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A "Snowceratops belgicae", submitted by reader Wim.

There has been virtually no snowfall where I live this year, dashing my hopes of making a snow dinosaur. One of our readers, Wim, has had better luck. In a comment on our last Dinosaur Sighting, Wim included the above picture and wrote:

I spotted a “Snowceratops belgicae” in my garden last week.

Unfortunately, it disappeared a few days later due to an unexpected temperature rise…

True, many snow dinosaurs do become extinct extremely rapidly, but that isn’t going to stop me from trying to make one of my own when the first big snowstorm of the season finally arrives.

Have you stumbled across a dinosaur in an unexpected place? If you have, and have a photo of the encounter, send it to us via dinosaursightings@gmail.com!

The skull of Sinornithomimus. Its toothless beak - and a "gastric mill" found in its skeleton - suggest that it was an herbivorous dinosaur. From Kobayashi Lü, 2003.

Coelurosaurs were one of the strangest groups of dinosaurs. In addition to the famous predators Tyrannosaurus and Velociraptor, the coelurosaurs included the small, fuzzy Sinosauropteryx; “ostrich-mimics” such as Struthiomimus; the long-necked, sickle-clawed giant Therizinosaurus; the tiny, ant-eating Albertonykus; the bird-beaked oviraptorosaurs like Citipati; and birds. Within the past decade, especially, new discoveries have radically changed our understanding of this group of dinosaurs. Now a study shows that, even though this group contained some of the most famous predators of all time, many of these dinosaurs were herbivorous.

Traditionally, dinosaur diets seemed to break down along neat evolutionary lines. The long-necked sauropods and all the ornithischian dinosaurs (ankylosaurs, ceratopsians, hadrosaurs, etc.) were herbivores, whereas all the theropods were carnivorous. This is no longer the case. Coelurosaurs were theropods, and in a review of their evolution  just published in PNAS by Lindsay Zanno and Peter Makovicky, the Field Museum scientists found that relatively few coelurosaurs had an exclusively carnivorous diet.

Zanno and Makovicky determined the different dietary habits of coelurosaurs by looking for gut contents, fossil feces and other evidence that would indicate whether a particular dinosaur was a strict carnivore or a herbivore. (They are just labels that are useful for categorization, of course. Alligators sometimes eat fruit, and cows sometimes eat other animals, and so even a primarily carnivorous dinosaur could have eaten plants sometimes and primarily herbivorous dinosaurs may have eaten meat on occasion.) These pieces of evidence, paired with what the authors called “putatively herbivorous traits” in the skeleton, allowed them to more rigorously test ideas about which coelurosaurs might have been herbivores. The ornithomimosaur Sinornithomimus, for example, had toothless, beaked jaws, and specimens have been found with evidence of a gastric mill (small stones in the stomach which would have ground up food), confirming that it ate a significant amount of plant food.

Zanno and Makovicky concluded that there is good evidence for herbivory in 44 known coelurosaur species spanning six groups: the ornithomimosaurs, therizinosaurs, oviraptorosaurs, alvarezauroids, several early birds, and the single troodontid Jinfengopteryx. (The carnivorous dinosaurs consisted of the compsognathids, the tyrannosaurs and most of the dromaeosaurs.) In other words, the coelurosaurs appear to have been “dietary opportunists” in which multiple lineages shifted to herbivorous diets or had more varied diets than the tyrannosaurs and raptors. No two lineages made the shift to herbivory in exactly the same way. Even though many herbivorous coelurosaurs shared similar traits, such as toothless beaks and long necks, these traits evolved independently and in different orders, and so this convergence might indicate some evolutionary constraints which shaped the herbivorous coelurosaurs in similar ways.

Viewed as a whole, the coelurosaurs were a diverse group of dinosaurs that also had an array of diets. In fact, most coelurosaur subgroups show adaptations to eating plant food, meaning that, contrary to what we might suppose, the hypercarnivorous species are actually the oddballs among the group. Further study will be required to better resolve the diets of individual species, but for now it is apparent that the coelurosaurs were the most varied group of dinosaurs to have ever evolved.

References:

Yoshitsugu Kobayashi and Jun-Chang Lü (2003). A new ornithomimid dinosaur with gregarious habits from the Late Cretaceous of China Acta Palaeontologica Polonica, 48 (2), 235-259

Zanno, L., & Makovicky, P. (2010). Herbivorous ecomorphology and specialization patterns in theropod dinosaur evolution Proceedings of the National Academy of Sciences DOI: 10.1073/pnas.1011924108

Spinosaurus, one of the dinosaurs found in the Kem Kem beds, as restored by artist Todd Marshall. From Dyke, 2010.

