| Summary: | Two new species of giant fossil penguin from near the Eocene-Oligocene boundary in Otago, New Zealand, are described. OU 22761 is from the Wharekuri Greensand of the Kye Burn upper river valley, probably from geomagnetic Chron 13r; close to the Eo-Oligocene boundary, upper Runangan - basal Whaingaroan (35.0 – 33.7 Ma). Bones are from the wing, leg, spinal column and shoulder of one individual. Most bones are fragmentary but with some surface preservation, especially for the humeri. OU 22106 is from the Ototara Limestone of the Kakanui River mouth, dated as Lower Whaingaroan (29.8 - 33.2 Ma, Early Oligocene). Bones are from the torso, wing, shoulder and leg, and some elements are articulated. Both specimens lack a tarsometatarsus, the primary bone used to diagnose Sphenisciformes of this age. Instead, both possess well-preserved humeri, used here for taxonomic description and for comparison with other fossil penguins from the Kaiatan to Waitakian Stages (upper Middle Eocene to lowermost Miocene = ‘mid-Cenozoic’). The humerus provides other features that have not yet been used as cladistic characters, but have potential to determine species-level relationships. Humeral features, for example, suggest that Inkayacu (MUSM 1444) and a previously undetermined fragmentary humerus (OM GL430 C47.17 ‘4’) belong to Palaeeudyptes. Detailed taxonomy and comparative morphology identify OU 22761 as a new species of Palaeeudyptes characterised by: a robust humerus with a small tricipital fossa; wide m. pectoralis impression, and other attachment sites enlarged; moderately sigmoidal shaft; and moderate humeral head size. OU 22106 is similar to Kairuku in its: weakly sigmoidal humerus with a crescent-like deep m. pectoralis impression; and flattened intumescence; ulna with a tab-like olecranon; and scapula with a bluntly-pointed glenoid process. Some key differences from Kairuku (gracile femur, long m. supracoracoideus groove on the coracoid) suggest a new genus. The specimen cannot be compared directly to Palaeeudyptes antarcticus because there are no elements in common, though morphological features suggest OU 22106 is not a species of Palaeeudyptes. This thesis has used bones other than the tarsometatarsus to diagnose and separate species and genera of ‘mid-Cenozoic’ penguins which are marked by a persistent polytomy. Features of the humerus should help resolve such polytomies.
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