Earliest true shark fossils

The earliest undisputed fossils from true sharks are various fossilized shark scales dating back approximately 420 million years, which have been obtained from early Silurian Period deposits in Siberia, Russia. They have been assigned to the genus Elegestolepis, but no other remains from this earliest-known true shark have been procured at yet, so its physical appearance currently remains unknown. The scales themselves are tiny, the crown of each one measuring a mere 0.4 mm or so. Similar true shark fossil scales of comparable age have also been uncovered in Mongolia, and been assigned to the genera Mongolepis and Polymerolepis.

Some earlier fossil scales are also on record, dating back even further, to the late Ordovician Period, approximately 455 million years ago, which some palaeontologists – but not all – consider may be shark scales. They were obtained from fossil beds in Colorado, USA, but they differ morphologically from scales of modern-day shark scales in several different respects, explaining the controversy surrounding their originators' taxonomic identity.