V is for Velafrons

When people ask me why I moved from central New Jersey to Salt Lake City, Utah, I always give the same response: “For the fossils.” The Beehive State is home to an exceptional array of fossil sites, and is quite simply a gorgeous place to do fieldwork in. Most friends and acquaintances get this immediately and don’t ask any follow-up questions. But one friend of mine was confused by my motivation. “Haven’t paleontologists already found all the dinosaurs?”, he asked.

Paleontologists have been scouring North America’s western deserts for fossils since the late 19th century. The most famous dinosaurs of all – Tyrannosaurus, Triceratops, Stegosaurus, Diplodocus, and the like – were all found over a century ago in the Mesozoic rock scattered through the basin and range. That might give the impression that paleontologists have only been retracing their own tracks for the last 100 years. Yet these dinosaurs come from relatively thin slices of prehistoric time, and the rock record of the west is far richer, expansive, and mysterious than most people know.

A few months before I moved to Utah, for example, paleontologists described eight new dinosaur species from various sites in the state, and there are even more that are still on their way to publication. (Not to mention those that still hide in the rocks.) Most of the major dinosaur discoveries in the west have yet to be made, and that’s true of Mexico as well as the United States. Among the latest finds that hints how much there is yet to be uncovered is Velafrons coahuilensis, a 73.5 million year old hadrosaur found near Coahuila, Mexico.

As described by paleontologist Terry Gates and colleagues in the 2007 description of the dinosaur, getting Velafrons out of the ground was a decade-long endeavor. Field crews from the “Dinamation International Society” uncovered most of the hadrosaur’s body in excavations between 1992 and 2001. But it wasn’t until a joint effort by multiple museums returned to the quarry in 2002 that paleontologists finally got the disarticulated skull bones that allowed them to gauge just how different the Cretaceous dinosaur was from similar species.

The skeletal chassis of hadrosaurs are frustratingly similar to each other. So much so that hadrosaurs without heads are often difficult to positively identify. With the preserved skull bones, though, Gates and coauthors were able to pin Velafrons as a lamebosaur – a member of a specific hadrosaur subgroup that also contains the famous tube-crested Parasaurolophus and dome-crested Corythosaurus. Indeed, these hadrosaurs are well known for showing off rather flashy skull ornamentation.

When pieced together, the skull of Velafrons looked quite similar to that of Corythosaurus and Hypacrosaurus. In these hadrosaurs, the nasal bones rose up to create a domed, compressed helmet. Even though the Velafrons individual that Gates and collaborators studied was a juvenile, and its crest would probably have continued to change as it grew, the overall shape was similar. Details of the Velafrons skull were enough to distinguish the dinosaur from these similar forms, but, not surprisingly, the newly-named species came out as a close relative to Corythosaurus and Hypacrosaurus.

Yet Velafrons lived far south from its kin. Velafrons was part of what appears to have been a distinct radiation of southern dinosaurs during the late Campanian – between about 75 and 72 million years ago. The dinosaurs that lived in southern Utah, Texas, and Mexico during this time belonged to the same lineages as the ones found in Montana and Canada, but were different genera and species.

Judged through the bird’s eye view paleontology provides, there seems to have been some kind of barrier that isolated these Cretaceous communities into northern and southern parts, spurring dinosaur populations to diverge in distinct ways. No one yet knows what this barrier might have been. Paleontologists are still assembling this puzzle. We’re only just starting to understand the outline of dinosaur evolution during this one narrow span of time, not to mention the story of the global Cretaceous. Some of the greatest stories in dinosaur history are still waiting to be discovered.

Previous entries in the Dinosaur Alphabet series:

U is for Uteodon

T is for Torvosaurus

S is for Segisaurus

R is for Rapetosaurus

Q is for Qiaowanlong

P is for Pelecanimimus

O is for Ojoceratops

N is for Nqwebasaurus

M is for Montanoceratops

L is for Leaellynasaura

K is for Kileskus

J is for Juravenator

A-I at Dinosaur Tracking.

