Paleopathology
from the book, "Petrified Lightning"

Book: 
Petrified Lightning

Paleopathology

For years many museum curators have kept special collections of fossil bones deformed by some disease or injury. Only recently have scientists actively begun to study such collections, creating a new field of research called paleopathology. These studies add much to existing data on how ancient animals looked and moved. Deformed remains offer clues concerning their lifestyle, how they interacted, and who roughed up whom.

A leading museum in Riverside, California, has a fossil leg bone of a deer that died seven million years ago. The leg shows a definite healed break. Apparently, while running at top speed the animal stepped into something like a gopher hole and broke its leg. The momentum of running would have kept it in motion, and the broken upper part of the leg bone slid down the side of the lower part of the leg. The broken ends are about two inches apart, and in this position the two bones fused together. The animal must have spent the remainder of its life with one leg significantly shorter than the other three.

Since carnivores always seek out the weak and disabled, this severely disabled animal's survival until its broken limb healed seems almost miraculous. After the healing it would have walked with a very noticeable limp. This otherwise healthy young deer was unable to survive very long with a permanent disability. Paradoxically, the very bone that disabled the animal was the only one that survived its predator's feast.

At the Tyrrell Museum of Paleontology in Drumheller, Alberta, the fossil collection contains a large number of damaged bones belonging to a particular family of dinosaurs, the hadrosaurs. Probably more is known about how this group of dinosaurs lived than any other because of the frequency of injuries exhibited by their bones. Commonly described as duck—billed herbivores, they lived during the last part of the era of dinosaurs and died out about 66 million years ago. An examination of their skeletons displayed frequently broken ribs that later healed, indicating that they had survived the encounter. These injuries appeared only in larger, probably adult male, skeletons. Similar rib injuries show up on hadrosaur skeletons at the Royal Ontario Museum in Toronto.

Scientists believe these injuries were the results of severe kicking between males as they fought for the attention of females during mating season. A violent kick from a four—ton dinosaur could be quite damaging; one skeleton showed evidence of a kick that broke six ribs at once. Along with mating rituals, fights between males may have been the means of establishing dominance in a herd. Males seem to have kicked at each other with their oversize hind feet in the manner of modern kangaroos.

Another injury common to hadrosaurs and many other dinosaur groups, including the terrible Tyrannosaurus rex, is broken vertebrae at the base of the tail where it attaches to the hindquarters. This injury is found mainly in dinosaurs that appear to have been females. The tops of the vertebrae are compressed and cracked as if a great weight had pressed down on them. The vertebrae often healed in their broken position.

At the risk of offending modest colleagues, a paleontologist demonstrated with illustrations how a larger male pressing down on a female during mating could crack these particular vertebrae. Since the vertebral cracks were not fatal, they were not counterproductive to the mating process. Mating was nevertheless a painful affair for the female dinosaur. Although she survived the encounter, she probably dreaded the next mating season.

Another injury common to herd animals such as the hadrosaurs was numerous cracks toward the end of the tail vertebrae. Here the bones were bent and broken as if they had also been squashed by a great weight. Scientists know that these animals, probably not the most graceful creatures, traveled in great herds numbering in the thousands. One hadrosaur in a resting position with its tail on the ground would be at the mercy of whatever awkward giant came lumbering by. Judging from the many such injuries in the fossil record, having one's tail stepped on must have been an ever—present hazard. Even though hadrosaurs have traditionally been portrayed as peaceful, mild—mannered animals, the injuries suggest that they were careless, aggressive, or accident prone—possibly all three.

Researchers have also detected stress fractures in the toe bones of several groups of Ceratopsian dinosaurs, the family of horned dinosaurs that includes the mighty triceratops. This living, moving tank weighed 8 to 10 tons. Stress fractures are not common in four—legged animals and usually occur when extraordinary demands are placed on the bones for brief, intense periods. In the case of the triceratops, the toe fractures imply that the great beasts were in the habit of stamping their feet. Scientists believe that this gesture was part of a challenge as one male defied another for the charm of the female or that it signaled a confrontation to determine leadership of the herd.

