Fruitadens: The Little Ornithischian that Could

Another swell piece of research published recently in PLoS One - the official favoritest journal of Love in the Time of Chasmosaurs - is a detailed description of the anatomy and phylogeny of Fruitadens haagororum, the little heterodontosaurid from the Morrison Formation of Colorado, a formation dating to 150 million years ago. It debuted with a brief paper during the infancy of this blog in 2009, but now it's been properly studied, so what's the scoop?

Lead author Richard Butler describes this paper as "the result of a nearly 30 year long project," building on a substantial body of work by coauthor Peter Galton. Heterodontosaurids were bipedal ornithischians, notable for their varied dentition. Many have pronounced fangs, or caniniforms, in addition to leaf-shaped teeth which would have been good for munching vegetation. And one of them, Tianyulong, was preserved well enough to reveal that it bore long, hollow quill-like filaments along its back.

Fruitadens restored by Nobu Tamura, featuring quills like those of Tianyulong.

Understanding the evolutionary trends of these primitive ornithischians is important for what it can reveal about the common ancestor of all dinosaurs. Unfortunately, there are few windows into heterodontosaurid evolution, with the most productive strata dating to the early Jurassic of South Africa, when Heterodontosaurus, Abrictosaurus, and Lycorhinus lived. The Middle Jurassic of Europe has offered a plethora of teeth which hint at substantial populations of heterodontosaurids, but so far has not coughed up any significant remains to help fill in the details of the heterodontosaurid story. But what we have is enough to build a rough sketch of how the clade evolved over the 55 million year stretch that it existed.

Fruitadens was likely an omnivore, eating what plants, insects, and other invertebrates it could find. Like closely related Tianyulong, it was smaller and less specialized for herbivory than the earlier Heterodontosaurus, which was made to process tough plant material. Butler notes that "it appears that Late Jurassic-Early Cretaceous heterodontosaurids were smaller than most Early Jurassic members of the clade, and displayed less sophisticated skull and dental morphologies." They were becoming generalists. As the clade spread across Pangaea, which was fragmenting by the Late Jurassic, evolutionary pressures - perhaps competition from the sauropodomorphs - were pushing the heterodontosaurids into a more opportunistic lifestyle. Sort of a dinosaurian version of a raccoon, scratching out a living any way they could.

More:
Andy Farke's take on PLoS Blogs
A note from lead author Richard Butler
Brian Switek at Dinosaur Tracking

Dinosaurs with ouchies on their noggins

A pair of Pachycephalosaurus put their heads together at Drayton Manor Theme Park. Photo by Matthew Wells, via Flickr.

Since I was a kid, one image has been stuck in my head when I think of the pachycephalosaurs, those rugged ornithischians with the outrageously thick frontoparietal bone: two males ramming into each other headlong like the two dudes in the photo above. I'm pretty sure I'm not alone in this. Even when I read a piece expressing skepticism about the behavior, I think to myself, "okay, but we're going to stick with the rule of coolness here." It's the same attitude that annoys me when people choose to not believe that many theropods wore feathery integument of some fashion. Again, I remind myself that science isn't about accepting things because they seem to make sense or they're pleasant to believe. So it's good that he head-butting hypothesis has recently had a spate of research devoted to it. The latest is a new paper in PLoS ONE, Cranial Pathologies in a Specimen of Pachycephalosaurus.

The rock has offered us scant remains to work from, which is probably a good reason why the pachycephalosaurs - who Tom Holtz refers to lovingly as "buttheads" in his Dinosaurs encyclopedia- have long been the subject of debate. Why were those heads so thickened? How many taxa might simply represent different growth stages of one species? Could they sustain direct head-to-head impacts or was it more likely that they smacked each other sidelong? Because of the patchiness of their fossil record, it's been difficult to put many of these ideas to the test.

In this new study, University of Wisconsin paleontologist Joseph Peterson, with the help of Christopher Vittore from the Department of Radiology at Rockford Memorial Hospital in Rockford, IL employ CT scanning of a Pachycephalosaurus frontoparietal dome at the Burpee Museum of Natural History and compare its apparent signs of injury to lesions in modern animals. Are these spots best interpreted as sites of bone resorption, as the rigors of decay, fossilization, and erosion, or are they evidence of traumatic impact?