Reference:

Gates, T., Sampson, S., Delgado de Jesús, C., Zanno, L., Eberth, D., Hernandez-Rivera, R., Aguillón Martínez, M., Kirkland, J. 2007. Velafrons coahuilensis, a new lambeosaurine hadrosaurid (Dinosauria: Ornithopoda) from the Late Campanian Cerro del Pueblo Formation, Coahuila, Mexico. Journal of Vertebrate Paleontology 27, 4: 917–930.

U is for Uteodon

Last week I wrote about the enormous Jurassic carnivore Torvosaurus. The theropod was undoubtedly a sharp-toothed nightmare, but what did the rapacious giant eat? The even-larger sauropod dinosaurs that plodded around during the same time are obvious candidates – big predators would seem well-suited to chasing even larger prey. Yet, as paleontologists such as Dave Hone and Oliver Rauhut have argued, large meat-eating dinosaurs probably relied on relatively small fare. An 80-foot-long adult Apatosaurus was probably too much for even the largest Torvosaurus to handle, and so the Jurassic megalosaur most likely targeted juvenile sauropods and other comparatively little herbivores. Among the possible menu items – a mid-sized, bipedal, beaked ornithopod called Uteodon aphanoecetes.

After studying the dinosaur’s nearly complete postcranial skeleton, paleontologist Andrew McDonald named Uteodon in 2011. But the dinosaur’s backstory goes deeper than that.

The bones of Uteodon were found nearly a century ago in the roughly 150 million year old rock of what is now known as Dinosaur National Monument, Utah. The animal’s remains closely resembled that of a classic Jurassic dinosaur called Camptosaurus – named by paleontologist Othniel Charles Marsh in 1885 – and so it’s not surprising that dinosaur expert Charles Gilmore assigned the skeleton to the species Camptosaurusmedius.” (Later, the skeleton was bumped to the species Camptosaurus dispar).

Slowly, paleontologists began to realize that the Dinosaur National Monument Camptosaurus was not quite what it seemed. In 2008, Kenneth Carpenter and Yvonne Wilson determined that the skeleton differed enough from other Camptosaurus to justify establishing a new species – Camptosaurus aphanoecetes. Andrew McDonald went a step further in his 2011 reanalysis of Camptosaurus. While superficially similar, the DNM skeleton differed in various details of the braincase, shoulder, hip, and other parts of the skeleton. Rather than being just another Camptosaurus, McDonald made the case that the dinosaur was distinct enough to justify a new genus. Keeping the new species name coined by Carpenter and Wilson, McDonland rechristened the dinosaur Uteodon aphanoecetes.

Like many other Morrison Formation dinosaurs, there’s still much we don’t know about the biology of Uteodon. The dinosaur appears to have been a relatively plain herbivore, and may have relied on speed to run away from Allosaurus and other carnivores of the era (as in the Planet Dinosaur clip above). Hopefully, as they continue to draw tales from bone, paleontologists will someday be able to visualize the role Uteodon and other dinosaurs played in Jurassic ecosystems in greater detail.

Previous entries in the Dinosaur Alphabet series:

T is for Torvosaurus

S is for Segisaurus

R is for Rapetosaurus

Q is for Qiaowanlong

P is for Pelecanimimus

O is for Ojoceratops

N is for Nqwebasaurus

M is for Montanoceratops

L is for Leaellynasaura

K is for Kileskus

J is for Juravenator

A-I at Dinosaur Tracking.

References:

Carpenter, J., Wilson, Y. 2008. A new species of Camptosaurus (Ornithopoda: Dinosauria) from the Morrison Formation (Upper Jurassic) of Dinosaur National Monument, Utah, and a biomechanical analysis of its forelimb. Annals of Carnegie Museum. 76, 4: 227-263

Hone, D., Rauhut, O. 2009. Feeding behaviour and bone utilization by theropod dinosaurs. Lethaia. 43, 2: 232-244

McDonald, A., 2011. The taxonomy of species assigned to Camptosaurus (Dinosauria: Ornithopoda). Zootaxa. 2783: 52-68

Top image: Photo by Daderot, image from Wikipedia.

