Meaning: The dinosaur’s full name translates to “Zhenyuan Sun’s dragon”, in honor of the man who “secured the specimen for study”.
Age: Early Cretaceous, around 125 million years ago.
Where in the world?: Liaoning Province, China.
What sort of critter?:Zhenyuanlong was a dromaeosaur – a feathery, carnivorous dinosaur closely related to Velociraptor.
Size: About five feet long.
How much of the creature’s body is known?: A nearly-complete skeleton, including fossilized feathers.
Claim to fame: Feathers didn’t evolve for flight. They allowed it. Paleontologists have recognized this since the 1970s, at least, and numerous discoveries of non-flying dinosaurs covered with fluff, bristles, and other types of wispy integument have confirmed that feathers and their forerunners must have had functions outside the aerodynamic realm. Described by Junchang Lü and Stephen Brusatte, the dinosaur Zhenyuanlong adds to that picture with its extravagant coat of feathers.
A cousin of the famous Velociraptor, the newly-named Zhenyuanlong belongs to a group of dinosaurs already well-known to have had protofeathers. What makes Zhenyuanlong remarkable, however, is that it offers a look at a different way to be a fuzzy raptor. Zhenyuanlong was large compared to other dromaeosaurs found around the same time and place, and the dinosaur had relatively shorter arms than its close relatives. Nevertheless, Zhenyuanlong had an extensive coat of well-developed feathers on its arms and along its tail (although it appears to be missing the long leg feathers dromaeosaurs like Microraptor sported).
Why a short-armed, probably flightless dromaeosaur would have such complex feathers isn’t clear. Perhaps, Lü and Brusatte write, they indicate Zhenyuanlong evolved from flying ancestors and maintained the plumage through a kind of evolutionary inertia. Then again, long arm feathers can still be useful in giving dinosaurs a better grip on inclined surfaces while running as well as keeping small prey down. Now that Zhenyuanlong has a name, paleontologists can start exploring these possibilities.
Since most dinosaur names consist of long, polysyllabic gargles—Parasaurolophus, Therizinosaurus, Pachycephalosaurus—it is refreshing that the latest addition to the family has the shortest one yet.
It is simply Yi.
In full, it is Yi qi, which comes from the Mandarin for “strange wing” and can be roughly butchered as “ee chee”. The name hints at this pigeon-sized animal’s most remarkable feature. Each of its hands had a long bony rod extending from the wrist. This rod seemed to support a membrane, much like that of a flying squirrel or bat.
Yi was a dinosaur with bat-like wings! What an astonishing find!
Until now, the assumption was that prehistoric reptiles took to the skies in one of two different ways. The dinosaurs did so with feathers. Many species were covered in downy insulating fuzz, and some small predatory species elaborated these into true, flight-capable feathers—long, flat vanes that protruded from their arms (and sometimes their legs). These winged creatures gave rise to the first birds. Meanwhile, the pterosaurs evolved a very different type of wing, by greatly lengthening their fourth fingers to support a membrane of skin and muscle. (Pterosaurs are often lumped with dinosaurs but belonged to a totally separate group.)
These wings were mutually exclusive: dinosaur or pterosaur, feathery or leathery. But Yi went for both options! It had membrane wings with a feathery covering on the leading edge. It shows that at least some dinosaurs had independently evolved the same kind of wings as pterosaurs—an extraordinary example of convergent evolution.
“This is refreshingly weird,” says Daniel Ksepka from the Bruce Museum, who was not involved in the study. “Paleontologists will be thinking about Yi qi for a long time, and we can surely expect some interesting research into the structure and function of the wing.”
There’s only one known fossil of Yi. A farmer in China’s Hebei Province found it around eight years ago., and the Shandong Tianyu Museum of Nature bought it shortly after. Xing Xu and Xioating Zheng from Linyi University, who discovered the creature, first laid eyes on it in 2009 and started working on it in 2013. “It looked special to me,” Xu recalls.
As the team exposed and analysed the specimen, they worked out that it was a scansoriopterygid—a group of small, feathered dinosaurs with very long third fingers. These species were reputedly good climbers (their name means “climbing wing”) but there was no evidence that their feathers were good enough for flight.
The same applied to Yi—its feathers, covering its skull, neck and limbs, were stiff filaments that ended in paintbrush-like tips. They were very different to the flight-capable plumes of birds.
Then, the team noticed the weird rod. It stuck out from each of the dinosaur’s wrists and was longer than its forearm. It’s not a finger, but its chemical composition revealed that it is indeed a bone, or perhaps a piece of hardened cartilage. The team had no idea what it was. “When I saw the bone, I was really confused,” says Xu. “There is nothing comparable in any other dinosaur.”
But, as Corwin Sullivan from the Chinese Academy of Sciences realised, there is something comparable in flying squirrels. These rodents glide from tree to tree by expanding a membrane that stretches from their wrists to their ankles. They deploy this membrane by splaying their limbs and extending a long piece of cartilage (called the styliform process) that protrudes from their wrists. Bats have a similar piece of cartilage (the calcar) on their feet, and pterosaurs had a similar bone (the pteroid) on their arms.
All of these structures do the same thing: they support a membrane that keeps their owner in the air. Yi’s wrist rod was almost certainly fulfilling the same role. “As far as i know, this is the only plausible interpretation,” says Xu. He even found several patches of what look like sheet-like membranes, surrounding the rods and fingers of both hands. Again, they’re unlike anything seen in other dinosaurs.
“The ‘bone’ seems to be what they say it is, and they have made appropriate studies to show it isn’t something else,” says Michael Benton from the University of Bristol. “So, yes, it seems real, and, my goodness, what a further broadening of flight capabilities in paravians!” (That’s the group of dinosaurs that includes the scansoriopterygids, celebrities like Velociraptor, and all birds.)
But Yi “is not necessarily as weird as it might first seem, in an evolutionary sense,” says Michael Habib from the University of Southern California. “Living birds actually have membranes around their forelimbs, including a well-developed membrane in front of the elbow called a propatagium. Feathers cover [these] parts of the wing, obscuring the soft tissues.” Yi simply extended these membranous parts with the help of their weird extra bone.
For the moment, the team can’t work out how it held its wrist rods, and so can’t reconstruct the true shape or capabilities of the extended wing. This is crucial. A broad membrane, Habib says, would have kept Yi qi stable in the air, and allowed it to launch and land safely. With a narrower membrane, it would have needed to fly or flap very fast to stay airborne, and to take off at high speeds.
“Yi might have moved through the air with a combination of flapping and gliding flight, though it probably relied more on gliding,” says Xu, who is planning to search for more specimens. “There are many questions remaining to answer about this bizarre dinosaur.”
For now, this discovery reminds us that the evolution of flight among birds and other dinosaurs was not a simple story. In the late Jurassic period, when Yi lived, there were all manner of dinosaurs with varying shapes, sizes, and numbers of wings. It was a world of not-quite-birds and just-about-birds—and now bat-winged dinosaurs, too! “What a grand age of experimentation!“ says Ksepka.
“This may also be evidence that flight evolved multiple times within dinosaurs—perhaps three or more times,” adds Habib.
Reference: Xu, Zheng, Sullivan, Wang, Xing, Wang, Zhang, O’Connor, Zhang & Pan. 2015. A bizarre Jurassic maniraptoran theropod with preserved evidence of membranous wings. Nature http://dx.doi.org/10.1038/nature14423
PS: Here’s another odd thing about Yi. Its feathers preserve traces of melanosomes—small sacs of coloured pigments. That’s not unusual in itself; several scientists have used melanosomes to reconstruct the colours of fossil feathers. But Yi has some of the largest melanosomes ever seen. “I had to double-check to make sure I did not misread the measurements,” says Ksepka.
