500-million-year-old tunicate fossil reveals new secrets

Tunicates’ close relationship to vertebrates makes studying them critical for understanding our own evolutionary origins. With so few fossils, scientists relied mainly on what could be learned from modern tunicate species. The researchers used dissected sections of the modern tunicate Ciona to identify the nature of Megasiphon’s dark bands. The comparisons revealed remarkable similarities between Ciona’s muscles, which allow the tunicate to open and close its siphons, and the dark bands observed in the 500-million-year-old fossil. “It’s so rare to find not just a tunicate fossil, but one that provides a unique and unparalleled view into the early evolutionary origins of this enigmatic group.”M. thylakos is the only definitive tunicate fossil with soft tissue preservation that has been discovered to date.