First Complete Wing of the Penguin Flipper (1 Viewer)

Gerald Mayr, Vanesa L. de Pietri, Leigh Love, Al A. Mannering, Joseph J. Bevitt and R. Paul Scofield, 2020

First Complete Wing of a Stem Group Sphenisciform from the Paleocene of New Zealand Sheds Light on the Evolution of the Penguin Flipper

Diversity 2020, 12(2), 46; https://doi.org/10.3390/d12020046

Abstract: https://www.mdpi.com/1424-2818/12/2/46
free pdf: https://www.mdpi.com/1424-2818/12/2/46/pdf

We describe a partial skeleton of a stem group penguin from the Waipara Greensand in New Zealand, which is tentatively assigned to Muriwaimanu tuatahi. The fossil includes the first complete wing of a Paleocene penguin and informs on previously unknown features of the mandible and tibiotarsus of small-sized Sphenisciformes from the Waipara Greensand. The wing is distinguished by important features from that of all geologically younger Sphenisciformes and documents an early stage in the evolution of wing-propelled diving in penguins. In particular, the wing of the new fossil exhibits a well-developed alular phalanx and the distal phalanges are not flattened. Because the wing phalanges resemble those of volant birds, we consider it likely that the wing feathers remained differentiated into functional categories and were not short and scale-like as they are in extant penguins. Even though the flippers of geologically younger penguins may favor survival in extremely cold climates, they are likely to have been shaped by hydrodynamic demands. Possible selective drivers include a diminished importance of the hindlimbs in subaquatic propulsion, new foraging strategies (the caudal end of the mandible of the new fossil distinctly differs from that of extant penguins), or increased predation by marine mammals.

Keywords: Aves; evolution; fossil birds; Muriwaimanu tuatahi; Sphenisciformes; wing-propelled diving

Enjoy,

Fred

Systematic Paleontology

Aves Linnaeus, 1758
Sphenisciformes Sharpe, 1891
cf. Muriwaimanu Mayr, De Pietri, Love, Mannering, and Scofield, 2017
cf. Muriwaimanu tuatahi Ando, Jones, and Fordyce, 2006

Referred Specimen: CM 2018.124.4: partial skeleton in two blocks of matrix. The main specimen includes the mandible, right wing, left femur and tibiotarsus, synsacrum, partial pelvis, as well as several thoracic vertebrae and ribs. A much smaller second block contains various smaller and fragmentary bones and was not part of this study

Figure 1. (A) Partial penguin skeleton from the Waipara Greensand in New Zealand (CM 2018.124.4, cf. Muriwaimanu tuatahi), view of exposed right wing and right tibiotarsus. (B) CM 2018.124.4, detail of wing skeleton. (C) Neutron tomography-based image of wrist joint. (D) Detail of distal end of the right tibiotarsus (craniolateral view) with distally-fused fibula. Abbreviations: cdl, condylus lateralis; fib, fibula; min, phalanx digiti minoris; ocr, os carpi radiale; ocu, os carpi ulnare; pda, phalanx digiti alulae; pdm, phalanx distalis digiti majoris; ppm, phalanx proximalis digiti majoris; rcm, right carpometacarpus; rhu, right humerus; rib, rib; rra, right radius; rsc, right scapula; rtb, right tibiotarsus; rul, right ulna; uib, unidentified bone fragment (possible right ramus mandibulae). The scale bars equal 50 mm.

Fred

An interesting quote from the paper is: "Here, we describe a newly found partial skeleton from the Waipara Greensand, which includes the first complete wing of a Paleocene stem group penguin. The fossil is from a small-sized species and is tentatively assigned to Muriwaimanu tuatahi, which is the smallest sphenisciform species from the Waipara Greensand. This assignment is based on the similar shape and concordant dimensions of the wing elements of the new fossil and those of M. tuatahi. We note, however, that there exists some morphological variability in the M. tuatahi-sized Sphenisciformes from the Waipara Greensand and these fossils probably represent more than one species. In light of a pending revision of the fossil material, our study mainly focuses on the morphology of the wing bones, but, as detailed in the following, the new fossil also elucidates other previously unknown aspects of the osteology of Paleocene stem group Sphenisciformes."

Fred