December 7, 2012
When paleontologist John Ostrom named Deinonychus in 1969, he provided the spark for our long-running fascination with the “raptors.” Similar dinosaurs had been named before–Velociraptor and Dromaeosaurus were named four decades earlier–but the skeleton of Ostrom’s animal preserved a frightening aspect of the dinosaur that had not yet been seen among the earlier finds. The assembled remains of Deinonychus included the dinosaur’s eponymous “terrible claw”–a wicked, recurved weapon held off the ground on the animal’s hyperextendable second toe. Combined with the rest of the dinosaur’s anatomy, Ostrom argued, the frightening claw indicated that Deinonychus must have been a active, athletic predator.
But how did Deinonychus and its similarly-equipped relatives use that awful toe claw? The appendage looks fearsome, but paleontologists have not been able to agree on whether the claw was using for slashing, gripping, pinning, or even climbing prey. Some researchers, such as Phil Manning and collaborators, have even argued that the claws of Velociraptor and related dinosaurs were best suited to scaling tree trunks–a conclusion consistent with the contentious hypothesis that the ancestors of birds were tree-climbing dinosaurs.
All this assumes that the claws of deinonychosaurs correspond to a special behavior, but can foot claw shapes really give away the habits of dinosaurs? That’s the question posed by a new PLoS One study by zoologist Aleksandra Birn-Jeffery and colleagues.
Based on observations of living animals, researchers have often tied particular claw shapes to certain behaviors–relatively straight, stubby claws likely belong to an animal that runs on the ground, while tree-climbing species have thin claws with small, sharp points. But nature isn’t quite so neat as to have a single, tell-tale claw shape for perchers, ground-runners, climbers, and predators. Even then, researchers don’t always interpret claw shapes the same way–depending on who you ask, the foot claws of the early bird Archaeopteryx either indicate that it was a climber or could only run on the ground.
To parse this problem, Birn-Jeffery and co-authors studied the geometry of the third toe claw–on dinosaurs, the middle toe claw–in 832 specimens of 331 species, together representing different lifestyles of birds, lizards, and extinct dinosaurs. The claw shapes didn’t strictly conform to particular behaviors. In the climber category, for example, the frill-necked lizard has lower claw curvature than expected, and, among predatory birds, the common buzzard, secretary bird, and greater sooty owl has less sharply recurved claws that anticipated for their lifestyle.
When the dinosaur data was dropped into the mix, the deinonychosaurs didn’t seem to fit in any single category. The sickle-clawed carnivores fell into the range shared by climbers, perchers, predators, and ground dwellers–these dinosaurs could be said to be anything from wholly terrestrial runners to perchers. And even though the researchers identified a general claw shape that corresponded to walking on the ground–deeper claws with less curvature–the dinosaurs did not strictly fit into this category alone.
Some dinosaurs, such as Microraptor, had claws that might have been suited to climbing. However, dinosaurs that we might regard as behaviorally similar showed differences–Velociraptor seemed to best fit the ground-dweller category, while the larger Deinonychus seemed to have claws more akin to those of predatory birds. This doesn’t mean that Microraptor was definitely a climber, or that Velociraptor wasn’t a predator. As the authors show, the different behavioral categories are not so easily distinguishable as previously thought, and saying that an animal definitely engaged in a particular behavior because of claw shape alone tempts oversimplification.
No wonder there has been such a range of interpretation about dinosaur foot claws! While the new study focused on the third toe claw rather than the famous, second deinonychosaur toe claw, the point of the analysis still applies. Claw geometry alone is not a reliable indicator of behavior. That’s to be expected–as the authors point out, claws are multi-functional, are are unlikely to represent just one type of behavior or habitat. Birds that use their claws to perch may also use them to kill prey, or birds that primarily live in the trees may also forage on the ground. Claw shape is constrained by different aspects of natural history, and reflect flexibility rather than strict adherence to a particular lifestyle. Deinonychosaur claws definitely hold clues to the natural history of dinosaurs, but drawing out those clues is a difficult, convoluted process.
