The Fish-Tetrapod Transition

With the vertebrate comparative anatomy lab quickly approaching in my Animal Diversity class, I was excited to fall upon a paper that appears well-tailored to the content of my own teaching schedule (for once! geesh). This is spankin' new, published March 17, 2009, from the journal Evolution: Education and Outreach.

This paper is paricularly interesting because it outlines both the history of tetrapod evolution and the history of human's perception of the animal transition from aquatic to terrestrial habitats. It highlights the helpful fossils unearthed that helps us trace this vertebrate history, such as Icthyostega spp., and those fossils, such as the Eryops cephalus, that hindered the pursuit. In the case of the latter organism (pictured below), despite its anatomy being characteristic of an early trasitional tetrapod, its ancestral origin was found to exist much later in tetrapod evolution.

This paper also describes the reason for the recent fame of the Tiktaalik transitional fossil, as it is known from several nearly complete specimens. Its excellent preservation and diagnostic transitional tetrapod features have made it an important tool for understanding the origin of the phylogenetic tree of Tetrapoda.

"In a nutshell, the 'fish–tetrapod transition' usually refers to the origin, from their fishy ancestors, of creatures with four legs bearing digits (fingers and toes), and with joints that permit the animals to walk on land. This event took place between about 385 and 360 million years ago toward the end of the period of time known as the Devonian. The Devonian is often referred to as the 'Age of Fishes,' as fish form the bulk of the vertebrate fossil record for this time."

This paper is a great read for eager young biologists like myself searching for readable scientific papers on phylogenetics and evolution. I recommend it!

The Fish–Tetrapod Transition: New Fossils and Interpretations