Australia: The Land Where Time Began
Dinosaur Biology - Diseases and Pathologies
Among the pathologies found on 'Sue', the T. rex on display in the Field Museum in Chicago, is one that has been associated with the eating of red meat, also in humans, gout. One of Sue's finger bones (metacarpals) shows some characteristic, smoothly rounded pits at the joint with its first finger bone. When studied by a pathologist who compared it with the bones of living reptiles and birds it was found to be the result of gout. The hands and feet are generally affected by this extremely painful condition involving swelling and inflammation, resulting from urate crystal deposition around the joints. It can also be caused by dehydration and kidney failure. In humans a diet rich in purines, found in red meat, can also cause it. .
Sue has also been found to have a number of other pathologies, a number involving bone breakages. Some of her ribs had been broken some time before her death and healed, and other breakages that healed in her tail and spine.
The author suggests it is surprising a predator such as this particular T. rex could survive such injuries that should have incapacited her for a while. It would be expected that an injured dinosaur would be vulnerable to attack from other predators in such a weakened state. He also suggests the the survival of such injured animals would indicate that they were either extremely durable or that they lived in a group that acted cooperatively, sometimes helping the injured individual.
Paleontologist Phil Manning4 has carried out biomechanical experiments on the repair of broken bones in dinosaurs. He demonstrated that dinosaur bone that had repaired itself was as strong or stronger at the break site than at other unbroken parts of the same bone, the opposite to what is the case in mammals, where the repaired bone is weaker. According to Manning4 the marrow cells that normally form blood cells form a callus that rapidly converts bone at the break site.
Other pathologies that have been found on dinosaur skeletons include destructive bone lesions resulting from periodontal abscesses, in the case of jaw bones, septic arthritis, chronic osteomyelitis elsewhere on the skull or skeleton.
An extreme example of a dinosaur with an injury that was survived from at least a year before death comes from Australia. The partial skeleton was discovered in deposits from the Early Cretaceous of southeast Australia, of which the hind limbs and pelvis were well preserved. The lower portion of the left leg was grossly deformed and shortened. It was not possible to determine the original cause of the infection, though a severe bite to its left leg near the knee has been suspected to have been the cause of the original infection. The tibia and fibula were severely overgrown by a very large, callous-like bone mass. It was revealed by examination and X-radiography that the original injury had become infected, the infection spreading down the marrow cavity of the shin bone, the process partially destroying the bone as it progressed. The body of the animal added bony tissue to the outside of the infected portions of the bone in an attempt to repair the damage by splinting the damaged section. The immune system of the animal was apparently unable to prevent the spread of the infection, large abscesses forming beneath the outer bony sheath. The author3 suggests the puss from these must have leaked through from the leg bones and may have run down on the surface of the skin as a sore. He has estimated by the amount of bone growth that the animal may have lived for as much as a year with this badly crippling injury before finally succumbing. As the skeleton shows no signs of tooth marks and the bones were not scattered it appears to not have died as a result of predation and it was apparently not scavenged after death.
It is very rare to find tumours on the bones of dinosaurs, though to study the actual frequency of tumours among dinosaurs would require taking histology sections from the bones of many dinosaurs, something that few museum curators would agree to. A technique involving X-radiography and fluoroscopy has been developed by Bruce Rothschild for scanning dinosaur bones. As the technique was limited to a thickness of 28 cm, more than 10,000 dinosaur vertebrae have been scanned using this technique. The vertebrae came from all major dinosaur groups. The results showed that the occurrence of cancers among dinosaurs were very rare overall, less than 0.2-3 %, and even these tumours were limited to hadrosaurs.
It was puzzling that the occurrence of tumours was restricted to hadrosaurs, and Rothschild wondered if this epidemiology was related to something in their diet. A few mummified hadrosaurs have been found that had in their gut large quantities of conifer tissues; plants that contain high levels of carcinogenic chemicals. It has been speculated that among hadrosaurs there was a predisposition to cancer, or possibly as a result of environmental induction, as in a mutagenic diet. Whatever the actual situation is, evidence is lacking at the present.
