosaurs. So much geologic time was unaccounted for, and so few dinosaurs were known, that Huxley could not point to any known fossil creature as the forerunner of birds. Instead he made his argument on anatomical grounds and removed the issue of time. Dinosaurs were proxies for what the actual bird ancestor would have been like, and flightless birds (such as the ostrich and emu) stood in for what Huxley thought was the most archaic bird type. (We now know that Huxley got this backwards—the earliest birds could fly, and flightless birds represent a secondary loss of that ability.) As Huxley went about collecting evidence for his case, though, he also gave dinosaurs an overhaul. They were not the bloated, plodding, rhinoceros-like creatures that Richard Owen had envisioned. Dinosaurs were more bird-like than anyone had imagined.

In October of 1867, Huxley met with John Philips, an English geologist and a curator of Oxford’s museum. As Huxley related in his 1870 paper “Further Evidence of the Affinity Between the Dinosaurian Reptiles and Birds,” Philips wanted to discuss details of marine reptiles called ichthyosaurs in his museum’s collection, but as he and Huxley made their way over toward the displays they stopped to look at the bones of the carnivorous dinosaur Megalosaurus. Then Huxley spotted something peculiar:

As Prof. Phillips directed my attention to one after the other of the precious relics, my eye was suddenly caught by what I had never before seen, namely, the complete pectoral arch of the great reptile, consisting of a scapula and a coracoid ankylosed together. Here was a tangle at once unravelled. The coracoid was totally different from the bone described by Cuvier, and by all subsequent anatomists, under that name. What then was the latter bone? Clearly, if it did not belong to the shoulder-girdle it must form a part of the pelvis; and, in the pelvis, the ilium at once suggested itself as the only possible homologue. Comparison with skeletons of reptiles and of birds, close at hand, showed it to be not only an ilium, but an ilium which, though peculiar in its form and proportions, was eminently ornithic in its chief peculiarities.

Earlier naturalists had made a mistake. They had misidentified the shoulder girdle, and one part of what was thought to be part of the shoulder was actually part of the hip. Another strange piece, previously thought to be a clavicle, also turned out to belong to the pelvis. This rearrangement immediately gave the dinosaur a more bird-like character. It wasn’t only the small, gracile forms such as Compsognathus that shared skeletal features with birds. Philips himself had been pondering the bird-like characteristics of Megalosaurus even before Huxley arrived, and Huxley’s visit confirmed what Philips had previously suspected. The resulting, updated conception of Megalosaurus was closer to the animal as we know it today—a theropod dinosaur with a short forelimbs, long legs, a long tail for balance and a deep head filled with sharp, recurved teeth.

Huxley’s Christmas revelation is apocryphal. Rather than being instantly struck by the idea that birds and dinosaurs were closely related, Huxley carefully built up an argument over many years that birds evolved from something dinosaur-like. As far as I know, his only sudden realization regarding Megalosaurus involved the rearrangement of bones in Philips’ care at Oxford. And I think this brings up a crucial point often missed or glossed over in accounts of Huxley’s work. Through his efforts to untangle bird origins, Huxley was pivotal in revising the image of dinosaurs into active, bird-like animals. New fossil finds, as well as a new anatomical framework, changed dinosaurs from ugly beasts into graceful, unique creatures during the 1870s, thanks at least in part to Huxley’s efforts. (Too bad that succeeding generations of paleontologists would unravel this vision by casting dinosaurs as dumb, cold-blooded reptiles.) Even if Huxley didn’t say birds are dinosaurs, he certainly made dinosaurs more bird-like.

For more information on Huxley’s thoughts on dinosaurs and birds, please see my paper “Thomas Henry Huxley and the Reptile to Bird Transition” and chapter 5 of my book Written in Stone.

References:

Huxley, T.H. 1870. Further Evidence of the Affinity Between the Dinosaurian Reptiles and Birds. The Quarterly Journal of the Geological Society of London, vol. xxvi. 12-31

Norell, M., Dingus, L., Gaffney, E. 2000. Discovering Dinosaurs: Expanded and Updated. Berkeley: University of California Press. p. 11

A large stone slab containing mudcracks and many footprints left by small theropod dinosaurs, as illustrated in Hitchcock's "Ichnology of New England."

