FOSSIL tracks on the seabed could be the handiwork of oversized amoebas that roamed the ocean 1.8 billion years ago, if their modern counterparts are anything to go by.
While exploring the Bahamas, Mikhail Matz of the University of Texas at Austin discovered a new species of giant amoeba called Gromia sphaerica. As the grape-sized protozoan rolls along the ocean floor, it sucks up and spits out sediment, leaving behind long grooves and ridges.
Similar tracks preserved in ancient mud have mystified palaeontologists. They assumed that the only creatures with the physiology to make such grooves were ancestors of multicellular animals that seemed to evolve at lightning speed in the Cambrian 525 million years ago. But they鈥檝e never found any fossils to match the traces. One theory to explain the anomaly is that the grooves were made by soft-bodied animals that left no skeletal trace in the fossil record. But the oldest tracks pre-date the evolution of multicellular life.
Advertisement
Matz believes that ancestors of his unicellular 鈥渟ea grapes鈥� explain the tracks better (Current Biology, ). 鈥淧retty much anything within the Precambrian fossil record can in principle be attributed to large protozoans.鈥� says Matz.