Camptosaurus

Kingdom: Animalia

Phylum: Chordata

Class: Reptilia

Order: Ornithischia

Family: Camptosauridae

Genus: Camptosaurus

Species: Camptosaurus dispar

Introduction

Camptosaurus represents a transitional genus that links the small, two-legged ornithopods with their large, four-legged descendants. The ornithopods are best known from more evolved genera, such as the giant Iguanodon and the crested Lambeosaurus, but Camptosaurus was the first large ornithopod to evolve. In Camptosaurus, we can observe that ornithopod hands were shifting from a grasping purpose to a weight-bearing purpose, the animal's muzzle was longer to accommodate more food, and it was the first dinosaur to have two rows of replaceable teeth purpose-designed for grinding tough vegetation. The animal lived in the formidable western plains of North America, where subtropical conditions were punctuated by seasonal droughts. It shared this harsh environment with a diverse range of dinosaur species, including well-known genera such as Apatosaurus, Brachiosaurus, and Stegosaurus.

Classification

Paleontologists have generally classified organisms using two major systems. Linnaean taxonomy hierarchically places them into groups based on overall physical similarity. In the late twentieth and early twenty-first centuries, paleontologists moved towards cladistic or phylogenetic classification systems to classify dinosaurs according to their common ancestry based on shared physical characteristics. In a cladistic analysis, Camptosaurus is a member of the Iguanodontia clade. This is a group of relatively large ornithopod dinosaurs characterized by heavy hind limbs, hands with spiked thumbs, and other physical features that adapted these animals for quadrupedalism (walking on four feet). The common characteristics in this clade also include a horse-like snout that sported larges nares (nostril channels) and a beak. Iguanodon is the best known genus of the group. It weighed around 3.5 tons (7,700 lbs) and was one of the first dinosaurs ever discovered.

Cladistic analysis is based on very specific physical characteristics, for example, the shape of the skull and features of bone and skeletal arrangement. Camptosaurus is a member of the Camptosauridae, which consists of only two genera, Camptosaurus and Draconyx. This group is considered a basal (primitive) group of Iguanodontia. Camptosauridae contains transitional genera that represent a link between the lighter, fully bipedal (two-footed) ornithopods and the more heavily evolved hadrosaur (“duck-billed”) dinosaurs. It is important to note that cladistic analyses can change over time, as new specimens are discovered and as science advances.

Anatomy

Camptosaurus grew up to 7.5 meters (24.6 ft) in length, stood around 2 meters (6.6 ft) tall and reached up to 900 kilograms (1,985 lbs) in weight. As such, it was the first heavily built ornithopod. Its neck ended in a long, pointed, triangular skull that was furnished with two rows of teeth in the upper and lower jaw. The teeth and jaw structure were designed for an herbivorous (plant) diet. A long, muscular tail was used to support the animal when it stood or rested on its hind limbs. Camptosaurus demonstrates a transitional adaptation to quadrupedalism (walking on four legs). The hind limbs were thick and sturdy, and the front limbs were relatively long, approximately two-thirds the length of the rear leg. The front limbs ended in strong hands and hoof-like fingers. While earlier ornithopods had hands that were capable of grasping, Camptosaurus demonstrates that ornithopod hands were shifting from a grasping function to a weight-bearing function. As such, scientists surmise that Camptosaurus spent most of its time on four legs. It very likely stood on its hind limbs when browsing higher foliage, and it may have adopted a bipedal (two-legged) gait while running. Galloping on all four legs seems unlikely because the shoulders have limited movement.

Intelligence

Ornithopod dinosaurs are rated among the most intelligent dinosaurs. The EQ score for ornithopods ranges from 0.9–1.5 (Hopson). Camptosaurus very likely falls within the middle of this range. This compares with 0.2 for sauropods, 1.0 for crocodiles, up to 2.0 for many theropods, and 5.8 for dromaeosaurids.