T is for Torvosaurus

At ScienceOnline 2013, marine biologist and Deep Sea News blogger Al Dove asked me about the reputation of Allosaurus. The 150 million year old hypercarnivore has often been treated as a smaller, weaker forerunner of the later Tyrannosaurus, as if the bones of Allosaurus testify “The one who comes after me is more powerful than I.” In the dinosaur books I grew up reading, Allosaurus was presented as the Jurassic theropod prototype which reached an apex in Tyrannosaurus, just before the non-avian dinosaurs were snuffed out. Al wanted to know whether such representations were accurate.

As I told Al, I hate to see Allosaurus get shortchanged. While the typical Allosaurus skeleton you’re bound to see in a museum is going to look small compared to Tyrannosaurus, there are rare, fragmentary skeletons which hint that Allosaurus could have grown to be 40 feet long or so – about as large as our favorite tyrant dinosaur. (These scrappy remains have often been given different names, such as “Epanterias” and “Saurophaganax.”) And while the bite of Allosaurus wasn’t as devastating as that of Tyrannosaurus, differences between two species of the Jurassic predator indicate that the skull of Allosaurus was being modified in a way to put more power into each chomp. While the older Allosaurusjimmadseni” had a relatively narrow cranium, the back of the skull in the later Allosaurus fragilis was expanded to provide more room for powerful jaw muscles (similar to the difference seen between Tyrannosaurus and its close, slim-skulled relative Tarbosaurus).

And Allosaurus was extremely successful. The dinosaur is the most commonly-found carnivore in the Jurassic Morrison Formation. Within eastern Utah’s Cleveland-Lloyd Dinosaur Quarry, for example, the remains of at least 46 Allosaurus have been found in one place – totally outstripping the counts of all other dinosaurs in the same quarry. But the prevalence of Allosaurus also highlights a Mesozoic mystery.

Allosaurus wasn’t the only giant carnivore stalking Jurassic floodplains. The Cleveland-Lloyd quarry, to pick just one site, has also yielded the partial remains of two other big predators – a remarkably large Ceratosaurus, and pieces of Torvosaurus. While both of these predators shared the same habitats as Allosaurus, they were apparently much rarer. Why this should be so is an enigma, made all the more complicated by the fact that there is comparatively little of these other carnivores to work with. Torvosaurus, especially, was a huge hunter that paleontologists know relatively little about.

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S is for Segisaurus

Segisaurus halli is an underappreciated little dinosaur. Described in 1936 by paleontologist Charles Camp, the three-foot-long theropod held telling clues about just how bird-like dinosaurs truly were, yet the significance of Segisaurus largely went unnoticed until other finds more prominently underscored the same lessons.

The only known remains of Segisaurus are a paltry lot of vertebrae, limb bones, and parts of the shoulders and hips. But the fact that we possess anything of Segisaurus at all is a minor miracle. The partial skeleton – discovered on July 27, 1933 by Robert F. Thomas and Max Littlesalt in Arizona’s Segi Canyon – was found entombed in a stack of Early Jurassic sediment called the Navajo Sandstone. These beds record a time when sprawling dune fields covered the American west, and tracks are more commonly found in this formation than skeletons. To find any skeletal material in the Navajo Sandstone is truly exceptional. To have a partial skeleton is even better.

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R is for Rapetosaurus

One sauropod deserves another. After briefly profiling the as-yet-little-known Qiaowanlong last week, it’s only natural to follow up with Rapetosaurus krausei – another recently-named Mesozoic herbivore that altered our understanding of the forms some sauropod lineages took.

