Were Ancient Fossil Bone Marks Made by Stone Tools or Biting Animals?

Leading scientist suggests need for universal standards for interpreting fossil evidence of early human stone tool use.
Are they marks left by a biting crocodile or an early human using a stone tool?

That's a question that deserves more careful consideration than it may have garnered in the past, according to Jackson Njau, an assistant professor at Indiana University Bloomington Department of Geological Sciences in the College of Arts and Sciences. An expert at reading bones, he is also former principal curator of the National Natural History Museum in Arusha, Tanzania and co-director of field research at paleontological sites in eastern Africa's Olduvai Gorge, one of the most famous regions bearing on human evolution and the fossil record.

"There's really no solid, standard method of analyzing these bones that is used by all researchers," he says. "And there is no universal guide, nothing that is part of one's training as a student, that tells you reliably how to judge one type of mark from another."

He maintains that the lack of agreement on interpreting fossil bone marks has resulted in uncertainty and controversy over when early hominids (early humans and early relatives of humans) began to use tools to kill and butcher animals, an important benchmark development in human evolution. He points to estimates of the earliest use of stone tools that vary by nearly 1 million years. For example, many scientists today accept the assertion that the earliest evidence of tools associated with butchered animal fossils come from findings at Gona, Ethiopia, establishing a date of 2.6 million years ago. But other researchers have argued that fossil bones found at Dikika, Ethiopia, dated to 3.4 million years, showed tool markings. Moreover, although generally used criteria today distinguish tool marks from other kinds of marks as V-shaped cuts or pits and grooves containing microscopic striations, Njau has shown through experimentation that crocodile teeth, for example, can create bite marks very similar to tool marks.

To address this problem, he suggests that researchers develop universally acceptable and recognized standards for properly interpreting the fossil record as it relates to prehistoric human tool use. He proposes creating a comprehensive collection of samples, developed from experiments in bone modification, and making the data available to researchers and students by sharing samples and posting photographs and information online. In addition, he suggests, it is important to very carefully consider the context of the fossil finds -- What is the frequency of bones within an assemblage that show what appear to be tool marks and were stone tools found in the same area and from the same layer or time period? Is there evidence of other animals that lived in the area at the time that could have caused similar marks -- such as crocodiles? In addition, he recommends continuing the integration of different disciplines to better understand the fossil record, and that researchers blind test bone samples to reduce interpretive bias.

Njau spells out the details in a Science Perspectives article, "Reading
Pliocene Bones," published on April 6, 2012.

http://popular-archaeology.com/issue/march-2012/article/were-ancient-fossil-bone-marks-made-by-stone-tools-or-biting-animals