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This famous Edmontosaurus skeleton was found with intricate traces of skin over much of its body. Image in Osborn, 1916, from Wikipedia.

Last week, I wrote about attempts by paleontologist Phil Bell and colleagues to extract biological secrets from fossilized traces of dinosaur skin. Among the questions the study might help answer is why so many hadrosaurs are found with remnants of their soft tissue intact. Specimens from almost every dinosaur subgroup have been found with some kind of soft tissue preservation, yet, out of all these, the shovel-beaked hadrosaurs of the Late Cretaceous are found with skin impressions and casts most often. Why?

Yale University graduate student Matt Davis has taken a stab at the mystery in an in-press Acta Paleontologica Polonica paper. Previously researchers have proposed that the abundance of hadrosaur skin remnants is attributable to large hadrosaur populations (the more hadrosaurs there were, the more likely their skin might be preserved), the habits of the dinosaurs (perhaps they lived in environments where fine-resolution fossilization was more likely) or some internal factor that made their skin more resilient after burial. to examine these ideas, Davis compiled a database of dinosaur skin traces to see if there was any pattern consistent with these ideas.

According to Davis, the large collection of hadrosaur skin fossils isn’t attributable to their population sizes or to death in a particular kind of environment. The horned ceratopsid dinosaurs–namely Triceratops–were even more numerous on the latest Cretaceous landscape, yet we don’t have as many skin fossils from them. And hadrosaur skin impressions have been found in several different kinds of rock, meaning that the intricate fossilization occurred in multiple types of settings and not just sandy river channels. While Davis doesn’t speculate about what made hadrosaurs so different, he proposes that their skin might have been thicker or otherwise more resistant than that of other dinosaurs. A sturdy hide might have offered the dinosaurs protection from injury in life and survived into the fossil record after death.

Still, I have to wonder if there was something about the behavior or ecology of hadrosaurs that drew them to environments where there was a greater chance of rapid burial (regardless of whether the sediment was sandy, silty or muddy). And the trouble with ceratopsids is that they have historically been head-hunted. Is it possible that we’ve missed a number of ceratopsid skin traces because paleontologists have often collected skulls rather than whole skeletons? The few ceratopsid skin fossils found so far indicate that they, too, had thick hides ornamented with large, scale-like structures. Were such tough-looking dinosaur hides really weaker than they appear, or is something else at play? Hadrosaurs may very well have had extra-sturdy skin, but the trick is testing whether that characteristic really accounts for the many hadrosaur skin patches resting in museum collections.

Reference:

Davis, M. 2012. Census of dinosaur skin reveals lithology may not be the most important factor in increased preservation of hadrosaurid skin. Acta Paleontologica Polonica http://dx.doi.org/10.4202/app.2012.0077

Osborn, H. 1916. Integument of the iguanodon dinosaur Trachodon. Memoirs of the American Museum of Natural History. 1, 2: 33-54

Sternberg, C.M. 1925. Integument of Chasmosaurus belli. The Canadian Field Naturalist. XXXIX, 5: 108-110

Dinosaur reconstructions often begin and end with bones. Dinosaur muscles and organs usually don’t survive the processes that turn bodies into fossils, with casts of the intestinal tract–called cololites–and other soft tissue clues being rarities. Restoration of those squishy bits relies on comparison with modern animals, muscle scars on bones and other lines of evidence. Yet paleontologists have found a great deal of dinosaur skin impressions, especially from the shovel-beaked hadrosaurs of the Cretaceous. We probably know more about the actual external appearance of hadrosaurs such as Edmontosaurus and Saurolophus than almost any other dinosaurs.

Hadrosaurs found with skin impressions are often called “mummies.” This isn’t quite right. Natural mummies–human and otherwise–preserve the organism’s actual skin due to any number of environmental conditions, from arid heat to extreme cold or preservation in a bog. What we know of hadrosaur skin isn’t the original organic material that made up the dinosaur’s flesh, but rock that has made a mold or cast of the dinosaur’s pebbly outer coating. Terminology aside, though, paleontologists have found enough dinosaur skin impressions that the fossils can be used to detect different ornamentation patterns and may even help distinguish one species from another. Earlier this year, paleontologist Phil Bell demonstrated that two Saurolophus species exhibited different patterns on their bumpy skins–an additional kind of ornamentation aside from their prominent head crests.

But how do skin impressions became preserved? And why are such traces so often found with hadrosaurs but not other dinosaurs? Is it because hadrosaurs frequented environments where such preservation was more likely, or are we just missing similar impressions associated with other fossils? There’s much about dinosaur skin impressions that we don’t yet understand. In the video above, Bell gives us a preview of new research on a recently collected hadrosaur that has skin traces, in the hope that some high-tech analysis will help him better understand how such fossils form.

