February 23, 2012
Despite belonging to one of the most famous dinosaur groups of all time, few people have heard of Stokesosaurus clevelandi. This predator, named in 1974 by paleontologist James Madsen, Jr., was a tyrannosauroid dinosaur that roamed North America tens of millions of years before Tyrannosaurus rex.
The bones of Stokesosaurus were initially discovered in the fossil-rich Cleveland-Lloyd Dinosaur quarry in eastern Utah. Although dominated by the remains of at least 46 Allosaurus, rarer traces of other theropod dinosaurs have come out of the quarry. (The mid-size carnivore Marshosaurus and possibly a distinct species of Ceratosaurus have also been recognized from bones found here.) In the case of Stokesosaurus, Madsen had identified two portions of the hip and a piece of the upper jaw, the premaxilla, as belonging to this small theropod. The complete animal probably didn’t stretch longer than 12 feet from nose to tail. While Madsen was tentative about this conclusion, the diminutive predator seemed to represent the early days of the tyrant dinosaurs in North America. Since then, one of the hips has been lost and the jaw fragment is thought to have belonged to a different dinosaur, but the primary hip Madsen relied upon for his description still indicates the presence of the tyrants in Jurassic Utah around 150 million years ago.
By now you may be wondering why I opened a post titled “England’s Jurassic Tyrant” with a note about a tyrannosauroid from Utah. The reason is because, until recently, Stokesosaurus was thought to have been present in Jurassic Europe, too. In 2008, paleontologist Roger Benson described a partial skeleton from the Late Jurassic of England that he attributed to a new species of the dinosaur, Stokesosaurus langhami. There was far more of this animal than the North American species, whose anatomy remains largely a mystery. The new species, on the other hand, was represented by numerous vertebrae, the majority of the hips, and most of a hindlimb.
But the dinosaur Benson described probably wasn’t Stokesosaurus, after all. In a paper to be published at Acta Palaeontologica Polonica, Benson and colleague Stephen Brusatte suggest that the more complete material from England represents a distinct genus of dinosaur. The change was spurred by the discovery of additional archaic tyrannosaurs in recent years. These finds indicated that some of the features Benson had used to link Stokesosaurus from Utah and the British form together were widely distributed among the tyrannosauroids and therefore might not reveal clear relationships. The more complete material from England now seems more distinct from Stokesosaurus than previously understood. Brusatte and Benson have renamed the animal Juratyrant.
But we still know very little about Stokesosaurus, Juratyrant and their close relatives. For Stokesosaurus, most of the skeleton is unknown, and significant portions of Juratyrant—such as the skull and forelimbs—have yet to be found. These tyrants are hardly unique in this respect. Other closely related dinosaurs such as Aviatyrannis are known from frustratingly incomplete remains. We know that these dinosaurs were small predators that set the stage for the later rise of more imposing tyrants, but what they looked like and how they lived remains mysterious.
Benson, R. (2008). New information on Stokesosaurus, a tyrannosauroid (Dinosauria: Theropoda) from North America and the United Kingdom Journal of Vertebrate Paleontology, 28 (3), 732-750 DOI: 10.1671/0272-4634(2008)28[732:NIOSAT]2.0.CO;2
Brusatte, S., & Benson, R. (2012). The systematics of Late Jurassic tyrannosauroids (Dinosauria: Theropoda) from Europe and North America Acta Palaeontologica Polonica DOI: 10.4202/app.2011.0141
Madsen, J. 1974. A new theropod dinosaur from the Upper Jurassic of Utah. Journal of Paleontology, 48 (1), 27-31
November 23, 2011
From museum displays to comic books and feature films, Tyrannosaurus rex has been celebrated as one of the biggest, meanest and ugliest predatory dinosaurs of all time. The image of this long-extinct carnivore as the apex of the apex predators has a nearly unstoppable amount of cultural inertia. Maybe that’s why people get upset when paleontologists and artists suggest that the tyrant dinosaur was at least partly covered in a coat of feathers. (Cracked.com even listed an illustration of a feathered Tyrannosaurus as one of “17 Images That Will Ruin Your Childhood.”) Such images make it seem as if the old “prize-fighter of antiquity” has gone soft—how could such an imposing predator go in for such a silly look? Tyrannosaurus was no turkey, right?
