Madrynornis, Acosta Hospitaleche, Tambussi, Donato & Cozzuol, 2007

Hospitaleche, Carolina Acosta, Tambussi, Claudia, Donato, Mariano & Cozzuol, Mario, 2007, A new Miocene penguin from Patagonia and its phylogenetic relationships, Acta Palaeontologica Polonica 52 (2), pp. 299-314 : 301-302

Genus Madrynornis nov.

Type species: Madrynornis mirandus sp. nov., monotypic.

Derivation of the name: From Madryn, for its stratigraphic provenance, the Puerto Madryn Formation, and ornis, Greek, referring to a “bird of Madryn”. Gender is masculine.

Diagnosis.—Differs from all other known spheniscids by the following combination of characters: transverse occipital crest expanded into posterolaterally directed wings (not developed in Pygoscelis Wagler, 1832 ); temporal fossa more triangular and deeper than in Paraptenodytes Ameghino, 1891 ; postorbital process slender and longer than in Spheniscus Brisson, 1760 ; jugal arch only slightly curved compared to that in Eudyptes Vieillot, 1816 and Pygoscelis ; interorbital narrower than in Spheniscus and Eudyptes ; nasal fossa without an external edge as in Spheniscus and Paraptenodytes (edge present in Pygoscelis ); parasphenoidal plate broader than in all living species. Mandibular ramus straight with the retroarticular process longer than in Paraptenodytes and Spheniscus , and extending beyond the articular fossa. Humeral diaphysis straight (slightly curved in Palaeospheniscus Moreno and Mercerat, 1891 and Spheniscus ); proximal and distal subequal and preaxial angle smaller than in Spheniscus and Pygoscelis ; shaft−trochlear angle (ca. 38 °) smaller than in Aptenodytes Miller, 1778 and Palaeospheniscus . Large rounded and bipartite tricipital fossa with ventral part smaller and deeper than the dorsal portion (undivided in Paraptenodytes ). Foramen ilioischiadicum smaller than the foramen acetabular (unlike Eudyptula Bonaparte, 1856 and Palaeospheniscus ). Femur with trochanter much higher than the head, unlike the living species; trochanter crest broad but poorly developed compared with extant species; intercondylar groove deeper and wider than in Paraptenodytes ; intercnemial groove reaches proximal end with uniform depth along its length (irregular depth in Pygoscelis ); supratendinosus bridge oblique and broader than in Paraptenodytes , Pygoscelis , and Spheniscus ; fossa flexoria shallower than in Pygoscelis and Spheniscus ; medial epicondyle single (double in Spheniscus ) and rounded (elongate in Pygoscelis ). Fibular crest with sharp edges as in Paraptenodytes , Spheniscus , and Pygoscelis adeliae (rounded in the remaining species). Elongation index (total length/proximal width) of tarsometatarsus 1.79 (smaller than in Palaeospheniscus ). Medial proximal vascular foramen smaller than the lateral (subequal in Pygoscelis , Eudyptes , Eudyptula , and Paraptenodytes ); only the lateral proximal vascular foramen opens directly on plantar side (both of them open on the plantar surface in Pygoscelis and Paraptenodytes ); trochlear edges sturdier than in Spheniscus .

Temporal and geographic distribution.— Early late Miocene, Puerto Madryn Formation, Argentina. Playa Villarino (S 42 ° 25’, W 64 ° 16’), Golfo San José, Chubut Province ( Fig. 1 ) .

Comments.— Simpson (1946) established five subfamilies of Spheniscidae based on characters of the humerus and tarsometatarsus: Palaeospheniscinae, Paraptenodytinae, Anthropornithinae, Palaeeudyptinae, and Spheniscinae (including all living forms).

Following the criticism of Marples (1952), Simpson (1971) abandoned his subfamilial division of the Spheniscidae after examining the fossil penguins from New Zealand.

Although we do not have enough evidence to propose the adoption of a suprageneric arrangement, our current studies on the penguin faunas from Antarctica and South America allow us (CAH and CT) to identify groups that are partially equivalent to those of Simpson’s classification ( Acosta Hospitaleche 2003, 2004; Tambussi et al. 2006; but see Ksepka et al. 2006).

Madrynornis differs from the Palaeospheniscus species and Eretiscus tonnii in having a shorter tarsometatarsus, smaller shaft−trochlear angle, and both proximal vascular foramina well developed. A bipartite tricipital fossa and a smaller shaft−trochlear angle differentiate Madrynornis from Paraptenodytes sp. and Arthrodytes andrewsi , the largest Patagonian penguin even discovered. Madrynornis is distinguished from Anthropornis grandis and A. nordenskjoeldi by having a shorter tarsometatarsus, a weakly curved rather than sigmoid humerus, and a larger and bipartite tricipital fossa. It differs from Palaeeudyptes species by the presence of both proximal vascular foramina and a larger and bipartite tricipital fossa. Finally, although the metatarsal fusion is stronger than in living species, a bipartite tricipital fossa, short tarsometatarsus, small shaft−trochlear angle and similar development of the proximal vascular foramina are shared with these forms.

Figures

Fig. 1. Map of Península Valdés, Chubut Province (Argentina) indicating Playa Villarino, Puerto Madryn Formation, early late Miocene, the locality from which the holotype of Madrynornis mirandus gen. et sp. nov., MEF−PV 100, was collected. The penguin locality is indicated by an arrow.