About 250,000 years ago, Stone Age human relatives butchered a bunch of animals with stone tools and didn't wash up afterwards. Now scientists have analyzed the gunk crusted to the tools and figured out what was on the menu.

Supper at the former oasis near Azraq, Jordan, at that time could have included beef, duck, horse, camel and rhinoceros, according to an analysis of protein residues on stone tools found at the site.

"We were really excited by the antiquity of the residue," said April Nowell, an anthropology professor at the University of Victoria and lead author of the research published online today in the Journal of Archaeological Science.

The study was led by University of Victoria researcher April Nowell, who took part in an archeological dig in the area called Shisan Marsh. (James Pokines)

She said the variety of animals butchered there suggests the people using the site had a lot of knowledge about the resources available in the area at different times of year and were socially sophisticated.

"How you hunt or scavenge a rhinoceros will be very different from how you take down a duck, for instance," she said. "You need a whole slew of different technologies and techniques."

Nowell took part in an archeological dig in the area called Shishan Marsh, which was an oasis in the desert used by many animals and prehistoric humans between 220,000 and 300,000 years ago. Geological and plant-based evidence shows it was originally a lake surrounded by lush vegetation, but over several thousand years became "as arid or more arid than today."

That made it a "challenging" environment for the Stone Age nomadic hunter-gatherers who used it, Nowell said.

Pre-modern humans

"They're definitely pre-modern humans," she added. They likely belonged to the species Homo erectus or Homo heidelbergensis.

Between 220,000 and 300,000 years ago, Shishan Marsh was an oasis in the desert used by foraging animals and prehistoric humans. Today, it is part of Azraq Wetland Reserve at the centre of the Azraq Basin of Jordan's Eastern Desert. (Jessica Hoskins)

None of their remains have been found at the site and the researchers don't think they lived at the oasis — they simply visited to forage for food and water. In the process, they left behind stone tools used for hunting, scavenging and butchering meat, such as spearheads or arrowheads, scrapers, knives and hand axes.

Some were larger tools made from stone found further away and likely brought with them. Others were smaller ones made from local pebbles.

The researchers excavated about 10,000 tools in all, and found protein residue on 17 of them.

In order to identify the proteins, the researchers exposed them to immune system antibodies, mostly produced from goat blood, designed to recognize different types of animals. The tools tested positive for horse, camel, cow, rhinoceros and duck blood, but not cat or goat.

The researchers say it's the first time this technique has been used to identify protein residues on such old stone tools. They're now working on making antibodies that can recognize elephant and ostrich so they can test for those in the future, Nowell said.

Scientists have previously found other evidence suggesting what Stone Age humans ate – generally animal remains featuring cut marks or signs of burning, such as a 400,000-year-old prehistoric meal of roast tortoise found in a cave in Israel and reported earlier this year.

Amer Al-Souliman of Hashemite University, Jordan (right) works with UVic students Jeremy Beller and John Murray at the dig site in 2015. The researchers excavated about 10,000 tools in all. (Courtesy Jeremy Beller and John Murray)

However, protein residues are more direct evidence of what people were eating, Nowell said. They can also preserve evidence of types of animals whose fragile bones don't preserve well, such as birds, or evidence at sites where animal remains in general don't preserve well.

Brian Kooyman is a University of Calgary archeologist who has used the protein residue analysis technique at Wally's Beach, a camel-hunting site in Alberta that's about 13,300 years old. Kooyman said Nowell's site is "way older" than any other that has ever been tested using that technique.

"I am a bit surprised they have gotten such a high success rate," he told CBC News in an email. "But proteins are robust and so it is not out of the question."

He added that the researchers appear to have been careful to follow proper scientific protocols. They used control samples, retested positive samples, and also tested sediments near the artifacts.

Nowell collaborated on the project with U.S. and Jordanian researchers. The study was funded by the Social Sciences and Humanities Research Council of Canada.