Paleontologists Kristina Curry Rogers and Catherine Forster named Rapetosaurus in 2001. As the researchers dubbed the dinosaur in the paper’s title, the sauropod was among “the last of the dinosaur titans.” At somewhere between 66 and 70 million years old, Rapetosaurus roamed Madagascar during what we can look back at and call the waning days of the Cretaceous. And the record of this dinosaur is particularly rich among its kind – scattered remains of multiple individuals, including articulated specimens, have been found within a ten square kilometers of Madagascar’s Cretaceous exposures.

Among the various sauropod lineages, Curry Rogers and Forster concluded, Rapetosaurus belonged to the titanosaur branch. This widespread group of long-necked leaf-munchers included some of the largest dinosaurs of all time, including the 100 foot plus Argentinosaurus, although adult Rapetosaurus stretched a more modest 50 feet or so. And unlike other titanosaurs, Rapetosaurus had a peculiar skull that superficially resembled those of diplodocid dinosaurs such as Apatosaurus and Diplodocus itself.

In a 2004 follow-up focused on the head of Rapetosaurus, Curry Rogers and Forster drew from two partial skulls to fill out the dinosaur’s anatomy and compare the sauropod to other titanosaurs. While closely-related dinosaur had relatively deep, stocky skulls, Rapetosaurus had a longer, more slender cranium with the nasal opening up between the eyes. Not all titanosaurs followed the same anatomical rules. Given the number of titanosaurs paleontologists have named, and how few skulls have been found, there may have been even more skeletal diversity than we presently understand. Despite being some of the largest and most impressive dinosaurs, titanosaurs are still prehistoric enigmas.

Previous entries in the Dinosaur Alphabet series:

Q is for Qiaowanlong

P is for Pelecanimimus

O is for Ojoceratops

N is for Nqwebasaurus

M is for Montanoceratops

L is for Leaellynasaura

K is for Kileskus

J is for Juravenator

A-I at Dinosaur Tracking.

References:

Curry Rogers, K., Forster, C. 2001. The last of the dinosaur titans: a new sauropod from Madagascar. Nature. 412: 530-534

Curry Rogers, K., Forster, C. 2004. The skull of Rapetosaurus krausei (Sauropoda: Titanosauria) form the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology. 24, 1: 121-144

Curry Rogers, K. 2009. The postcranial osteology of Rapetosaurus krausei (Sauropoda: Titanosauria) from the Late Cretaceous of Madagascar. Journal of Vertebrate Paleontology. 29, 4: 1046-1086

Q is for Qiaowanlong

I knew the “Q” entry in the Dinosaur Alphabet was going to be a challenge. There are only a handful of Q dinosaurs known so far, most are scrappy, and none are famous. How could Qingxiusaurus and Quaesitosaurus compete with Tyrannosaurus, Diplodocus, and other household names? But, of course, the whole point of the series is to highlight some dinosaurs that are lesser-known and that I’ve never talked about before. Today, I’m picking out the 100 million year old sauropod Qiaowanlong kangxii from the dinosaurian ranks.

Described in 2009 by paleontologists Hai-Lu You and Da-Qing Li, the tapering titanosaur was discovered in northwestern China’s Yujingzi Basin. All that was left of the dinosaur were eight neck vertebrae, the right side of the hips, and unidentifiable scraps. Despite the incomplete nature of the specimen, though, there was enough left to distinguish the sauropod from others as a new genus and species.

You and Li initially cast Qiaowanlong as a brachiosaurid – dinosaurs with impressively bulky arms and shoulders and a more upright posture, much like Brachiosaurus itself. The sauropod, the researchers proposed, was the first of this hefty herbivorous lineage found in China.

As paleontologists have gone about excavating and comparing other fossils, though, the  identity of Qiaowanlong has shifted. A 2010 study by Daniel Ksepka and Mark Norell found that Qiaowanlong wasn’t actually a brachiosaur, but belonged to another lineage with the tongue-twisting name somphospondyli. This is a big group of sauropods, encompassing the rightly-named titanosaurs, that split from brachiosaurs from an earlier common ancestor. These dinosaurs also had heavier forelimbs and shoulders than sauropods like Apatosaurus, even if they didn’t hold themselves with quite the same proud air as Brachiosaurus.