Birn-Jeffery, A., Miller, C., Naish, D., Rayfield, E., Hone, D. 2012. Pedal Claw Curvature in Birds, Lizards and Mesozoic Dinosaurs – Complicated Categories and Compensating for Mass-Specific and Phylogenetic Control. PLoS ONE. 7,12: e50555. doi:10.1371/journal.pone.0050555
December 6, 2012
The most famous set of arms in the history of dinosaurs belong to Deinocheirus–eight foot long appendages from a huge ornithomimosaur that roamed Mongolia around 70 million years ago. But the immense ostrich-mimic wasn’t the only giant omnivore of its time, nor the only one made famous by its imposing arms. About 20 years before the discovery of Deinocheirus, a joint Soviet-Mongolian expedition found extremely long, tapering claws and a few other bones from a gigantic reptile. The identity of this animal took decades to untangle.
Paleontologist Evgeny Maleev described the paltry remains in a 1954 paper. Based on rib fragments, a bone from the hand, and three claws, Maleev believed that he was looking a gargantuan turtle. He named the creature Therizinosaurus cheloniformis–roughly, the “turtle-like scythe lizard.”
The animal’s claws played a key role in the identification. No terrestrial animal had such claws, he argued. Such armaments “may have been originally used by the animal for cutting aquatic vegetation or for another function, constrained by movement and acquiring food.” And even though Maleev only had pieces to work with, he proposed that Therizinosaurus was about 15 feet long with claws at least three feet long. This aquatic, apparently armor-less turtle lived in a time of hadrosaurs, tyrannosaurs, and sauropods.
Therizinosaurus wasn’t recognized as a dinosaur until 1970. In that year, paleontologist Anatoly Konstantinovich Rozhdestvensky published a re-evaluation of Maleev’s fossils that found the rib to be from a sauropod dinosaur, but the hand bone and the claws to be from some as-yet-unknown theropod. This recognition only spawned a new mystery–what sort of theropod dinosaur was Therizinosaurus, and what was the creature doing with such fearsome claws?
More complete forelimb and shoulder material described by Rinchen Barsbold in 1976 showed that Therizinosaurus had extraordinarily robust arms–quite a departure from the trend seen in large carnivorous dinosaurs, in which the arms seemed to become smaller as skulls became more heavily-built. At a time when theropod was generally considered to be synonymous with “carnivorous dinosaur”, it’s not surprising that experts speculated that Therizinosaurus was a monstrous predator who used claws, rather than teeth, to slice up the hadrosaurs and sauropods of its time. That’s the way I encountered the dinosaur in the books I read as a kid–a little-known, Cretaceous hadrosaur-shredder.
What researchers didn’t recognize was that Therizinosaurus represented an entirely new variety of theropod dinosaur. More complete skeletons of related forms such as Segnosaurus, Erlikosaurus, Alxasaurus, and Beipiaosaurus revealed the presence of a previously-unknown group of dinosaurs with long necks, beaked mouths, fat bodies, and stout arms tipped with ludicrously-long claws. These were omnivorous or herbivorous dinosaurs, not carnivores, although paleontologists didn’t immediately agree on what lineage they belonged to. Some thought they might be aberrant ornithischians–on the opposite side of the dinosaur family tree from theropods–or strange variations on the sauropod theme. By the mid-90s, however, paleontologists recognized that these truly were theropods, and ones belonging to the maniraptoran group that also encompasses the strange alvarezsaurs, beaked and crested oviraptorosaurs, the sickle-clawed deinonychosaurs, and birds. This group of tubby, feathery dinosaurs became known as the therizinosaurs.
Although Maleev didn’t recognize it when he named Therizinosaurus, he had found one of the most spectacular dinosaurs of all time–a giant, fluffy, omnivorous dinosaur that challenged what we thought we knew about theropods. Still, our image of Theriziniosaurus relies on the skeletons of more complete, closely-related dinosaurs. So far, we only really know what the arms of this dinosaur looked like, and the hindlimb elements described in the 1980s may or may not belong to another creature. We’re still waiting for the true nature of this undoubtedly bizarre dinosaur to come into focus.
Barsbold, R. 1976. New data on Therizinosaurus (Therizinosauridae, Theropoda) [translated]. In Devâtkin, E.V. and N.M. Ânovskaâ (eds.), Paleontologiâ i biostratigrafiâ Mongolii. Trudy, Sovmestnaâ Sovetsko−Mongol’skaâ paleontologičeskaâ kspediciâ, 3: 76–92.
Maleev, E.A. 1954. “New turtle−like reptile in Mongolia [translated].” Priroda, 1954, 3: 106–108.