Ninety-five million years ago, in what is now southeastern Morocco, giant predators ruled the land. The reddish Cretaceous rock of these arid localities—called the Kem Kem Beds—has yielded the remains of the theropods Deltadromeus, Carcharodontosaurus (seen in Mark Hallett’s exquisite painting “Thunder Across the Delta“), Spinosaurus and several other, poorly-known species. In fact, based on the described fossils, there would appear to be a greater abundance and diversity of predatory dinosaurs than herbivorous ones (!), but was there really such a surplus of carnivores at just one time?

As Charles Darwin aptly recognized over a century and a half ago, the fossil record is an archive “imperfectly kept.” Geological processes and the capricious nature of fossilization have obscured the windows into the past that fossil-bearing rocks present, and one of these confounding factors is called time averaging. Simply put, fossils from different times can be mixed together to make it look as if all those organisms lived alongside one another when they may have actually lived hundreds, thousands, or even millions of years apart. Hence, when paleontologists try to reconstruct an area’s prehistoric ecology, they must always investigate how the fossil-bearing deposits formed and how long a time period they represent.

In the case of the Kem Kem Beds, Queen’s University paleontologist Gareth Dyke has recently argued that the richness of theropod dinosaurs is likely the result of time-averaging and not an indication of there truly being more predators than herbivores. In an short article just published in Current Biology, which draws from a Geology study published with Alistair McGowan last year, Dyke argues that both the nature of fossilization in this place and the way in which those fossils have been collected have skewed our perspective of prehistoric ecology. Since many of the Kem Kem fossils are fragmentary, most are never collected, and it is the sturdier teeth which often get picked up. Given that theropod teeth are abundant and can fetch a good price for local fossil hunters, this leads to an over-representation of predatory dinosaurs in Morocco’s rock shops.

The collecting bias of the local fossil hunters has trickled through the scientific community. Many of the Kem Kem theropod fossils were not collected in the field by professional paleontologists but purchased from rock shops—without detailed geological information—and then later deposited in museums. The Kem Kem dinosaur specimens in many museums, therefore, represent only a snippet of the actual diversity of the prehistoric ecosystem, and the lack of geological data makes it difficult to figure out which species actually lived alongside one another. Indeed, thorough fieldwork in the Kem Kem beds is rarely carried out, and therefore it has been easy to create the impression that these fossil sites represent a strange ecosystem in which hordes of predatory dinosaurs feasted on each other.

The prehistoric ecology of the Kem Kem beds has yet to be fully worked out. Among the questions that remain: How many species of predatory dinosaur were there? Were they all present at one time, or does the formation represent a succession of different assemblages predators over time? What species of herbivorous dinosaurs were present, and how abundant were they? How did these fossil beds accumulate, and how long did it take? Answering these questions will take years of difficult work, both in the lab and the field, but in the process of doing so we will be better able to restore this lost world of Mesozoic Morocco.

References:

McGowan, A., & Dyke, G. (2009). A surfeit of theropods in the Moroccan Late Cretaceous? Comparing diversity estimates from field data and fossil shops Geology, 37 (9), 843-846 DOI: 10.1130/G30188A.1

Dyke, G. (2010). Palaeoecology: Different Dinosaur Ecologies in Deep Time? Current Biology, 20 (22) DOI: 10.1016/j.cub.2010.10.001

The skeleton of Juravenator under UV light. If you look closely around the middle of the tail, you can see the traces of soft tissue. From Chiappe and Göhlich, 2010.

In 1861, as debates about evolution were brewing among naturalists, two important skeletons were discovered from the Late Jurassic limestone quarries of Germany. Both would be relevant to ideas about how birds evolved. Although not recognized as such until the late 20th century, Archaeopteryx was the first feathered dinosaur ever discovered and was a confirmation that birds had evolved from reptiles. The other creature, Compsognathus, represented a small, exceptionally bird-like dinosaur, and the anatomist T.H. Huxley took it as a proxy for the kind of animal from which birds originated. “There is no evidence that Compsognathus possessed feathers,” Huxley said during his 1877 American lecture tour, “but, if it did, it would be hard indeed to say whether it should be called a reptilian bird or an avian reptile.”

Now another feathered dinosaur has been discovered from the famous German limestone quarries. Named Juravenator starki in 2006, this dinosaur was a close relative of Compsognathus which lived just a little bit earlier on the same prehistoric archipelago. It is one of the most complete dinosaurs from these limestone deposits. From the tip of the snout to very nearly the end of the tail, the whole skeleton was preserved, but there was something special about this animal that could only be seen in the right light.

