Biological factors have an apparent effect on the geographic distribution patterns of Jurassic bivalves in the Proto Atlantic. The most important factor is the larval type. The planktotrophic larvae

which are the most common ones

are able to disperse much more widely than non planktotrophs and can achieve an extensive geographic distribution. Bivalves with non planktotrophic larvae tend to have smaller geographic ranges and may develop endemics

which are useful in recognizing bioprovinces. The proportion of non planktotrophs declines from the temperate zone to the equatorial areas. The other biological factors influencing bivalve distribution include life habit and feeding type

reproductive capacity

adaptability and competition.