Peterson's study concludes that it ain't the first two. Bone resorption, studied extensively in chasmosaurine fossils, leaves a smooth surface, as opposed to the roughness of the lesions in the studied Pachycephalosaurus dome. Signs of likely taphonomic suspects - such as scavenging, insect traces, and water wear - are also absent. But the lesions do match the marks left on the the crania of modern birds which have sustained impact and lived to tell the tale. Moreover, Peterson writes that the marks "are clustered over the thickest region of the dome; this distribution corresponds well to the location of expected traumatic pathologies resulting from agonistic behavior proposed for pachycephalosaurids." That would be head-butting, though they could have been smacking into boulders instead, I suppose. It's less absurd than some recent dinosaur stories in the popular press.

This follows another recent study by Eric Snively and Jessica Theodor, who compared the skull of Stegoceras to modern "buttheads" and found that "some pachycephalosaurs were as competent at head-to-head impacts as extant analogs displaying such combat," including musk oxen and duikers. (check out Eric's guest post at Archosaur Musings for more on this). On Facebook, Andy Farke joked that the "P" in PLoS ONE may as well stand for "pachycephalosaur." That wouldn't be so bad, would it?

Also be sure to follow Dr. Peterson on Twitter and at his blog (which has been dutifully added to the LITC blogroll).

The Spinosaurids Arrive in Asia

This week in the journal Naturwissenshaften, we have the advance online publication of research describing a new spinosaurid, which the authors, led by Ronan Allain, dub Ichthyovenator laosensis: the Laotian Fish Hunter.

Ichthyovenator is described from portions of the spine and pelvis. Unfortunately, it's headless, but based on the postcranial remains, the authors are confident that it belongs to the baryonychine tribe of spinosaurids, allied with Suchomimus and Baryonyx. It possessed elongated neural spines, as is common in the family. In Ichthyovenator, these created a "sinusoidal" shape; that is, it rose and fell like a sine wave when viewed in profile, with a dip at the base of the tail enclosed by two peaks. Concerning the sail's function, the authors favor species recognition and sexual display over a thermoregulatory use. When trying to sort out who's who, a spinosaur would identify potential rivals or mates by the shape of their sail.


Baryonyx walkeri, a close relative of Ichthyovenator, illustrated by Mark Witton. Shared via Flickr.

Spinosaurids have been represented by notoriously scrappy material; the discovery of Baryonyx in England about thirty years ago shed more light on their anatomy (Baryonyx may not be as flashy as its bigger, more extravagantly ornamented cousins, but it's the one who delivers the goods). Now, Ichthyovenator is the first definitive spinosaurid from Asia, living during the Early Cretaceous, like most of its described relatives. Teeth found elsewhere hint to a few stragglers persisting into the Late Cretaceous, and Allain et al's phylogenetic analysis places the poorly understood late Cretaceous theropod Chilantaisaurus in the spinosaurids, making it the youngest member of the clade - as well as a second one from Asia.

Tantalizingly, the authors reappraise a single finger bone from the Late Jurassic Morrison formation of the US, previously thought to be from a Torvosaurus, a member of the closely related megalosaurids (also known as the villain in the second episode of Dinosaur Revolution). Allain et al maintain that the proportions of this ungual phalanx - the bone to which that big thumb claw attached - fit better within the baryonychines. They are one of the only theropod groups known to have such an outsized first digit (you'll see the spinosaurines reconstructed this way as well, but this is inferred from baryonychine material). The Allosauroid megaraptorids also possessed an enlarged "thumb," though their claw is so recurved they were first thought to come from the foot of a dromaeosaur. As usual, this hypothesis depends upon the serendipity of new fossil discoveries.

