Killer Cats Hunted Human Ancestors
Shaun Smillie in Johannesburg
for National Geographic News
|May 20, 2002|
Three South African scientists believe they have identified several predators that preyed upon human ancestors millions of years ago.
The potential hominid killers include Megantereon, an extinct saber-toothed cat with oversize fangs, the leopard, and spotted hyena.
Archaeologists Julia Lee-Thorp and Nikolaas van der Merwe of the University of Cape Town, and paleontologist Francis Thackeray of the Transvaal Museum in Pretoria, South Africa, believe these carnivores were stalking and killing early hominids on the South African savanna 2.5 million years ago.
Tracking the Past with Tooth Enamel
The team's findings are based on a study of the chemical composition of the tooth enamel of several prehistoric carnivores. Tooth enamel is composed mostly of calcium and phosphate, but includes small amounts of carbon. Stable carbon isotope analysis involves tracing the changes in the ratios of two naturally occurring carbon isotopescarbon 12 and carbon 13through the food chain.
Carbon 13 concentrations are higher in grasses than in trees and shrubs.
"In ecosystems with a warm growing season, most grasses use a C4 pathway of photosynthesis that leaves them relatively enriched in C13," says Lee-Thorp. "Trees, shrubs and herbs follow a C3 pathway that discriminates strongly against C13. The carbon isotope signature of these two groups is therefore distinct."
Farther along the food chain, the tissue and bone of animals that fed on grasses will also reflect more C13, while browsing animals that foraged on trees and shrubs show lower concentrations of C13.
Predators also reflect the carbon isotope ratios of their prey. To identify possible hominid predators, the researchers first ascertained what the hominid species excavated at Swartkrans, a site situated in the Sterkfontein valley about 25 miles (40 kilometers) northwest of Johannesburg, South Africa, were eating.
"Paranthropus robustus and the early Homo species, Homo ergaster, had a diet that reflected a mix of carbon isotopes, suggesting that they were omnivorous, which is similar to what modern humans are today," said Lee-Thorp.
Knowing the hominid carbon isotope ratios, Lee-Thorp and her colleagues were able to compare the ratios to those found in various carnivores found at the site. The team examined fossilized tooth enamel of leopards, lions, and spotted hyenas, in addition to three extinct species: Megantereon; Dino felis, a false saber-toothed cat; and Chasmoporithetes nitidula, an extinct hunting hyena.
The tooth enamel of the leopard, spotted hyena, and Megantereon drew a match, indicating that the individual specimens studied, at least, may have feasted on hominids. The findings were published in the Journal of Human Evolution.
To most paleontologists, the leopard and spotted hyena have long been obvious predators of hominids; even today, the modern descendants of these flesh-eating mammals have been known to attack and devour humans.
Megantereon, however, is a surprise to some scientists.
Bob Brain, a paleontologist who pioneered the investigation into hominid predators in his book The Hunters or the Hunted?, doesn't think that Megantereon fits the hominid killer profile. He believes their canine teeth would have caused little damage to a hominid skeleton.
"Its long canines were too delicate and probably only effective in slicing up larger prey," Brain said.
In his book, Brain suggested that Dino felis, the false saber-toothed cat, was a specialist primate killer, picking off hominids and baboons and then dragging them back to its cave lair.
Lee-Thorp's research, on the other hand, seems to clear the false saber-toothed cat; its carbon isotope ratios suggest that it concentrated on grazing animals, filling a niche that modern lions occupy today.
Larry D. Martin, curator of vertebrate paleontology at the University of Kansas Natural History Museum, has no problem seeing Megantereon as a hominid killer.
"Although Megantereon has large teeth, it is fairly small bodied and I doubt that it took larger prey than does the modern lion, which is a serious potential threat to modern hominids. I have no doubts that Megantereon would take a hominid whenever one might become available," he said.
Professor Phillip Tobias, emeritus professor of Anatomy and Human Biology at the University of the Witwatersrand, believes Lee-Thorp's study has greatly enhanced scientific understanding of the diets of early hominids, apes, and that of some of the large carnivores.
"For a long time this has been the object of much study; (Raymond) Dart first claimed that ape men hunted all other mammals, then C.K. (Bob) Brain determined through a series of brilliant analyses that it was primates that were the hunted and not the hunters. Now Lee-Thorp and her colleagues' research appears to provide proof that ape men were being hunted," Tobias says.
There is not enough isotopic evidence yet to absolutely convict any of these predators, and Lee-Thorp is looking forward to collecting more evidence at other dig sites.
"Our study was limited to only a few specimens. It could be a case of where those individuals tested ate one thing while their peers concentrated on something else. Only further testing will tell," she said.
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