Produced by the Population Genetics and Evolution class, Furman University

The Devonian: Ichthyostega
Ichthyostega were the first known tetrapods studied from the Devonian period (DevonianTimes 2006; Wikipedia 2010). Ichthyostega was a “labryinthodont”, which is a clade of vertebrates intermediate to fish and amphibians (Wikipedia 2010). Even though it is not considered to be a true amphibian, it does posses key similarities (Wikipedia 2010). Specifically, it possessed lungs and limbs, which allowed it move efficiently through shallow water and onto land. These four-legged animals were found in fossils in eastern Greenland. The basic morphology of these animals are very similar to modern day tetrapods. They were approximately 1m in length and possessed a small dorsal fin along its tail (Encyclopedia Britannica 2006). Interestingly, the series of bony supports found in the tail are also found in fishes (Encyclopedia Britannica 2006). In fact, there are many similarities between Ichthyostega and early aquatic vertebrates including: short snout region, presence of preopercular bone in the cheek region (gill cover in fish), and small scales on the body (Encyclopedia Britannica 2006). It also shares many traits with tetrapods including: walking legs, robust bones, a lack of gills, and strong ribs (protection of lungs) (Devonian Times 2006; Encyclopedia Britannica 2006). Ichthyostega and its relatives “represent forms slightly more advanced than the aquatic Eusthenopteron and appear to be near the evolutionary line leading to the first tetrapods on land” (Encyclopedia Britannica 2006).


Page by Matt Medlin
Picture 1: Ichthyostega fossil; skull and hind limb. From: Scienceblogs.com
Picture 2: Model of Ichthyostega. From: Marcella Gutierrez

Curley R. 2010. Ichthyostega spp. Encyclopaedia Britannica Online.Accessed February 25, 2010.

Murphy D. 2006. Ichthyostega. Devonian Times. Accessed February 2010.

Wikipedia. 2010. Ichthyostega. Accessed February 2010.