Edward Hitchcock was one of America’s first dedicated dinosaur paleontologists. He just didn’t know it. In fact, during the latter part of his career, he explicitly denied the fact. To Hitchcock, the tracks skittering over red sandstone in the Connecticut Valley were the marks of prehistoric birds from when the Creation was new. Hitchcock could not be dissuaded. As new visions of dinosaurs and the notion of evolution threatened to topple his life’s work, the Amherst natural theologian remained as immutable as the fossil footprints he studied.

Hitchcock was not the first to wonder about the prehistoric imprints. Members of the Lenape, a Native American group in Canada and the northeastern United States, had seen the bizarre, three-toed tracks and ascribed them to monsters and other beings. These were the footsteps of creatures that ruled the world before humans came to dominance. European settlers and their descendants had to stretch their mythology a little more to accommodate the tracks. Some thought such tracks might have been left by Noah’s raven after the biblical deluge, although many simply called them “turkey tracks” and apparently were little concerned with where they had come from.

It wasn’t until 1835 that James Deane, a doctor with a curiosity for natural history, found out about a sample of the peculiar tracks near Greenfield, Massachusetts. He knew that they represented prehistoric organisms, but he wasn’t sure which ones. He wrote to Hitchcock, then a geology professor at Amherst, to inquire about what could have left such markings in stone. At first Hitchcock didn’t believe Deane. There might be some quirk of geological formation that could have created track-like marks. But Deane was persistent. Not only did he change Hitchcock’s mind, but the geologist became so enthusiastic that he quickly became the most prominent expert on the tracks—a fact that frustrated Deane and led to tussles in academic journals over who really was the rightful discoverer of the Connecticut Valley’s lost world.

Hitchcock began publishing about the peculiar trace fossils in 1836. He was confident from the very start that they must have been created by prehistoric birds. (He was so enthused by the idea he even wrote poetry about the “sandstone birds.”) No variety of creature matched them better. The word “dinosaur” had not even been invented yet; the British anatomist Richard Owen would establish the term in 1842. The few dinosaurs that had been found, such as Iguanodon, Megalosaurus and Hylaeosaurus, were known only from paltry remains and all were believed to have been enormous variations of lizards and crocodiles. Dinosaurs were a poor fit for the tracks, and became even worse candidates when Owen gave them an anatomical overhaul. Owen not only named dinosaurs, he re-branded them as reptiles with mammal-like postures and proportions. The huge sculptures of the Crystal Palace exhibition, created with the help of artist Benjamin Waterhouse Hawkins, are a testament to Owen’s view of dinosaurs as reptiles that had taken on the anatomical attitudes of rhinoceros and elephants.

But Owen and other paleontologists did not agree with Hitchcock’s interpretation. They argued that the tracks could have been made by some unknown variety of amphibian or reptile. This was not so much because of the anatomy of the tracks—anyone could see that they were made by creatures with bird-like feet—but because no one thought that birds could have lived at so ancient a time or grown large enough to make the biggest, 18-inch tracks Hitchcock described. Even though early 19th century paleontologists recognized that life changed through the ages, they believed there was a comprehensible progression in which so-called “higher” types of creatures appeared later than others. (Mammals, for example, were thought to have only evolved after the “Secondary Era” when reptiles ruled since mammals were thought to be superior to mosasaurs, ichthyosaurs, and other creatures of that middle time.)

Hitchcock remained steadfast, and his persistence was eventually rewarded with the discovery of the moa. These huge, flightless birds recently lived on New Zealand—they were wiped out more than 500 years ago by humans—and in 1839 Richard Owen rediscovered the birds through a moa thigh bone. He hypothesized that the bone must have belonged to a large, ostrich-like bird, and this idea was soon confirmed by additional skeletal bits and pieces. Some of these ratites stood over nine feet tall. When the news reached Hitchcock in 1843, he was thrilled. If recent birds could grow to such sizes, then prehistoric ones could have been just as large. (And, though Hitchcock died before their discovery, preserved moa tracks have a general resemblance to some of the largest footprints from the Connecticut Valley.) Opinion about the New England tracks quickly changed. There was no longer any reason to doubt Hitchcock’s hypothesis, and paleontologists hoped that moa-like bones might eventually be found to conclusively identify the trackmakers.