The reason the authors mention this single phalanx is because of its implications for the early geographical distribution of spinosaurids. They are known from Europe, Africa, South America, possibly Australia and now Asia. It's likely that in the middle-to-late Jurassic as Pangaea slowly splintered, early spinosaurids enjoyed a distribution over much of the globe. If new finds can sort out the owner of this finger, Allain writes that it "may not only be the first record of Spinosauridae from North America but also the oldest known spinosaurid specimen," showing that they had indeed lived across Pangaea, and giving crucial insights into their origins. It would just be nice to have something relatively complete. As productive as the Morrison has been over the years, it's amazing to think of what wonders it still hides.

I'm a sucker for the -venator suffix; it just sounds cool. But of course, without cranial material for this animal, it's being named by the spinosaurid fish-eating reputation alone. If a head of Ichthyovenator turns up, there's the possibility it may have had a different diet, which would be a pretty interesting kink in this kinky-sailed dinosaur's story.

Revised 4/26/12 to include the bits on megaraptorids and Australia. Thanks to Mark Robinson and Tony Martin for catching these goofs.

More on Ichthyovenator:
Theropoda
Domain of the C-Rex
Dinosaur Tracking

Also of interest: Baryonyx, illustrated by Jim Conaway, made an appearance in an old post in the Vintage Dinosaur Art series

Mesozoic Miscellany #37: Mega Turbo Research Explosion Edition

There are many weeks that see the publication (or at least, publicization) of several papers relating to those archosaurs we so dearly love. But this week, there's been a surge of research of the sort that has the potential to grab the attention of those with only a casual interest in paleontology or, heaven forbid, little at all. Dinosaur colors, tyrannosaurs, and anatomical weaponry are all topics that tend to dazzle the public-at-large, and they all got press this week.

Another method for reading feather colors. Dr. Phil Manning of Manchester University is one of several authors on a Science Express paper that describes a new way to glean information about feather coloration from fossil animals. At his Dinosaur CSI blog, Manning writes, "Pigment is a critical component of colour. Our team can map the presence of pigments over whole fossils, revealing original colour patterns (but through a monochrome filter). Our findings indicate that pigment chemistry holds the future key to the ultimate goal of discovering the full colour palette of past life, from dodos to dinosaurs and beyond."



Even James Gurney hopped on this story at his blog, and for the second week, USA Today has covered a piece of dinosaur news.

Raptorex reevaluated
The embattled little theropod posited by Paul Sereno to be evidence of the tyrannosaur bauplan evolving in smaller form much earlier than expected - in the Early Cretaceous - has taken a hit this week. A team of researchers from the Black Hills Institute and Museum of the Rockies examined Raptorex kriegsteini, determining that the hypothesis that it is actually a juvenile Tarbosaurus, and not a distinct species all its own, is correct. The provenance of the fossil, obtained through private hands, was never established to the satisfaction of the paleontological community at large. "Variability in personal communications regarding the specimen makes it difficult to ascertain exact details that were known at the time of purchase, highlighting the problems of dealing with commercial specimens that have been illegally collected," write the authors. Read what Mark Wildman has to say about this at Saurian.

It's best not to be thagomized by Kentrosaurus. From Heinrich Mallison comes research, published in Palaeo-Electronica, that looks at the mechanics of the thagomizer in the stegosaur Kentrosaurus. Conclusion: it's a really, really bad idea to find yourself staring down the business end of a stegosaur. Mallison writes about it in detail, with great reconstructions from David Maas, at the Palaeo-Electro blog.

You should also avoid being headbutted by Stegoceras. How did the pachycephalosaur Stegoceras compare to modern head-butting analogs like bighorn sheep? Pretty darn well, thank you very much, report Eric Snively and Jessica M. Theodor in PLoS ONE. "The head-butting duiker Cephalophus leucogaster," they write, "is the closest morphological analog to Stegoceras, with a smaller yet similarly rounded dome." Read more from Wired UK.

But that's not all! There's another paper on Stegoceras published in PLoS ONE, and it's also the second this week with Jack Horner attached to it. Of course, as both deal with the taxonomic implications of ontogeny, that's hardly a surprise. The team of researchers conclude that pachycephalosaurs were indeed capable of dramatic changes in cranial structure as they grew up. This is another brick in Horner's position that Dracorex and Stygimoloch are merely juvenile specimens of Pachycephalosaurus. Jaime Headden talked about this at The Bite Stuff, as does Everything Dinosaur. Victoria Arbour is a big fan of Stegoceras, and she shares some great photos of the mount at the University of Alberta. Nice to see two papers in quick succession about pachycephalosaurs, who leave behind such fragmentary remains and sit at the center of an important debate in dinosaur paleontology.

