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The AMNH skeleton of Styracosaurus, one of the dinosaurs from the upper zone of the Dinosaur Park Formation. Image from Brown and Schlaikjer, 1937 via Wikipedia.

Dinosaurs didn’t all live at the same time. Not counting the avian species that have thrived during the last 65 million years, dinosaurs proliferated throughout the world during a span of over 160 million years. As I’ve pointed out before, it’s amazing to think that less time separates us from Tyrannosaurus than separated Tyrannosaurus from Stegosaurus.

Even within specific geologic formations, not all the dinosaurs found in those layers lived side by side. Dinosaur-bearing strata accumulated over millions and millions of years and record both ecological and evolutionary changes. Look closely enough, and you can even see particular communities of dinosaurs give way to different assemblages. In an in-press Palaeogeography, Palaeoclimatology, Palaeoecology paper, Jordan Mallon and colleagues have done just that.

Canada’s Dinosaur Park Formation is one of the most spectacular slices of Late Cretaceous time found anywhere in the world. Spanning approximately 76.5 to 74.8 million years ago, the formation has yielded lovely specimens of dinosaurs such as the crested hadrosaur Corythosaurus, the spiky ceratopsid Styracosaurus, the lithe tyrannosaur Gorgosaurus, the heavy-armored ankylosaur Euplocephalus and many others. Not all of these dinosaurs were neighbors, though. Since 1950, at least, paleontologists have recognized that some kinds of dinosaurs are restricted to certain slices of the formation, and the dinosaur community changed over time. Mallon and co-authors decided to have another look at the dinosaur turnover, focusing on the large herbivores and investigating what might have shook up the dinosaur populations during the time the Dinosaur Park Formation was being laid down.

The paleontologists identified two broad divisions in the Dinosaur Park Formation, which they call “megaherbivore assemblage zones.” Each zone lasted roughly 600,000 years each. There are a lot of names here, so bear with me. In the lower zone, the horned dinosaur Centrosaurus and the crested hadrosaur Corythosaurus are found throughout; other dinosaurs restricted to this half of the formation include the ceratopsid Chasmosaurus russelli, the hadrosaurs Gryposaurus and Parasaurolophus, and the ankylosaur Dyoplosaurus.

Yet there are some dinosaurs that first appear in the lower zone and persist into next one. The ceratopsid Chasmosaurus belli, the ankylosaur Euoplocephalus and the hadrosaurs Lambeosaurus clavinitialis and Lambeosaurus lambei show up in the lower zone but pass through into the second zone as well. And, as with the lower swath, there were dinosaurs that were only found in the second zone. The hadrosaurs Prosaurolophus and Lambeosaurus magnicristatus, as well as the horned dinosaurs Styracosaurus, Vagaceratops and a pachyrhinosaur, are only found in the upper zone.

So the big picture is that the lower zone is characterized by Centrosaurus and Corythosaurus, the upper zone is distinguished by Styracosaurus and Prosaurolophus, and there are some dinosaurs–such as Lambeosaurus and Chasmosaurus–that are smeared across the two. As the researchers note, it’s even possible to break down the two halves into even smaller subsets, although the picture gets a little muddier at these levels.

What does all this evolutionary dinosaur shuffling mean? Other researchers have proposed that the Dinosaur Park Formation represents a series of turnover pulses–after a period of stability, rapid ecological change wiped out some dinosaurs while creating opportunities for a new community. The now-vanished Western Interior Seaway has been invoked as a possible mechanism for this. As this shallow sea, which once split North America in two, expanded and encroached further inland, the area of the Dinosaur Park Formation became a mostly coastal, muddy, swampy habitat. This may have put pressure on some forms of dinosaur while providing opportunities for others. As the seaway fluctuated, the attendant changes would have altered the environment and therefore affected dinosaur populations.

According to Mallon and collaborators, though, there’s no strong evidence for the turnover pulse hypothesis. We simply don’t have the resolution to tell how closely certain dinosaurs were tied to particular habitats or niches, and shifts in ecology would have influenced dinosaur evolution. Other possible influences–such as dinosaurs migrating to the area from elsewhere, or the evolution of one species into another within the formation–are also frustratingly unclear. As the researchers state, “Whether the appearance and disappearance of the megaherbivorous taxa of the [Dinosaur Park Formation] was due to evolution, migration, or to a combination of these factors, is difficult to determine.” We don’t yet know what drove the alterations in the formation’s dinosaur communities.

