Fossil embryos reveal prehistoric reproduction secrets

A rare discovery of embryos within fossil specimens of primitive jawed fishes (placoderms), collected in Western Australia, indicates that reproduction by internal fertilization and live birth was much more widespread in early vertebrate history than previously thought.

John Long of Museum Victoria, Australia, and colleagues found the unborn embryos inside specimens of Incisoscutum ritchiei, which is an arthrodiran fish — a large and diverse group of the placoderms. Collected from the Upper Devonian Gogo Formation of approximately 380 million years ago, the specimens provide the first evidence for reproduction using internal fertilization in the Arthodira, according to the authors writing in Nature this week. Also, the authors show that Incisoscutum had pelvic girdles of the right structure to support organs like the claspers of sharks that are used for internal fertilization.

Long and colleagues conclude that their observations provide informative new data to contribute to the ongoing debate concerning the origins and interrelationships of the first jawed vertebrates.

In a related News and Views article, Per Ahlberg of Uppsala University, Sweden, notes that the discovery puts our biological understanding of an extinct group of organisms on a much firmer footing. Ahlberg also observes that the embryos of Gogo provide the tools to untangle the origins of jawed vertebrates, as well as providing intimate glimpses of life in a lost world.