Every day I’m home, I’m surrounded by cats. The clowder is rarely more than a few feet away while I tap away on the keyboard. One of them is lounging on the back of my chair as I write this, considering whether she wants to oust me from my seat or not. So you can believe me when I tell you that I’m very familiar with whiskers, and seeing feline faces all day got me wondering about whether one of my other favorite groups of animals sported stiffened structures on their faces, too.
Whiskers – technically called vibrissae in mammals – are an important part of my cats’ sensory arrays. When Margarita abruptly tears across the apartment for reasons I can only speculate about, her whiskers can tell her if she’s cutting to close to a wall so that she doesn’t run headlong into the doorway. And they’re certainly useful when she plays fetch. She fans her whiskers forward so that those hairs send vibrations back to the skin and she can orient her mouth just right to catch her “prey”, and the vibrissae on her arms help her triangulate the right angle of attack.
Such sensory structures aren’t unique to mammals, though. Some birds independently evolved feathers that act like whiskers.
While prominent feathers on birds’ faces might look showy, in many cases they actually carry alternate – or, at least, additional – functions. Simple, whisker-like feathers around the eye and nose can help keep out dust and dirt. And the motion of these bristle-like feathers can be felt in the skin, helping birds like the whiskered auklet navigate tight spaces. Now here’s where Velociraptor and company come in.
Non-avian dinosaurs keep getting fluffier and fluffier. Protofeathers and feather-like body coverings keep popping up all over the dinosaur family tree. While paleontologists have often focused on how these feathers may have been useful for insulation, display, and, in some cases, flight, the similarities between the ways my cats and whiskered auklets use their independently-evolved bristles made me wonder if predatory dinosaurs such as Velociraptor and Tyrannosaurus might have had specialized, whisker-like feathers on their arms or faces to help them make precision movements of claw and jaw when taking down prey.
I wasn’t the only one entertaining such scenarios. In a new Evolution article, University of Alberta paleontologists W. Scott Persons and Philip Currie speculate that some non-avian dinosaurs partially felt their way around the Mesozoic world with brushes of facial feathers. More than that, Persons and Currie suggest that the very first feather forerunners might have had more to do with touch than keeping warm.
Since the discovery of fluffy little Sinosauropteryx in 1996, paleontologists have centered on two different functions for the first feathers. A downy coat was probably useful for insulation, and, as reinforced by work on fossil feather colors as well as the anatomy of these structures, protofeathers could have been startling display feathers.
Each of these scenarios presents unresolved issues for feather origins. For protofeathers to be effective as insulation, Persons and Currie write, the fluff had to cover a significant part of the dinosaur. Perhaps fuzz really did start out this way, in swaths rather than as isolated wisps, but we need more exceptionally-preserved early dinosaurs to find out. And as for display, flashy dinosaur plumage is often said to be some sort of sexual or signaling structure without much further investigation. Given that paleontologists have been entertaining an ongoingdebate about whether or not bizarre dinosaur structures can be considered signs of sexual selection, experts shouldn’t assume that what stands out to us was therefore the result of dinosaurian style preferences without more detailed investigation.
As an alternative, Persons and Currie suggest that feathers may have started as simple sensory structures. (They call them “bristles”, but paleontologists often use that as a general term for structures on dinosaurs like Psittacosaurus. Given the functional interpretation of the protofeathers, I’m going to keep calling the facial feathers whiskers here.) Cylindrical, whisker-like feathers on a non-avian dinosaur’s face may have had the dual benefits of trapping debris and providing another way to detect nearby prey or avoid smacking into a tree. From there, the researchers propose, additional fluff may have spread over dinosaurian bodies, eventually being co-opted to become warm coats, biological billboards, and structures useful for taking to the air.
While speculative, the idea that some dinosaurs had feathery whiskers isn’t outlandish. Today’s avian dinosaurs have feathers modified for this purpose, and perhaps some of their non-avian forerunners and relatives independently evolved the same structures. But the idea that whiskers were the original feathers is a little shakier.
No one, Persons and Currie point out, has found dinosaur whiskers yet. This might be because non-avian dinosaurs didn’t actually have them. But it may be that whiskers are only rarely preserved or haven’t been recognized just yet. For now, we can only hope that researchers stay on the lookout for possible dinosaur whiskers – and other odd plumage – as they continue to discover and study fossil dinosaurs.
The real test may be dinosaurs like Sinosauropteryx and Sciurumimus. These small dinosaurs had extensive coverings of simple protofeathers, but they haven’t yet shown any sign of whiskers on their arms or faces (where an enhanced sense of touch would be most advantageous). Either the structures haven’t been found or they were absent.
If the latter option is the case, it would be strange for carnivorous dinosaurs to evolve useful structures for detecting prey and then later lose those structures. Mammals offer a parallel case. The origins of hair are murky, too, but one hypothesis proposes that vibrissae were the first hairs. Rather than losing whiskers, though, mammals – particularly predatory beasts – retained them as fur covered the rest of their bodies. A lack of sensitive face feathers on archaic dinosaurs coated in fluff is a hurdle to the hypothesis that whiskers came first.
Whether dinosaurs had whiskers and what those plumes had to do with the origin of feathers are questions that may not be resolved for years to come. But there has never been a more wonderful and productive time for dinosaur paleontology. New finds and analyses are coming out at a rapid-fire rate, and Persons and Currie have formally articulated a hypothesis than can be checked against the fossil record. We’ve learned time and again that non-avian dinosaurs were stranger than we possibly could have imagined, and I wouldn’t be shocked if one day paleontologists came forward with whiskery, kitten-faced dinosaur.
[In a similar vein, I wrote about the possible acoustic properties of non-avian dinosaur feathers here.]
Birds are dinosaurs. That’s a fact underscored by dozens upon dozens of discoveries in the last 30 years. Free of the historic blinders that cast dinosaurs as monstrous reptiles, we’re now gaining an ever-greater appreciation for how bird-like Tyrannosaurus and its famous relations really were.
In fact, many traits we think as unique to birds evolved hundreds of millions of years ago. Reproduction by laying shelled eggs goes back to some of the first vertebrates to carve out a living on land, around 315 million years ago. Fluffy body coverings might go back to the earliest dinosaurs. And air sacs that radiate out from the respiratory system into bone go back to the last common ancestor of dinosaurs like Apatosaurus and Allosaurus, at least.
But what about flight? More than anything else, the ability to take to the air seems to distinguish birds from most of the extinct dinosaurs, and this is where the picture starts to get a little fuzzy. For symbolic reasons, at least, avian flight marks the arrival of something new and different on the evolutionary scene, and paleontologists have spent over a century trying to tease out the transition.
The latest entry into the field was just published by Yale University researchers Teresa Feo, Daniel Field, and Richard Prum. They focused on one particular part of dinosaurian anatomy – asymmetrical feathers.
The presence of asymmetrical wing feathers – with a short leading edge and longer trailing edge, such as the primaries on the wing – has often been taken as a rough proxy for some kind of flying behavior in extinct, feathered creatures. That’s because this shape helps create lift. As Feo and colleagues point out, though, associating a general shape with the ability to fly is too coarse an interpretation. Many flightless birds have asymmetrical feathers that they inherited from their flying ancestors, including streamlined penguins that flap through the water. In order to tease out the clues of how these feathers contributed to flight, researchers have to comb over the plumage in closer detail.
Feo, Field, and Prum looked to geometry to see how the feathers of non-avian dinosaurs like Microraptor compared to those of early birds, such as Archaeopteryx, and their living relatives. Specifically, the researchers zeroed-in on the angles and lengths of asymmetrical feather barbs – the shafts that run perpendicular to the central rib that the rest of the feather branches out from. Given that the length and the angle of the feather barbs alter flight ability, Feo and coauthors could come up with a better idea of how skilled extinct dinosaurs would have been in the air.
In some ways, the primaries of Archaeopteryx and Microraptor were like those of other birds, including living species. The barbs on the “cutting edge” of their feathers were held at small angles relative to the shaft they branched from. This kept the leading edge of the feather relatively rigid and better for pitch control. But, on the trailing edges of their feathers, Archaeopteryx and Microraptor were different from flying birds.
