Pneumodesmus newmani is a species of millipede that lived 428 million years ago, in the Late Silurian. It is the first myriapod, and the oldest known creature to have lived on land. It was discovered in 2004, and is known from a single specimen from Stonehaven, Aberdeenshire, Scotland.
Discovery and naming
The fossil of P. newmani was found by Mike Newman, a bus driver and amateur palaeontologist from Aberdeen, in a layer of sandstone rocks on the foreshore of Cowie, near Stonehaven. The species was later given the specific epithet "newmani" in honour of Newman. The holotype is kept in National Museum of Scotland, Edinburgh. The genus name derives from the Greek pneumato ("air" or "breath") and desmus ("band", a common millipede root word) in reference to the inferred air-breathing habit.
Description
The single, 1Â cm-long fragment of P. newmani depicts small paranota (keels) high on the body, long, slender legs. The dorsal portion of each body segment is ornamented with a horizontal bar and three rows of roughly hexagonal bosses (bumps).
Significance
The fossil is important because its cuticle contains openings which are interpreted as spiracles, part of a gas exchange system that would only work in air. This makes P. newmani the earliest documented arthropod with a tracheal system, and indeed the first known oxygen-breathing animal on land.
Trace fossils of myriapods are known dating back to the late Ordovician (the geologic period preceding the Silurian), but P. newmani is the earliest body fossil of a millipede, and has been dated to 428 million years ago (late Wenlock epoch to early Ludlow epoch). The earliest centipedes follow some 10 million years later, and the first known vertebrate on land, Tiktaalik, is 50 million years younger than Pneumodesmus.
During the Silurian, the rocks that would later be part of Scotland were being laid down on the continent of Laurentia, in a tropical part of the Southern Hemisphere.