It's time to leave theoretical discussions and talk about the specifics of raptor predation on ancestral hominids. The first evidence that eagles preyed on the human line appears, coincidentally, as part of the same fossil evidence that humans evolved in Africa. The very same child's fossilized skull and brain that Raymond Dart carefully removed from its mineralized crust in 1924 holds the clues to raptor predation on hominids.
After much scientific debate and investigation during the past decade, it is now considered likely that this first South African hominid fossil found by Raymond Dart—the Taung child, which he named Australopithecus africanus—was the consequence of predation by a raptor at least the size and strength of a crowned hawk-eagle.48
A three-person University of Michigan team composed of a primatologist, paleontologist, and geologist reviewed the bone assemblages found under the nests of modern crowned hawk-eagles and then applied the information and identification marks to the Taung child fossil. Certain indicators of crowned hawk-eagle predation are routinely found on nonhuman primate remains: these include nicks, punctures, and "can opener" perforations on thin bones such as the skull and pelvis, plus
"Can opener" perforations on the skull of the Taung child indicate that this fossil hominid was the victim of predation by a raptor much like the modern crowned hawk-eagle. (C. Rudloff, redrawn from Zihlman 2000)
heavy raking and shattering of shoulder blades. Similarly, distinct patterns of bone damage can also identify the "signatures" of large-raptor predation on fossils. The Taung child fossil that Dart freed from its breccia husk exhibits these marks of raptor talons.49
Despite their impressive weaponry in the form of talons and beak, the crowned hawk-eagles are quite fastidious in their dining habits. Compared to the bone crunching of modern or fossil carnivorous mammals, raptors tend to dismember the trunk of the prey delicately and consume the organ contents of the body cavity with the precision of a well-mannered diner. Crania are usually left intact, but intense manipulation is exhibited by visible nicks, perforations, and lacerations inflicted during the eagles' efforts to get at the brain through thin facial bones. The great pressure of the talons probably leave the signature marks—the sharp talons can move through some thin bones just as a can opener slices through steel. A small bone flap is created with each turn of the can-opener talons.
Phillip Tobias, a paleontologist of great repute who was Raymond Dart's successor at the University of Witwatersrand, hypothesized that the eagle responsible for the Taung child predation must have had a hind talon length of over 5.5 inches.50 The crowned hawk-eagle surfaces as the best extant representative of the type of bird that lived approximately 2.5 million years ago and could inflict the marks found on the Taung child cranium.51
The Taung child is the only hominid fossil found at this paleontolog-ical site so far, but over 33 baboon skulls were present and, as we predicted earlier, one primate probably looks just like another to a raptor. What might have been the circumstances that surrounded the death of the Taung youngster? Was it wrested away from its mother's arms? Did she lay the child down on the ground for a moment and turn away for a few fateful seconds? Were the mother and child so far away from their social group that no others were around to prevent the abduction?
We will never know the exact story, but there are a few details that might help us put the puzzle together. First, the Taung child was most likely between the ages of 3 and 4 years and weighed about 20—24 pounds. This is deduced from the dimensions of its skull which correlate to a modern juvenile chimpanzee in size.52 A 3- or 4-year-old child would have been at that developmental transition point where constant
carrying by an adult was not a necessity. If raptor predation was a fact of life for young hominids, then natural selection would have opted for parents who invested protracted intensive care in their youngsters. A type of social organization that promoted group investment in each child might also have been an adaptation resulting from predation directed at offspring. Or both of these assets might have been selected for, which is the case in many hunter-and-gatherer societies that exist today.
We must explain, too, how the head of the youngster might have gotten into the quarry at Taung. That may be the easiest part of this puzzle to match. Much work has been done to analyze the non-hominid relics found in the Taung quarry area. Small- to medium-sized animal remains discovered at Taung correspond to what is found under living crowned hawk-eagle nests. Intact mandibles (lower jaws)—as found on the Taung child—are a rarity in hominid fossils. The only time intact mandibles seem to be usual in prey remains is when raptor predation is involved.
Because the eagle is fastidiously removing the base of the cranium or the facial bones of prey to get at brain matter, rather than crunching up the whole head, the lower jaw is not removed from the skull.53
We may have fit a few puzzle pieces together, but many niggling questions linger. Because these early hominids were not living in deep forest with thick, obscuring foliage, were large fierce hawk-eagle predecessors still able to swoop down unnoticed? With all the large terrestrial predators around, were raptors the least of the hominid worries?
One can look at the Taung child as an unusual accident or it can be considered a representative sample of widespread predation by birds of prey. The latter opinion opens up the question of the evolutionary effects of raptor predation on young hominids. For example, did this type of predation stimulate adaptations in infant care?
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