Zanno, L. 2010. A taxonomic and phylogenetic re-evaluation of Therizinosauria (Dinosauria: Maniraptora). Journal of Systematic Palaeontology. 8, 4: 503–543.
December 5, 2012
For the past twenty years, Eoraptor has represented the beginning of the Age of Dinosaurs. This controversial little creature–found in the roughly 231-million-year-old rock of Argentina–has often been cited as the earliest known dinosaur. But Eoraptor has either just been stripped of that title, or soon will be. A newly-described fossil found decades ago in Tanzania extends the dawn of the dinosaurs more than 10 million years further back in time.
Named Nyasasaurus parringtoni, the roughly 243-million-year-old fossils represent either the oldest known dinosaur or the closest known relative to the earliest dinosaurs. The find was announced by University of Washington paleontologist Sterling Nesbitt and colleagues in Biology Letters, and I wrote a short news item about the discovery for Nature News. The paper presents a significant find that is also a tribute to the work of Alan Charig–who studied and named the animal, but never formally published a description–but it isn’t just that. The recognition of Nyasasaurus right near the base of the dinosaur family tree adds to a growing body of evidence that the ancestors of dinosaurs proliferated in the wake of a catastrophic mass extinction.
In March of 2010, Nesbitt and a team of collaborators named a leggy, long-necked creature from the same Triassic rock unit in Tanzania they named Asilisaurus kongwe. This creature was a dinosauriform–a member of the group from which the first true dinosaurs emerged–and, even better, appeared to to be the closest known relative to the Dinosauria as a whole. The find hinted that the dinosaur lineage had probably split off from a common ancestor by this time, meaning that the most archaic dinosaurs may have already existed by 243 million years ago. Roughly 249-million-year-old footprints of dinosauriforms found among Poland’s Holy Cross Mountains, described by different researchers later the same year, added evidence that the dinosauriforms were diversifying right from the beginning of the Triassic–not long after the catastrophe that decimated life on earth at the end of the Permian, around 252 million years ago.
Nyasasaurus is another step closer to the first true dinosaurs, and is just as old as Asilisaurus. To find an animal with such distinctive, dinosaur-like traits in the Middle Triassic indicates that dinosaurs already existed, or their ancestral stem was already established. Either way, Eoraptor and kin from South America can no longer be considered as the first dinosaurs, but rather a later radiation of forms. Even though our knowledge of Nyasasaurus is only fragmentary–the dinosaur is represented by a right humerus and a collection of vertebrae from two specimens–the dinosauriform nonetheless marks an additional 12 million years of dinosaur time that paleontologists are only just starting to explore.
Whether or not we ever achieve a more complete view of Nyasasaurus depends on the luck and the caprices of the fossil record. In the new paper, Nesbitt and coauthors point out that the rare, fragmentary nature of the remains found so far reflects that dinosauriforms–and early dinosaurs–were marginal parts of the ecosystems they inhabited. Dinosaurs did not dominate from the very start. They were relatively meek, small animals that lived in a world ruled by archosaurs more closely related to crocodiles. It was only in the Late Triassic and Early Jurassic, when their archosaurian competition was diminished, that dinosaurs became dominant. That means the earliest dinosaurs and their ancestors are few and far between in the Triassic record.
Still, when I asked Nesbitt what Nyasasaurus might have looked like, he cited other dinosauriforms and early dinosaurs as templates to constrain our expectations. Nyasasaurus may have looked quite like Asilisaurus–a leggy animal with an elongated neck–although Nyasasaurus may have been bipedal. Future finds will test this idea, but the fact remains that paleontologists are closing in on what the very first dinosaurs were like. As paleontologists uncover more early dinosaurs and dinosauriforms, the dividing line between the two disappears–scientists are starting to smooth out the evolutionary transition between the first dinosaurs and their ancestors. What role Nyasasaurus played in that transformation isn’t yet clear, but the creature is a signal that over 10 million years more of uncharted dinosaur history remains in the rock.
