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Line drawings of the skulls of Acristavus (top), Maiasaura (middle), and Brachylophosaurus (bottom). From Gates et al., 2011.

Hadrosaurs don’t get enough respect. Often called the “cows of the Cretaceous,” these big herbivores are often cast as relatively uninteresting animals that primarily served as fodder for the more charismatic tyrannosaurs and other predators. Even I fall into this trap—there is a relative scarcity of posts about hadrosaurs on this blog. A new paper by Terry Gates and colleagues in the Journal of Vertebrate Paleontology, however, gives me a chance to start evening up the score.

As a group, the hadrosaurid dinosaurs differed from their ancestors and earlier relatives—known as iguanodontians—in exhibiting an impressive array of ornaments on their skulls. The snouts of these dinosaurs, according to Gates and colleagues, “display[ed] a variety of protrubrances, paddles, and scoops,” and the only one to lack such modifications was one of the last hadrosaurs, Edmontosaurus. Rather than being a retention of the archaic, unornamented state, Gates and co-authors argue, the plain profile of Edmontosaurus probably represents a reversal from an ornamented ancestor. The discovery of a previously unknown species of hadrosaur from even older rock informs this hypothesis.

The new dinosaur, named Acristavus gagslarsoni, lived about 79 million years ago in western North America. Its remains have been found in both the Two Medicine Formation of Montana and the Wahweap Formation of Utah, and the dinosaur is represented by at least two nearly complete skulls and other skeletal elements. Contrary to what might be expected, though, what makes this dinosaur special is that, in the terminology of the paper’s authors, it was “unadorned.” Dinosaurs with weird structures such as sails, crests and arrays of horns often make the news, but in this case, the lack of specialized structures is more important.

Placed in an evolutionary context, Acristavus belonged to a peculiar subgroup of hadrosaurs known as the Brachylophosaurini—a group proposed in the paper that contains Maiasaura and (surprise) Brachylophosaurus. Whereas the other two dinosaurs expressed modified, ornamented snouts, Acristavus had a more archaic-looking skull which lacked such specializations. The significance of this is that the skull of Acristavus is consistent with the idea that the earliest hadrosaurid dinosaurs did not have ornamentation on their skulls. This means that the array of cranial ornaments seen among the two major subgroups of hadrosaurs—lambeosaurines, such as the long-crested Parasaurolophus, and hadrosaurines like Maiasaura—evolved independently in each lineage.

As the authors note, Acristavus is just one discovery. It is entirely possible that, like Edmontosaurus, this dinosaur secondarily lost ornamentation that was present in its ancestor, and this would indicate that crests were a common hadrosaurid feature which simply became modified differently in the two sides of the family tree. Nevertheless, the age and evolutionary position of Acristavus appears to favor the hypothesis that each of the two major hadrosaurid subgroups independently developed different modes of ornamentation. With luck, future discoveries will help paleontologists better understand how hadrosaurs wound up with such fancy skulls.

References:

Gates, T., Horner, J., Hanna, R., & Nelson, C. (2011). New unadorned hadrosaurine hadrosaurid (Dinosauria, Ornithopoda) from the Campanian of North America Journal of Vertebrate Paleontology, 31 (4), 798-811 DOI: 10.1080/02724634.2011.577854

One of the many dinosaur tracks figured in Edward Hitchcock's Ichnology of New England.

Way back in 1839, no one had any idea what dinosaur tracks looked like. In fact, the word “dinosaur” did not even exist yet—the term would be coined by the British anatomist Richard Owen in 1842. Little wonder, then, that tracks now readily recognizable as belonging to dinosaurs were once attributed to prodigious birds and other creatures.

Edward Hitchcock, a New England geologist and theologian, established the study of dinosaur tracks in North America thanks to the abundance of trace fossils found in the Connecticut Valley. People had known about these tracks for a long time—the Lenape Native American tribe even had legends about them—but it wasn’t until the mid-1830s that they came under the scrutiny of naturalists who wanted to know how they were made and what sort of animals they represented. But Hitchcock and other American naturalists were not the only ones interested in these fossil impressions.

In 1839, while Hitchcock was pondering his tracks from New England, the German geologist Carl Degenhardt discovered what appeared to be large bird footprints left in the red sandstone of a Colombian mountain range. No illustration of the tracks was ever published, but given that dinosaur tracks were often confused with the footprints of large birds, it seems probable that Degenhardt truly did find imprints left by dinosaurs. According to paleontologist and historian Eric Buffetaut, this was probably the first recorded dinosaur tracks found in South America.