To date, no one has found the fossilized remnants of feathers with a Tyrannosaurus skeleton. A few patches of scaly skin are known from some big tyrannosaur specimens, and those scraps represent about all we know for sure about the body covering of the largest tyrants. So why is Tyrannosaurus so often depicted with a coat of dino-fuzz these days? That has everything to do with the evolutionary relationships of the great tyrannosaur lineage.
Until the early 1990s, paleontologists often placed tyrannosaurus with Allosaurus, Spinosaurus, Torvosaurus and others inside a group called the Carnosauria. These were the biggest of the carnivorous dinosaurs. But the group didn’t make evolutionary sense. As new discoveries were made and old finds were analyzed, paleontologists found that the dinosaurs within the Carnosauria actually belonged to several different and distinct lineages that had branched off from one another relatively early in dinosaur history. The tyrannosaurs were placed within the Coelurosauria, a large and varied group of theropod dinosaurs which includes dromaeosaurs, therizinosaurs, ornithomimosaurs, oviraptorosaurs and others. Almost every single coelurosaur lineage has been found to have feather-covered representatives, including the tyrannosaurs.
In 2004, paleontologist Xing Xu and colleagues described Dilong paradoxus, a small, roughly 130-million-year-old theropod which may be one of the earliest tyrannosauroid dinosaurs known. (The Tyrannosauroidea contains all the big, famous tyrannosaurids, such as Tyrannosaurus and Albertosaurus, as well as their closest relatives.) Small patches of filamentous protofeathers were found along the dinosaur’s neck and tail, indicating that—at least during their early evolutionary history—tyrannosaurs may have been covered in feathers, too. But the relevance of Dilong to the question of feathered tyrannosaurs partially rests on what Dilong turns out to be. The initial description cast the dinosaur as a tyrannosauroid, but subsequent analyses have differed as to whether Dilong is an early tyrannosauroid (as in Carr and Williamson, 2010) or belongs to some other coelurosaur group (as in Turner et al., 2011).
For the sake of argument, though, let’s say that Dilong was not a tyrannosauroid and actually belonged to a different coelurosaurian lineage. Would this mean that tyrannosaurs didn’t have feathers? Certainly not. Feathers were a widespread trait within the coelurosaurs, and simple, fuzzy protofeathers may go back to the last common ancestor of the group. Otherwise feathers would have to have evolved near the base of every lineage, and there is no indication that feathers evolved so many times. The spread of feathers among almost all coelurosaur groups hints at a shared origin.
Since so many other coelurosaurs had feathers, it is fair to infer that tyrannosaurs also did. This hypothesis is no more unreasonable than saying that close relatives of the earliest mammals such as Morganucodon were covered in fur on the basis of their evolutionary relationships. And, to pick another dinosaurian example, no one has yet described an ornithomimid dinosaur with evidence of feathers, yet we are comfortable attributing feathers to them because they are coelurosaurs. (Maybe their vaguely ostrich-like appearance helps a bit in this regard.) If feathers can reasonably be inferred for ornithomimosaurs on the basis of their family tree, then we can do so for tyrannosaurs.
So, within this evolutionary bracket, what kind of feathers might have clothed Tyrannosaurus and kin? The simple dino-fuzz of Dilong is a fair bet. Perhaps such a body covering would have served for insulation, but then again, the patchy distribution of filaments on Dilong and other coelurosaurs has raised the suggestion that some dinosaurs were only partly coated in feathers. Whatever their distribution on tyrannosaur bodies, though, the feathers probably didn’t look like those which allowed other coelurosaurs to eventually take to the air. After all, feathers were probably used for display and the regulation of body temperature first, and since no tyrannosauroid even came close to flying we should expect for them to have relatively simple feathers related to these functions.
