hynerpeton skeleton

Hynerpeton bassetti

Hynerpeton bassetti is the first tetrapod found from North America (excluding Greenland). It was described on the basis of shoulder elements from two individuals. Anatomical details of the shoulder (cleithrum and scapulocoracoid) indicate that there was an extensive muscular attachment between the shoulder and the spine and powerful muscles for the protraction, retraction and elevation of the front limb. These features suggest that the forelimbs of Hynerpeton were better suited for weight-bearing and possibly terrestrial locomotion than those of other Late Devonian tetrapods. It shares some advance features with Tulerpeton, a Russian tetrapod widely regarded as the Late Devonian form most similar of the terrestrial tetrapods of the Carboniferous. One shared feature is the absence of post-branchial lamina, which indictates that both tetrapods lacked internal gills. On the other hand, the cleithrum and scapulocoracoid of Tulerpeton are separate whereas those of Hynerpeton exhibit the more primitive, combined state.

Several additional tetrapod elements have been recovered from the lens that yielded the original Hynerpeton shoulders. These include belly scutes, a skull fragment (jugal) and —most importantly— a lower jaw. (Lower jaws are the single element most readily identifiable as belonging to early tetrapods.) This jaw as distinct from another tetrapod jaw (now named Densignathus rowei) recovered within the same stratigraphic layer but some 50 m removed from the Hynerpeton lens. All of these elements, similar in inferred size and state of preservation, were attributed to Hynerpeton.

The subsequent discovery of the Red Hill humerus (ANSP 21350) in the same lens qualifies the attribution of these elements to Hynerpeton. The new humerus (upper arm) is substantially larger than would be predicted by the shoulder of Hynerpeton. The presence of two distinct jaws in the same stratigraphic layer demostrates the presence of two species of tetrapods at Red Hill, but it's no longer clear whether the shoulder and the attributed jaw belong to the same species.

A detailed presentation of associated fauna and flora is presented in Who's Who at Red Hill.

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National Geographic. May 1999. "From Fins to Feet."
Scientific Papers
Daeschler, E.B., N.H. Shubin, K.S. Thomson and W.W. Amaral. 1994. "A Devonian tetrapod from North America." Science 265: 639-642.
Daeschler, E.B. 2000. "Early tetrapod jaws from the Late Devonian of Pennsylvania, USA." J. Paleont. 74(2): 301-308.

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