Non-random decay of chordate characters causes bias in fossil interpretation

A hard look at soft fossils Our knowledge of the earliest stages in the evolution of the vertebrates is limited to what can be gleaned from fossils left by the early chordates. And as these animals were soft bodied and lacked bones and shells, the record is sparse and is dominated by relatively few exceptionally preserved specimens. The interpretation of such fossils is fraught with difficulty. Now, as if that were not sufficient, a study of the decay of modern specimens of amphioxus and ammocoetes (larval lampreys), the nearest living relatives of the early soft-bodied chordates, suggests that the loss of typically chordate characteristics during decay is non-random, and that it is the more phylogenetically informative characters that are lost most easily. Such vagaries, firmed up in the fossil record, may result in bias towards wrongly placing fossils on the chordate stem. If this decay bias is widespread, many important evolutionary episodes that are understood from the fossil record of exceptionally preserved soft-tissue remains will need careful reassessment.