Camarasaurus

Credit: Gabriel Ugueto.

*Camarasaurus* is an extinct genus of sauropod dinosaur that lived in North America during the Late Jurassic.

## History

*Camarasaurus* was first recorded in 1877 from several vertebrae collected by Oramel W. Lucas in Colorado. Edward Drinker Cope bought, quickly transported and named the remains during the same year during the Bone Wars. Marsh named another set of remains *Morosaurus grandis*, later considered to be *Camarasaurus* remains. Naming disputes were exceedingly common during this time. In 1925, the first complete skeleton was named by Charles W. Gilmore. The specimen was immature, leading to many illustrations at the time portraying the dinosaur as much smaller than it actually was.

*C. supremus*, "the biggest chambered lizard", was named as the type species of *Camarasaurus* by Cope in 1877. *C. grandis*, "giant chambered lizard", was named in 1877, *C. lentus* in 1889 and *C. lewesi* (originally as *Cathetosaurus*) in 1988. *C. supremus* is the largest species of *Camarasaurus* and one of the largest Morrison sauropods. However, the animal was found indistinguishable from *C. lentus* apart from size. Atypical of *Camarasaurus*, remains are known from the Latest Uppermost Morrison. *C. grandis* and *C. lentus* were smaller and lived earlier. From stratigraphic evidence, an evolutionary progression may be visible due to chronological sequence and morphological difference. *C. grandis* appears in the oldest and lowest rock layers. *C. lentus* appears later, coexisting with *C. grandis* for several million years. They likely coexisted because of different niche occupation, due to differences in the spinal anatomy. Later, *C. grandis* disappears, leaving *C. lentus*. The latter disappears at the moment *C. supremus* is first recorded. The succession and close anatomy between *C. lentus* and *C. supremus* suggests *C. supremus* is a larger and late-surviving population of *C. lentus*. *C. lewisi* was named as *Cathetosaurus lewisi*, and was synonymized with *Camarasaurus*. In 2013, both genera split.

## Description

*Camarasaurus* lived in the Morrison Formation, Colorado and Utah. *Camarasaurus* had hollow chambers in its vertebrae to lighten the load on its sturdy legs. *Camarasaurus* browsed in the high treetops of the Late Jurassic. *Camarasaurus* was about 23 meters long, 10 meters high and weighed about 20,000 kilograms. *Camarasaurus* are among the most frequently well-fossilized and common sauropods ever discovered. The most common species is *C. lentus*, and the largest species is *C. supremus*. The skull of *Camarasaurus* is arched, and very squared. It is known for a blunt rostrum and many large fenestrae. Many sturdy and intact skulls are documented. Teeth are about 19 centimeters (7.5 inches), and are spatulate in tightly-packed even rows arranged around the jaws. Teeth of *Camarasaurus* are remarkably strong, indicating individuals likely ate coarser foods, unlike the more slender-toothed diplodocids. Each forelimb adorns five toes; the innermost having a large sharp claw. The forelegs were smaller than the back, but the highly-arranged hips indicate a minor slope along the animals back.

As seen in other sauropods, *Camarasaurus* had pneumatic vertebrae that reduced the creatures' weight. When first discovered, little was known about what function they held, but they inspired the name "chambered lizard". The neck and tail were proportionally smaller compared to similarly-sized sauropods. It had an enlarged spinal cord by the hips, which some interpreted as evidence for a second brain, as they though such a large creature could not function with one small brain. The area was likely a reflex or automatic activity hotspot, but there is no such evidence of a brain, since some vertebrates have similar features. *C. grandis*, compared to *Venenosaurus*, has a more robust radius. In the past, the specimen SMA 0002 'E.T.' (sometimes as *Cathetosaurus*), originating from Howe-Stephens Quarry in Wyoming, shows trace of soft tissue, The ossified remains of what may be gums near the jawline were recovered, showing that *Camarasaurus* had deep-set teeth covered up-to-the-crown with gum tissue. As the remains decay, the teeth fall out of their sockets, and tightened as the tissue decayed. Marks on the teeth show they were covered by something, either tough scales or some sort of beak. This theory is not certain.

Some specimens of *Camarasaurus* have a skull <50% of the femoral length, which is a supposed synapomorphy of sauropoda, but other specimens have a skull >50& of the femoral length. This results in a morph with a large head that have been nicknamed "bobbleheads". This large-headed morph is seen in all species, across maturities and across the geographic an stratigraphic range. This has been hypothesized to be extreme individual variation or even sexual dimorphism.

## Paleobiology

### Herding

Around 150 million years ago in Wyoming, two 12.2 meter (40 foot) long juvenile *Camarasaurus* died together. This was suggested to have been washed together in a flood, or that *Camarasaurus* lived in herds or family groups. Other sites preserve their eggs in lines rather than mounds, which may insinuate these animals did not care for their young.

### Feeding

It was previously assumed these dinosaurs ate gastroliths to help grind food, which would become smooth. However, research shows *Camarasaurus* had more robust, developed teeth, with D'Emic et al. finding they replaced teeth every 62 days, indicating it masticated food in it's mouth before swallowing. Others find *Camarasaurus* preferred different vegetation, allowing sauropods to share an ecosystem without competing.

### Growth

Griebeler et al. in 2013 determine the long-bone histology of C. sp. CM 36664, found a weight of 14,247 kilograms (15.7 short tons), a sexual maturity of 20 years and a death age of 26 years.

### Metabolism

In the teeth of various Jurassic sauropods, Eagle et al. performs clumped isotope thermometry in the enamel. The temperature obtained was 32.4-36.9 °Celsius (90.3-98.4 °Fahrenheit). This is comparable to modern mammals.

