Thomashuxleya externa Ameghino, 1901

SHOCKEY, BRUCE J. & FLYNN, JOHN J., 2007, Morphological Diversity in the Postcranial Skeleton of Casamayoran (? Middle to Late Eocene) Notoungulata and Foot Posture in Notoungulates, American Museum Novitates 3601, pp. 1-28 : 11-12

Thomashuxleya externa Ameghino, 1901

Material: AMNH 28905 consists of many postcranial elements of a single individual that Simpson (1936a) referred to Thomashuxleya externa . It was found at Cañadón Vaca and was the primary source of postcranials for the skeletal reconstruction of Thomashuxleya (Simpson, 1938: fig. 1, 1967: fig. 35), which also included AMNH 28698 and 28447 for skull and jaw morphology. Postcranials of ‘‘contemporaneous, closely related animals’’ ( Simpson, 1936: 10) from Cañadon Vaca were also used in the reconstruction. The ‘‘closely related animals’’ he referred to were AMNH 28904 and 28906, which we refer to Anisotemnus distentus (above) and Pleurostylodon similis (below), respectively.

We refer AMNH 28653 to T. externa as these associated elements are indistinguishable from homologous elements of AMNH 28905. This specimen is composed of postcranial elements only, including a partial right forelimb, which includes a distal humerus, complete radius, ulna lacking only the distal region, unciform, and Mc V.

Description: AMNH 28905 was associat- ed with cranial remains ‘‘too extremely disintegrated to be worth restoration or even collecting, but permitted certain field identification as a species of Thomashuxleya ’’ ( Simpson, 1936: 1). Of the postcranial remains available from Cañadón Vaca, these are the largest; they are similar in size to the cranial and dental remains of Thomashuxleya externa , supporting referral of these remains to that taxon.