Earlier this year David Hone and colleagues published a paper showing how examining fossils under ultraviolet light can illuminate soft-tissue structures—like feathers—that would otherwise be hidden. Paleontologists Luis Chiappe and Ursula Göhlich applied the same technique to the Juravenator skeleton, and near the middle of the dinosaur’s tail they found an area of preserved soft tissue. The most easily seen parts of the soft tissue were patches of tiny bumps consistent with the skin impressions of other dinosaurs. Yet there were wispy protofeathers, too. Thanks to high-resolution photography, the remains of downy feathers were also detected, and these were similar to the structures that covered the body of a relative of Juravenator from China called Sinosauropteryx.

The presence of both scaly skin and filamentous feathers makes Juravenator unique among feathered dinosaurs. This combination has not been seen before, but it is consistent with laboratory models of how feathers evolved from scaly skin. Furthermore, it appears that Juravenator was not wholly covered by a coat of fluffy feathers like baby chicks, perhaps indicating that feathery structures appeared on some parts of the bodies of dinosaurs before others. Frustratingly, the extent of soft-tissue preservation on the first Juravenator specimen is extremely limited, but further discoveries of this animal may help us better understand the origins of feathered dinosaurs.

References:

Chiappe, L., & Göhlich, U. (2010). Anatomy of Juravenator starki (Theropoda: Coelurosauria) from the Late Jurassic of Germany Neues Jahrbuch für Geologie und Paläontologie – Abhandlungen, 258 (3), 257-296 DOI: 10.1127/0077-7749/2010/0125

The upper jaw of Geminiraptor as seen from the side (left, front is facing left) and from the bottom (right, holes are tooth sockets). From Senter et al., 2010.

2010 has been a bumper crop year for Utah’s dinosaurs. No fewer than eight new species have been named, including the iguanodonts Hippodraco and Iguanacolossus; the ceratopsids Utahceratops, Kosmoceratops and Diabloceratops; the sauropodomorph Seitaad and the sauropod Abydosaurus. (A few other Utah dinosaurs were previewed at the 70th annual Society of Vertebrate Paleontology meeting, too, but have not been published yet.) Now, just two and a half weeks before the end of the year, another Utah dinosaur has been described, and it is quite different from all the other new species.

Even though our understanding of dinosaurs is increasing at an astonishing rate, there are still significant gaps in our knowledge. Many of these gaps can be attributed to literal vacancies in the fossil record where creatures we would expect to find have not yet been uncovered. Such has been the case with troodontid dinosaurs in North America. These were small, lightly-built cousins of the famous “raptor” dinosaurs like Deinonychus. Although the evidence is disputable, they may have been present in North America as early as the Late Jurassic, and they were most definitely there by the Late Cretaceous. If this is so, however, it creates an Early Cretaceous gap in which no troodontids have been found.

A new, approximately 127-million-year-old troodontid from the Cedar Mountain Formation of eastern Utah now fills in this gap. Named Geminiraptor suarezarum and described by paleontologists Phil Senter, James Kirkland, John Bird and Jeff Bartlett in PLoS One, this dinosaur lived during a time when some of the dinosaurs we consider to be indicative of the Late Cretaceous, such as the troodontids, mixed with sauropods and other dinosaurs with a more Jurassic style. Looking at dinosaurs described this year alone, the large sauropod Abydosaurus and the iguanodonts Hippodraco and Iguanacolossus also were found within the Early Cretaceous rock of the Cedar Mountain Formation. This does not mean that all these dinosaurs were contemporaries—the Cedar Mountain Formation spans material from about 127 to 98 million years ago—but this collection of dinosaurs serves to illustrate the change from the Jurassic, sauropod-dominated world to a different mix of dinosaurs.

Frustratingly, all scientists found of Geminiraptor was part of the upper jaw (the maxilla). This makes it difficult to ascertain its closest relatives among the troodontids, and more complete material will be required to resolve its relationship to its kin. What is significant about the new dinosaur, however, is its size. It is big for an Early Cretaceous troodontid—closer in size to the Late Cretaceous, 6-foot-long Troodon than to Early Cretaceous types found in Asia like Sinusonasus—indicating that the larger forms of troodontid evolved earlier than previously thought. With any luck, paleontologists will find more of this unique dinosaur and its Cedar Mountain Formation contemporaries to better flesh out the strange world of the Early Cretaceous.

References:

Senter, P., Kirkland, J., Bird, J., & Bartlett, J. (2010). A New Troodontid Theropod Dinosaur from the Lower Cretaceous of Utah PLoS ONE, 5 (12) DOI: 10.1371/journal.pone.0014329