SCIENTISTS have refuted a recent challenge to the age of the sedimentary rocks off Cowie – meaning Stonehaven can once again assert itself – confidently – as home to the world’s oldest air-breathing creature.
Back in 2004, an amateur fossil-hunter, Mike Newman, was exploring the sandstone rocks on the Cowie foreshore when he discovered the remains of a small millipede-like creature. Critically, he spotted small holes down the side of its segmented body. These were spiracles, part of a gas-exchange system that would only work in air.
The fossil was sent to Edinburgh, where it was examined. The location of the find and surrounding material allowed scientists to date it as having lived 428 million years ago in the late Silurian.
To no little excitement in the world of palaeontologists, the centipede was announced as the oldest creature known to have lived on land. The scientists in Edinburgh named it Pneumodesmus newmani.
This meant land that was once part of an ancient tropical continent called Laurentia – and what is now Stonehaven – was recognised as the site of that huge leap of evolution, where life crawled out of the swamps.
428 million-year-old age of fossil later disputed
It appears the Cowie Harbour Fish Bed is renowned for having a rich fossilized terrestrial ecosystem. Plant spores found in the sandstone have been used to help date the ancient rocks.
But in 2017, a team based at the University of Texas used a dating system based on zircon mineral deposits. And, slashing 14 million years off the age of the fossils, they claimed they were (only) 414 million years old. This placed Pneumodesmus newmani into the Devonian period, when life on land was well established.
So nothing special then.
Scottish geology thrown into disarray
The Americans’ dating clearly did not sit well with the established understanding of the time-line of movements of the Highland Boundary Fault, along with the deposition of sediments and associated organisms. This apparently brings knock-on effects on the calibration of comparative dating techniques.
Indeed, it appears the entire dating of the landmass of Scotland would be called into question.
So much work was done – fresh rock samples were gathered and plant specimens were taken from the root of a fallen tree on the banks of the Carron (same in geological terms to Cowie).
Now, in a report published last month, the findings of the American scientists have been thorougly dismissed.
The authors – Charles H. Wellman, Gilda Lopes, Zoë McKellar and Adrian Hartley – are from Aberdeen and Sheffield Universities. They discuss the dating techniques for spores, plant material and sedimentary deposition.
And they conclude: ”The basal upper Silurian–Lower Devonian ‘Lower Old Red Sandstone’ deposits of the Stonehaven Group of the Midland Valley of Scotland are late Wenlock (late Silurian) in age.
”This provides a reliable age constraint for one of the oldest known terrestrial biotas (which includes the oldest reported air-breathing land animal, the myriapod Pneumodesmus newmaniWilson and Anderson 2004). It also has implications regarding the early appearance of various ichnofauna (Shillito and Davies 2017).
”The new age constraint is compatible with the geological setting and recent models regarding the timing of terrane accretion and the onset of ‘Lower Old Red Sandstone’ sedimentation in Scotland.”
In short, Pneumodesmus newmani is 428 million-years-old and Stonehaven is back in the record books.
Craigeven Bay – where the line of the Highland Boundary Fault is most easily seen