The reconstructed skull of Eolambia–based on a partial adult skull and scaled juvenile elements–and a restoration by artist Lukas Panzarin. From McDonald et al., 2012.

Hadrosaurs were not the most charismatic dinosaurs. Some, such as Parasaurolophus and Lambeosaurus, had ornate, hollow crests jutting through their skulls, but, otherwise, these herbivorous dinosaurs seem rather drab next to their contemporaries. They lacked the garish displays of horns and armor seen among lineages such as the ceratopsians and ankylosaurs, and they cannot compete with the celebrity of the feathery carnivores that preyed upon them. Yet in the habitats where they lived, hadrosaurs were among the most common dinosaurs and essential parts of their ecosystems. What would tyrannosaurs do without ample hadrosaurian prey?

While many hadrosaurs might seem visually unremarkable next to their neighbors, the wealth of these dinosaurs that paleontologists have uncovered represent a huge database of paleobiological information waiting to be tapped for new insights into dino biology and evolution.

In order to draw out dinosaur secrets, though, paleontologists need to properly identify, describe and categorize the fossils they find. We need to know who’s who before their stories can come into focus. On that score, paleontologist Andrew McDonald and colleagues have just published a detailed catalog of Eolambia caroljonesa, an archaic hadrosaur that was once abundant in Cretaceous Utah.

Eolambia is not a new dinosaur. Discovered in the roughly 96-million-year-old rock of the Cedar Mountain Formation, this dinosaur was named by paleontologist James Kirkland–a coauthor on the new paper–in 1998. Now there are multiple skeletons from two different localities representing both sub-adult and adult animals, and those specimens form the basis of the full description.

While the new paper is primarily concerned with the details of the dinosaur’s skeleton, including a provisional skull reconstruction accompanied by an excellent restoration by artist Lukas Panzarin, McDonald and coauthors found a new place for Eolambia in the hadrosaur family tree. When Kirkland announced the dinosaur, he named it Eolambia because it seemed to be at the dawn (“eo”) of the crested lambeosaurine lineage of hadrosaurs. But in the new paper McDonald, Kirkland and collaborators found that Eolambia was actually a more archaic animal–a hadrosauroid that falls outside the hadrosaurid lineage containing the crested forms.

Much like its later relatives, Eolambia would have been a common sight on the mid-Cretaceous landscape. The descriptive paper lists eight isolated animals and two bonebeds containing a total of 16 additional individuals. They lived in an assemblage that was right at the transition between the early and late Cretaceous faunas–tyrannosaurs, deinonychosaurs and ceratopsians have been found in the same part of the formation, as well as Jurassic holdouts like sauropods. How this community fit into the grander scheme of dinosaur evolution in North America is still coming together, though. The Early and Middle parts of the Cretaceous are still poorly known, and paleontologists are just getting acquainted with Eolambia, its kin and contemporaries.

References:

McDonald, A., Bird, J., Kirkland, J., Dodson, P. 2012. Osteology of the basal hadrosauroid Eolambia caroljonesa (Dinosauria: Ornithopoda) from the Cedar Mountain Formation of Utah. PLOS One 7, 10: e45712

Fossil teeth, found by Ferdinand Hayden in Montana, which Joseph Leidy attributed to the dinosaur “Trachodon.” From Leidy, 1860, image from Wikipedia.

More than 150 years ago, a young naturalist picked up a collection of isolated teeth and bones weathering out of the ground in what is now northern Montana. These weren’t the remains of any living animals but vestiges of Cretaceous life that naturalists had only just begun to recognize and categorize. Even the young explorer who picked them up, Ferdinand Hayden, didn’t know what they were, and so he sent them back east for identification. As the Philadelphia-based polymath Joseph Leidy later determined, some of Hayden’s scrappy finds were dinosaurs–among the earliest recorded dinosaur discoveries in the American West.

Hayden wasn’t the first person to discover fossils in North America. First Nations peoples were familiar enough with strange fossil bones that the prehistoric remnants inspired their legends, and naturalists such as Thomas Jefferson puzzled over what was left of Ice Age mammals such as mastodons and giant ground sloths. Dinosaurs got a relatively early start, too, although naturalists didn’t always realize what they had found. Even though he misidentified the fossil as part of a giant fish, explorer Meriwether Lewis found part of a dinosaur rib in the vicinity of what is now Billings, Montana, when he passed through the area in 1806 on his famous expedition with William Clark. And starting in the 1830s, the Amherst geologist Edward Hitchcok described scores of Early Jurassic dinosaur tracks, which he attributed to prehistoric birds.

All the same, the bits and pieces Hayden found showed that the wilds of the western territories harbored dinosaurs and were a portent of the “Bone Wars” that would later unfold among the badlands of Montana, Wyoming and Colorado. Now, the Great Falls Tribune reports, paleontologist Kristi Curry Rogers and her geologist husband Ray Rogers believe that they have located the place where Hayden stumbled across the Cretaceous tidbits.

