An Adelaide-based researcher has identified human links to "alien-looking" fossils that lived in the seas over 500 million years ago.

Dr Diego Garcia-Bellido inspects a fossil bed. ( University of Adelaide: Supplied )

The new vetulicolians, called Nesonektris, were relatives of modern-day swimming salps and sessile sea-squirts.

They contained remnants of a cartilage that researcher Diego Garcia-Bellido believes linked the odd-looking sea creatures to humans.

The tails of the fossils have a cartilage structure comparable to those found in the early development of human embryos.

"We have the notochord, a cartilage that is used by the muscles to move," Dr Garcia-Bellido said.

"We have found a structure that is similar to the ones we have in our backs."

The finding made these animals relatives of humans and other vertebrates, Dr Garcia-Bellido said.

Researchers from the University of Adelaide and the South Australian Museum have published their research findings in BMC Evolutionary Biology.

The findings were a collaboration between the University of Adelaide, South Australian Museum, University of South Australia, the Natural History Museum of London and the University of New England.

Dr Garcia-Bellido said the fossils dated back to 500 million years ago and were found on Kangaroo Island near Emu Bay.

"We are looking at the earliest animals on earth," he said.

The discovery has enabled scientists to properly place vetulicolians on the tree of life. ( University of Adelaide: Dr Garcia-Bellido )

Adelaide has become the perfect base for Dr Garcia-Bellido, the ARC Future Fellow at the Environment Institute of the University of Adelaide, as the Flinders Ranges to the north and Kangaroo Island to the south provided some of the world's richest fossil beds.

The fossils were also found in the arctic region of Canada and China.

The tunicate fossils that Dr Garcia-Bellido was basing his current research on date back to an era known as the early Cambrian period.

"These animals lived by filter-feeding and using that tail as a propulsion system," Dr Garcia-Bellido said.

The cartilage findings meant scientists may need to re-evaluate findings of the past 20 years with new technology to reveal such previously undiscoverable connections, Dr Garcia-Bellido said.