This evidence of handedness in trilobites may link the behavior of Los Angeles Dodger southpaw Sandy Koufax to the biases of primitive marine animals. "For a long time scientists have assumed that human beings are the only creatures that are handed. Now we not only know such biases are common among animals, but such biases go back to the Cambrian Period 500 to 570 million year ago," said Loren Babcock, an assistant professor of geological science at Ohio State. His proof - bite marks left behind on the right rear end of the bug-shaped trilobites, distant relatives of today's horseshoe crabs. Babcock found that 70 percent of all scars left by predators were on the right side of the trilobites. In an article published in the magazine Natural History, he explains that the unusually high number of right - side scars suggests that the behavior of either the trilobites, their predators, or both tended to favor one side. Babcock's work was also published earlier this year in the Journal of Paleontology.
Babcock and his colleague Richard Robison from the University of Kansas studied the remains of 158 trilobites that had healed from injuries sustained while still alive. Each fossil had a region that was callused where the trilobites' crusty exoskeleton had been broken and had subsequently healed.
Seventy-seven of those had injuries of unknown origin, perhaps caused by accidents during molting or mating, while 81 were caused by attacks. Seventy percent of those scars caused by attacks were on the right side of the trilobites. Many of the scars on Cambrian trilobites were Wshaped, conspicuously matching the mouth size and shape of the trilobite's most likely predator, Anomalocaris. Scars on trilobites from later phases of the Paleozoic Era were caused by cephalopods (relatives of the modern Nautilus), fishes, and various arthropods.
After examining Cambrian and post-Cambrian specimens, Babcock and Robison found that almost three-fourths of all scars left by predators were confined to the right side of the primitive creatures.
"This was true everywhere we looked. Using specimens from every continent, no matter what kind of sample we looked at, the pattern reappeared," Babcock said. . "This is probably one of the strongest pieces of evidence to suggest that we are looking at real biological patterns of behavioral asymmetry."
The question is: which animal acted with a bias, the trilobite or its predator? "It’s most likely that both animals were handed," Babcock said. The trilobite probably veered to one side when trying to evade its attacker, and the predator probably tended to attack from the same side." Such asymmetrical behavior is commonly seen today, as when a horse tends to turn its head to the left, and when a panda bear chews food on the right side of its mouth.
Because scientists think there is an association between some forms of handedness and the development of complex nervous systems. Babcock's findings not only link trilobite scars with human handedness, but may also link primitive behavioral biases to the specialization of the right and left hemispheres of the human brain.
But to pinpoint the beginnings of handedness in humans, which is probably closely linked to our brain's specialization and ability to perform higher tasks, researchers have been looking for evidence of behavioral biases, or asymmetries.
"Ninety percent of all human beings favor their right hand when writing, and evidence from Cro- Magnon cave paintings suggest that our human ancestors were right-handed," said Babcock. "Just how far back do these tendencies go and what advantage might handedness have conferred during evolution? We're still working on that question."
Sara
Williams
Ohio
State
University
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