Lacking any better hypotheses, Hitchcock prominently featured his avian interpretation of the three-toed tracks in his 1858 book The Ichnology of New England. It was a gorgeous fossil catalog, but it also came at almost precisely the wrong time. Gideon Mantell, the British doctor and paleontologist who discovered Iguanodon, was beginning to wonder if some dinosaurs primarily walked on their hind limbs in a bird-like fashion, and the Philadelphia polymath Joseph Leidy described Hadrosaurus, a dinosaur certainly capable of bipedal locomotion on account of having shorter forelimbs than hindlimbs, the same year that Hitchcock’s monograph came out. Dinosaurs were undergoing another major overhaul, and the few that were known at the time were being recast as relatively bird-like creatures. Even worse for Hitchcock, the following year another student of the Connecticut Valley tracks, Roswell Field, reinterpreted many of the footprints and associated traces as being made by prehistoric reptiles. Especially damning was the fact that deep tracks, left when the creatures sunk into the mud, were sometimes associated with drag marks created by a tail. Hitchcock’s tableau of ancient Massachusetts moas was becoming increasingly unrealistic.

If Hitchcock ever doubted his interpretation, he never let on. He reaffirmed his conclusions and modified his arguments in an attempt to quell dissent. In his last book, A Supplement of the Ichnology of New England, published in 1865, a year after his death, Hitchcock used the recently discovered Jurassic bird Archaeopteryx as a way to save his interpretation. Tail drags were no obstacle to the bird hypothesis, Hitchcock argued, because Archaeopteryx was generally regarded as being the primordial bird despite having a long, reptile-like tail. Perhaps such a bird could have been responsible for the trace fossils Hitchcock called Anomoepus, but the tail drags left by the animals that dwelled in Jurassic New England were also associated with tracks indicating that their maker walked on all fours. In response, Hitchcock cast Archaeopteryx as a quadrupedal bird—a representative of a new category different from the classic, bipedal bird tracks he had promoted for so long.

Other paleontologists took a different view. If Archaeopteryx looked so primitive and lived after the time when the red Connecticut sandstone was formed, then it was unreasonable to think that more specialized, moa-like birds created Hitchcock’s tracks. Furthermore, a few bones found in a Massachusetts quarry of roughly the same age in 1855 turned out to belong to a dinosaur—a sauropodomorph that Othniel Charles Marsh would later name Anchisaurus. The bird bones never turned up, and all the while dinosaur fossils were becoming more and more avian in nature. By the 1870s the general paleontological opinion had changed. New England’s early Jurassic was not filled with archaic birds, but was instead home to dinosaurs which were the forerunners of the bird archetype.

Our recent realization that birds are the direct descendants of one group of coelurosaurian dinosaurs has led some of Hitchcock’s modern day fans to suggest that he was really right all along. In an essay for the Feathered Dragons volume, paleontologist Robert Bakker extolled Hitchcock’s scientific virtues and cast the geologist’s avian vision for the tracks as essentially correct. Writer Nancy Pick, in her 2006 biography of the paleontologist, wondered, “What if Hitchcock clung to his bird theory because he was right?” But I think such connections are tenuous—it is a mistake to judge Hitchcock’s work by what we have come to understand a century and a half later.

While Bakker is right that Hitchcock stuck to his bird hypothesis early on because dinosaurs were not known in the 1830s to 1850s to be suitably avian, this does not explain why Hitchcock refused to entertain a dinosaurian origin for some of the tracks when evidence for such a connection began to accumulate. By sticking to the same point, Hitchcock went from being right to being so wrong that he tried to fit creatures like Archaeopteryx into the footprints to preserve his point. More importantly, though, Hitchcock promoted a variety of creationism that we would probably label as intelligent design today—he detested the idea of evolution by means of natural selection that Charles Darwin articulated in 1859. Hitchcock would not have accepted the idea that birds are the evolutionary descendants of dinosaurs. He likely would have rejected the idea of avian dinosaurs that some writers wish to attribute to him.