Despite the importance of Degenhardt’s discovery, though, news of his find quickly sank from view. The reasons why, Buffetaut hypothesized, had to do with how the discovery was communicated. A description of the discovery had been included in a report of a geographical, rather than a geological, journal, and a later newspaper blurb about the find mistakenly placed the tracks in Mexico instead of Colombia. These quirks of publication kept Degenhardt’s discovery obscure—it took over a century and a half for news of the tracks he found to be rediscovered.

References:

Buffetaut, E. 2000. A forgotten episode in the history of dinosaur ichnology: Carl Degenhardt’s report on the first discovery of fossil footprints in South America (Colombia 1839). Bulletin de la Societe Geologique de France, 171 (1): 137-140

A roadside dinosaur in Jensen, Utah. Photo by author.

While driving along Interstate 40 toward eastern Utah’s Dinosaur National Monument, you can’t miss the roadside dinosaurs. They’re all over the place. Many are concentrated in Vernal, about a 20-minute drive to the west of the national park, but a few stand near the highway in the small town of Jensen. One of my favorites is this fellow—an old, cracked dinosaur that could probably be called “Crocosaurus.” The thing looks more like an alligator doing a dinosaur impression than a real dinosaur, yet there is something unmistakably dinosaurian about it. I’ve been wondering about why this should be. Is it just the upright posture, or is there something else that clearly makes the model a dinosaur? As crude as it is, this restoration always makes me think about what—in the cultural realm, at least—makes a dinosaur.

Have you seen a prehistoric creature in an unusual place? Submissions of dinosaurs—and other ancient beasts—should be sent to dinosaursightings@gmail.com.

The opening of a new dinosaur hall is always cause for celebration, and the new permanent exhibition at the Natural History Museum of Los Angeles County sounds wonderful. Buzz about the new displays—particularly a trio of Tyrannosaurus growth stages—has been growing for months. Now the public can finally see the exhibits for themselves.

I’m a little too far away from L.A. to just bop over there and check out the new exhibits, but fortunately, other paleo bloggers have got you covered there. A Central Coast Paleontologist has a hyperbolic review, replete with videos from the museum, and David Orr at Love in the Time of Chasmosaurs has collected a number of Flickr snapshots taken by others at the opening event. The exhibit certainly looks wonderful, and I will certainly share my thoughts on it when I eventually make my way out to the west coast.

Have you seen the new NHM dinosaur exhibit? Share your reactions in the comments.

A dinosaur egg with preserved wasp cocoons inside. From Genise and Sarzetti, 2011.

Dinosaur eggs were wonderful things. For the dinosaurs, reproducing by laying eggs may have played an important role in why many species reached enormous sizes. And for the animals that fed on them, dinosaur eggs were tasty packages of protein. Early last year, for example, researchers announced the discovery of a prehistoric snake that probably crushed sauropod eggs to reach the dinosaur embryos inside. Now paleontologists Jorge Genise and Laura Sarzetti have proposed that wasps may have made the most of dinosaur eggs, too.

The Cretaceous rock of Argentina has yielded many dinosaur eggs. The egg at the center of the new study was part of a clutch found in rock dating between about 77 million and 67 million years ago. There were five spherical eggs altogether, but one was special. Cracked in half, the fossil preserved eight cocoons inside. These were delicate structures—the sort that could not be transported without damaging or destroying the cocoons—and so it seems that the association between the egg and cocoons is real and not attributable to some accident of preservation. Invertebrates had been using this dinosaur egg, but what sort of creatures, and why?

As reconstructed by Genise and Sarzetti, the cocoon-containing egg was probably broken by some kind of force which did not affect the other eggs in the clutch. (If the egg had been crushed during burial in sediment, for example, the other eggs in the clutch would have been similarly broken, yet they were not.) Exactly what cracked the egg is unknown, but as the paleontologists point out, the egg would have filled in with sediment while still decaying. This turned the egg into a food source and place where insect scavengers could burrow into the soil filling the structure.

Exactly what species of insect the cocoons belonged to is unknown, but the structure of the preserved cocoons most closely resembles that of wasp cocoons. This finding helps flesh out the story of what happened to the egg after it was crushed. The location and orientation of the cocoons seems to fit a pattern for parasitoid wasps that track down spiders and crickets in their own burrows, immobilize them, and then lay eggs on them. If correct, this means that the wasps were relatively late arrivals at the rotten dinosaur egg—the wasps were there to take advantage of the other invertebrates that had come to feed on and burrow into the impromptu home. Still, even though they did not directly feed on the dead dinosaur egg, the wasps would have been part of a prehistoric cleaning crew—a temporary ecosystem whose existence we now know of thanks to the chance preservation of a special egg.

References:

GENISE, J., & SARZETTI, L. (2011). Fossil cocoons associated with a dinosaur egg from Patagonia, Argentina Palaeontology, 54 (4), 815-823 DOI: 10.1111/j.1475-4983.2011.01064.x