We'll return to the usual format of the roundup next week, which will be cram-packed with excellent stuff. The dinosaur blogosphere has been hopping with interesting content lately.

Shastasaurus sucks, in a good way.

It's too easy to think "ichthyosaur" and automatically conjure an image of a vaguely dolphin-shaped Mesozoic reptile, represented by a famous member of the group like Ichthyosaurus or Opthalmosaurus. It becomes just another role-player in the Mesozoic seas that now exist solely in our imaginations. But these were living animals, important members of lost ecosystems. Like a host of other extinct organisms, the deeper scientists look, the more nuanced and fascinating they become.

New research published in PLoS ONE demonstrates just how much you miss if you arrive at a superficial description of these animals and stop there. The study, by the University of Bonn's P. Martin Sander and Xiaohong Chen, Long Cheng, and Xiaofeng Wang of the Wuhan Institute of Geology and Mineral Resources in Hubei, China, takes a look at new fossil material representing the genus Shastasaurus, as well as a reevaluation of S. pacificus.

The shastasaurs are an odd offshoot of the ichthyosaur family, with short, slender snouts that appear to be truly toothless. While not entirely unknown in the ichthyosaur fossil record, toothlessness this plainly obvious is a unique characteristic of Shastosaurus: the upper surface of the Shastosaurus dentary, one of the lower jawbones, is smooth with no trace of grooves or pits for teeth. In others, toothlessness may be a mere artifact of poor preservation.

In seeking an explanation for these strange features, the authors draw a comparison to a living family of the ocean dwellers, the beaked whales of the family Ziphiidae, which have reduced dentition and similarly proportioned snouts as well as enlarged hyoid bones. In the PLoS ONE paper, the team writes, "the ziphiid whales are suction feeders in which the tongue is pulled back rapidly by strong retractor muscles that are attached to hypertrophied hyoid bones. In this way, prey items are taken up by the negative pressure generated in the oral cavity, obviating the need for teeth to hold them before swallowing."


Cuvier's Beaked Whale, shared by Navy Currents Magazine on Flickr.

The Ziphiids are a poorly understood family overall, with only a few species having been the subject of study. One thing we do know is that they are some of the whale family's gold medal divers, able to hunt deep water cephalopods and fish and crustaceans from near the sea floor, sometimes as deep as 500 meters. The authors paint a picture of Triassic oceans populated by a diverse range of ichthyosaurs including swift-swimming Shastasaurus in the open ocean, diving deep to prey on bioluminescent cephalopods, among other benthic delicacies. They suggest that as oxygen levels rose at the end of the Triassic, gill-breathing fish were able to supplant many of the creatures the ichthyosaurs relied on, instigating the dramatic decrease in ichthyosaur diversity in the Jurassic, presaging the family's eventual extinction. Except, naturally, in the imagination of a bizarre primate millions of years later.

What I'm getting at here is... let's see some Shastasaurus hunting glowing cephalopods, paleoartists!

The Mysteries of the Pterosaur Wing

A pterosaur model from the 2010 Royal Society Summer Festival. Photo by Mark Hillary, via Flickr.

Pterosaurs, among the most enigmatic of the prehistoric beasts, have been the subject of a colorful variety of reconstructions in the two centuries of their study. From their essential nature - even once imagined to have been flying marsupials - to their feeding habits and methods of locomotion, they've kept the brains of paleontologists buzzing and whirring.

In the newest issue of the journal Acta Palaeontologica Polonica, Ross Elgin, Dave Hone, and Eberhard Frey take a look across the pterosaur family to determine what evidence we have for the extent of their wing membranes. This may sound familiar to you; Hone posted about it at Archosaur Musings in September, but noted that what had come available then were uncorrected proofs. The published version is now available online. [PDF].

