Magazine article Science News

A Question of Crushers: Why Animals throughout History Have Developed a Taste for Bones

Magazine article Science News

A Question of Crushers: Why Animals throughout History Have Developed a Taste for Bones

Article excerpt

Best known as a cowardly scavenger that scrounges leftover carcasses, the hyena's reputation ranks about equal with that of, say, a pickpocket. The carnivore's maniacal laugh and brooding posture do nothing to improve its image. The hyena appeals so little to the general public, in fact, that relatively few zoos around the world bother to exhibit this king of carrion.

But to paleontologist Larry D. Martin of the University of Kansas in Lawrence, the hyenas scavenging habits raise an intriguing evolutionary question that reaches back through some 30 million years of mammalian history, Although hyenas are skillful hunters and often kill live prey, they have for some reason developed a body specialized for crunching through bone - a relatively non-nutritious source of food.

Hyenas are not alone in this. Looking back in the fossil record, Martin sees numerous examples of extinct mammals sporting the robust teeth and jaws necessary for cracking open carcasses. That history leads Martin to wonder why carnivores from vastly different families have time and again turned to dining on bone.

The answer may relate indirectly to variations in Earth's climate and the strength of seasons, Martin proposed in October at a meeting of the Society for Vertebrate Paleontology in Albuquerque, N.M. For some periods in the past, most of the continents had equable weather all year round, with little difference between winter and summer. Other times had a climate more like today's, with seasons swinging between warm and cold in the mid-latitudes and wet and dry in the tropics. For animals living through such a boom and bust cycle, says Martin, the capacity to reach marrow inside a bone may mean the difference between life and death.

In developing this theory, Martin credits research on human diets conducted by anthropologist John D. Speth of the University of Michigan in Ann Arbor. Speth gleaned his first insights about diet while excavating a series of prehistoric deposits in southeastern New Mexico that contained the bones of bison butchered around 1450 A.D. The remains puzzled Speth because the ancient hunters displayed a peculiar appetite: They left most parts of the female bodies to rot at the butchering site yet lugged home as much of the male carcasses as they could carry,

What was wrong with the female bison, Speth wondered? The only clue was the season of the bison hunt. Although most known prehistoric bison kills happened in fall and winter, the New Mexico site contained animals killed in springtime. Speth consulted the literature on wildlife research to understand what could make female animals so unappetizing during that season.

The answer turned out to be fat - or rather, a lack of it. "The wildlife literature said what was obvious in hindsight, that pregnant and nursing cows are often severely stressed in the spring because they are carrying a full-grown fetus or nursing a newborn while the forage has yet to start growing. So they live off their fat reserves and get fat-depleted," says Speth.

When animals start to starve during cold or dry seasons, their body fat can drop to only a few percent of their total weight. That's far less than what appears in even the leanest cuts of steak. A diet made up of almost pure protein contains too few calories and leads to protein poisoning, says Speth, which may explain why the hunters rejected the extremely low-fat meat of the female bison.

Searching through more recent accounts, the anthropologist found a similar concern about the quality of meat during harsh seasons. For instance, members of the Lewis and Clark expedition made references to the inadequacy of lean meat, as did the lore of American Indians, says Speth. Hunters in various societies from North America to Australia often abandon fat-depleted meat, even at times of food shortage.

Speth recounts one extreme example in which a military officer named Randolph Marcy ran out of food in southwestern Wyoming during the winter of 1857-1858. …

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