Nesbitt, S., Sidor, C., Irmis, R., Angielczyk, K., Smith, R., Tsuji, L. 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464, 7285: 95–98. doi:10.1038/nature08718
Nesbitt, N., Barrett, P., Werning, S., Sidor, C., Charig, A. 2012. The oldest dinosaur? A middle Triassic dinosauriform from Tanzania. Biology Letters. http://dx.doi.org/10.1098/rsbl.2012/0949
December 4, 2012
When I think of oviraptorosaurs – feathered, beaked, omnivorous theropods–my mind immediately jumps to Mongolia’s famous brooding dinosaurs and other forms extracted from Asia’s Cretaceous rock. But these weird dinosaurs were present in North America, too. Among the latest to come to the attention of paleontologists is Hagryphus giganteus–a large oviraptorosaur known from little more than a hand and pieces of foot.
Paleontologists started to report on the oviraptorosaurs of North America’s Late Cretaceous in the 1930s. They just didn’t immediately recognize the dinosaurs for what they were. Scrappy remains of these dinosaurs were attributed to the ostrich-like ornithomimosaurs and Cretaceous birds. It was only in the 80s and 90s that researchers began to untangle the identities of these dinosaurs. Based on specimens found in Canada, Montana, and the Dakotas, there may have been at least three different genera present–Caenagnathus, Chirostenotes, and Elmisaurus–around 75 million years ago. That depends on who you ask, though. Researchers disagree about which genera are valid. The material from these dinosaurs is so fragmentary that it’s difficult to tell just how many different forms we’re looking at.
But Hagryphus, described by paleontologists Lindsay Zanno and Scott Sampson in 2005, was different. Represented by a nearly-complete left hand, part of the left radius, and fragments of the foot, this theropod lived further to the south in the 75-million-year-old swampy environment preserved in Utah’s Grand Staircase-Escalante National Monument. Much like other dinosaurs found in the same formation, and other southern species from roughly contemporaneous deposits, the known remains of Hagryphus are distinct from the equivalent bones known from the northern species. Not only was Hagryphys bigger–Zanno and Sampson estimated that the dinosaur was about 10 feet long, quite large for an oviraptorosaur–but bones in the dinosaur’s hand were much more robust.
Zanno and Sampson considered that the unique nature of Hagryphus might be because the individual was an older specimen of one of the northern oviraptorosaurs. They rejected this hypothesis, arguing the the dinosaur’s distinctive hand proportions were more consistent with being it a different taxon than changes due to growth. If they’re right, this fits the general pattern of Utah’s Kaiparowits Formation in preserving dinosaurs that were related to those found in Montana and Alberta but were unique genera and species.
So how many oviraptorosaurs were there in North America around 75 million years ago? We probably haven’t found traces of all of them, but based on what has been described so far there were probably at least two and as many as four. We need more complete skeletons to be sure.
The same problem affects other small-bodied theropod dinosaurs from the Late Cretaceous. Based on teeth and fragmentary remains, paleontologists used to think that the deinonychosaur Troodon had a range from southern Utah to Alaska. As parts of additional specimens come out of the ground, paleontologists are starting to realize that what seemed to be just one dinosaur is really a collection of different genera or species spread across the latitudes. And regardless of what Hagryphys is, the existence of an oviraptorosaur in Utah greatly extends the range of these dinosaurs during the 75-million-year-old time frame. Exposures between southern Utah and Montana may very well hold additional oviraptorosaur specimens–individuals that will be critical to understanding how these dinosaurs evolved.
This is the latest post in the Dinosaur Alphabet series.
Zanno, L., Sampson, S. 2005. A new oviraptorosaur (Theropoda, Maniraptora) from the Late Cretaceous (Campanian) of Utah. Journal of Vertebrate Paleontology. 35:4, 897-904
November 30, 2012
The dinosaurs I grew up with were both intensely exciting and incredibly dull. They were creatures unlike anything I had ever seen, but their drab, scaly flesh was always fit snugly to their bones with little embellishment. For decades, this has been the paradox of prehistoric restorations. Reconstructed skeletons are gloriously magnificent and introduce us to strange creatures that we never could imagined if we did not already know they existed. Yet the art of reviving these organisms has often been incredibly conservative. Dinosaurs, in particular, have often been “shrink-wrapped”–their skin tightly pulled around a minimalist layer of muscle distributed over the skeleton. This may be part of why dinosaur restorations look so weird. As John Conway, C.M. Kosemen, Darren Naish and Scott Harman argue in their new book All Yesterdays, no living lizard, fish, bird or mammal adheres to such a limited “skin on the bones” fashion. Dinosaurs were not only skeletally distinctive, but they undoubtedly looked stranger and behaved more bizarrely than we have ever imagined. The recently-published Dinosaur Art started to realize these possibilities, but All Yesterdays goes even further in melding science and speculation about dinosaur biology.