Along the trailing edge of the primaries, Feo and coauthors point out, the barbs of flying birds are positioned at relatively large angles. This helps gives the feathers flexibility and maintain a stable airfoil. But in Archaeopteryx and Microraptor, the trailing-edge barbs were held at small angles. This kept their primaries stiff and less responsive, limiting their degree of flight control.
From their fossil sample, Feo and colleagues hypothesize that “modern” asymmetrical feathers with small leading and trailing barb angles first evolved in early, toothed birds like Confuciusornis and Eopengornis, around 125 million years ago. Along with other traits that evolved around the same time – such as a “winglet” called the alula and expanded bony keel – the barb angles hint that these birds really were flying.
But what about Archaeopteryx and Microraptor? Paleontologists have gone back and forth over whether or not these dinosaurs could fly for years. The emerging consensus is that they were able to move through the air somehow, but perhaps not in a way that would be familiar to us. While they weren’t capable of the “modern avian flight stroke” – the crux of these investigations – Archaeopteryx and Microraptor may have used some combination of gliding and flapping. Watching an airborne Archaeopteryx must have been quite a sight, and, from feather and bone, that is exactly what many paleontologists are trying to envision.
What did Tyrannosaurus sound like? The movies tell us that the dinosaur shrieked and roared, befitting its status as one of the largest carnivores of all time, but the truth is that we don’t really know. The soft tissues needed to reconstruct the dinosaur’s sounds have never been found, rendering the ancient bones mute. The same is true for almost every other species of non-avian dinosaur yet discovered. The only exceptions are the crested hadrosaurs, whose circuitous nasal passages have allowed paleontologists reconstruct their tuba-like calls.
Without preserved soft tissues, the nuances of the dinosaur vocal range remain out of earshot. But it’d be a mistake to simply lament the silence of the fossil record and move on. Dinosaurs would have been able to make noise in other ways. As paleontologist Phil Senter pointed out in a review of prehistoric animal sounds, non-avian dinosaurs may have communicated with each other by “hissing, clapping jaws together, grinding mandibles against upper jaws, rubbing scales together, or use of environmental materials (e.g. splashing against water).” Even without dinosaurian roars, the Mesozoic wouldn’t have been entirely quiet.
And there’s another possibility. Enfluffled dinosaurs may have been able to talk with their plumage.
Each year dinosaurs keep getting fuzzier and fuzzier. Feathers, protofeathers, and strange bristles are turning up on an increasing number of non-avian dinosaurs, indicating that such secondary body coverings either evolved multiple times in the dinosaur family tree or were inherited from the last common ancestor of all dinosaurs. And while such dinosaurian fluff and fuzz is often considered in the context of visual displays, it’s also relevant to sound.
Modern, avian dinosaurs may be our window into the past here. When male club-winged manakins try to impress females of their species, they make a “Tick-Tick-Ting” sound. They do this with their feathers. Thanks to some specialized feather anatomy, ornithologists Kimberly Bostwick and Richard Prum found, the male manakins are able to rub their feathers together to make sexy sounds that are just as loud as a typical bird song. And birds are hardly the only vertebrates to use structure for sound. Little mammals called streaked tenrecs can make clicking noises with specialized quills they rub against each other thanks to a unique patch of soft tissue called a “quill vibrator disc.”
Perhaps non-avian dinosaurs could have sounded with stridulating feathers and bristles, too. Maybe bird-like species such as Anchiornis or even Velociraptor could rub their exquisite feathers together to tick or buzz, and I can’t help but imagine Psittacosaurus shaking its tail to rustle its quill-like bristles.
Whether any extinct dinosaurs actually behaved this way, however, relies on first discovering intact sound-specialized structures along with the bones. Such a find seems like a long shot. But if paleontologists someday find a dinosaur fossil with acoustic feathers, they might be able to do something long thought to be impossible.
Just as paleontologists have been able to reconstruct dinosaur colors on the basis of feather microanatomy, structure may allow researchers to replay dinosaur sounds. In fact, paleontologists have already achieved such a feat with a very different animal. Working from a delicately-preserved fossil, paleontologist Jun-Jie Gu and colleagues were able to reconstruct the sound of a Jurassic katydid that had acoustic “files” on its wings which created a chirping noise when rubbed the right way. If paleontologists someday find a dinosaur with similarly musical plumage, we will be able to hear them sing again for the first time in over 66 million years.
[Thanks to Phil Torres for telling me about the club-winged manakins and inspiring this foray into speculative paleontology. Top art by the most-excellent John Conway.]
Birds are dinosaurs. This fact is easily understood by looking at the scaly feet of a chickadee or by comparing a chicken wing to a Velociraptor arm. But given that birds are the only “terrible lizards” around today, it’s easy to forget that they also thrived alongside their non-avian kin for 84 million years. The first birds evolved in the Late Jurassic, roundabout 150 million years ago, and they became a widespread and successful branch of the dinosaur family tree.
The trouble is finding those birds. They were often so small and so delicate that their bones didn’t make it into the fossil record in the same abundance as their larger, more robust relatives. And that’s where a different sort of fossil comes to the rescue. Thanks to tracks, paleontologists have been able to detect the presence of Mesozoic birds in strata where their bones have remained elusive. Among the latest to be uncovered are dozens of birds tracks found in eastern Utah.
Discovered in 2005 by fossil reconstruction expert Rob Gaston and paleontologist John Foster, the tracks were distributed across eight blocks that had tumbled out of their original position as “float” upon the older rocks below. With a little geological sleuthing, though, Foster, Martin Lockley, Lisa Buckley, Jim Kirkland, and Don Deblieux were able to trace the slabs back to the 122-119 million year old Poison Strip Member of the Cedar Mountain Formation. This formation has been producing a fantastic array of discoveries over the past few years, including a group of Utahraptor mired in quicksand that was discovered near the bird tracksite.
All told, Lockley and colleagues counted over 130 tracks representing 43 different trackways. Most were made by the same species of bird but two were left by non-avian theropod dinosaurs. Exactly what the birds looked like is unknown. No one has found the bones to reconstruct their skeletons and see, if like other Cretaceous birds, they still had teeth. But the thin-toed, spread anatomy of their feet was very similar to that of modern shorebirds. Along with the fact that the tracks were imprinted in the sand along a Cretaceous lake, the collection of tracks likely represents a single species of bird that inhabited ancient shores.
The Utah traces are among the oldest bird tracks in North America. (Shorebird tracks found in South Dakota are the only ones known from the continent that may be a little older.) This helps fill in the pattern of how avian dinosaurs evolved alongside their non-avian relations.
As is the case with tracks of about the same age in South Dakota and Canada, the Utah fossils represent a single species of shorebird. But bird tracks from later in the Cretaceous show multiple foot shapes and, therefore, multiple species. This pattern could be upset by future finds of Early Cretaceous tracksites preserving the footprints of multiple bird species, but, as it stands now, North America’s fossils suggest increasing diversity through time. If you were to walk along a lake shore in 122 million year old Utah, you’d likely see a gaggle of similar shorebirds skittering along the sand – an early look at an evolutionary bloom that birds are carrying on to this day.
Hesperornis isn’t a celebrity fossil, but it used to be. Soon after paleontologist O.C. Marsh named the toothed bird in 1872, the Cretaceous avian had the dual distinction of being a wonderful example of evolutionary change – that birds truly had their origin among ancient reptiles – and a target for conservatives who saw the description of such fossils as a waste of government funding. (“Birds with teeth” Capitol Hill politicians incredulously grumped.) But even though Hesperornis has lost its status among the public, paleontologists have not forgotten this diving bird. Researchers are still striving to understand how Hesperornis made its living along a seaway that once washed over the middle of North America. Among the remaining questions – did these toothy birds stay put their entire lives, or did the migrate to follow seasonal warmth?
