Hynerpeton bassetti

Hynerpeton is an extinct genus of early four-limbed vertebrate that lived in the rivers and ponds of Pennsylvania during the Late Devonian period, around 365 to 363 million years ago. The only known species of Hynerpeton is H. bassetti, named after the describer's grandfather, city planner Edward Bassett. Hynerpeton is known for being the first Devonian four-limbed vertebrate discovered in the United States, as well as possibly being one of the first to have lost internal gills.

In 1993, paleontologists Edward "Ted" Daeschler and Neil Shubin found the first Hynerpeton fossil at the Red Hill fossil site near Hyner, Pennsylvania, USA. They were surveying the Devonian rocks of Pennsylvania in search of fossil evidence for the origin of limbed vertebrates. This initial find was a robust left endochondral shoulder girdle, belonging to an animal which had powerful appendages.

Hynerpeton individuals were presumably similar to other early limbed vertebrates such as Ichthyostega or Acanthostega. Although a lack of sufficient fossil material makes it unwise to come to specific conclusions about the anatomy of Hynerpeton, the structure of the preserved endochondral shoulder girdle offers some information on its classification.

Hynerpeton was found at the Red Hill site of Pennsylvania. This roadcut preserved fossils from the Duncannon member of the Catskill Formation, which was laid down in an ancient coastal floodplain. During the late Devonian, the floodplain was close to the equator, so the climate was warm and humid, with a dry and wet season. It formed along the coast of a shallow sea which bisected the continent Euramerica, and was dominated by several small, slow rivers flowing down from the Acadian mountain…