Hitchcock himself acknowledged that he was a stubborn man. Perhaps his obstinacy prevented him from accepting new ideas during a critical period of change within geology, paleontology and natural history. We may never know. Unless a letter or journal entry articulating his thoughts on the subject appear, his anti-dinosaur interpretation will remain a mystery. All we know for sure is that, regardless of whether he agreed with the label or not, Hitchcock was one of the first interpreters and promoters of North American dinosaurs.

References:

Bakker, R. 2004. “Dinosaurs Acting Like Birds, and Vice Versa – An Homage to the Reverend Edward Hitchcock, First Director of the Massachusetts Geological Survey” in Feathered Dragons. Currie, P.; Koppelhus, E.; Shugar, M.; Wright J. eds. Bloomington: Indiana University Press. pp. 1-11

Pick, N. and Ward, F. 2006. Curious Footprints: Professor Hitchcock’s Dinosaur Tracks & Other Natural History Treasures at Amherst College. Amherst: Amherst College Press.

Switek, B. 2010. Written in Stone. New York: Bellevue Literary Press. pp. 91-104

A reconstructed model of a young Tyrannosaurus at the Natural History Museum of Los Angeles County. Were these little tyrants covered in feathers? Photo by the author.

From museum displays to comic books and feature films, Tyrannosaurus rex has been celebrated as one of the biggest, meanest and ugliest predatory dinosaurs of all time. The image of this long-extinct carnivore as the apex of the apex predators has a nearly unstoppable amount of cultural inertia. Maybe that’s why people get upset when paleontologists and artists suggest that the tyrant dinosaur was at least partly covered in a coat of feathers. (Cracked.com even listed an illustration of a feathered Tyrannosaurus as one of “17 Images That Will Ruin Your Childhood.”) Such images make it seem as if the old “prize-fighter of antiquity” has gone soft—how could such an imposing predator go in for such a silly look? Tyrannosaurus was no turkey, right?

To date, no one has found the fossilized remnants of feathers with a Tyrannosaurus skeleton. A few patches of scaly skin are known from some big tyrannosaur specimens, and those scraps represent about all we know for sure about the body covering of the largest tyrants. So why is Tyrannosaurus so often depicted with a coat of dino-fuzz these days? That has everything to do with the evolutionary relationships of the great tyrannosaur lineage.

Until the early 1990s, paleontologists often placed tyrannosaurus with Allosaurus, Spinosaurus, Torvosaurus and others inside a group called the Carnosauria. These were the biggest of the carnivorous dinosaurs. But the group didn’t make evolutionary sense. As new discoveries were made and old finds were analyzed, paleontologists found that the dinosaurs within the Carnosauria actually belonged to several different and distinct lineages that had branched off from one another relatively early in dinosaur history. The tyrannosaurs were placed within the Coelurosauria, a large and varied group of theropod dinosaurs which includes dromaeosaurs, therizinosaurs, ornithomimosaurs, oviraptorosaurs and others. Almost every single coelurosaur lineage has been found to have feather-covered representatives, including the tyrannosaurs.

In 2004, paleontologist Xing Xu and colleagues described Dilong paradoxus, a small, roughly 130-million-year-old theropod which may be one of the earliest tyrannosauroid dinosaurs known. (The Tyrannosauroidea contains all the big, famous tyrannosaurids, such as Tyrannosaurus and Albertosaurus, as well as their closest relatives.) Small patches of filamentous protofeathers were found along the dinosaur’s neck and tail, indicating that—at least during their early evolutionary history—tyrannosaurs may have been covered in feathers, too. But the relevance of Dilong to the question of feathered tyrannosaurs partially rests on what Dilong turns out to be. The initial description cast the dinosaur as a tyrannosauroid, but subsequent analyses have differed as to whether Dilong is an early tyrannosauroid (as in Carr and Williamson, 2010) or belongs to some other coelurosaur group (as in Turner et al., 2011).

For the sake of argument, though, let’s say that Dilong was not a tyrannosauroid and actually belonged to a different coelurosaurian lineage. Would this mean that tyrannosaurs didn’t have feathers? Certainly not. Feathers were a widespread trait within the coelurosaurs, and simple, fuzzy protofeathers may go back to the last common ancestor of the group. Otherwise feathers would have to have evolved near the base of every lineage, and there is no indication that feathers evolved so many times. The spread of feathers among almost all coelurosaur groups hints at a shared origin.

