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A restoration of Gigantspinosaurus. Art by Conty, image from Wikipedia.

Stegosaurus was a weird dinosaur. We’ve known that for well over a century, but, as Darren Naish has often pointed out, Stegosaurus was strange even compared to its Jurassic relatives. The dinosaur’s arrangement of broad, alternating plates is a departure from the arrangements of smaller plates, back spikes and accessory spines seen on many other stegosaurs, including the perplexingly well-armed Gigantspinosaurus sichuanensis.

Ornamented with a double row of short, narrow plates along its back, the roughly 160-million-year-old Gigantspinosaurus generally resembled other stegosaurs from Late Jurassic Asia, such as Tuojiangosaurus. But, as you might be able to guess from the dinosaur’s name, the feature that immediately sets Gigantspinosaurus apart from similar species is a enormous hooked spine that jutted out from behind the shoulder blade. These striking spikes were found close to their life position on the first skeleton of this dinosaur to be found–erroneously attributed to Tuojiangosaurus, before being redescribed as Gigantspinosaurus in 1992–although their exact orientation isn’t entirely clear. Did the shoulder spikes curve straight backward, or were they tiled slightly upwards? And, more significantly, how did such prominent ornaments evolve? No one knows.

As yet, we know relatively little about the natural history of Gigantspinosaurus. The dinosaur has a name, and skin impressions have helped researchers restore what the stegosaur looked like, but many aspects of the spiky herbivore’s biology remain mysterious. In the grand scheme of stegosaur evolution, though, the ornamentation of Gigantspinosaurus has sometimes been taken as evidence that similar forms had shoulder spikes. In addition to paired spikes along its tail, the Late Jurassic stegosaur Kentrosaurus possessed an extra pair of spikes along its side. These were originally placed over the hips, but, due to the discovery of Gigantspinosaurus, some researchers have argued that the spikes truly belong at the shoulders.

Frustratingly, paleontologists have yet to find a Kentrosaurus skeleton with side spikes in place. But the discovery of Gigantspinosaurus doesn’t necessarily mean that its cousin Kentrosaurus had the same arrangement. Among stegosaurs, the two genera were relatively distantly related, and it’s entirely possible that more than one side spike arrangement evolved. As paleontologist Heinrich Mallison has argued, the hips of Kentrosaurus seem to possess areas where the spikes could have articulated, and this arrangement would be consistent with the dinosaur’s ornamentation pattern–small plates at the front give way to spikes along the stegosaur’s back and tail. Indeed, the side spikes on Kentrosaurus more closely resemble the same structures along the dinosaur’s back and tail and the shoulder spike of Gigantspinosaurus. If Kentrosaurus had plates up front and serially homologous spikes along the back, then why shouldn’t the hip spikes remain a reasonable hypothesis? Together, Gigantspinosaurus and Kentrosaurus might represent different alternatives in the stegosaur armory.

Thanks to a row of huge bony plates, Stegosaurus remains one of the strangest dinosaurs ever found. Photo by the author at the Utah Field House of Natural History in Vernal, Utah.

Undoubtedly familiar to any dinosaur fan, Stegosaurus remains one of the strangest dinosaurs ever discovered. Even among others of its kind, the iconic Jurassic herbivore looks like an oddball. Many other stegosaur species sported long rows of spikes and short plates, but the flashy Stegosaurus had an alternating row of huge bony plates along its back and a relatively modest set of four tail spikes. How could such a strange arrangement of adornments have evolved?

From the arms of tyrannosaurs to the necks of sauropods and the armor of stegosaurs, bizarre dinosaur structures have frequently made paleontologists wonder “What was that for?” There had to be a reason for the deviations in form, and, paleontologists believe, the immediately recognizable plates on the back of Stegosaurus must have had some function. There has been no shortage of hypotheses. Off-the-wall ideas about flying stegosaurs aside, researchers have proposed that the plates along the spine of Stegosaurus protected the dinosaur from attack, were the Jurassic equivalent of solar panels or acted as sexy billboards to attract the attention of potential mates.

Although Stegosaurus certainly had much to fear from the contemporary Morrison Formation predators Allosaurus, Torvosaurus and Ceratosaurus, the dinosaur’s defensive weapons were its tail spikes (called a “thagomizer” by some). If Stegosaurus was anything like its spikier cousin Kentrosaurus, it could swing its tail with deadly force, and a damaged Allosaurus bone suggests that the “roof lizard” did just that. But the keratin-covered plates of Stegosaurus probably didn’t provide the herbivore with much additional protection. The immobile structures jutted upwards, leaving the dinosaur’s flanks exposed to attack. To call the plates “armor” isn’t quite right.

