Lampreys are of special interest to biologists as they and hagfish are the only surviving jawless fish – descendants of the group that was ancestral to jawed vertebrates, including ourselves. Since the 1870s it has been widely believed that the evolutionary transition from invertebrates to vertebrates was preserved in the development (ontogeny) of living lamprey larvae (called ammocoetes) into adult lampreys. Ammocoetes are simple, blind wormlike creatures that burrow into stream beds and filter water for microscopic food. They then gradually transform into adult lampreys that are clearly vertebrates, have well developed eyes and swim around looking for other fish to attack – latching onto them with a special sucker disk and drinking their blood. Thus, the last invertebrate ancestor of vertebrates is often portrayed as ammocoete-like and the earliest vertebrate as being lamprey like.
But for it to be biologically possible that this key transition could be preserved in the development of lampreys, both they and their ammocoete larvae would have to date back to the dawn of vertebrate evolution some 500 million years ago. From a palaeontological (fossil based) perspective it was for a long time impossible to test this hypothesis as lampreys are virtually never preserved as fossils, having not a bone in their bodies. Careful excavation of the Waterloo Farm shales from near Makhanda has revealed many unique soft tissue fossils due to its exceptional preservation. Amongst these are a near complete growth series of the world’s oldest lampreys – which turn this long-held dogma on its head.
