TUCSON, Jan. 23 (UPI) -- A 33,000-year-old dog skull found in a Siberian cave is among the oldest evidence of dog domestication ever found, researchers say.
Scientists at the University of Arizona say the discovery also suggests man's best friends may have originated from more than one ancient ancestor.
They base that on dog remains of the same age found in a cave in Belgium.
"Both the Belgian find and the Siberian find are domesticated species based on morphological characteristics," researcher Greg Hodgins said in a university release Monday.
That indicates domestication of dogs may have occurred repeatedly in different geographic locations rather than with a single domestication event, he said.
"The argument that it is domesticated is pretty solid," Hodgins said, referring to the well-preserved Siberian skull unearthed in the Altai Mountains. "What's interesting is that it doesn't appear to be an ancestor of modern dogs."
At 33,000 years old, the Siberian skull predates a period known as the Last Glacial Maximum between about 26,000 and 19,000 years ago when the ice sheets of Earth's last ice age severely disrupted living patterns of humans and animals alive during that time.
Neither the Belgian nor the Siberian domesticated lineages appear to have survived the period, Hodgins said.