As the two living tanks squared off at each other and stamped out their challenge 80 million years ago, the ground must have shook under the impact. Then with heads lowered, the two tanks charged each other. The repercussions of 20 tons of bone and muscle colliding would have reverberated through the primeval surroundings.

More and more physicians study ancient injuries and diseases to gain valuable insight into modern physical disabilities. One specialist in arthritic diseases teamed up with a paleontologist at the Kansas University Museum of Natural History. They examined the bones of a mosasaur, a large sea lizard that lived about 75 million years ago. One of the tailbones appeared to the doctor to be diseased; it was gnarled in appearance, with tiny bumps and holes. The physician, who had seen many bones like this, presumed correctly that the holes eaten into the bones were the result of viral or bacterial invasion.

Slicing the suspect vertebra into sections, the scientists found, in addition to healthy bone, bone with blotches, swirls, and squiggles; it looked more like bone soup than bone structure. The sea giant had definitely been infected. The cause of the infection, found deeply imbedded in the bone, was a fingernail—sized tip of a shark tooth. As the scientist remarked, "A dirty—mouthed shark had taken a bite out of this mosasaur." From the tooth they were able to identify the shark as one of several species that lived in this inland sea. This body of water, a thousand miles wide and stretching from the Gulf of Mexico to the Arctic Sea, covered the area where the state of Kansas exists today.

The two scientists also examined what appeared to be perfectly healthy tail vertebrae. Within the bone marrow, bands of decay wove through the delicate lacework pattern of the normal bone. The physician immediately recognized the first evidence in any animal other than humans of a vascular necrosis, tissue death due to a lack of blood supply. In simple language, the mosasaur had the bends!

Bends occur in human divers who rise too rapidly. The increase in pressure that accompanies a diver's descent causes nitrogen gas to dissolve in the blood. As the diver returns to the surface the gas precipitates out again. This is harmless if the diver's ascent is gradual, but in a rapid ascent the pressure changes too quickly, and bubbles of nitrogen form in the blood, blocking small blood vessels and cutting off circulation. This is extremely painful and sometimes fatal.

Scientists have long accepted that this species of mosasaur dived to great depths in the ocean, but a diving lizard should have known how fast to surface to avoid excruciating pain. In this case, the ascent was extremely rapid perhaps because, as the evidence shows, a hungry shark was on the mosasaur's tail. Continued research also uncovered a giant prehistoric sea turtle with a similar problem. Teeth marks on the bone show it had been pursued by a mosasaur that managed to grab one of the turtle's legs and bite it off. The turtle, whose wound healed completely during its lifetime, must also have ascended rapidly, with a hungry mosasaur in pursuit.

The researchers went on to confirm that mosasaurs throughout the seas of the world were subjected to the bends. Despite the excruciating pain they must have endured during a hasty retreat, suffering the bends did not prove fatal. And their rapid though painful ascent helped them to avoid a fatal encounter with a hungry shark. The mosasaur, as well as the sea turtle, never did evolve the decompression resistance that has protected other types of marine reptiles. A relative newcomer to the ancient seas, the mosasaur existed for only about 25 million years, becoming extinct along with the dinosaurs at the end of the Cretaceous Period.

At a recent medical meeting at the Field Museum of Natural History in Chicago, the physician delivered a lecture on paleopathology. Afterward a member of the audience brought him a piece of the backbone of an 11,500—year—old bear. It had been discovered in Indiana and was streaked with strange scars. The physician took the bone to his laboratory, where x—rays revealed familiar—looking bone damage. Medical tests and immunoassays performed on the bear bone confirmed his diagnosis, and he moved paleopathology to a new plateau of precision and validity; even in fossilized bone the original bacteria, antibodies, and soft tissue were responsive to the immunologic tests.

Fortified by unequivocal results of these tests and immunoassays, the paleophysician presented his bear findings to a community of his medical peers. With courage and conviction he was able to announce, "This bear had syphilis!"