Reproduction and Population

In 1991, a fossil hunter discovered the remains of a partial Camptosaurus hatchling or advanced embryo in Utah's Morrison Formation. The discovery demonstrated that Camptosaurus young had poorly developed bones when they hatched. This implied a great deal about Camptosaurus's reproductive behavior. Scientists have also observed a similar phenomenon in the ornithopod genus Maiasaura. Their babies hatched with such poorly developed bones that the young were not able to properly walk or run until they were eight to nine months old. Fossilized Maiasaura nesting sites show that these animals nested in colonies and laid clutches of approximately 20 eggs that were insulated with soil and plant material. These animals provided parental care of their young for up to nine months, which included bringing food to the nest for their babies. The young did not leave the nest until they were nearly half their adult size. Fossilized groupings of Maiasaura young also imply that they lived in family or similar-age groupings after leaving the nest. Scientists believe that Camptosaurus and other large ornithopods may have provided a similar level of parental care to their young. The finding certainly confirms that these dinosaurs were oviparous (egg-laying).

After hatching, it is believed that ornithopod dinosaurs grew quickly, with the larger genera reaching full-grown size in approximately 4 or 5 years. The specific lifespan of dinosaurs is unknown, largely because scientists do not fully understand dinosaur growth rates or how dinosaurs regulated their body temperature. Scientists continue to debate whether dinosaurs were endothermic (warm-blooded), ectothermic (cold-blooded), or something in between.

Diet

The shape of Camptosaurus's teeth and jaw indicate that it was herbivorous (ate only plants). Among ornithopods, Camptosaurus is the first genus to demonstrate an extended muzzle. Scientists believe that this feature was an adaptation to fit more food in the mouth (an important adaptation given Camptosaurus's large size). Camptosaurus is also the first ornithopod to have two rows of replaceable teeth. In later ornithopods, the teeth evolve into dental batteries (multiple rows of replaceable teeth). Extensive wear marks found on the teeth of fossilized specimens confirm that Camptosaurus ate a diet of coarse vegetation that very likely consisted of ferns, cycads, and small conifers. Cheek pockets would have allowed the animal to chew mouthfuls of leaves and twigs while continuously browsing. Extensive mastication (chewing), coupled with helpful bacteria in the gut, would have been vital to Camptosaurus deriving sufficient nutrients from its diet.

Camptosaurus's high energy requirement and diet of low-energy plant matter would have made constant grazing imperative. The animal's high food demand also suggests that it roamed over a wide geography. Some paleontologists have suggested that ornithopods may have moved in large herds in search of new sources of food. They propose that these animals may have practiced mass migrations, much as antelope and other modern animals do today. Long distance ranging behavior would also explain the rapid spread of ornithopods during the Jurassic and Cretaceous periods. Ornithopod remains have been discovered on every continent, including Antarctica.

Behavior

Few specifics are known about Camptosaurus's behavior and life stages, but it was very likely a social animal. The remains of more evolved ornithopod dinosaurs have been discovered in bonebeds that contain large numbers of a single species. This implies that ornithopods lived and traveled in groups for at least part of the year. Elaborate physical display features developed in later ornithopods also imply an inclination towards social behavior. Many of the hadrosaur (“duck-billed”) dinosaurs were equipped with elaborate crests on their heads that are believed to have been used in mating displays and social ordering.

Another key to Camptosaurus's behavior may be implied from the animal's lack of defensive features. The thumb claw seen in other iguanodontians is less developed in Camptosaurus. The animal's main defensive method, therefore, was very likely running. While Camptosaurus was probably a slower runner than many theropod predators, the ornithopods in general would have exhibited excellent agility. Camptosaurus's wide pelvis and strong hind legs would have made the animal highly maneuverable. Scientists who study dinosaur movement suggest that the large ornithopods may have been able to out-maneuver many fast theropods. Coupled with herding behavior, this would have made Camptosaurus challenging prey. Traveling in numbers would have also provided protection from predators, especially for the young.

Habitat and Other Life Forms

The original Camptosaurus specimen was discovered in the Morrison Formation in Wyoming in the United States. Excavations in the western plains of North America have since provided multiple specimens and species. Camptosaurus discoveries have also occurred in Europe. The climate and geography of Wyoming during the Late Jurassic period was somewhat different than it is today. During the Late Jurassic period, Pangaea was splitting into Gondwana and Laurasia. As a consequence, North America was shifting northwards. The geography of Wyoming during this period was mainly flat with some hills and low mountains that produced river valleys. The Rocky Mountain Range had not yet formed. The climate was subtropical, but the area was subject to long dry periods. The vegetation consisted of conifers, cycads, and ferns that grew mainly in river valleys and near other permanent and intermittent water sources. Angiosperms (flowering plants) were only recently beginning to evolve.

