Between water and land

摘要

The most informative examples of large-scale evolution are provided by major transitions between environments. Fresh research on an ancient amphibian shows how it adapted to locomotion both in water and on land. One of the defining events in the history of life was the emergence of terrestrial vertebrates from early fish. The oldest known fossils that illustrate the transition to land are those of Ichthyostega from the Upper Devonian of East Greenland. This 360-million-year-old amphibian resembled fish in many features of its skeleton, but possessed pelvic (hip) and pectoral (shoulder) girdles and limbs capable of supporting the body and allowing movement on land (Fig. 1). Ichthyostega was initially described by Saeve-Soederbergh and Jarvik, but many aspects of its anatomy remained unknown, limiting understanding of aspects of the transition from water to land.