Bones of Hesperornis have been found in rocks between 83 and 72 million years old from Arkansas to the Arctic. That’s quite a range, and the distribution of their fossils roughly map out the extent of the Western Interior Seaway – a stretch of warm, shallow ocean that once connected the Arctic Ocean with the Gulf of Mexico. Conditions varied significantly along this marine corridor. While sea temperatures in the prehistoric Gulf of Mexico were a comfy 75ºF or so, those in the Late Cretaceous Arctic ranged from about 28 to 46ºF. The presence of Hesperornis bones so far north means they tolerated cool temperatures as well as warm ones, but did it’s been unclear whether they did so year round.
To investigate these competing ideas, paleontologists Laura Wilson of the Sternberg Museum of Natural History and Karen Chin of the University of Colorado looked inside the bones of Hesperornis from Kansas and the Arctic. That’s because bones can act as records of major events in a vertebrate’s life. During a particularly difficult time of an animal’s life when resources are scarce – such as an Arctic winter or a stressful migration – an animal’s bone growth may slow or stop in response, often leaving a marker known as a line of arrested growth (or LAG).
Wilson and Chin didn’t just look at fossil bones. While Hesperornis has most often been compared to loons based on appearance alone, the paleontologists decided to look at the internal bone structure of some modern day penguins to see what patterns overwintering and migration might leave in bone. In particular, they studied sections of bone from gentoo penguins – which stay put through the winter – as well as Adélie and chinstrap penguins, which migrate. If the habits of these penguins were recorded in their bones, then they could be used as proxies for prehistory.
Unlike the carefully-prepared bone sections themselves, though, conclusions from fossil bones are not always clear cut. Wilson and Chin did not find any LAGS or other signs of “hurry up and wait” growth in the bones of Hesperornis. The bird bones showed a pattern of rapid early growth that only slowed towards adulthood, culminating in an outer bone layer called an OCL in the Kansas Hesperornis samples that marks adulthood. (The Arctic sample lacked an OCL but the details of its bone show that it was very close to completing its skeletal growth when it perished.) The modern penguin bones didn’t show any signs of withstanding harsh winters or undertaking long journeys, either. How birds grow explains this confounding twist.
Baby Adélie, chinstrap, and gentoo penguins grow fast. They go from hatchlings to adults within a year. That’s why there aren’t any lines or signs of stopping in their bones, Wilson and Chin point out. It’s too rapid for any environmental triggers to leave such marks. And it looks like the same was true of Hesperornis. Whether born in prehistoric Kansas or the Arctic, Hesperornis chicks achieved their full skeletal development within one year. That means that they were done growing by time the first winter set in. Regardless of whether the Arctic individuals stayed put or started swimming back down in the latitudes, their bones could no longer record the stresses of migration or withstanding the winter.
But there was one curious clue. In the gentoo penguin – the species that doesn’t migrate to escape winter – Wilson and Chin found evidence of even quicker growth rates than the other penguins. This may be because the only way for these penguins to survive is to become adults before the too-short summer is over and winter sets in again. There’s more pressure on them to get to adult size than in migratory species, and the signs of this extra-rapid growth differ from both the other penguins in the study and Hesperornis. Wilson and Chin note that more work needs to be done on living penguins, but perhaps there are still subtle details that will allow paleontologists to piece together the life history of the toothed birds that once swam through the sea that split America.
[For another take on this paper, read Andy Farke’s post here.]
Almost twenty years after fluffy little Sinosauropteryx hopped onto the scene, the existence of feathery dinosaurs is no longer much of a surprise. Paleontologists have found evidence of body coverings from “dinofuzz” to flight feathers on a score of non-avian dinosaur species, ranging from the pigeon-sized, magpie-patterned Anchiornis to the 30-foot long Yutyrannus. But despite this flood of fossil discoveries, paleontologists are still puzzling over the bigger questions behind the plumage. Among the most pressing is when these downy splashes of fluff and fuzz first evolved. A newly-named dinosaur found in Siberia only complicates the question.
Late last year, at the annual Society of Vertebrate Paleontology meeting in Los Angeles, experts and amateurs crowded into a presentation hall to see Royal Belgian Institute of Natural Sciences paleontologist Pascal Godefroit present a new feathered dinosaur. The buzz around the specimen, fueled by the conference program, was that the dinosaur in question was an ornithischian.
Most feathery and fluffy dinosaurs found so far are theropods. This is a major dinosaur subgroup that includes birds and their close relatives, as well as carnivorous terrors like Ceratosaurus and weirdos like Therizinosaurus, going all the way back to where this “beast footed” lineage split from all other dinosaurs. But the dinosaur Godefroit was set to unveil was all the way on the other side of the dinosaur family tree. Ornithischians included the armored, shovel-beaked, and horned dinosaurs, among others, and were as distantly-related to birds as it was possible to be while still being dinosaurs. That’s what made a fluffy ornithischian so strange.
Paleontologists had found two different ornithischians with peculiar body coverings before. In 2002 Gerald Mayr and colleagues announced bristle-like structures jutting from the tail of Psittacosaurus, an early horned dinosaur, and in 2009 Xiao-Ting Zheng and coauthors described Tianyulong, an archaic form of dinosaur called a heterodontosaurid with a mane of similar quills. Together, these animals raised two alternatives: either dinosaurs evolved feather-like body coverings multiple times, or wispy body coverings were an ancestral trait that went all the way back to the last common ancestor of all dinosaurs.
Godefroit’s animal promised to add one more data point to this cluster of flashy ornithischians. Sadly, he couldn’t present his animal during the SVP meeting. Excited dinomaniacs, myself included, trudged out of the hall and into other concurrent sessions. From a geologic perspective, though, the wait for the details hasn’t been long. Today, Godefroit and colleagues have presented their peculiar dinosaur, named Kulindadromeus zabaikalicus, in the pages of Science.
This new dinosaur is already known from a wealth of material. A pair of bonebeds, estimated to be between 169 and 144 million years old, yielded “six partial skulls and several hundred disarticulated skeletons” of Kulindadromeus scattered through the remnants of a Jurassic lake. The bones showed the five-foot-long dinosaur to be a neornithischian, a bipedal herbivore that was not so archaic as Tianyulong but not so specialized as the hadrosaurs or horned dinosaurs. And some of these skeletons not only included different types of scales, but what Godefroit and colleagues interpret as “avianlike feathers.”
In terms of typical dinosaur tubercles, Kulindadromeus had hexagonal scales on its lower legs, rounded scales around the hand and ankle, and rows of large scales along the tail. But the fossils also preserved a trio of feathery structures. Single filaments surrounded the dinosaur’s head, torso, and back, while the dinosaur’s upper arms and legs were covered in multi-filament plumes and the dinosaur’s lower leg sported “ribbon-shaped elements” that have not been seen in any other species so far.
The question is whether these fluffy structures are true feathers or fluffy imitations. This has major implications for when true feathers and their immediate forerunners evolved in dinosaurs. If the dinofuzz on Kulindadromeus really is equivalent to that borne by theropods like Sinosauropteryx, then the beginnings of feathers probably coincided with the origin of dinosaurs. If the structures are superficially the same, but not truly equivalent, then feather-like structures either evolved more than once or diverged from some earlier, as-yet-unseen type of integument.
For the moment, there’s still no way to distinguish between these alternative scenarios. At a basic anatomical level paleontologists have yet to discern whether the structures on Psittacosaurus, Tianyulong, and Kulindadromeus can truly be called feathers. Not to mention the need for better fossils of older dinosaurs, close to where the major lineages split, to follow feather origins, as well as a more refined understanding of the circumstances under which fluff, fuzz, and bristles are likely to be preserved.
But while the headline that “alldinosaurshadfeathers” stretches the evidence too far, Godefroit and colleagues are correct that dinosaurs probably sported a variety of filamentous body coverings in addition to scales.
