Abstract

Barnacles are highly modified crustaceans, which have attached to substrates by the head, grown a calcareous shell to protect the body and filter feed by use of modified limbs. Charles Darwin undertook a detailed study of living and fossil barnacles in the period immediately preceding completion and final publication of the Origin of Species. He had hoped to demonstrate the fundamental transition between stalked and sessile forms, but the fossil material then available proved to be too sparse to allow this. However, he identified homologies between living representatives of the two groups and famously quipped that we now live in the “Age of Barnacles”, in view of the exceptional success of acorn barnacles in shallow marine habitats.

Recent finds of fossil barnacles fill in many of the gaps in evolution which Darwin identified, but significantly modify his conclusions regarding homologies. Taken together with a new molecular phylogeny, it is now possible to trace critical events in the evolutionary history of these bizarre animals. A major breakthrough appears to immediately postdate the Cretaceous-Palaeogene boundary, when the occurrence of empty niches coincided with evolutionary innovation, leading to the extraordinary radiation of the acorn barnacles. They now occupy almost every marine habitat – boring into whales, sticking to rocks, infesting corals and fouling ships. They also display huge diversity in reproductive strategies, which intrigues zoologists.

Andy Gale studied Geology at King’s College, London, where he obtained a BSc and a PhD in the study of fossil starfish. He worked in the Palaeontology Department of the Natural History Museum and as a lecturer in Imperial College, before moving to the University of Portsmouth where he is now Professor of Geology. His interests include Cretaceous chalks, fossil echinoderms, sea-level change, Milankovitch Cycles and stable isotope stratigraphy. He lives on the Isle of Wight, where he grows potatoes and collects edible fungi.