Paleontology: Fever Chart for Fossils

Working with bits of bone, fossilized impressions in stone and educated intuition, scientists have cleverly deduced the appearance, weight, speed and even habits of animals that have long been extinct. Now, University of Arizona Paleontologist-Biochemist Tong-yun Ho has gained an unexpected new insight into the metabolism of many of these extinct animals. He has learned to take their temperature.

Paleontologist Ho depends on neither time travel nor thermometers for measuring ancient body temperatures. Instead, he works with collagen, a protein found in human and animal connective tissue and skeletal structures. Aware that the proportion of an imino acid, hydroxyproline, is lower in the collagen of cold-water fish than in fish that swim in warmer waters, Ho reasoned that the composition of collagen in warm-blooded animals might vary with their body temperatures.

Searching through biological literature, Ho recorded the imino-acid content of the collagen from a variety of animals, ranging from man to whales, and compared it with their normal temperatures. There was an unmistakable and direct relationship. With the increase of each degree in body temperature, he discovered, there was a specific increase in the proportions of imino acids in collagen.

Now, Cold-Blooded. Assuming that the variation had been similar in prehistoric animals, Ho turned to late Pleistocene epoch (10,000 to 200,000 years ago) fossil remains containing well-preserved collagen. Chemically analyzing the collagen in fossil specimens recovered from Los Angeles’ famed La Brea tar pits, he applied his formula and calculated the temperatures of such extinct species as the browsing ground sloth, the dire wolf, the short-faced bear and the saber-toothed cat.

Without exception, he found that his estimates of body temperatures of the fossil animals were within 3% of the normal temperatures of their modern descendants. The estimated temperature of the browsing ground sloth, for example, was about 96° F., only two degrees above the temperature of its modern contemporary, the two-toed sloth.

Paleontologist Ho’s findings have already led him to the conclusion that Pleistocene mammals did not have substantially higher body temperatures—as many scientists believed—to protect them against the cold of the ice age.

Thus, he reasons, they should have been able to adapt to the warmer temperatures that heralded the end of the ice age, and probably became extinct for reasons other than climatic changes.

Ho now plans to turn his attention to cold-blooded fossil animals, whose temperatures, unlike those of warmblooded creatures, varied with climatic changes. By using his collagen method to take their body temperatures, he believes, he can determine the approximate temperature of the prehistoric climate in which they lived.