The largest T. Rex fossil found is 'Sue' in the Field Museum in Chicago. It had a number of injuries that had healed, including 2 tail vertebrae that had been broken, the break being covered by bony struts. An infection that ate into the bone of the left leg, the tendon to the upper arm had been torn from the bone, and 3 broken ribs.
When bone breaks marrow from the broken bone shores up the break by filling it with a callus tissue that is converted into bone. Bone growth healed Sue's ribs but in 1 rib the callus formed at the site of the break but the broken ends didn't come together properly leaving an open space between them. In mammals broken bones don't always heal as strongly as those of dinosaurs. In Sue's right arm the tendon had pulled off the bone. When birds break a bone a lot of tissue is produced in the wound that is rapidly converted to bone. Because of the high metabolic rate of birds plenty of soft tissue is made. In reptiles the repair of bone is much slower because of their lower metabolic rate. Birds can reduce the repair time by raising the temperature of the break site. Tests were carried out on broken dinosaur bones to determine the temperature at which the repair was carried out. It was found that the temperature of the bone at the time of formation was highest, being raised by 4-6o C , at the site of the break. The dinosaur bone repair began as in reptiles but as the temperature was raised the speed of repair by conversion to bone increased. Manning4 suggests that dinosaurs may have been the first to do this. The age of dinosaurs can be estimated by the layers of bone as in tree rings. It is estimated that Sue matured at 19 and lived for at least 10 years longer
Dinosaur infection resistance2
The immune system activity of alligators was tested to find if they could give some indication of how dinosaurs appeared to be so good at resisting infection. When MRA were plated they produced 500-600 bacterial colonies but when the MRA was mixed with the serum from alligators the plated serum/MRA mixture produced 95 % fewer colonies. The immune system of crocodilians is primed to fight infection as soon as they come into contact with the bacteria, whereas the human immune system functions only following infection. The author2 suggests this indicates that immune system of crocodilians and dinosaurs may have evolved in the common ancestor of dinosaurs and crocodilians.
The author suggests that the tropical conditions of the Mesozoic would have been ideal for the presence of many infectious organisms as well as the biting insects that could spread disease among dinosaur populations. The immune systems of mammals differs from those of birds and reptiles, the lymphatic system is of particular importance in birds. The author suggests the immune system of dinosaurs was probably closer to those of reptiles and birds than to mammals.
Pathologies have often been found in the skeletons of dinosaurs, some appearing to indicate internal diseases and disorders. One of the common pathologies are fused vertebrae, and there are also growths that are believed to be benign conditions or cancers. But most pathologies are the results of wounds, such as stress and infection when the wound became infected, causing long-term lesions that affected the structure of the bone, probably producing puss. The author says a lot can be discovered about the activities of dinosaurs by examining their injuries.
Combat-related injuries are common among theropods. The skeleton of one Allosaurus has been studied that displayed damage to its ribs, tail, shoulder, feet and toes, as well as chronic infections of a rib, its foot, finger and a rib. The injury to the tail is suggested to probably have been caused by a kick or a fall that had happened early in its life. Of the injuries some to the feet and ribs appear to be serious enough to limit its activities, possibly eventually contributing to its death. Another Allosaurus tail has been found that had a wound that is believed to have been caused by the spike of a stegosaur. In dromaeosaurs and troodonts the toe bearing the sickle claw frequently has signs of stress damage.
Damage is also often found in the skeletons of herbivorous dinosaurs, such as the tail spikes of stegosaurs being damaged or even broken and subsequently healed, the author suggesting it is evidence that they were used in combat. A Triceratops has been found that a horn bitten off, and the tooth marks indicate that the attacker was a Tyrannosaurus, but as the horn had healed over the following years it is proof that it had survived head-on combat with a Tyrannosaurus. Among the sauropods and hadrosaurs bite damage to their tails indicate that that had also survived an attack from allosaurs or tyrannosaurs respectively. The skeletons of sauropods show relatively little evidence of injury.
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