Turn your head and roar: can diagnosing disease in fossils shed light on modern maladies?

Science News, Dec 15, 2001 by Sid Perkins

In one of the early scenes of Jurassic Park, the 1993 film in which dinosaurs were resurrected from their DNA, paleobiologist Ellie Sattler leaves her jeep during a guided tour to assist the park veterinarian, who is tending an obviously sick Triceratops.

The animal's symptoms: Every 6 weeks it became disoriented, lost its sense of balance, and had difficulty breathing. Sattler noticed that the dinosaur's pupils were dilated and there were pustules on its tongue. Her diagnosis: The Triceratops' condition was a reaction to its nibbling on park plants that wouldn't have been a part of its diet 65 million years ago.

Contrast this fanciful scene with the situation that faces nonfictional scientists. When paleontologists unearth what's left of an ancient animal, they don't find much that can indicate the creature's health. Only rarely have the sands of time preserved remnants of a creature's soft tissue, such as skin. Much more often, there's nothing left but bones or bone fragments--and scattered ones, at that.

The challenge for scientists is to eke out as much information about ancient life as they can from these fragmentary remains. Although fossils are often used to characterize an entire species, the relics also harbor some part of the biography of an individual animal. They carry evidence that the prehistoric world contained not only healthy predators and prey, but also the sick, the weak, and the deformed. In some cases, a better understanding of the prehistoric afflictions may help scientists grasp the causes and courses of today's diseases.

Based on fossil bones alone, when there are no obvious signs of trauma or predation, paleontologists normally can't discriminate between frail animals that died quickly from a disease and healthy creatures that met an untimely end. Elizabeth A. Rega, a physical anthropologist at the Western University of Health Sciences in Pomona, Calif., calls this limitation "the osteological paradox." Only the fossils of what Rega terms robust individuals--those that were strong enough to survive for at least a while with a chronic condition--are marred by lesions that can provide clues about ancient disease.

At least one such individual swam the Jurassic seas about 200 million years ago. Along the English coast, paleontologists in 1970 unearthed the partial remains of a mature plesiosaur--a long-necked, fish-eating reptile with a broad body shaped like a turtle. The 27 vertebrae and a dozen or so ribs that were collected sat in the geology museum at the University of Bristol until the late 1990s. Then, Philip J. Hopley, a vertebrate paleontologist now at the University of Liverpool, began to remove the well-preserved bones from the rock that encased them. As he did so, he discovered a number of lesions on the faces of the vertebrae that in life had been in contact with the fluid-filled discs between the vertebrae.

In all, 58 blemishes showed up on 24 of the vertebrae. The deepest of the scars appeared in nearly the same spot on eight of the bones. When Hopley showed the vertebrae to radiologists at the Bristol Royal Infirmary, the specialists noted that the distinct lesions looked like those characteristic of a common spinal condition known as Schmorl's nodes. Although this malady is relatively common in people, it's almost unknown in the rest of the animal kingdom. The discovery in the British plesiosaur marks the first time the disease has been diagnosed in a reptile, an aquatic animal, or a nonhuman fossil, says Hopley. He reported his finding in the June JOURNAL OF VERTEBRATE PALEONTOLOGY.

Physicians have described Schmorl's nodes in people when portions of an intervertebral disc bulge into weak spots on the endplate of a vertebra, which are typically only about 5 millimeters thick. As the bone slowly reforms around the bulge, it thickens and creates a distinct, mushroom-shaped lesion that shows up on magnetic resonance imaging scans. Inflammation associated with the healing process can cause the nodes to be painful, but after the bone has mended the pain often goes away.

In a 1994 study of spinal abnormalities in 98 men and women who didn't report any back pain, scans by a team of Japanese researchers showed that 20 of the subjects had a Schmorl's node in at least one vertebra in their lower back. More recently, the autopsies of 100 men and women between 43 and 93 years of age revealed that 58 of them had one Schmorl's node, and 41 had more than one. These new findings by radiologist Donald L. Resnick of the Veterans Affairs hospital in San Diego and his colleague, Christian W. A. Pfirrmann, appeared in the May RADIOLOGY.

Most medical research suggests that the nodes result from unusually high stress on the spine, Resnick adds.

Hopley proposes that high stress also caused the Schmorl's nodes in the plesiosaur specimen that he analyzed. Two of the eight lesions occurred in vertebrae located where the animal's long neck joined the body. He suspects that the stresses that led to these lesions resulted from the aquatic reptile's arched spinal column, which was kept bowed by the tension from a series of ligaments and muscles. Hopley found the other six Schmorl's nodes in bones in the middle of the plesiosaur's neck, which probably would have experienced large stresses as the animal suddenly flexed its neck to capture a meal.