Punctuated morphological change in a Neogene diatom lineage: “Local” evolution or migration?

A biometric analysis of the morphology of a late Pliocene planktic diatom lineage, Rhizosolenia praebergonii Mukhina indicates that it appeared abruptly in the fossil record in the Indian Ocean at 2.9 Ma after which it remained virtually unchanged. The observed pattern can be explained by “local”; evolution from the ancestral form Rhizosolenia bergonii, Peragallo or by migration from thecentral Pacific Ocean, where it originated gradually, in conjunction with an accelerated rate of evolution. At present time, it is not possible to conclude which one of the two hypotheses is more likely.

Key words:

• Diatom
• punctuated change
• migration
• ancestral‐descendant relationship
• geographic variation
• parallel evolution