May 30, 2012
Stegosaurus is undoubtedly one of the most perplexing dinosaurs. What was all that iconic armor for? (And how did amorous stegosaurs get around that complication?) Paleontologists have been investigating and debating the function of Stegosaurus ornamentation for decades, but without much consensus. The dinosaur’s spectacular plates were certainly prominent visual signals, but could they also have been used for regulating body temperature? Or might there be some evolutionary impetus we’re not thinking of?
Of course, a few ideas have been tossed in the scientific wastebasket. Despite what 19th and early 20th century paleontologists thought, Stegosaurus plates were not protective armor. And, contrary to numerous restorations I saw as a child, Stegosaurus could not waggle or flap its plates around. But the weirdest idea of all was forwarded by paleontology enthusiast and writer W.H. Ballou in 1920. Stegosaurus plates were not armor, heat regulators, or flashy ornaments, Ballou wrote, but were wings that allowed the dinosaur to glide.
Ballou’s article appeared in the Utah’s Ogden Standard-Examiner. And, fortunately for fans of bizarre fossil ideas, a large illustration of flying Stegosaurus graces the piece. One stegosaur crouches to take off, another perches on a rock, and a third buzzes a prehistoric human. (Ballou pointed out in the article that humans originated after dinosaurs, but apparently the artist decided to take some historical license.) This ungainly and aerodynamically-challenged dinosaur, the paper said, was the “Father of All the Birds.” “Crude aeroplane or glider as the Stegosaur was, the principle of all flight was there in the parallel rows of flaps upon his back,” Ballou wrote, concluding, “Certainly he was the factory in which the first bird was built.”
There wasn’t any scientific evidence behind this. While Ballou mentioned the recent discovery of the lovely Stegosaurus skeleton now on display at Smithsonian’s National Museum of Natural History as the inspiration for the idea, the wild notion seems to have been entirely his. The vision of swooping stegosaurs isn’t attributed to any paleontological authority.
But Ballou did draw from a few references that offer a clue to his bizarre vision of gliding stegosaurs. Ballou pointed out that Stegosaurus was an ornithischian, or “bird-hipped” dinosaur. If Stegosaurus was bird-hipped, he reasoned, it must have been close to avian ancestry. Yet Ballou was confused by terminology. Despite having generally bird-like hips, the ornithischian dinosaurs—the hadrosaurs, ceratopsids, ankylosaurs, stegosaurs and others—were nowhere near the bird lineage. Their hip shape was a red herring, a case of superficial convergence. Ironically, the hips of birds were modified from an earlier “lizard-hipped” saurischian form. Ballou wasn’t the only one to be fooled by ornithischian hips—from the 1870s to the 1960s, some paleontologists thought that birds evolved from an ornithischian root—but he certainly ran with his mistaken assumption as far as he could possibly go.
Ballou wasn’t the only one taken with the dramatic idea. In a comment thread about the strange article at Dave Hone’s Archosaur Musings, paleontologist Mike Taylor points out that science fiction writer Edgar Rice Burroughs later imagined a flying stegosaur in one of his novels. In Burroughs’ world, Stegosaurus was a formidable aerial attacker that used its fearsome, thagomizer-tipped tail as a rudder, and it’s certainly possible that the ludicrous image was inspired by Ballou’s article. Sadly, though, Stegosaurus was less aerodynamic than a brick, so we shouldn’t expect any paleo documentary scenes of angry stegosaurs dive-bombing Allosaurus.
[Hat-tip to Dave Hone, by way of John Hutchinson and Jeff Martz.]
September 13, 2010
Dinosaur skin impressions are pretty rare, and, even among the known collection of these soft-tissue traces, not all dinosaurs are equally well-represented. There are plenty of skin impressions from hadrosaurs, but stegosaurs are among the dinosaurs in which the skin texture is still largely unknown. Now, as reported by paleontologists Nicolai Christiansen and Emanuel Tschopp, an exceptional specimen from northern Wyoming gives scientists a first look at the skin and other body coverings from a North America stegosaur.
The individual described by Christiansen and Tschopp, nicknamed “Victoria,” is an approximately 150-million-year-old, nearly complete skeleton of the stegosaur Hesperosaurus mjosi. Discovered in 1995, it came from the well-known Howe-Stephens quarry site, where soft tissue impressions of other Jurassic dinosaurs have been found before. Based on the state of the skeleton, it appears that the dinosaur died, was partially buried, and then completely buried by a second flow of sediment, with the best preserved elements being found on the dinosaur’s right side.
The soft-tissue impressions found in association with the skeleton were scattered around the section of the ribs just before the hips and on one of the large armor plates on the dinosaur’s back. The preservation was not complete, but rather shows bits and pieces within these areas. Even so, enough of the skin impressions were preserved to show what the skin of Hesperosaurus was like. Overall it consisted of the same kind of honeycomb scale pattern seen in hadrosaurs, horned dinosaurs and another stegosaur from Asia called Gigantspinosaurus. Rather than being uniform, however, the scale pattern differed over the dinosaur’s body, with larger, domed scales surrounded by the smaller tubercles found on skin impressions from its back.
Among the most remarkable aspects of Victoria’s remains were the soft tissue impressions from the plate. For decades paleontologists have debated what the plates would have looked like, how they were arranged, and what function they might have had, and while this new specimen probably won’t resolve the ongoing discussions about the purpose of stegosaur plates, it appears to show a relatively smooth plate covering marked by shallow grooves. That this preserved material is really from a kind of plate sheath cannot be confirmed without any doubt, but Christiansen and Tschopp make the case that this interpretation is the most consistent with the structure of the material and the existing hypothesis that stegosaur plates were probably covered in this kind of material. If further remnants of these plate sheaths can be found, they can help paleontologists better understand the anatomy of these armored dinosaurs and better test ideas about the function of their plates.
The report was published in the Swiss Journal of Geoscience as part of the proceedings from the Symposium on Stegosauria held last year. The papers cover a range of topics, from new species to the bite mechanics of Stegosaurus, and several of this week’s Dinosaur Tracking posts will feature new findings presented at the meeting. Stay tuned for more on this bizarre group of dinosaurs.
Christiansen, N., & Tschopp, E. (2010). Exceptional stegosaur integument impressions from the Upper Jurassic Morrison Formation of Wyoming Swiss Journal of Geosciences DOI: 10.1007/s00015-010-0026-0