Aside from the ongoing mystery about what caused the changes between the two zones, the revised look at the Dinosaur Park Formation also raises a few questions about dinosaur ecology. Despite the shifts in dinosaur communities, the paleontologists note, there were about six to eight different megaherbivorous dinosaur species living alongside each other. That’s a lot of big herbivores on the landscape, especially since the hadrosaurs and ceratopsids may have formed huge herds. Such vast, hefty dinosaur communities would have required a large amount of vegetation, and the disparate megaherbivores were in competition with each other for food. In order to live alongside one another, then, we can assume that there was some kind of niche partitioning–the dinosaurs were adapted to have restricted diets or live in particular habitats as a result of their competition for resources. How exactly this happened, though, requires further study into the ecology and evolution of these dinosaurs.

And there was something else that caught my eye. The new study focused on the megaherbivores, but what about the large carnivores? The large tyrannosaur Gorgosaurus was also present in the Dinosaur Park Formation and was rejected by the researchers as a zone marker because this theropod ranges throughout the formation. Think about that for a moment. We can see a significant amount of change and turnover among the big herbivores, but one of the large carnivores stays the same throughout the entirety of the formation. Why should this be so? Perhaps it has something to do with the fact that the ornamentation and headgear of hadrosaurs and ceratopsids changed quite a bit, but their general body plans were conservative–a Gorgosaurus could take down a Corythosaurus just as well as a Lambeosaurus.

Likewise, I wonder if the same pattern might hold true elsewhere. The Kaiparowits formation of southern Utah, laid down around the time of the Dinosaur Park Formation further north, also hosts an array of hadrosaurs, ceratopsids and ankylosaurs, but there seems to be just one large dinosaurian predator, the tyrannosaur Teratophoneus. (The giant alligator cousin Deinosuchus was another megacarnivore in the Kaiparowits.) We need more fossils to be sure, but perhaps, like Gorgosaurus, the short-snouted Teratophoneus remained the same as different large herbivores came and went. If this turns out to be the case, the lack of an arms race between predator and prey would be further evidence that the ornamentation of ceratopsids and other dinosaurs had more to do with decoration and combat among each other than defense.

Indeed, the new study of the Dinosaur Park Formation lays some important groundwork for future studies. Paleontologists are currently investigating and debating why the roughly 75-million-year-old dinosaurs from Alberta are different from the roughly 75-million-year-old dinosaurs from southern Utah. What factors drove the diversity and disparity of these dinosaurs across the latitudes, and who really lived alongside whom? So far, the Dinosaur Park Formation is the best-sampled slice we have, and there is much work to be done. With any luck, and a few more decades of careful sampling, we’ll be able to put together an intricate picture of how dinosaurs lived and evolved during this brief span of Late Cretaceous time.

Reference:

Mallon, Jordan C., Evans, David C., Ryan, Michael J., Anderson,, & Jason S. (2012). Megaherbivorous dinosaur turnover in the Dinosaur Park Formation
(upper Campanian) of Alberta, Canada Palaeogeography, Palaeoclimatology, Palaeoecology DOI: 10.1016/j.palaeo.2012.06.024

As much fun as a dinosaur party sounds, the latest installment of Dinosaur Office shows us the dangers inherent in even a little after-work social. The key take home lesson: Never anger anyone with a thagomizer.

A Parasaurolophus at the Natural History Museum of Utah. Photo by the author.

Of all the crested hadrosaurs, Parasaurolophus is one of my favorites. The long, slightly-curved tube that projects from the back of the dinosaur’s head is a wonderful ornament. But why did this peculiar dinosaur decoration evolve?

Parasaurolophus was initially described by paleontologist William Parks  in 1922 on the basis of a skeleton found in the vicinity of Alberta’s Red Deer River. This dinosaur was clearly different from other ornamented hadrosaurs–such as Corythosaurus and Saurolophus–that had been found before, and especially perplexing was the makeup of the dinosaur’s crest. The structure was not solid–a break in this part of the skull revealed a series of internal tubes separated by thin walls of bone.