Feathers or scales aren’t mutually exclusive – look at the feet of a chickadee or pigeon sometime – but are different kinds of body coverings that non-avian dinosaurs wore in startling combinations. This opens up tantalizing possibilities for familiar dinosaurs whose outer appearances are still poorly known. Imagine Allosaurus with whisker-like wisps around its face to help it better nab prey, or an Apatosaurus with a shock of fluff running down its back. I have no doubt that as paleontologists uncover more and more dinosaurs with weird, fuzzy body coverings, our image of what a dinosaur is will become ever-stranger.
What’s scarier than a tyrannosaur? Three tyrannosaurs. That’s simple, undeniable math. The question is whether or not the tyrant dinosaurs ever prowled together in real life. Up until now, the evidence has been equivocal. But a trackway found in British Columbia finally provides firmer ground for speculation on the social lives of these celebrated carnivores.
The idea that large tyrannosaurs – like Albertosaurus and the mighty Tyrannosaurus itself – worked together to bring down prey isn’t new. University of Alberta paleontologist Philip Currie has been championing the hypothesis for over a decade, citing bonebeds that contain multiple individuals of the Late Cretaceous tyrannosaurs Albertosaurus and Daspletosaurus. And three years ago Currie went to the public with his idea in the form of a book and documentary called Dino Gangs. “If dinosaurs hadn’t become extinct, would gangs of killer tyrannosaurs now rule the world?”, the hyperbolic documentary asked.
At the time, I wasn’t sold on tyrannosaurs being communal carnivores. Just because a whole bunch of dinosaurs ended up buried together doesn’t mean that they actually lived and hunted together. A mass of dinosaur skeletons – such as an Albertosaurus bonebed containing 12 individuals – can contain elements from animals that died at different times or were brought into a small area by unusual circumstances. Accumulations of dinosaur bones represent the circumstances of death and burial more than clues about life.
If evidence for social tyrannosaurs exists, it has to be in a less ambiguous form. Tracks hold the most potential.
Tracks and other traces are signs of prehistoric behavior and biology. For example, we know tyrannosaurs fought by biting each other on the face from healed wounds on their skulls. Whether tyrannosaurs lived in groups, though, requires something more. While an Albertosaurus bonebed is ambiguous evidence for social behavior, a trackway showing that tyrannosaurs walked together would be a much clearer sign of social tyrants.
This is what happened with “raptors.” The pack-hunting idea played out in Jurassic Park was based on a Deinonychus quarry that contained multiple predators as well as the apparent prey, but the site only really shows that several of the sickle-clawed predators died at the site. It has only been more recently, with the discovery of distinctive, two-toed tracks that paleontologists have been able to confirm that raptors at least sometimes walked together.
The problem for tyrannosaurs is that their footprint record is very poor. Some supposed tyrannosaur tracks – such as a big, three-toed prints found in a Utah coal mine – turned out to be prints left by shovel-beaked hadrosaurs. Other, authentic tyrannosaur tracks are isolated specimens, recording a single footfall on the Cretaceous ground and nothing more. This historic dearth of trace evidence is what makes the tyrannosaur trackway discovered in Canada so important.
In October 2011, a few months after Dino Gangs debuted, local outfitter Aaron Fredlund discovered two dinosaur tracks in the roughly 75 million year old rock of northeastern British Columbia’s Wapiti Formation. An excavation by the Peace Region Palaeontology Research Centere turned up a third track in the sequence, but the best find didn’t come until the following summer. In August 2012 paleontologists and volunteers found two more sets of tracks right next to each other.
Unfortunately for paleontologists, the dinosaurs who left the footprints did not die in their tracks. But, as reported by Peace Region Palaeontology Research Centre researcher Richard McCrea and colleagues in a new PLoS One paper, there was only one type of dinosaur alive in the area that could have left such prints. All of the tracks are big – with a length of over 19 and a half inches – and were made by a dinosaur with three forward-pointed toes that ended in sharp claws. The tracks had to be made by a tyrannosaur.
Which species of tyrannosaur created the tracks is unknown. Three large tyrannosaurs – Albertosaurus, Gorgosaurus, and Daspletosaurus – all lived in western Canada at the time the tracks were made. But the tracks are distinctive enough that, following trace fossil convention, McCrea and coauthors have given them their own name. The tracks have hence been labeled Bellatoripes fredlundi, an homage to the “warlike foot” shapes of the tracks found by Fredlund.
While they might superficially look like trident-shaped potholes, the tracks provide a wealth of information about the animals that made them. The animal that made the first-discovered trackway, for example, was apparently missing the end part of the second toe of the left foot, leaving impressions of the nub as it walked. And the details of the footprints showed that these tyrannosaurs walked in a different way than some other carnivorous dinosaurs. Trackways made by predatory dinosaurs typically show that the dinosaur put their foot down and lifted their foot out in a forward motion, while the tyrannosaur tracks suggest that these animals lifted their feet out in a backwards motion.
But the arrangement of the tracks is what has gained the most attention and plays into speculations of tyrannosaur packs. All three trackways face the same direction and were made in close proximity, with 18 feet between Trackway A and B, and eight feet between B and C. While there’s a chance that the trackways were made by three individuals that traveled the same area at different times, McCrea and colleagues consider this unlikely. Tyrannosaurs were a rare part of the fauna, there is no sign of an obstacle that would create a bottleneck requiring tyrannosaurs to walk the same path, and the detail of the tracks – down to foot scales on some – hint that they were all made around the same time, while substrate conditions were consistent. That two, if not three, tyrannosaurs were walking together is the simplest explanation of the pattern.
So did tyrannosaurs hunt in packs? Maybe. The tracks, stunning as they are, can only take us so far.
There remains a shred of doubt that these footprints were made by a single social group. If the tracks showed some sign of interaction between the animals – like raptor footprints that show one adjusting its course to move out of the way of another – then we could be sure. In fact, I’ve encountered this problem out in the field while looking for tyrannosaurs and their Mesozoic kin. Sometimes I’ll find myself closely following the tracks of another fossil hunter, even though they passed by minutes or hours before I did, and I’ll leave my own trail right alongside theirs.
But let’s say the site really does record a social group, as it seems to. We don’t know why the tyrannosaurs were walking together. Was this a family? A hunting party? Suitors trying to follow a mate? Nor do we know how long the band remained together. The tracks only record a few brief moments in Late Cretaceous time when, if even for a moment, tyrants flocked together.
Early last week, in the pages of PNAS, paleontologist Dan Ksepka unveiled one of the largest dinosaurs ever to fly. With a 21 foot wingspan, the 25 million year old Pelagornis sandersi was a pseudotoothed, albatross-like bird that would dwarf any avian in the skies today, and even gives the previous record holder – the heftier Argentavis magnificens – some close competition. And now, in a case of fossil coincidence, paleontologists have announced a much, much older dinosaur that sets the size record for some the very earliest feathery fliers.
Named Changyuraptor yangi, this 125 million year old dinosaur was not a bird. But it was close. Described by Bohai University paleontologist Gang Han and a team of experts in Nature Communications, this feathery creature was a non-avian dinosaur that took to the air in forests that once clothed Cretaceous China.
And while Changyuraptor shared many traits with close relative Microraptor, such as “hindwings” on the legs and elaborate tail feathers, this newly-named dinosaur was far bigger. While Microraptor was hawk-sized, Changyuraptor was about as big as an eagle, stretching about 4.3 feet from snout to tail tip. And on that big body, Changyuraptor had tail feathers stretching almost a foot long – the longest yet found on any non-avian dinosaur.
Despite all that plumage, though, Changyuraptor was not a bird. The very first birds split off from the rest of the dinosaur family tree about 25 million years earlier, and Changyuraptor, like Microraptor, belonged to a close, but non-bird lineage called dromaeosaurids. Nevertheless, Changyuraptor and kin may yield essential insights into how dinosaurs took to the air.