### Paleopathology

A pelvis recovered from Dinosaur National Monument, Utah has gouging marks from an *Allosaurus*. In 1992, a *C. grandis* specimen from Bryan Small *Stegosaurus* Quarry near Canon City, Colorado was discovered, among the remains were a partial right humerus (DMNH 2908) and vertebrae from the back and tail. Pathologies in the humerus were described in 200 by Lorie McWhinney, Kenneth Carpenter and Bruce Rothschild. A juxtacortical lesion 25x18 centimeters that resembles woven fibers was noted, appearing as a sign of injury/illness. The "undulating fibrous bundles" oriented by the m. brachialis, with the lesion's lack of porosity near the ends indicating the periostitis was either inactive, or healed. McWhinney and others argue the pathology would have been extremely difficult for the animal, exerting pressure on the muscles, compressing the blood vessels and nerves. This would have reduced the range of motion in the forelimb's flexor and extensor muscles. This would have hindered the mM. brachialis, m. brachoradialis and the m. biceps brachii (to a lesser degree) to the the lesion's position. It was found the muscle and periosteum inflammation would have complicated the lower forelimb. Such a lesion would have caused long-term fasciitis and myositis. All of these combined would have caused moderate-severe effects on the limb's movement, making activities such as foraging and escaping predators harder than normal. McWhinney et al. performed a CT scan in 3-millimeter increments, finding the mass has a consistent radiodensity, separating from the bone's cortex via a radioleucent line. No evidence of a stress fracture or infections like osteomyelitis or periostitis were found. Osteochondroma was ruled out due to the spur having an axis of 25°, relative to the humerus' vertical axis, where osteochondroma would form a 90° angle. Others identify the source as:

1. Hypertrophic osteoarthropathy, ruled out because of the spur-like formation.
2. Osteoid osteoma, which would not explain the spur or osteoblastic reactions.
3. Shin splints and tibial stress syndrome, being a possible origin that has similar symptoms, the former not explaining the spur.
4. Myositis ossificans traumatica (circumscripta) was deemed possible but unlikely.
5. Avulsion injury, introduced by McWhinney and others, this injury is caused by repetitive overexertion in the muscles, which was deemed the most likely cause. It is thought it originated in the m. brachialis, forming an elliptical mass sloping downward. The spur was caused based on the osteoblastic response of the base of the m. brachioradialis, caused by flexor motion.

## Classification

*Camarasaurus* is given a upper right box in the Linnaean system, supplanted by the cladistics-inspired phylogenetic taxonomy among paleontologists. Today, Camarsaurus is considered a basal macronarian, closer related to the macronarian common ancestor than to derived forms like Brachiosaurus. A simplified macronaria cladogram after D'Emic (2012):

## Paleoecology

The Morrison sat along the edge of the eastern end of the Rocky Mountains. A large amount of dinosaurs are known from this formation, including fellow sauropods *Diplodocus*, *Apatosaurus* and *Brachiosaurus*, with *Camarasaurus* being the most common dinosaur in the formation. Specimens from Colorado, New Mexico, Utah and Wyoming are often found in stratigraphic zones 2-6. The Morrison Formation is 156.3 million years old at the base and 146.8 million years old at the top. This places it as ranging from the Oxfordian-Kimmeridgiann in the Early Tithonian of the Late Jurassic. The formation was semiarid, with wet and dry seasons that are distinct. The Morrison Basin, stretching from New Mexico to Alberta and Saskatchewan, being formed when the precursor of the Front Range in the Rocky Mountains pushed upwards to the west, preserves dinosaur and trace fossils. The formation was formed when material eroded off an east-facing drainage basin, carried by streams and rivers and depositing into swampy lowlands, lakes, river channels and floodplains. This is similar to the Solnhofen Limestone and Tendaguru Formations. The Morrison was the center of the Bone Wars, starting in 1877.

The Morrison was dominated by *Barosaurus*, *Diplodocus*, *Apatosaurus*, *Brontosaurus* and *Brachiosaurus*. Other herbivores include *Camptosaurus*, *Gargoyleosaurus*, *Dryosaurus*, *Stegosaurus* and *Othnielosaurus*. Predators include *Saurophaganax*, *Torvosaurus*, *Ceratosaurus*, *Marshosaurus*, *Stokesosaurus*, *Ornitholestes* and *Allosaurus*. The latter listed make up 75% of all Morrison theropods. *Camarasaurus* is often found alongside *Allosaurus*, *Apatosaurus*, *Stegosaurus* and *Diplodocus*. The region also contains bivalves, snails, ray-finned fish, frogs, salamanders, turtles, spheonodonts, lizards, both terrestrial and aquatic crocodylomorphs, docodonts like *Docodon*, multituberculates, symmetrodonts, triconodonts and pterosaurs such as *Harpactognathus* and *Mesadactylus*. Flora includes green algae, fungi, moss, horsetails, cycads, ginkgoes, several conifer families, tree ferns, ferns (the latter two in river-lining forests) and fern savannas with the occasional *Brachyphyllum* tree.

## Gallery

### Mounts

An "off-the-shelf" cast bought for the 1990s dinosaur hall in the Natural History Museum in London.An "off-the-shelf" cast bought for the 1990s dinosaur hall in the Natural History Museum in London.An "off-the-shelf" cast bought for the 1990s dinosaur hall in the Natural History Museum in London.*Camarasaurus* mount at the Royal Tyrrell Museum.*Camarasaurus* mount at the Royal Tyrrell Museum.
## References

* https://en.wikipedia.org/wiki/Camarasaurus
* https://twitter.com/DoubleBeam/status/1475164192101470212
* https://twitter.com/Bhmllr/status/1477830363019894784/photo/3