Fossil evidence for the escalation and origin of marine mutualisms

Mutualism is an interactive, mutually beneficial relationship between two or rarely more unrelated taxa. It is ubiquitous in most environments. In the marine environment it is most likely to occur in shallow marine, oligotrophic regions, the open marine photic zone and oxygen-limited environments. Whereas the eukaryote cell is of some antiquity, other mutualisms may have been acquired during the Phanerozoic. The fossil record provides inferential evidence for the minimum time of origin and occurrence of mutualisms. This suggests that a variety of mutualisms may have occurred during the Palaeozoic with most apparently being terminated by the Permian mass extinction. Tracing back the origin of extant mutualisms suggests that the majority of these began in the Mesozoic or Cenozoic and indicate an increase to the present day. Whether the increase in mutualisms is a product of increased biodiversity or whether mutualisms may have partly driven biodiversity is unclear.