Since so many other coelurosaurs had feathers, it is fair to infer that tyrannosaurs also did. This hypothesis is no more unreasonable than saying that close relatives of the earliest mammals such as Morganucodon were covered in fur on the basis of their evolutionary relationships. And, to pick another dinosaurian example, no one has yet described an ornithomimid dinosaur with evidence of feathers, yet we are comfortable attributing feathers to them because they are coelurosaurs. (Maybe their vaguely ostrich-like appearance helps a bit in this regard.) If feathers can reasonably be inferred for ornithomimosaurs on the basis of their family tree, then we can do so for tyrannosaurs.

So, within this evolutionary bracket, what kind of feathers might have clothed Tyrannosaurus and kin? The simple dino-fuzz of Dilong is a fair bet. Perhaps such a body covering would have served for insulation, but then again, the patchy distribution of filaments on Dilong and other coelurosaurs has raised the suggestion that some dinosaurs were only partly coated in feathers. Whatever their distribution on tyrannosaur bodies, though, the feathers probably didn’t look like those which allowed other coelurosaurs to eventually take to the air. After all, feathers were probably used for display and the regulation of body temperature first, and since no tyrannosauroid even came close to flying we should expect for them to have relatively simple feathers related to these functions.

A fuzzy juvenile tyrannosaur puppet at the Natural History Museum of Los Angeles County. Photo by author.

Regarding Tyrannosaurus specifically, the tyrant king may have had feathers only during the early years of life. A fuzzy coat may have helped hatchling and juvenile Tyrannosaurus regulate their body temperature, but as the animals grew, the benefits provided by insulation may have disappeared. (Retaining heat is a problem often faced by small animals, while shedding excess heat is a problem faced by larger animals due to changes in surface-to-volume ratios as animals grow.) Maybe an adult Tyrannosaurus would have patches of protofeathers here and there, as in Peter Schouten’s illustration of the dinosaur, But given the evidence at hand, it is likely that baby Tyrannosaurus would have been fuzzier than their parents.

Frustratingly, though, we may never know for sure what sort of feathers Tyrannosaurus might have had, or during what part of life. Circumstances of fine preservation are required to detect feathers, and even then, sometimes only patches are preserved. The types of environments Tyrannosaurus lived in were not exactly amenable to the kind of rapid, fine-detail preservation required to detect feathers. Even in cases where skin patches are preserved, it is difficult to know whether there might have been protofeathers on other parts of the body, or whether some of those feathers fell off or otherwise eluded preservation. Delicate structures require delicate preservation to detect.

What we can say is that the idea of a feather-covered Tyrannosaurus is a reasonable hypothesis. We still know so little about the body covering of this dinosaur that artists can reasonably restore the dinosaur with scaly skin, a coat of feathers, or a patchwork of both (I would especially like to see more renditions of that third possibility). Perhaps future fossil discoveries will provide us with a clearer picture of what Tyrannosaurus looked like, but the current unknowns are fascinating. Asking what Tyrannosaurus looked like is not just a matter of speculation—obtaining an answer requires that we consider the patterns and processes of evolution, as well as the methods we use to restore creatures that have been dead for millions upon millions of years. Feather-covered or not, though, I wouldn’t want to call Tyrannosaurus a turkey to its face. If I did, I don’t think I could run away fast enough to avoid becoming the dinosaur’s Thanksgiving dinner.

From everyone here at Dinosaur Tracking, we hope that you enjoy your holiday dinosaur and have a warm Thanksgiving.

References:

Carr, T., & Williamson, T. (2010). Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea
Journal of Vertebrate Paleontology, 30 (1), 1-16 DOI: 10.1080/02724630903413032

Turner, A., Pol, D., & Norell, M. (2011). Anatomy of Mahakala omnogovae(Theropoda: Dromaeosauridae), Tögrögiin Shiree, Mongolia American Museum Novitates, 3722 (3722), 1-66 DOI: 10.1206/3722.2

Xu, X., Norell, M., Kuang, X., Wang, X., Zhao, Q., & Jia, C. (2004). Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids Nature, 431 (7009), 680-684 DOI: 10.1038/nature02855