“There are two possibilities, which we still need to resolve,” says University of Southern California flight expert and study co-author Michael Habib. “This first possibility is that this tells us something about the evolution of flight because it’s a different way of flying than what leads to true birds,” Habib says, particularly because dinosaurs like Changyuraptor might represent an independent origin of flight that nevertheless shared some common facets with what early birds were doing. This sort of evolutionary convergence might indicate shared constraints on how feathered dinosaurs could evolve flight.
“The other possibility, which is better-supported at present,” Habib says, “is that these four-winger kinds of morphology were actually quite common amongst paravians”, or the larger group that includes birds as well as their close, feathery, non-avian relatives. The fact that many dinosaurs near the base of the bird family tree – either on that line or close to it – had elongated leg feathers means that dinosaurs like Changyuraptor can act as proxies for how birds evolved flight.
In either scenario, Habib notes, Changyuraptor and other quad-winged dinosaurs suggest that “protobirds would have a lot of different control surfaces.” Rather than the long leg and tail feathers being oddities indicative of a weird way of flying, these structures may have been crucial for flying dinosaur stunts in the days before the majority of flight control shifted to the front wings. Changyuraptor doesn’t represent the addition of extra wings, but may embody critical surfaces that the first birds and other flying dinosaurs needed to turn, brake, and land early in their evolution.
But despite the clear hallmarks of aerodynamic adaption in the bones and plumage of Changyuraptor, “We don’t know how it was actually moving through the air,” Habib says. As yet, paleontologists are still narrowing down possibilities.
Soon after the discovery of Microraptor, for example, some paleontologists reconstructed the dinosaur flying with a spread-eagle or biplane posture. But this doesn’t make anatomical sense.
“Until we find a microraptorine that shows anything else, I wouldn’t expect them to have much more flexibility at the hip than other theropods,” Habib says, meaning that Microraptor and Changyuraptor probably held their legs directly beneath their bodies while moving through the air. And even if these dinosaurs had a little more hip flexibility than usual, Habib adds, that could be an adaptation to tree-climbing or some other mode of locomotion on a surface rather than flight. Changyuraptor was not the dinosaur equivalent of a flying squirrel.
Rather than acting like a modern bird or like an earth-bound Velociraptor, Changyuraptor probably had unique habits that were lost to Cretaceous time. If forced to sketch the dinosaur’s lifestyle, Habib says, he’d expect that “these things are semi-arboreal, landed on the ground but like to be in trees, and probably could execute dynamic and relatively short aerial maneuvers” like turning and braking fast to get to the ground, perhaps to pin down small prey. Maybe they were even able to flap their wings a little to give themselves a little more push, Habib says, but even within such scenarios, the extensive feathering of dinosaurs such as Changyuraptor indicates that once these creatures got into the air, they were able to use their arms, legs, and tails to deftly navigate through the dense stands of trees they flew through.
Understanding how Changyuraptor flew, and what the dinosaur means in the broader picture of how flight evolved, relies on future research. No paper stands alone. Habib is already on it. “One nice thing about doing the analysis with this animal, developing predictions of its tail performance, is that it’s probably applicable” to other feathered dinosaurs, Habib says. “The interest in the animal – new species, big, nice tail – is that it’s a springboard for a broader analysis of paravian tails.” Putting all those pieces together, plumage and prehistoric bone alike, connect toothy little raptors to the chickadees hopping about outside your window.
Baby flamingos are fluffy and adorably awkward. But they’re not pink. The fuzzy infants start off as white or gray, only later earning a distinctive rosy hue. That’s because these beautifully dorky birds don’t make their own color, but co-opt it from their microscopic meals.
Flamingo pink is created by carotenoids – organic pigments present in the algae and tiny crustaceans flamingos sieve from the water. Rather than breaking down in the birds’ stomachs, though, the pigments enter the bloodstream and get sucked up into feathers as they form. How pink a flamingo is depends on what the bird is eating.
This biological borrowing isn’t unique to flamingos. Many other birds have carotenoid-created colors in shades of red, orange, yellow, pink, and purple. But when did such dazzlingly-daubed feathers evolve?
The fossil record is only of limited help here. Even though a surfeit of gorgeous fossils has shown that feathers go back deep into the dinosaur family tree – 160 million years at the very least – paleontologists have so far only been able to reconstruct the colors of preserved feathers on the basis of microscopic organelles called melanosomes. These itty bitty bodies are related to colors like black, gray, brown, and rust, but the brighter carotenoid colors left no such structural trace in prehistoric plumage. Nevertheless, by looking at modern birds a team of researchers has outlined when they expect carotenoids to have become an important part of the avian palette.
The first step was looking for how many modern birds have carotenoid-consistentcolors. This, as detailed in a new Proceedings of the Royal Society B study, involved a great deal of poring over plumage patterns.
Using the Hanbook of the Birds of the World and internet resources, Smithsonian scientist Daniel B. Thomas looked at image after image of 9,993 species of living birds for feather colors that could have been created by carotenoids. This wasn’t always straightforward. Ornithologists know that some birds – such as turacos, parrots, and penguins – have red, orange, or yellow feathers that aren’t actually created by carotenoids. Leaving out these possibly-confounding cases, Thomas eventually came up with a count of 2,956 bird species that could have carotenoid coloration.
To check if his identifications were on the mark, Thomas and colleagues ran a pair of tests on previously-collected bird feathers. A technique called high-performance liquid chromatography showed the presence of carotenoids based on light-absorption patterns, while another known as Raman spectroscopy gave away the pigments through spectral bands. Running these tests on feathers from every bird species wasn’t possible, but the scientists picked examples representing all known families of living bird to get an idea of how widely this form of coloration is spread. The researchers even investigated feathers of 124 bird species without apparent carotenoids, just to be sure that they weren’t missing any.
The researchers found that 95 of the 236 living bird families had species with carotenoid-created colors. That figure more than doubles the previous count, and suggests that the ability to express these brilliant pigments evolved multiple times through bird evolutionary history. And to find out when birds started wearing these particular colors, Thomas and coauthors traced the color patterns back through the A Global Phylogeny of Birds supertree.
Drawing backwards from modern species, Thomas and colleagues hypothesize that the first birds to have carotenoid-created colors lived around 56 million years ago. They were likely passeriforms, or “perching birds”, related to the majority of bird species living today. This is 94 million years afterArchaeopteryx, the first bird. But even at it’s avian origin, carotenoid coloration wasn’t especially widespread. Gradually, as birds proliferated, more and more lineages independently evolved to use carotenoids in their plumage, with most carotenoid-carrying lineages evolving the ability after 23 million years ago. Starting at the Miocene, at least, avians have displayed a rainbow of colors comparable to the brilliant birds we see around us today.
So should we avoid coloring feathery, non-avian dinosaurs in pink and yellow? There isn’t yet any direct evidence for such color. A pink Triceratops or purple Brachiosaurus is entirely speculative. Then again, in addition to the many bird lineages that use carotenoids for their colors, there are lizards and snakes that evolved to do the same. If the transfer of carotenoids from food to feather or scale has happened so many times, then perhaps there were non-avian dinosaurs that were decked in red, orange, yellow, and purple. We just need to find a way to see what has been obscured through the lens of hundreds of millions of years.
When people say that scientists are always changing their minds, it’s usually meant as a slight. How can anyone trust conclusions that are so prone to revision? But the fluctuating nature of science is a feature not a bug. It means that our knowledge of the world is constantly being updated in the face of new evidence.
For example, scientists from the University of Bristol recently showed that the evolutionary relationships between different dinosaurs are continuously changing in the light of new fossils. It’s a bit of an etch-a-sketch science—no sooner are family trees drawn before they’re re-drawn again. Even well-known transitions are prone to big shake-ups.
But which of these creatures were the first birds, and which specific group of paravians were their closest relatives? That’s still the subject of heavy debate.