At the moment, the story of Qiaowanlong is primarily one of a minor change in the big picture of dinosaur paleontology. Still, the findings help provide the context for how sauropod dinosaurs proliferated and spread around the world. We as yet know little of Qiaowanlong, but, with new finds and studies, the dinosaur helps document the success of some of the strangest animals that ever lived.

Previous entries in the Dinosaur Alphabet series:

P is for Pelecanimimus

O is for Ojoceratops

N is for Nqwebasaurus

M is for Montanoceratops

L is for Leaellynasaura

K is for Kileskus

J is for Juravenator

A-I at Dinosaur Tracking.

References:

Ksepka, D., Norell, M. 2010. The illusory evidence for Asian Brachiosauridae: New material of Erketu ellisoni and a phylogenetic reappraisal of basal titanosauriformes. American Museum Novitates. 3700: 1-27

You, H., Li, D. 2009. The first well-preserved Early Cretaceous brachiosaurid dinosaur in Asia. Proceedings of the Royal Society B: Biological Sciences, 276: 4077-4082

P is for Pelecanimimus

At the end of 2012, I took a moment to look back at some of the fantastically fluffy feathered dinosaurs that paleontologists had uncovered during the year. In so doing, I mentioned that researchers have been quite busy ever since Sinosauropteryx – a little theropod clothed in dinofuzz – popped onto the scientific scene in 1996. What I neglected to mention that the little compsognathid may not have been the first feathery non-avian dinosaur ever found. There were other, unconfirmed candidates before 1996, including the strange Pelecanimimus.

Even though Sinosauropteryx was the beginning of a resounding confirmation that many dinosaurs were fuzzy, if not feathery, paleontologists had been toying with the idea for decades. In fact, the Victorian anatomist Thomas Henry Huxley unintentionally anticipated the discovery of Sinosauropteryx when he rhapsodized that the closely related Compsognathus, if covered in feathers, would have looked exceptionally bird-like. Other paleontologists and artists entertained similar visions in decades to come, the most famous being Gregory S. Paul’s 1988 fan-favorite Predatory Dinosaurs of the World – a book brimming with rich black-and-white illustrations of bird-like, enfluffed dinosaurs.

But, prior to the 1990s, restorations of feathery dinosaurs were marred by the simple fact that no one had ever found direct evidence of such body coverings. Hypotheses about the relationship between birds and dinosaurs (or, in Huxley’s case, birds and as-yet-undiscovered dinosaur-like reptiles) hinted that feathers should have originated long before the origin of the first flying birds, and there were only the barest hints that this was the case. Among the enigmatic clues were what appeared to be feather imprints in stone.

In the mid 19th century, American naturalist Edward Hitchcock acquired an impression of what he thought was a resting bird, complete with feather traces around the legs and feet. Paleontologists later realized that Hitchcock’s “sandstone birds” were really Early Jurassic dinosaurs, which raised the possibility of fuzzy dinosaurs. Only, as relatively recent analyses have shown, the apparent feather imprints are actually subtle sedimentary structures the bipedal dinosaur created as it stood up off the ground.

All the same, the skeletal connections between birds and dinosaurs eventually led many paleontologists to conclude that birds are truly dinosaur descendents. Pelecanimimus had the potential to further underscore that idea.

In 1994, a paper in Nature by paleontologist Bernardino Pérez-Moreno briefly described the partial skeleton of an exceptionally-preserved theropod dinosaur with soft tissue impressions. They called the long-snouted, many-toothed animal Pelecanimimus polyodon, and the dinosaur was an archaic ornithomimosaur closely related to forms such as Harpymimus.

Included with the 128 million year old specimen, discovered in central Spain, were “subparallell fibres” found near the lower neck and the right arm. Pérez-Moreno and coauthors didn’t call these structures feathers, nor were the fibers included in the restoration of the animal created by Mauricio Antón, but the paper still counted them as “integumentary structures” that would have covered part of the dinosaur’s body.

