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True to Life?

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Species: dispar, aphanoecetes?
Range: Late Jurassic (Tithonian, 150-145 MYA) from Utah, Wyoming, Colorado, Oklahoma, possibly Germany, Spain
Size estimate: 18-25 ft length, 800-1000 lbs
Discovery: Othniel Charles Marsh, 1885
Classification: dinosauria, ornithischia, ornithopoda, iguanodontia, ankylopollexia

True to Life?

Since no one has ever seen a living dinosaur, and the missing pieces of the fossil record withhold important clues to their appearance, no artistic representation of a dinosaur ever gets it 100% right. On top of that, new discoveries can change our ideas of extinct creatures drastically. So, how close does this sculpture come to what we know of the original animal?

• Many older depictions, like this sculpture, get the head wrong. As shown by the Camptosaurus skeleton in the Stewart Museum, its head should be shorter and more triangular. Three reasons drive this trope: first, a complete Camptosaurus head simply wasn’t discovered until the latest 20th century. Science didn’t recognize this because of the second reason, an isolated skull found in what was thought to be Late Jurassic rocks which scientists attributed to Camptosaurus. Decades later, a study discovered the source quarry for the skull really dated to the early Cretaceous, leading scientists to assign the skull to its own taxon, called Theiophytalia. Finally, many sources view Camptosaurus in light of its later and more famous relative, Iguanodon, and therefore alter its appearance according to Iguanodon’s features, like a long, boxy skull (and large thumb spike, but more on that later). The skull of the Camptosaurus mount in the Stewart Museum was cast from the best Camptosaurus skull currently known, one where the bones had separated at its sutures, allowing detailed examination of its interior. It shows what the general parameters of Camptosaurus’ head really looked like.
• Art of the bird-hipped ornithischian dinosaurs often tips their jaws top and bottom with a generic sort of beak. Scientists have described such beaks based on roughened areas of bone at the front of the jaws and a uniquely ornithischian bone at the tip of the lower jaw called a predentary. The true extent of those beaky areas is more complicated and less extensive than artists often draw. To get the best view of these roughened areas, take a look at the Prosaurolophus and Gryposaurus jaws in the Stewart Museum—hadrosaurs’ wide mouths took the roughness and the broadness of their beaks to an extreme, making the pattern easier to see. In Camptosaurus’ case, the top beak had an upside-down Y shape when viewed from the front, covering a minimal portion of the snout tip right in front of the nostrils and a little more of the lower margin of the tip of the upper jaws. The lower jaw had a wider and broader beak probably covering the extent of the predentary bone. This sculpture ignores the beak altogether and sticks to lizard lips, resulting in an awfully cow-like snout that even displaces the nostrils a bit.
• What about those puffy cheeks? That question gets an even more complicated answer than ornithischian beaks, with a wide variety of structural variations for the different families and species of the group. Check out other bird-hipped dinosaurs of the Park for details specific to those groups (or should we say, “cheek” them out?).
  
  Generally, multiple studies have shown that dinosaurs lacked the facial muscles necessary for mammalian-style cheeks. That doesn’t pose many problems for the earliest members of the group, which probably engaged in a minimum of oral processing, not unlike iguanas. The teeth of later, more derived members of the clade show design features and wear clearly indicative of chewing motions, with ceratopsians even adopting an almost mammal-like chewing pattern. Chewing tends to force partially processed food, called “bolus” by scientists, from the mouth if some oral structure doesn’t stop it. Fossils suggest that different ornithischian groups may have adopted different strategies to compensate for loss of bolus by chewing motions, including some cheek-like but probably non-muscular organs—cheeks, but not as we know them. Curiously, ornithischian teeth tend to be set inward from the outer lines of the skull, a condition seen in many mammals and which therefore led many scientists to surmise cheeks for this group. This “buccal emargination of dentition” (translation: cheek outline around the teeth) sandwiched between “labial ridges” (“labial” means “lips”) on the upper and lower jaws only superficially resembles the cheek condition in mammals, though the ridge on the lower jaws may have formed an attachment site for non-cheeky jaw muscles which facilitated an efficient chewing motion. The ridge of the upper jaw may have accommodated other soft tissues replicating the function of a cheek, as shown by the pattern of foramina—holes for admitting blood vessels to tissues around the margins of the mouth–but science has little data to speculate on their exact nature. Like I said, it gets complicated!
  
  In Camptosaurus’ case, its narrow snout hints at a picky diet focused on the most nutritious parts of the plants and which may have required some sort of processing before ingestion. If it tore food apart before eating it, or if it focused on already tender, nutrient-rich plant parts, they may not have required as much chewing, allowing Camptosaurus to get away with thick lip-like structures in the cheek area instead. On the other hand, tooth wear suggests a diet of relatively tough plants. We may not know exactly what Camptosaurus’ face may have looked like, but at any rate, puffy chipmunk cheeks for this animal have been pretty thoroughly discredited since this sculpture’s creation.
• Now we come to the thumb spike, as promised. Again, a glance at the hand of the Camptosaurus’ skeleton debunks this rather Iguanodon-like portrayal. Camptosaurus did indeed bear a spiky thumb on its hand, but unlike Iguanodon, Camptosaurus’ thumb still bore a couple of phalanges as a base for the ungual, or claw. The spiky claw itself doesn’t look much bigger than the largest claws on the rest of the hand, but it is still the biggest. Scientists have traditionally considered this spike as a means of defense, but limitations on the arm’s joints and range of motion argue against such an interpretation. Likewise, it fails to explain why hadrosaurs lost their thumb spikes. Though the following hypothesis remains untested, since loss of the thumb spike also loosely correlates with the development of wider snouts, and therefore a less specialized diet, the thumb spike of Camptosaurus and its closest kin may well indicate a food-processing function instead of defense.
• The posture of this sculpture evokes the famous Bernissart Iguanodon mounts (again with the Iguanodon!), which used kangaroo posture as a model. Fossil preparators working on those mounts actually had to break some of the tail bones to get them to fit! Camptosaurus’ tail may have proved more flexible in life than Iguanodon’s, but their joints don’t particularly resemble those of a kangaroo. Even if Camptosaurus could adopt the torso angle seen here, the tail would more likely have curved over the whole of its length to accommodate the pose; the kink seen in the sculpture’s tail here recalls the tail breakage in some of those old Iguanodon mounts. Ouch!

• Size-wise, the sculpture better represents above-average for the species, measuring roughly 18 feet. A big Camptosaurus might measure 22 feet. The Stewart Museum skeleton only measures about 12-13 feet, representing a below-average or subadult size.
• Like so many of the Park’s sculptures, this Camptosaurus adopts a wrinkly, cross-hatched toughened hide more like a rhinoceros or an elephant. Though Camptosaurus skin fossils remain undiscovered at this time, its later relatives—especially hadrosaurs—preserve enough samples to make a skin of mosaic scales the default for ornithopods, especially large ones. Think basketball-style texture on a more massive scale and you’ll get close to what Camptosaurus probably looked like.
• Behind the Scenes: the current color scheme for this sculpture, designed by Kirk Larsen, uses the patterns of light filtering through the surrounding trees as its inspiration. It’s a plausible camouflage strategy, but it also just looks neat, especially during autumn.