When I was a kid, though, Stegosaurus plates were more often said to help the dinosaur regulate its body temperature. Presuming that Stegosaurus was an ecothermic animal–that is, had a body temperature determined by the surrounding environment–the plates could have helped the dinosaur heat up by turning broadside in the morning and shed heat by turning toward the sun during midday. Using models of plates in wind tunnel experiments, paleontologist James Farlow and colleagues reported in 1976 that the plates could very well have been used to dissipate heat. This doesn’t mean that the plates evolved for that function, though.

In 2010, Farlow and coauthors followed up on the work by comparing the plates of Stegosaurus to the bony armor along the backs of modern crocodylians. While stegosaur plates might have played some passive role in regulating body temperature, they concluded, there was no indication that Stegosaurus plates evolved for that reason, or even were principally used as thermoregulatory equipment. (Not to mention the fact that we now know that dinosaurs were not lizard-like reptiles whose internal physiology was primarily dictated by the temperature outside.) If Stegosaurus plates made any difference in managing body temperature, it was a happy little quirk that rode along with the principal function of the plates.

At present, it appears that the impressive bony fins on the back of Stegosaurus evolved as display structures. A 2005 study by Russell Main and  collaborators, which focused on the microstructure of stegosaur plates, couldn’t find any evidence that the structures were used to radiate heat. Indeed, if stegosaurs truly required such radiators, it’s surprising that Stegosaurus seems unique in its plate arrangement–if plates were really used to regulate body temperature, you’d expect to see the same arrangement in many closely related species. Instead, much like the horns of ceratopsid dinosaurs, the plates and spikes of stegosaurs varied greatly between species. This suggests that visual display was driving the evolution of these structures. Being recognized as a member of a particular species, or displaying an individual’s maturity and vigor during mating season, probably drove the divergence in form among stegosaur ornaments. The question is whether stegosaur plates made any difference in the mating season or they simply served to help species recognize members of their own kind. That debate–over the sexiness of plates, spikes, horns, crests, sails and domes–is just heating up.

References:

Farlow, J., Thompson, C., Rosner, D. 1976. Plates of the dinosaur Stegosaurus: Forced convection heat loss fins? Science. 192,4244: 1123-1125

Farlow, J., Hayashi, S., Tattersall, G. 2010. Internal vascularity of the dermal plates of Stegosaurus (Ornithischia, Thyreophora). Swiss Journal of Geosciences. 103, 2: 173-185

Hayashi, S., Carpenter, K., Watabe, M., McWhinney, L. 2011. Ontogenetic histology of Stegosaurus plates and spikes. Palaeontology. 55, 1: 145-161

Main, R., de Ricqlès, A., Horner, J., Padian, K. 2005. The evolution and function of thyreophoran dinosaur scutes: implications for plate function in stegosaurs. Paleobiology. 31, 2: 291-314

Padian, K., Horner, J. 2010. The evolution of “bizarre structures” in dinosaurs: biomechanics, sexual selection, social selection, or species recognition? Journal of Zoology. 283,1: 3-17

A gliding Stegosaurus. From the Ogden Standard-Examiner, 1920.

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.]

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.

That sauropod looks quite frustrated. These dilapidated dinosaurs rest at Berlin's abandoned Spreepark. Photo by Flickr user davidrush.

In an abandoned Berlin amusement park, dinosaurs are slowly suffering a second extinction. The creatures, attractions at what was once the German Democratic Republic’s Kulturpark Plänterwald, have toppled over, are decorated with graffiti and are slowly rotting away in a setting perfect for a Scooby-Doo episode or another tedious found-footage horror film (your choice).

A felled Stegosaurus at Berlin's Spreepark. Photo by Flickr user extranoise.

Kuriositas recently laid out the park’s backstory. When the static dinosaurs were put in place, Kulturpark Plänterwald was in Soviet-controlled East Berlin. The theme park was the only one on the communist side of the Berlin Wall. But when East and West Germany reunited in 1989, the park quickly collapsed. Even though the attractions at the relabeled Spreepark were expanded, a lack of parking and an unpopular single-price entry fee rapidly cut attendance. By 2001, the park was mired in a pit of debt with no way out. Spreepark closed, and the dinosaurs have gradually been decaying ever since.

For more photos, see the Kuriositas blog post about Spreepark.

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