Hynerpeton

Hynerpeton (/haɪˈnɜːrpətɒn/; from Hyner and Ancient Greek ἑρπετόν (herpetón), "creeping animal," meaning "creeping animal from Hyner") is an extinct genus of early four-limbed vertebrates 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 Hynerpeton bassetti, named after the describer's grandfather. 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 (fish-like) gills.[1]

This genus is known from few remains, the most notable being a large endochondral shoulder girdle consisting of the cleithrum, scapula, and coracoid, all connected into one shoulder bone. The inner surface of this shoulder bone possesses an array of depressions believed to have been attachment points for a unique set of powerful muscles around the chest. This may have given Hynerpeton improved mobility and weight-bearing abilities compared to other Devonian stem-tetrapods such as Icthyostega and Acanthostega. The cleithrum is fused to the scapulocoracoid, unlike in most tetrapods, but the shoulder girdle is independent of the skull, unlike in most fish.[1]

Hynerpeton hails from the Red Hill fossil site, which during the Late Devonian was a warm floodplain inhabited by a diverse ecosystem of aquatic fish and terrestrial invertebrates. Hynerpeton was one of several genera of four-limbed vertebrates known from the site, although it was the first to be discovered. It has been theorized that animals like Hynerpeton were able to use their amphibious lifestyle to find shallow pools where they could spawn, isolated from predatory fish which inhabited the deeper rivers.[1]