Had protofeathers finally been find on a dinosaur? Paleontologists were cautious about the possibility. In fact, in 1997 Pérez-Moreno joined Derek Briggs and colleagues in a reassessment of the Pelecanimimus soft tissue structures that recharacterized the mysteries fibers as muscle remnants. Pelecanimimus truly did have a throat pouch and a crest atop its head, as originally envisioned, but the paleontologists concluded that the dinosaur’s skin was smooth and lacked feathers or scales. As with another small theropod fossil found in Brazil and described by Alexander Kellner the year before, the preservation of Pelecanimimus was so detailed that clear evidence of feathers would have been expected if they were truly present.

Maybe they are. Even though the 1997 study was taken as solid evidence that the sole Pelecanimimus was not preserved with feathers, the specimen deserves another look. After all, Pelecanimimus was a coelurosaur, and, as multiple studies over the past decade and a half have indicated, there was some kind of feather or dinofuzz in every branch of the coelurosaur family tree. Pelecanimimus almost certainly had feathers, and the detecting the presence of simple protofeathers on this dinosaur would alter the often-told story of how fuzzy and fluffy dinosaurs emerged on the scientific scene. Sinosauropteryx may have kicked out the Dinosaur Feather Rush, but we should not forget odd little Pelecanimimus in the history of enfluffled dinosaurs.

Previous entries in the Dinosaur Alphabet series:

O is for Ojoceratops

N is for Nqwebasaurus

M is for Montanoceratops

L is for Leaellynasaura

K is for Kileskus

J is for Juravenator

A-I at Dinosaur Tracking.

References:

Briggs, D. Wilby, P., Pérez-Moreno, B., Sanz, J., Fregenal-Martinez, M. 1997. The mineralization of dinosaur soft tissue in the Lower Cretaceous of Las Hoyas, Spain. Journal of the Geological Society, London. 154: 587-588

Kellner, A. 1996. Fossilized theropod soft tissue. Nature. 379: 32.

Pérez-Moreno, B., Sanz, J., Buscalloni, A., Moratalla, J., Ortega, F., Rasskin-Gutman, D. 1994. A unique multitoothed ornithomimosaur dinosaur from the Lower Cretaceous of Spain. Nature. 370: 363-367

Unwin, D. 1998. Feathers, filaments and theropod dinosaurs. Nature. 391: 119-120

O is for Ojoceratops

Paleontologists have  named both too many and too few dinosaurs. The tricky business of taxonomy is to blame. While hundreds of dinosaur species rest as-yet-undiscovered in geologic formations and museum collections, researchers also tussle over the identities of specimens given new names. The continuing academic struggle over whether Torosaurus and Nedoceratops really represent growth stages of Triceratops is one such struggle, and, even among ceratopsid dinosaurs, isn’t the only debate. Paleontologists are also unsure about the identity of Ojoceratops fowleri, a poorly known horned dinosaur found in New Mexico.

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N is for Nqwebasaurus

When a dinosaur starts coming out of the ground, what species the creature might be isn’t always clear. Paleontologists and field volunteers try to uncover enough to figure out the extent of the bone and trim down the size of the block, leaving the majority of careful, fine-scale preparation for the lab. And even once that skeleton has been painstakingly excavated, glued, and cleaned to the utmost, the dinosaur’s identity still might be mysterious. Such was the case with Nqwebasaurus thwazi, an early “ostrich mimic” dinosaur whose affinities only became clear a decade after first being described.

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M is for Montanoceratops

Of all the dinosaurs that have ever lived, ceratopsians were some of the most impressive. There was the huge, three-horned Triceratops; Kosmoceratops, the so-called “horniest dinosaur“; and the hook-horned Einiosaurus, to name just a few. Yet ceratopsians were not just prickly giants. (All the big-bodied forms fall into a particular ceratopsian subgroup called ceratopsids.) The wider ceratopsian family included smaller forms with deep tails and skulls that generally lacked the imposing ornaments of their larger cousins. Protoceratops from the Cretaceous of Mongolia’s Gobi Desert is the most familiar of these often-overlooked ceratopsians, but North America sported a variety of genera, too. Among them was Montanoceratops, a comparatively small horned dinosaur that coexisted with its burlier, spikier relatives.

