How are the fossils Fordilla troyensis and Pojetaia runnegari important to bivalve evolution?

Fordilla troyensis and Pojetaia runnegari are significant to bivalve evolution because they are generally considered the oldest known bivalves, dating back to the Cambrian Period.12

Their importance lies in their roles as potential ancestral forms for major bivalve lineages:

• Fordilla troyensis: Best preserved in lower Cambrian rocks in New York, this species is believed to be ancestral to the pteriomorph order Mytiloida.1
• Pojetaia runnegari: Found in Cambrian rocks in Australia, this species is thought to be ancestral to the Palaeotaxodonta order Nuculoida.1

By representing the earliest stages of the class Bivalvia, these fossils provide critical evidence for the group's deep evolutionary history, which began with the first radiation of bivalves during the Paleozoic Era.1