(Reuters)

An assemblage of tools found in Tanzania that was fashioned about 1.5 million years ago from the limb bones of elephants and hippos reveals what scientists are calling a technological breakthrough for the human evolutionary lineage – systematic production of implements made from a material other than stone.

The 27 tools, discovered at a rich paleoanthropological site called Olduvai Gorge, were probably created by Homo erectus, an early human species with body proportions similar to our species Homo sapiens, according to the researchers.

The implements, which were up to 15 inches (37.5 cm) long and came in a variety of sharp and heavy-duty forms, may have been used for purposes including butchering animal carcasses for food, they said.

The adoption of tools heralded the dawn of technology, and the oldest-known stone tools date to at least 3.3 million years ago. There have been examples of sporadic use of tools made from bone dating to about 2 million years ago, but the Olduvai Gorge discovery represents the earliest example of systematic production of such implements – by about 1.1 million years.

The Olduvai Gorge bone tools were found alongside various stone implements made around the same time.

The addition of bone implements to the human tool kit was an important moment, according to the researchers, reflecting cognitive advances and growing technological skills as well as a recognition that animals can provide a source not only of meat but of raw materials.

“Precise anatomical knowledge and understanding of bone morphology and structure is suggested by preference given to thick limb bones,” said archeologist Ignacio de la Torre of the Spanish National Research Council (CSIC), lead author of the study published on Wednesday in the journal Nature.

Limb bones are the densest and strongest kind.

Olduvai Gorge cuts through the southeastern plains of the Serengeti region in northern Tanzania. At the time these tools were created, our ancestors lived a precarious hunter-gatherer existence on a landscape teeming with wildlife. Tools of various types – for instance, for cutting and pounding – were of increasing importance for hominins, the name referring to the bipedal species in the human evolutionary lineage.

The hominins who made the Olduvai Gorge bone tools used a technique similar to how stone tools are made – chipping away small flakes to form sharp edges in a process called knapping.

“The study indicates our ancestors used subtly different techniques to create tools from different materials. This suggests a level of cognitive ability that we previously lacked evidence for during that period,” said University College London archaeological conservator and study co-author Renata Peters.

“For instance, when they knapped the tools we examined, the bone was likely to still contain some collagen and water. Collagen provides elasticity to the bone, making it softer to knap – shape – than stone. However, bone can also break if struck too forcefully,” Peters said.

Collagen is a fibrous protein that serves as the main structural component of bones, as well as muscles and skin.

In addition, the outer layers of bone are tough, while the inner layers – composed of a spongy material – are softer.

“These characteristics mean that working bone demands different skills from working stone or wood, for example,” Peters said.

Wood is less durable than either stone or bone. Any wooden tools from this time period likely would have decomposed long ago.

The sheer number of tools – bone and stone – found at the site suggests hominins visited there regularly. The tools date to a transition period between simple tools called Oldowan technology and more advanced ones called Acheulean technology including the likes of handaxes.

All but one of the 27 tools were made from elephant or hippo bone. Hippos were common in the area but elephants were not, meaning their bones were probably carried to Olduvai Gorge from elsewhere, according to the researchers.

No ancient human fossils were found at the site. While Homo erectus is the leading candidate as the maker of the bone tools, another more archaic hominin species, called Paranthropus boisei, also is known to have inhabited the region at the time.

“There is no direct evidence of who made the bone tools,” de la Torre said.