Red Hill humerus (early tetrapod)

fossil humerusVentral view of ANSP 21350. Photo courtesy of Ted Daeschler, ANS.

The Red Hill humerus (ANSP 21350) is a single specimen that was recovered near the spot where Hynerpeton bassetti was found several years earlier. The identity of the specimen is unresolved. Its spatial proximity to Hynerpeton is suggestive, but the humerus is 50% larger than what would have been expected given the size of shoulder girdles belonging to two separate individuals of Hynerpeton. The other Red Hill tetrapod, Densignathus, is somewhat larger and more robust than Hynerpeton. However, it's known only from a single lower jaw that was found 50 m from the spot where ANSP 21350 and Hynerpeton were found.

This fossil is the only tetrapod limb bone recovered from Red Hill. Although it can't be attributable to either of the two known tetrapods (or to a third, new species), it's very informative. This humerus exhibits a mosaic of derived and primitive features that elucidates limb evolution in early tetrapods. Functionally, the forelimb of this tetrapod appears better suited to propping-up the trunk and head than for swimming. Although probably ill-suited for walking. it suggests an intermediate adaptive stage which ultimately led to the evolution of tetrapod terrestriality. Further discussion of this specimen is presented on the Red Hill humerus page in Recent Findings Upset Old Order.

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Scientific Papers:
Shubin, N.H., E.D. Daeschler, and M.I. Coates. 2004. "The Early Evolution of the Tetrapod Humerus." Science 304: 90-93.

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