The famous Archaeopteryx, with its winged arms, clawed hands, toothed jaws, and long bony tail, was one of the first fossils to suggest a link between birds and other dinosaurs. Since its discovery in 1861, it has been widely heralded as one of the earliest birds (avialans). But two years ago, Chinese palaeontologist Xing Xu cast its pivotal position into doubt.
Xu, who has discovered more feathered dinosaurs than anyone else, had just found a new species called Xiaotingia. By comparing this creature with Archaeopteryx and other related species, Xu created a family tree that put Archaeopteryx outside the avialans (see diagram below). Instead, it sat next to the dromaeosaurids and troodontids, together with relatives like Xiaotingia and Anchiornis. The first bird was no bird at all.
If Xu was right, the implications would have been profound. For a start, Archaeopteryx clearly had wings with what looked like flight feathers. If it was a bird, then flapping flight probably evolved once in the lineage leading to modern birds. If it wasn’t a bird, then flight evolved twice—once in Archaeopteryx’s groupand again in modern birds. (Or, alternatively, the dromaeosaurids and troodontids all lost the ability by reducing their wings.)
But was Xu right? He himself said that his revised family tree only had “tentative statistical support”. Later in 2011, Mike Lee from the South Australian Museum showed that a different tree, built with different methods, reinstated Archaeopteryx as a bird.
Pascal Godefroit from the Royal Belgian Institute of Natural Science entered the debate this January, with a new dinosaur called Eosinopteryx. There were many echoes of Xu’s study: Godefroit also placed the paravians on a family tree, also concluded that Archaeopteryx was no bird, and also said that the result was statistically weak.
Now, his team is back with yet another maybe-a-bird fossil and yet another revised paravian family tree… and this one contradicts his own earlier conclusions (see diagram below). It once again restores Archaeopteryx as an early bird, while settling related species on different perches.
The fossil in question is called Aurornis xui, and it lived 160 million years ago in northeastern China. Aurornis is Latin for “dawn bird” but the animal’s species name honours Xing Xu. For Godefroit, the decision was an easy one. “Xu has completely revolutionised our vision of dinosaur biology and evolution,” he says. “Although he is still very young and extremely modest, he is probably the most important living vertebrate palaeontologist.” Modest is right—in typical form, Xu says that he’s treating the “great honour” as recognition of the contributions that Chinese palaeontologists have made as a group.
Aurornis is beautifully preserved and has much the same features as Xiaotingia, Anchiornis, Eosinopteryx, and Archaeopteryx. Godefroit’s team believe that it’s a distinct species based on a few characteristic features, although Steven Brusatte from the University of Edinburgh says, “I can’t shake a nagging suspicion that some of these may be juveniles and adults of the same [species]. The only way to know for sure will be to check the internal structures of the specimens’ bones.
Regardless, it’s clear that these animals all lived at roughly the same time, in the same place—the Tiaojishan Formation in northeastern China. This treasure trove of fossils was once home to an entire flock of not-quite-birds and just-about-birds that all and looked rather similar and lived near each other. It’s no wonder that their evolutionary relationships are difficult to entangle.
Godefroit’s team didn’t want to create another weak family tree, so they started from scratch. Italian scientist Andrea Cau scoured the literature and compiled data on 101 species of dinosaurs and birds, scoring each skeleton according to almost 1,000 characteristics. “It’s very impressive,” says Lee. “They considered more than twice as much anatomical information as even the best previous analyses.”
The results put Archaeopteryx back in its traditional roost as an avialan, but no longer as the earliest one. That honour goes to Aurornis itself. It’s now the most primitive bird, followed by Anchiornis, Archaeopteryx and Xiaotingia in that order. (Eosinopteryx, perhaps surprisingly, emerges as a very early paravian that preceded the groups I’ve already mentioned.)
“If Aurornis is the most primitive bird, then it is a huge discovery,” says Brusatte, “but I am not convinced that this paper resolves the early history of birds.” Xu agrees. He says the results deserved to be taken seriously, but adds that several parts of the family tree are inconsistent with earlier work. He’s not just talking about Archaeopteryx. For example, among the other dinosaurs, the troodontids emerge as the group that’s closest to the birds. And the biggest surprise isn’t even mentioned in the paper! Here it is:
Balaur is a Romanian dinosaur that was discovered in 2010. Its discoverers (including Brusatte) concluded that it was a close relative of Velociraptor; the two dinosaurs look very similar, although Balaur is stockier of build and has two sickle-claws on each foot rather than one. But Godefroit’s family tree has it perching firmly within the birds! It’s not alone; other supposedly non-bird species like Rahonavis and Shenzouraptor have been similarly displaced.
That’s a huge shake-up, and puzzling one given these animals’ appearances. “I am suspicious,” says Brusatte. “It is certainly possible that Balaur is a bird but I would be surprised if this is the case.” Godefroit says, “It was also a big surprise for us!” One of their team—Gareth Dyke—even went to check the original specimen to make sure that they hadn’t made any obvious mistakes.
Godefroit plans to publish a separate paper to address this discrepancy. For the moment, it raises some scepticism that has spread to other parts of the tree. “It suggests that some other results, such as the status of Archaeopteryx, Anchiornis, Aurornis and Xiaotingia need further evaluation,” says Xu.
“I am confident that specimens from the Tiaojishan Formation will end up solving this debate somewhere down the line,” says Brusatte, “and I predict that something that all workers agree is a true bird will eventually be found there. Maybe Aurornis is that bird; maybe not.”
As more evidence comes in, the etch-a-sketch will almost certainly shake again, and new versions of the paravian family tree will emerge. “I hope so,” says Godefroit. “Otherwise, palaeontology will become as dull as dishwater!”
Reference: Godefroit, Cau, Yu, Escuillie, Wenhao & Dyke. 2013. A Jurassic avialan dinosaur from China resolves the early phylogenetic history of birds. Nature http://dx.doi.org/10.1038/nature1216
I don’t know why a raven is like a writing desk, but I do know that Microraptor was like a cat. The feathery little dinosaur was cute and glossy, but those adorable features were offset by the carnivore’s excessive pointiness. Even though the non-avian dinosaur was about the size of a raven, and even had feathers with an iridescent corvid sheen, Microraptor still bore pointed teeth, grasping hand claws, and the classic deinonychosaur switchblade talons on each foot. All of this made Microraptor a cuddly-looking little cutter, much like a cat. And the dinosaur shared something else with felines – a fondness for fish.
Since the time the dinosaur was named in 2000, paleontologists have discovered multiple specimens of Microraptor in the 120 million year old lake deposits of China. Many of these are not only articulated, but fossilized to such a fine degree that the petrified remains of their feathers remain intact. This hi-def preservation also safeguarded tatters of Microraptor meals. One Microraptor individual, described two years ago, had feasted on an early bird shortly before perishing in a case of non-avian dinosaur eats avian dinosaur. But a Microraptor known as QM V1002 enjoyed a different last meal.
Fossilized in the position of QM V1002’s stomach, paleontologist Lida Xing and colleagues explain in a new Evolution paper, are the scraps of bony fish. A small mass of fin rays, vertebrae, and other piscine tidbits are tucked between the dinosaur’s ribs, some of which had been etched by digestive fluids when the Microraptor was still alive. The question is whether this Microraptor actually caught fish or just happened along some convenient snacks thrown up onto the lakeshore.
The Microraptor known as QM V1002 fed on fish, just as the one designated IVPP V17972A ingested an archaic bird. But even such intimate associations as food in the guts of predators does not tell us how those carnivores actually obtained that ingesta.
In their paper on the bird-eating Microraptor, Jingmai O’Connor and colleagues proposed that the quad-winged dinosaur actively caught avian prey, thus supporting an arboreal lifestyle for the feathery deinonychosaur. But the Microraptor could have just as easily happened upon a dead bird and snaffled up the free meal. (The ground-dwelling, fuzzy dinosaur Sinocalliopteryx may have done the same.) Without a time machine, there’s no way to tease apart the evidence into a clear case of hunting or scavenging. We only have the mashed-up aftermath.
