Developments in Brief : Traces of Land Animal That Lived 440 Million Years Ago Discovered

Traces of what are believed to be the oldest land creatures ever discovered have been found and identified in central Pennsylvania by two geologists.

Prof. Gregory J. Retallack of the University of Oregon and Carolyn R. Feakes, now studying at Harvard, discovered a series of burrows left behind by a small, hard-shelled creature that may have resembled modern millipedes--although no complete fossil of the creature itself has been found.

The site near Potters Mills was dated in the late Ordovician Period, about 440 million years ago. The burrows were found in sedimentary soils and were dated with the help of encrustations of a mineral called dolomite.

Previously, the oldest known land creatures were believed to have been millipede-like animals from sites in Scotland and Wales dating back 414 million years.

The findings, reported in Science magazine, contribute one more piece of evidence in the puzzle of how land-based creatures evolved.

Marine fossils, preserved in rock formations around the world, have been found to predate the existing fossil record of land-based creatures. This led geologists to believe that organisms that evolved in the oceans either crawled up or were stranded on land and evolved structures to adapt to their new environment.

“Some people are starting to think that organisms didn’t march onto the land or get stranded there and just happened to survive,” said Retallack. “Maybe they evolved from unicellular organisms that were in the soil in the first place.”