NASA sparked a frenzy earlier this month by releasing images captured by its Curiosity rover showing what may have been signs of past life.
It was theorised the small shapes – between one and two millimetres in width and five millimetres in length – may be trace fossils.
Trace fossils are signs of past life, either from dead remains of living creatures of things left behind them.
Now Barry DiGregorio – research fellow for Buckingham Centre for Astrobiology – has exclusively revealed he believes trace fossils are the only explanation.
Dr DiGregorio told Daily Star Online: "If trace fossils are on Mars, as I think they are and new Curiosity images show, it moved through ancient shallow marine sediments in a lake in Gale Crater.
"And like the multicellular life on Earth during the Ordovician, left evidence of its movements through shallow marine sediments.
"Trace fossils record the movement of soft bodied creatures through marine and mud-like sediments, they are not body fossils."
After the discovery, Dr DiGregio said he struggles to see how NASA will come to a different conclusion.