Such is frustratingly the case with the fish-eating dinosaur, too. While Xing and collaborators mention that fish flesh has a relatively short spoilage time, perhaps arguing against scavenging, there’s no way to distinguish between the two alternatives on the basis of the available evidence. All we know for sure is that Microraptor sometimes ate fish, just as the dinosaur consumed birds and (based on yet another specimen) small mammals. Microraptor was a predatory generalist, Xing and coauthors conclude, probably capable of snatching small prey while also enjoying the occasional opportunity to horf down carrion.
Of course, technical papers must be conservative by nature. Saying that Microraptor hunted fish simply because one specimen was found with partially-digested fish flotsam inside, without considering other possible routes of ingestion, would be careless science. But dinosaurs are not just animals of technical journal arcana. Dinosaurs live where science and imagination meet, and, based on the spread of evidence, there is nothing illegitimate about picturing a Microraptor casting its wings over the water to create fish-friendly shade to attract swimming prey that could be then speared with a quick jab of a talon. Nor are visions of Microraptor gliding through Cretaceous forests to snatch early birds unreasonable or outlandish. These vignettes are prehistoric possibilities – what may have existed but remain just beyond the strict reach of direct scientific examination. The scattered data dots about the natural history of Microraptor may seem to be a sparse, limiting set of criteria, but, connected, they allow us to speculatively revive one of the most magnificent little carnivores of any era.
[Hat-tip to paleontologist Thomas Holtz, Jr. for pointing out the cat-deinonychosaur similarities that inspired this post’s opening lines.
The animal above, with the fetching punk haircut is Anchiornis huxleyi—a small Chinese feathered dinosaur, about the size of a pigeon. If you look at any image of this creature from the past several years, you’ll probably find the same colour scheme—a body of black and grey, black-and-white stripes on the wings, and a red crest and freckles.
That’s because, in 2010, a group of scientists reconstructed Anchiornis’ colours. It was one of the first of several papers that heralded a renaissance of dinosaur art, assigning actual palettes to creatures whose colour schemes were long thought to be unknowable. Colours, after all, don’t fossilise.
But melanosomes do. These tiny pigment-containing structures are found in feathers and contribute to the colours of living birds. They were also found in the feathers of dinosaurs, and withstood the harsh fossilisation process. Look at the right fossil feathers, and you can still see the melanosomes. Their shape reflects their hues—round meatball-shaped ones are reddish-brown, while long sausage-shaped ones are blackish-grey. By studying the shapes of the fossilised melanosomes, scientists like Jakob Vinther from the University of Bristol have been able to reconstruct dinosaur colours.
But a new study raises some questions about their technique. Melanosomes, it turns out, shrink and distort when they become fossilised, so Anchiornis might have looked very differently to the image above.
Is the melanosomes technique in trouble? Not quite. I cover the new study, and the counterarguments, over at Nature News. Head over there for the rest of the story.
Jurassic Park is the greatest dinosaur movie of all time. Aside from being an exceptionally entertaining adventure, the film introduced audiences to dinosaurs that had never been seen before – hybrids of new science and bleeding-edge special effects techniques. The active, alert, and clever dinosaurs that paleontologists had recently pieced together were revived by way of exquisite puppetry and computer imagery, instantly replacing the old images of dinosaurs as swamp-dwelling dullards. Despite the various scientific nitpicks and some artistic license overreach – let’s not talk about the “Spitter” – Jurassic Park showed how science and cinema could collaborate to create something truly majestic. That’s why it’s so disappointing to hear the the next Jurassic Park sequel is going to turn its back on a critical aspect of dinosaur lives. In Jurassic Park 4, the film’s director has stated, there will be no feathery dinosaurs.
Three years after the first Jurassic Park debuted, paleontologists announced that the small theropod Sinosauropteryx was covered in a fine coat of fuzzy protofeathers. This was just the initial drop in a flood of feathery dinosaur discoveries which confirmed that a wide variety of dinosaurs bore archaic forms of plumage, from simple filaments to asymmetrical feathers that would have allowed them to fly. And not only did these discoveries confirm the fact that birds are one lineage of dinosaurs, but that many bird traits – such as feathers – evolved long before the first avians took to the air.
Velociraptor was definitely a feathery dinosaur, and Tyrannosaurusprobably was, as well. In fact, other dinosaurs more distantly-related to birds – such as Triceratops – at least sometimes sported swaths of bristles, quills, or similar body coverings in addition to the pebbly tubercles of their skin. Dinosaurs were far stranger and flashier than anyone expected.
The Jurassic Park franchise quickly fell behind the times. There was not a feather to be seen in 1997’s The Lost World: Jurassic Park. Granted, maybe the filmmakers didn’t have time to incorporate new designs that fluffy little Sinosauropteryx could have inspired. But 2001’s Jurassic Park III blundered by making the barest token effort to update their dinosaurs. The Velociraptor pack that harries fictional paleontologist Alan Grant and companions have little feathery wisps on their otherwise bald bodies. If you’re going to put feathers on dinosaurs, you really have to commit to the bit. The Jurassic Park franchise actually made their dinosaurs look sillier by holding back while science was giving dinosaurs a major makeover.
I have no idea what dinosaurs are due to appear in Jurassic Park 4. I wish that I did. But if Velociraptor and Tyrannosaurus are reprising their roles, these dinosaurs should certainly have some kind of plumage. That comes right from fossil evidence and evolutionary logic. But this is about more than just visuals. A blockbuster summer film has the opportunity to introduce audiences to dinosaurs as have never been seen before on the big screen while simultaneously throwing some much-needed support to evolution by visualizing one of the critical traits that connects avian and non-avian dinosaurs. And speaking as an unabashed dinosaur fan myself, a dinosaur bearing fuzz, feathers, or quills is so much stranger and more wonderful than yet another olive green, scaly monstrosity. Hollywood, let paleontologists help you push the boundaries of fantastic dinosaurs.
Franchise purists might point out that Trevorrow’s plan is in the spirit of the original Jurassic Park. Nobody loves a retcon. But the franchise has already changed its dinosaurs several times with no explanation. The first sequel introduced new color palettes for the dinosaurs, as did the third film. (Not to mention the fact that Jurassic Park III raises the mystery of why Site B contains species that InGen didn’t clone, and never actually resolves this point.) If the dinosaurs are changing from film to film to start with, why not take a jump and show audiences something they have never witnessed before?
We shouldn’t feel bound by what audiences are comfortable with. I’ve never seen a major feature create a truly well-done, scary feathered dinosaur, mostly because they have been afraid to commit to science that differs from our cherished childhood imagery of what dinosaurs were. But if the creators of the original Jurassic Park showed the same fealty to old dinosaurs – tail-dragging, lumbering idiots – then the film might not have had the major cultural impact that it did. It’s time to take a calculated risk and update Jurassic Park‘s dinosaurs.
Of course, I don’t have much any sympathy for complaints that feathery dinosaurs look lame. If feathered dinosaurs look silly, that’s because of a lack of care and attention from those that restore them. Paleoartists John Conway, Emily Willoughby, Julius Csotonyi, and others, by contrast, have aptly demonstrated that feathered dinosaurs can be just as awe-inspiring and fascinating as the naked-skinned monsters we used to know. The only trick is fostering those dinosaurs according to science and looking to living animals to bound our speculation. Dipping a digital Velociraptor in electronic glue and shaking some feathers over it just won’t do.
If you’re being chased by a tyrannosaur, a carefully-arranged coat of fuzzy feathers doesn’t make the dinosaur any less fierce or threatening, just as there is something undeniably unsettling and scary about envisioning a Velociraptor cleaning blood from its colorful plumage after a kill. Letting feathery dinosaurs run wild could inspire a whole new generation of young fossil fans, thrill audiences, and give evolutionary science a much needed boost. When we eventually return to Jurassic Park, I most certainly hope to see feathery dinosaurs strut their stuff.