Like Victoria Arbour's recent paper on the pelvic shields of ankylosaurs, what Elgin, Hone, and Frey do here is provide a summary look at a contested bit of anatomy and lay groundwork for future research. Their conclusion is that this membrane - the brachiopatagium for you lovers of multisyllabic jargon - attached at the ankle. In the past, various researchers have attached it to places all along the leg or to the body, free of the leg completely. Based on their analysis of numerous fossils, Elgin et al concluded that these other attachment sites are erroneous, and chosen due to distortions in the wing profile before or after the animal died and was preserved.

As Hone wrote in September, though the exact arrangement of the branches and twigs of the pterosaur family tree is still a contested matter, "it’s hard to ignore the possibility (and indeed most parsimonious explanation) that all pterosaurs likely had this attachment. At the very least, it should be the default assumption."

Just in case you don't already know, Hone is essential reading for pterosaur lovers. This week, he's been posting photos of various pterosaur fossils (start here) from the Institute of Vertebrate Paleontology and Paleoanthropology in Beijing, and in 2008 he gave a nice review of knowledge about pterosaur soft tissues.

Pareidoliasaurus, a new sauropodomorph of Utah

"Until now that claim has gone unchallenged."

So write Phil Senter and Sally J. Cole, coauthors of a newly published paper in Palaeontologia Electronica examining the purported dinosaur petroglyphs of Kachina Bridge, a rock formation in Utah's Natural Bridges National Monument. While folks have criticized the attempts of Young Earth Creationists to use these and other ancient markings of indigenous people as evidence of humanity's coexistence with dinosaurs - visit Stupid Dinosaur Lies to see a comparison of different images they've used in this particular case - it's now been addressed in the scientific literature. Analyzing the markings under a variety of lighting conditions, Senter and Cole were able to discern that what seemed to be superficially resemble a generic sauropod was actually an amalgam of deliberate ancient markings and natural variations in color on the rock.


From Senter and Cole's "Dinosaur" petroglyphs at Kachina Bridge site, Natural Bridges National Monument, southeastern Utah: not dinosaurs after all.

In their discussion section, Senter and Cole write of pareidolia, "the psychological phenomenon of perceiving significance in vague or random stimuli, e.g., seeing animals in clouds or the face of a religious figure in a food item. The results of this investigation indicate that the dinosaurs of Kachina Bridge are examples of this phenomenon and exist only as pareidolic illusions." This is one of the great perceptual hurdles we must leap in our attempt to accurately perceive our world. It happens to all of us. It's happened to me. In the latest episode of Point of Inquiry, Neil DeGrasse Tyson makes the point that science is essentially a tool to protect our observations from the biases and failings of our brains. One of these failings is our zeal for pattern-recognizing. Drop the Mentos candy of pareidolia into the Diet Coke of ideology and stand back.

While this study could be seen as just a bit of housecleaning to dispense with yet another creationist claim, it perfectly illustrates the power of science to allow us to observe that which fools the eye. It demonstrates that science is about the willingness to admit our physical limitations, to go beyond the superficial and rigorously analyze that which seems obvious. Creationists don't do this. They don't attempt to test and strengthen their arguments by poking holes in them. Any creationist proclaiming Kachina Bridge as evidence for a young Earth could have done exactly what Senter and Cole did; their methods were not beyond the capabilities of anyone with the time and will to try. But none did, because the truth of the claim wasn't their concern. And that says everything.

It also must be said that if you look at the alleged sauropod, it doesn't quite match our understanding of the real animals' physiology. If the Kachina Bridge petroglyph was the work of an ancient artist who had actually had seen a sauropod, it would have sported a horribly broken tail. On a more basic level, I'd imagine that had any early artists actually shared their environments with dinosaurs, their depictions in petroglyphs would be so widespread that the creationists would have no trouble finding abundant evidence for their claims. Bison and aurochs and horses are really cool animals, but if I was a guy in a cave with a bit of ochre paint, I'd personally be more interested in populating the stone walls with the titanic saurian beasts that dwarfed them. Then again, who am I to make assumptions about the priorities of ancient artists?