Regarding Tyrannosaurus specifically, the tyrant king may have had feathers only during the early years of life. A fuzzy coat may have helped hatchling and juvenile Tyrannosaurus regulate their body temperature, but as the animals grew, the benefits provided by insulation may have disappeared. (Retaining heat is a problem often faced by small animals, while shedding excess heat is a problem faced by larger animals due to changes in surface-to-volume ratios as animals grow.) Maybe an adult Tyrannosaurus would have patches of protofeathers here and there, as in Peter Schouten’s illustration of the dinosaur, But given the evidence at hand, it is likely that baby Tyrannosaurus would have been fuzzier than their parents.
Frustratingly, though, we may never know for sure what sort of feathers Tyrannosaurus might have had, or during what part of life. Circumstances of fine preservation are required to detect feathers, and even then, sometimes only patches are preserved. The types of environments Tyrannosaurus lived in were not exactly amenable to the kind of rapid, fine-detail preservation required to detect feathers. Even in cases where skin patches are preserved, it is difficult to know whether there might have been protofeathers on other parts of the body, or whether some of those feathers fell off or otherwise eluded preservation. Delicate structures require delicate preservation to detect.
What we can say is that the idea of a feather-covered Tyrannosaurus is a reasonable hypothesis. We still know so little about the body covering of this dinosaur that artists can reasonably restore the dinosaur with scaly skin, a coat of feathers, or a patchwork of both (I would especially like to see more renditions of that third possibility). Perhaps future fossil discoveries will provide us with a clearer picture of what Tyrannosaurus looked like, but the current unknowns are fascinating. Asking what Tyrannosaurus looked like is not just a matter of speculation—obtaining an answer requires that we consider the patterns and processes of evolution, as well as the methods we use to restore creatures that have been dead for millions upon millions of years. Feather-covered or not, though, I wouldn’t want to call Tyrannosaurus a turkey to its face. If I did, I don’t think I could run away fast enough to avoid becoming the dinosaur’s Thanksgiving dinner.
From everyone here at Dinosaur Tracking, we hope that you enjoy your holiday dinosaur and have a warm Thanksgiving.
Carr, T., & Williamson, T. (2010). Bistahieversor sealeyi, gen. et sp. nov., a new tyrannosauroid from New Mexico and the origin of deep snouts in Tyrannosauroidea
Journal of Vertebrate Paleontology, 30 (1), 1-16 DOI: 10.1080/02724630903413032
Turner, A., Pol, D., & Norell, M. (2011). Anatomy of Mahakala omnogovae(Theropoda: Dromaeosauridae), Tögrögiin Shiree, Mongolia American Museum Novitates, 3722 (3722), 1-66 DOI: 10.1206/3722.2
Xu, X., Norell, M., Kuang, X., Wang, X., Zhao, Q., & Jia, C. (2004). Basal tyrannosauroids from China and evidence for protofeathers in tyrannosauroids Nature, 431 (7009), 680-684 DOI: 10.1038/nature02855
July 28, 2010
I love visiting the fossil halls of natural history museums, but I have to admit that I sometimes yearn to see new specimens on display. Tyrannosaurus, Apatosaurus, Triceratops, Allosaurus, Edmontosaurus—their skeletons remains as impressive as ever, but given all the new dinosaur species discovered during the past century, it would be refreshing to see some new, lesser-known dinosaurs on display.
If I had free reign to set up a dinosaur hall as I saw fit, for example, I would want to create an exhibit all about the tyrannosauroid dinosaurs. It used to be that we knew only the last and the biggest of the tyrant dinosaurs, but during the past decade our knowledge of tyrannosauroids and their evolution has greatly expanded. Among others, I would love to see tyrannosauroids like Dilong, Appalachiosaurus and Raptorex on display next to their well-known relatives like Gorgosaurus and Tyrannosaurus to illustrate how these predators evolved.
The same could be done with sauropods. We’re all familiar with the classic sauropods such as Diplodocus and Camarasaurus, but what about some of the really bizarre sauropods few people know about? By presenting oddballs like the hoover-mouthed Nigersaurus, the sail-necked Amargasaurus and the armored Saltasaurus next to the classic forms, museum visitors could gain a fuller appreciation for sauropod diversity.
What about you? If you could design a museum dinosaur hall, what would you put in it?