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K is for Kileskus

Tyrannosaurus rex was the ultimate carnivorous, non-avian dinosaur. Even though lesser-known theropods – such as Spinosaurus and Carcharodontosaurus – were supposedly a little longer or heavier, they simply can’t compete with the celebrity of T. rex. For over a century, the giant tyrannosaur has represented the biggest, most powerful, and last of its lineage.

But tyrannosaurs were not always so imposing. Over the past few decades, paleontologists have been able to trace tyrannosaurs back into the Jurassic, when the predators were small, fuzzy carnivores that skittered around landscapes dominated by a cast of different carnivores. The recently-named Kileskus aristotocus was one of these meek tyrannosaurs.

Much like Stokesosaurus from Utah, England’s Proceratosaurus, and archaic tyrannosaurs from elsewhere, relatively little of Kileskus has been found. Paleontologist Alexander Averianov and coauthors described the dinosaur in 2010 on the basis of a few skull elements and possible bones from the theropod’s hands and feet. The fossils had been found in the roughly 165 million year old rock of West Siberia, Russia.

Despite the paucity of the known remains, however, Averianov and colleagues picked out characteristics that ally Kileskus with Proceratosaurus and the crested Guanlong from China’s Jurassic fossil beds. Specifically, within the greater tyrannosauroid family, Kileskus fell within a group of early tyrannosaurs that had different forms of cranial ornamentation called proceratosaurids. No sign of such adornments can be seen on the available bones of Kileskus, but, given its relationships, it wouldn’t be surprising if the dinosaur had some sort of nasal horn or flashy crest.

Kileskus was not a big dinosaur. Although it’s impossible to say exactly how long the tyrannosaur was, the dinosaur’s maxilla – the major tooth-bearing part of the upper jaw – is just under a foot long. The same bone in adult Tyrannosaurus is two feet long or longer, so Kileskus was a pipsqueak compared to its later relatives. And even during the time Kileskus roamed prehistoric Russia, the megalosaurs, ceratosaurs, and allosaurs were the large-bodied top predators. Tyrannosaurs would not rise to dominance and expand their range of body sizes until tens of millions of years later. Thanks to geological hindsight, we can see Kileskus at the humble beginnings of one of the most voracious dinosaur lineages of all time.

Previous Entries in the Dinosaur Alphabet series:

J is for Juravenator

A-I at Dinosaur Tracking

Reference:

Averianov, A., Krasnolutskii, S., Ivantsov, S. 2010. A new basal coelurosaur (Dinosauria: Theropoda) from the Middle Jurassic of Siberia. Proceedings of the Zoological Institute RAS 314, 1: 42–57.

J is for Juravenator

Juravenator starki had both scales and simple dinofuzz. Photo by Ghedoghedo, image from Wikipedia.
http://en.wikipedia.org/wiki/File:Juravenator_starkae.JPG

Juravenator starki was a fluffy little dinosaur. The theropod’s delicate preservation in a 151 million year old limestone slab gives away its primitive plumage, particularly under ultraviolet light. While the two-and-a-half foot long carnivore had pebbly skin often seen among dinosaurs, fine filaments along the specimen’s pelvis and tail indicate that Juravenator was at least partly covered in a coat of simple protofeathers.

Juravenator was named by Ursula Göhlich and Luis Chiappe in 2006, and it was immediately apparent that the dinosaur bore simple “integument.” Within the context of early analyses, the fuzzy appearance of Juravenator made perfect sense. The theropod seemed to be a compsognathid – a lineage of small, predatory dinosaurs already known to have feathery members among their ranks. Since compsognathids such as Sinosauropteryx had feathers, it wasn’t surprising that Juravenator did, as well.

But Juravenator may not be a compsognathid.

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