No one was exactly sure why Parasaurolophus had a hollow crest, but the supposed hadrosaur lifestyle generated a number of speculative answers. Hadrosaurs were supposed to be amphibious dinosaurs who acted like giant, dabbling ducks. After all, their broadened snouts gave them the popular moniker “duckbill dinosaurs.” Paleontologists therefore considered the dinosaur’s crest in reference to a life spent foraging for soft plants in Cretaceous swamps.

Paleontologist James Hopson reviewed these ideas in a 1975 Paleobiology paper about the role hadrosaur crests may have played in display. In 1933 Alfred Sherwood Romer speculated that the crest might have been used as a snorkel or an air storage chamber. While there was no hole in the crest to allow air to come in–the snorkel idea was scuttled–the air tank hypothesis was popular. As a young dinosaur fan, I remember encountering an image of a submerged Parasaurolophus in Edwin Colbert’s The Dinosaur Book with a solid black line running through the crest to indicate the amount of stored air. Another book, Rudolph Zallinger’s Dinosaurs and Other Prehistoric Reptiles, featured an even more detailed vision of Corythosaurus and Parasaurolophus paddling around beneath the surface of a prehistoric lake. But this notion didn’t last either. The anatomy of hadrosaurs has undeniably cast them as terrestrial animals, not expert swimmers, and the amount of air these dinosaurs were able to store in their crests would have been miniscule compared to their lung volume–the supposed air tanks would not have done them much good.

Charles Mortram Sternberg, son of the celebrated dinosaur collector Charles H. Sternberg, proposed a different variation of the aquatic feeding theme. In 1935 Sternberg wrote a paper on the “hooded” hadrosaurs from the Late Cretaceous of Canada and proposed that a U-shaped bend in the tubular crest passage prevented water from entering the respiratory system while the dinosaur was feeding underwater. Again, this idea is based on the notion that hadrosaurs frequently dipped their heads underwater to feed, and paleontologist John Ostrom later pointed out that, in such a scenario, the water pressure would have overcome the air pressure inside the crest and flooded the passage. Whatever the function of the Parasaurolophus crest, the structure was certainly ill-suited to underwater feeding.

Paleontologists kicked around a few other ideas. In a series of papers published in the late 30s and 40s, Martin Wilfarth suggested that elaborate hadrosaur crests were attachment areas for long, fleshy snouts. No evidence was found to support this. Likewise, Ostrom’s later suggestion that the nasal passages were extended to give the dinosaurs a better sense of smell was refuted–there was no indication that  the convoluted passageways had anything to do with a better sense of smell.

Hopson himself considered the crests to primarily be visual display structures, and hadrosaurs with hollow crests, such as Parasaurolophus, may have also used their crests as resonating chambers to send low-frequency sounds over long distances. This is the view generally taken now, but settling on particular functions for the crests does not necessarily illustrate how those structures evolved. Perhaps the origin of the various hadrosaur crest shapes was driven by pressures associated with species recognition–the need to identify members of one’s own kind, be they parents, rivals, mates, etc. Then again, perhaps some aspect of sexual selection was at play. Exactly what evolutionary factors led to the origin of such strange skull shapes is difficult to ascertain. Much remains unknown about the evolution and social significance of fantastic ornaments in dinosaurs.

References:

Hopson, J. 1975. The Evolution of Cranial Display Structures in Hadrosaurian Dinosaurs. Paleobiology, 1 (1). pp. 21-43

Naish, D. 2009. The Great Dinosaur Discoveries. Berkeley: University of California Press. pp. 72-73

Hanging with Parasaurolophus at the Museum of Life & Science in Durham, North Caroline. Photo courtesy Christine Teander.

Typically our Dinosaur Sightings are of prehistoric creatures spotted in unexpected places—that is, not at museums—but today’s submission was too darned cute not to share.

