Evolutionary History
The corallines have an excellent fossil record from the Early Cretaceous onwards, consistent with molecular clocks that show the divergence of the modern taxa beginning in this period. The fossil record of nonarticulated forms is better; the nonmineralized genuiculae of articulated forms break down quickly, scattering the mineralized portions, which decay more quickly.
The earliest "corallines" known date from the Ordovician, although modern forms radiated in the Cretaceous. True corallines are found in rocks of Jurassic age onwards. Stem group corallines are reported from the Ediacaran Doushantuo formation; later stem-group forms include Arenigiphyllum, Petrophyton, Graticula, and Archaeolithophyllum. The corallines were thought to have evolved from within the Solenoporaceae, a view that has been disputed. Their fossil record matches their molecular history, and is complete and continuous.
The Sporolithaceae tend to be more diverse in periods of high ocean temperatures; the opposite is true for the Corallinaceae. The group's diversity has closely tracked the efficiency of grazing herbivores; for instance, the Eocene appearance of parrotfish marked a spike in coralline diversity, and the extinction of many delicately branched (and thus predation-prone) forms.
Read more about this topic: Coralline Algae
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