Pachydyptes simpsoni Jenkins, 1974

Park, Travis & Fitzgerald, Erich M. G., 2012, A review of Australian fossil penguins (Aves: Sphenisciformes), Memoirs of Museum Victoria 69, pp. 309-325 : 317-318

Pachydyptes simpsoni Jenkins, 1974

Holotype. Partial skeleton ( SAM P14157 ) consisting of: a partial left coracoid; partial right humerus; partial left humerus; a right radius; a partial left carpometacarpus; a left phalanx II- 1; and a partial vertebra. ( Fig. 4 ; Table 2).

Type locality. Blanche Point , 37 km SSW of Adelaide, South Australia (35°14'S, 138°27'E) .

Horizon and age. Occurs in the Gull Rock Member and the Tuketja Member of the Blanche Point Formation. The Gull Rock Member consists of green and grey, glauconitic and fossiliferous calcareous mudstone with a few limestone lenses; the Tuketja Member consists of alternating bands of tough, dark grey chert and friable clays, silts and calcareous clays ( Jenkins et al., 1982). Both members are in the P15 foraminiferal zone; Late Eocene (Bartonian–Priabonian), 36.5–38.0 Ma ( James and Bone, 2000).

Referred material. A partial right humerus ( SAM P14158a) ( Fig. 5 ), a partial right radius ( SAM P14158b) ( Fig. 5 ) and a rib fragment ( SAM P17913). ( Table 2)

Diagnosis. Following Marples (1952), the generic diagnosis of Pachydyptes is as follows: humerus relatively wide; m. deltoideus minor insertion (referred to as the ‘external tuberosity’ by Marples, 1952) projects distally; articular surface flattened; fossa pneumotricipitalis undivided; m. supracoracoideus insertion slightly oblique, almost parallel to long axis of shaft and widely separated from the m. latissimus dorsi insertion; shaft has slight sigmoid curve and slight angulation of the cranial border; angle between long axis of shaft and tangent of condylus dorsalis and condylus ventralis is acute; shelf adjacent to condylus ventralis approximately the same width as condylus ventralis; and coracoid convex at base. Following Jenkins (1974), Pachydyptes simpsoni differs from Pachydyptes ponderosus Oliver, 1930 by having: more concave medial margin of the coracoid; more pronounced angulation of the cranial margin of the humerus (referred to as the “preaxial tuberosity on the shaft at the proximal limit of attachment of brachialis internus” by Jenkins, 1974); more widely separated insertions of the musculi supracoracoideus and the musculi coracobrachialis caudalis (referred to as the pectoralis secundus and pectoralis tertius respectively by Jenkins, 1974); metacarpal III extends further distally than metacarpal II; and the bones are generally less robust.

Remarks. The referred humerus ( SAM P14158a) is similar to Pachydyptes ponderosus with its large head, expanded muscle attachments and wide shaft. The skeleton however is overall less robust than P. ponderosus and the overall morphology of the coracoid, radius and carpometacarpus shows similarities to Anthropornis and Palaeeudyptes ( Jenkins, 1974) . The coracoid has a broadly flared base and an oval foramen nervi supracoracoidei. On the radius, the insertion site of the m. brachialis is hollowed, forming a distinct notch similar to that of Paraptenodytes robustus Ameghino, 1905 , although the bone itself resembles that of Palaeeudyptes and Anthropornis ( Jenkins, 1974) . Systematic revisions of Pachydyptes simpsoni have seen it first synonymised with Anthropornis nordenskjoeldi ( Jenkins, 1985) , and most recently considered as Sphenisciformes indet. (Ksepka and Clarke, 2010). The latter authors concluded that it occupied a more crownward position than Antarctic A. nordenskjoeldi specimens. We therefore consider the systematics of P. simpsoni to be unresolved.

Figures

Figure 4. Pachydyptes simpsoni holotype, SAM P14157: A, right radius in ventral view, left carpometacarpus and left phalanx II-1 in dorsal view; B, head of right humerus in dorsal view; C, left coracoid in dorsal view; D,?twelfth cervical vertebra in ventral view.

Figure 5. Pachydyptes simpsoni paratype, SAM P14158: proximal end of right radius in (A) ventral view and (C) dorsal view; partial right humerus in (B) ventral and (D) dorsal views.