Reader Christine Teander snapped this photo at Durham, North Carolina’s Museum of Life & Science, where she got up close and personal with the crested hadrosaur Parasaurolophus. “It’s my favorite dino of all time,” Christine writes, “so to see it for real, to touch it, to climb on it was a weird little childhood dream come true.” Even better, an affinity for lambeosaurine dinosaurs seems to run in the family. Christine says, “then my daughter climbs up and says ‘Parry-sloffy’ is her favorite in the whole wide world… oh just melts mommy’s heart!” Adorable.

Have you seen a dinosaur or other prehistoric creature in an unusual place? Please send your photo to dinosaursightings@gmail.com.

The skull of Parasaurolophus (a), showing the internal anatomy of the crest, and a cross section of the crest (b). From Weishampel, 1997.

It’s Valentine’s Day, and that means that millions of people will be riffling through their record and CD collections to find the right music to set the proper mood with their special someone. Seventy five million years ago, though, there was no Barry White, and so some deep-voiced dinosaurs made beautiful music together in their own way.

For decades, the crest of the hadrosaur Parasaurolophus puzzled scientists. Such a prominent ornament must have had a function, but what? There were almost as many opinions as there were scientists. Depending on who you asked, the crest was used as a weapon, a foliage deflector, a cranial air tank, or even as a snorkel.

But James Hopson had a different idea. In 1975, he hypothesized that the crests of hadrosaurs like Parasaurolophus were visual display structures that doubled as resonating chambers for vocal communication. (A notion that had also been suggested by Carl Wiman decades before.) The crests were signs of dinosaur sociality. The question was how to test these ideas, but in a landmark 1981 Paleobiology paper David Weishampel looked to the internal anatomy of hadrosaur skulls to see if they could have been using their skulls in the way Hopson had proposed.

Studied from an acoustical perspective, Weishampel found that the crest of Parasaurolophus truly was capable of acting as a resonating chamber for sound. In fact, the internal anatomy of the Parasaurolophus crest was very similar to a woodwind instrument called the crumhorn, and Weishampel proposed that adult Parasaurolophus communicated over long distances through low-frequency sounds. Though not included in this paper itself, Weishampel even created a model of a Parasaurolophus crest using PVC pipe, which sounded something like a tuba when played. Likewise, a recent study of the crested hadrosaurs Lambeosaurus, Corythosaurus and
Hypacrosaurus by David Evans and colleagues found that their nasal passages may have had similar sound-producing capabilities and that their ears were also suited to detecting low-frequency sounds. One can only imagine what an entire hadrosaur symphony—encompassing all the different crest shapes—might have sounded like.

YouTube video of Weishampel playing his hadrosaur horn:

Parasaurolophus did not sound throughout its lifetime, though. By comparing crest shape to the structure of the inner ear, Weishampel suggested that young individuals produced higher-frequency sounds—which traveled shorter distances—whereas adults could produce low-frequency honks that could be heard over much wider areas. (On the basis of potentially different crest shapes for males and females, he also suggested that the different sexes made slightly different sounds, but this difference has not been supported by additional evidence.) During mating season, one could imagine dozens of Parasaurolophus calling to each other, much like living alligators and crocodiles do today. The Late Cretaceous certainly would have been a very noisy place.

For more on dinosaur romance, see my recent Smithsonian article Everything You Wanted to Know About Dinosaur Sex.

References:

Evans, D., Ridgely, R., & Witmer, L. (2009). Endocranial Anatomy of Lambeosaurine Hadrosaurids (Dinosauria: Ornithischia): A Sensorineural Perspective on Cranial Crest Function The Anatomical Record: Advances in Integrative Anatomy and Evolutionary Biology, 292 (9), 1315-1337 DOI: 10.1002/ar.20984

Hopson, J.A. (1975). The Evolution of Cranial Display Structures in Hadrosaurian Dinosaurs Paleobiology, 1 (1), 21-43

Vergne, A., Pritz, M., & Mathevon, N. (2009). Acoustic communication in crocodilians: from behaviour to brain Biological Reviews, 84 (3), 391-411 DOI: 10.1111/j.1469-185X.2009.00079.x

Weishampel, D.B. (1981). Analyses of Potential Vocalization in Lambeosaurine Dinosaurs (Reptilia: Ornithischia) Paleobiology, 7 (2), 252-261

Weishampel, D.B. (1997). Dinosaurian Cacophony Bioscience, 47 (3), 150-159