Camptosaurus shared this challenging environment with a diverse number of dinosaur species. This included well-known genera such as Stegosaurus, Diplodocus, Brachiosaurus and Apatosaurus. Other species included Allosaurus, a large carnivorous theropod, and its smaller cousin Ornitholestes; early ankylosaurs, such as Mymoorapelta and Gargoyleosaurus; and rare specimens such as Haplocanthosaurus and Barosaurus.

Research

The Morrison Formation is a sequence of rock centered in Wyoming and Colorado in the United States. The formation covers a huge area, with outcrops stretching through other western states and into Canada. The majority of the formation is covered in prairie, but exposed areas have produced an abundance of fossils from the Late Jurassic period. The discoveries were so plentiful in the late nineteenth century that it led to a rivalry between paleontologists Othniel Charles Marsh and Edward Drinker Cope. The rivalry has since been dubbed the “Bone Wars.” Both scientists accused each other of theft, bribery and the destruction of fossil specimens. Their behavior brought American paleontology into disrepute among the international scientific community, but the fossil frenzy also led to the discovery and naming of 142 extinct species that were instrumental in understanding how dinosaurs lived and evolved.

When a Camptosaurus skeleton that had been mounted for display at Pennsylvania's Carnegie Museum of Natural History was removed from rock and assembled for a new standing display at the museum between 2005 and 2006, some scientists took the opportunity to analyze the bones further. In 2008, Kenneth Carpenter and Yvonne Wilson suggested that the skeleton differed enough from Camptosaurus dispar to warrant it being established as a new species, Camptosaurus aphanoecetes; it was then displayed under this species name at the museum. However, this justification was disputed by Andrew McDonald, who argued in 2011 that differences in certain skeletal parts such as the braincase meant that the dinosaur should belong to a new genus as Uteodon aphanoecetes.

Bibliography

"Bone Wars: The Cope-Marsh Rivalry." The Academy of Natural Sciences of Drexel University, ansp.org/exhibits/online-exhibits/stories/bone-wars-the-cope-marsh-rivalry/. Accessed 22 Apr. 2020.

Brett-Surman, M. K. “Ornithopods.” The Complete Dinosaur, edited by James O. Farlow and M. K. Brett-Surman, Indiana UP, 1999.

"Camptosaurus." Natural History Museum, www.nhm.ac.uk/discover/dino-directory/camptosaurus.html. Accessed 22 Apr. 2020.

"Camptosaurus aphanoecetes." National Park Service, United States Department of the Interior, 22 May 2019, www.nps.gov/dino/learn/nature/camptosaurus-aphanoecetes.htm. Accessed 22 Apr. 2020.

Chure, Daniel, et al. “An Embryo of Camptosaurus from the Morrison Formation (Jurassic, Middle Tithonian) in Dinosaur National Monument Utah.” Dinosaur Eggs and Babies, edited by Kenneth Carpenter, et al., Cambridge UP, 1994.

Deeming, D. C. “Ultrastructural and Functional Morphology of Eggshells Supports the Idea that Dinosaur Eggs Were Incubated Buried in a Substrate.” Paleontology, vol. 49, no. 1, 2006, pp. 171–85.

Fastovsky, David E., and David B. Weishampel. “Ornithopoda: The Tuskers, Antelopes, and ‘Mighty Ducks’ of the Mosozoic.” The Evolution and Extinction of the Dinosaurs. 2nd ed., Cambridge UP, 2005.

"Morrison Formation." National Park Service, United States Department of the Interior, 12 May 2016, www.nps.gov/dino/learn/nature/morrison-formation.htm. Accessed 22 Apr. 2020.

"U Is for Uteodon." National Geographic, 4 Mar. 2013, www.nationalgeographic.com/science/phenomena/2013/03/04/u-is-for-uteodon/. Accessed 22 Apr. 2020.