On a superficial level, All Yesterdays is a gorgeous collection of speculative artwork. Divided into two sections–the first featuring Mesozoic life in new or little-seen vignettes, and the second imagining how we would restore modern animals if we only had partial skeletons to work from–the book features some of the most wonderful paleoart I’ve ever seen. Scott Hartman’s crisp skeletal reconstructions form the framework from which Conway and Kosemen play with muscle, fat and flesh, and, following Naish’s introductory comments, Kosemen provides scientific commentary about how each illustration is not quite so outlandish as it seems. A curious Camptosaurus approaching an Allosaurus at rest is a reminder that, much like modern animals, prey and predators were not constantly grappling with each other, just as a snoozing rendition of the Tyrannosaurus “Stan” shows that even the scariest dinosaurs had to snooze. The gallery’s feathered dinosaurs are especially effective at demonstrating the fluffy weirdness of the Mesozoic. Conway’s peaceful scene of feather draped Therizinosaurus browsing in a tree grove is the best rendition of the giant herbivore I’ve ever seen, and his fluffy, snowbound Leaellynasaura are unabashedly adorable.
The second half of the book continues the same theme, but in reverse. How would artists draw a cat, an elephant or a baboon if we only had skeletons or bone fragments? And what would those scraps suggest about the biology of long-lost animals? If there are paleontologists in the future, and they have no other source of information about our world, how will they restore the animals alive today? They might have no knowledge of the fur, fat, feathers and other structures that flesh out modern species, creating demonic visions of reptilian cats, eel-like whales and vampire hummingbirds.
Working in concert, the two sections will give casual readers and paleoartists a jolt. While some might gripe about Todd Marshall adding too many spikes and dewlaps to his dinosaurs, or Luis Rey envisioning deinonychosaurs at play, the fact of the matter is that dinosaurs probably had an array of soft tissue structures that made them look far stranger than the toned-down restorations we’re used to. As All Yesterdays presents in various scenes, maybe sauropods liked to play in the mud, perhaps hadrosaurs were chubbier than we ever imagined and, as depicted in one nightmare-inducing panel, Stegosaurus could have had monstrous genitals. None of these scenarios are supported by direct evidence, but they are all within the realm of possibility.
More than a gallery of speculative art, All Yesterdays is an essential, inspirational guide to any aspiring paleoartist. Those who restore prehistoric life are limited by the evidence at hand, this is true, but “more conservative” does not mean “more accurate.” Using comparisons with modern animals, artists have far more leeway than they have ever exercised in imagining what prehistoric life was like. We’ve seen enough Deinonychus packs tearing apart Tenontosaurus, and far too many malnourished dinosaurs. We need more fat, feathers, accessory adornments and scenes from quieter moments in dinosaur lives that do not involve blood and spilled viscera. Professional paleoartists are beginning to embrace these ideas–Jason Brougham’s recent restoration of Microraptor is an appropriately fluffy, bird-like animal rather than the flying monster Naish and collaborators decry–but All Yesterdays is a concentrated dose of prehistoric possibilities that are being artistically explored.
Some of the book’s restorations may turn out to look quite silly. As lovely as Conway’s rendition is, I still don’t buy the “bison-back” idea for high-spined dinosaurs such as Ouranosaurus. Then again, depending on what we discover in the future, some of the illustrations might seem quite prescient. The important thing is that All Yesterdays demonstrates how to push the boundaries of what we imagine while still drawing on scientific evidence. The book is a rare treat in that each section explicitly lays the inspiration for each speculative vision, providing references for those who want to dig deeper.
If anything, All Yesterdays shows that we should not be afraid of imagination in science. Even though we know far more about dinosaur biology and anatomy than ever before, there are still substantial gaps in our understanding. In these places, where bones might not have much to tell us, science meets speculation. The result is not anything-goes garishness, but an exploration of possibilities. Somewhere within that murky range of alternatives, we may start to approach what dinosaurs were truly like.
You can purchase All Yesterdays in any of its various formats here.