Even though Hayden did not keep detailed field notes, a brief mention in a technical paper of the area in which he found the fossils helped the Rogers team narrow down their search area. From there, they followed game trails and looked for sites that would have produced the kinds of fossils Hayden picked up. They can’t be entirely certain that their site is the very same Hayden sampled, and they are wary of divulging the exact location given how often fossil sites are vandalized, but the Rogers have placed Hayden’s stop somewhere in Montana’s Missouri River Breaks north of Winifred. With assistance from the Bureau of Land Management, they want the area to be placed in the National Register of Historic Places–a testament to Hayden’s lasting contribution to American paleontology.

One of the vertebrae–as seen from the front (a) and back (b)–used to name the dinosaur Arkharavia heterocoelica. Although originally thought to come from a sauropod, it turns out that this bone belonged to a hadrosaur. From Alifanov and Bolotsky, 2010.

Dinosaurs come and go. Even though paleontologists are naming new dinosaurs at a fantastic rate–hardly a week seems to go by without the announcement of a previously-unknown species–researchers are also sinking and revising previously-discovered taxa as new finds are compared against what has already been found. The ever-growing ontogeny debate–which threatens the horned dinosaur Torosaurus and the hadrosaur Anatotitan, among others–is just one part of these paleontological growing pains. Sometimes dinosaur identity crises can be even more drastic.

Yesterday I wrote about a new paper by paleontologist Pascal Godefroit of the Royal Belgian Institute of Natural Sciences and co-authors that redescribes the charismatic hadrosaur Olorotitan. As I read through the paper, a brief, but significant, side note caught my eye. In the section describing the deposits in which the known Olorotitan skeletons were found, the paper mentions that paleontologists V.R. Alifanov and Yuri Bolotsky described a sauropod–one of the long-necked, heavy bodied dinosaurs–from the same locality. On the basis of a tooth and several isolated tail vertebrae, Alifanov and Bolotsky named the dinosaur Arkharavia in their 2010 description. Since the encasing rock was deposited during the latest Cretaceous, around 70 million years ago or so, this was apparently one of the last sauropods on earth.

Only Godefroit and colleagues, including Yuri Bolotsky, have now revised the identity of Arkharavia. In their paper on Olorotitan, the paleontologists make the passing comment that “those vertebrae [used to name the sauropod] likely belong to hadrosaurid dinosaurs.” Rather than being a previously-unknown kind of sauropod, then, the fossils used to name “Arkharavia” probably belonged to one of the two hadrosaurs that dominate the locality–Olorotitan or Kundurosaurus.

This isn’t the first time a hadrosaur has been confused for a sauropod. Two years ago, paleontologists Michael D’Emic and Jeffrey Wilson of the University of Michigan and Richard Thompson of the University of Arizona determined that so-called “sauropod” vertebrae found in the 75-million-year-old rock of Arizona’s Santa Rita Mountains should actually be attributed to a hadrosaur akin to Gryposaurus. Fragmentary dinosaurs can be extremely tricky to identify correctly.

These changes aren’t frivolous. Identifications of isolated bones affect our understanding of dinosaur evolution and history. In the case of the misidentified hadrosaur bones from Arizona, the revised diagnosis altered the picture of when sauropods returned to North America after an absence spanning tens of millions of years. (This is called the “sauropod hiatus” by specialists.)

In the case of Arkharavia, the fossils represented one of the last dinosaurs in eastern Russia before the end-Cretaceous mass extinction. Misunderstood as sauropod bones, the fossils appeared to be the scrappy evidence for an entire group of dinosaurs at the locality. Properly understood as hadrosaur tail bones, though, the fossils become isolated elements from a group already known to be numerous in the fossil beds. While these changes might sound small, they can certainly influence grand-scale analyses of when certain groups of dinosaurs appeared or went extinct. There’s a big difference between sauropods living alongside hadrosaurs just before the end-Cretaceous mass extinction and a habitat dominated by hadrosaurs and devoid of sauropods. Even isolated bones can make a big difference.

References:

Alifanov, V., Bolotsky, Y. (2010). Arkharavia heterocoelica gen. et sp. nov., a New Sauropod Dinosaur from the Upper Cretaceous of the Far East of Russia Paleontological Journal, 44 (1), 84-91 DOI: 10.1134/S0031030110010119

Godefroit, P., Bolotsky, Y.L., and Bolotsky, I.Y. (2012). Olorotitan arharensis, a hollow-crested hadrosaurid dinosaur from the latest Cretaceous of Far Eastern Russia. Acta Palaeontologica Polonica DOI: 10.4202/app.2011.0051