Belongs within: Aequornithia.
Contains: Spheniscinae.
The Spheniscidae, penguins, are a group of flightless, wing-propelled diving birds found primarily in cold waters of the Southern Hemisphere. As well as features related to their mode of swimming, members of the clade have marked supraorbital fossae on the skull for the salt glands (Mayr 2009). The earliest described fossil penguins belong to the Late Palaeocene genus Waimanu, found in New Zealand (Mayr 2009).
The wingless penguin
Published 9 April 2017
A couple of weeks ago, I put up a page on the ‘terrestrial penguin’ Cladornis pachypus, described from the Oligocene of Patagonia by the Argentine palaeontologist Florentino Ameghino. As it happens, Cladornis wasn’t the only unusual penguin recognised from the Patagonian fossil record by Ameghino nor was it even necessarily the most unusual. That title should probably go to another species, the wingless Palaeoapterodytes ictus.
Like Cladornis, Palaeoapterodytes was based on only a single bone, in this case a humerus (upper wing bone) from the Early Miocene. And also like Cladornis, Ameghino’s description of this bone indicated a truly remarkable bird. The distal part of the humerus lacked any sign of the facets that would normally articulate with the succeeding wing bones and, as a result, Ameghino concluded that the wing skeleton had been reduced to the humerus only. The crest and pits on the humerus marking the attachment of the wing muscles were also reduced. Ameghino’s Palaeoapterodytes presumably had wings reduced to the merest nubs, effectively functionless and probably of little mobility. Nevertheless, the humerus of Palaeoapterodytes remained relatively robust, its breadth little less than that of other penguins.
I am not aware of any other bird with a wing structure anything like this. In other birds without functional wings, the entire wing skeleton becomes reduced, not simply truncated. Perhaps the closest approximation I have found is the wing of Hesperornis, which also lacks known wing bones beyond the humerus. However, the Hesperornis humerus is slender and gracile, and even without direct indication of the presence of more distal bones, it still looks to retain some remnant of the ancestral articulation. Also, the whole concept of a wingless penguin is decidedly problematic. Hesperornis derived its main propulsion in swimming from its feet and so its wings became reduced because they served little function. Penguins, on the other hand, get most of their propulsion from their wings, swimming in a manner that has been compared to flying underwater. Despite being flightless, penguins retain a wing skeleton that is, if anything, even more well developed than that of their flying relatives. For Palaeoapterodytes to have lost functional wings, it would have somehow had to change its mode of propulsion.
As a result, even while authors were cautiously considering Ameghino’s interpretation of Cladornis, they treated Palaeoapterodytes with more scepticism. This scepticism was eventually validated when the humerus was re-examined by Acosta Hospitaleche (2010). The reason for the lack of structure at its distal end was very simple: the original distal end had been broken off. The apparent lack of development of the muscle attachment structures was the result of erosion, not any indication of the bone’s original appearance. When alive, Palaeoapterodytes had probably been very similar to, if not identical with, one of the several other penguin species known from around the same time and place. Unfortunately, the state of preservation of the type humerus is so poor that its exact identity cannot be determined, and Palaeoapterodytes ictus has been cast into the taxonomic limbo of nomen dubium. Ameghino’s Cladornis may remain an intriguing mystery, but his Palaeoapterodytes is just a red herring.
Systematics of Spheniscidae
<==Spheniscidae [Dypsicleidae, Sphenisciformes]
|--Waimanu Jones, Ando & Fordyce in Slack et al. 2006M09, CC10
| |--*W. manneringi Jones, Ando & Fordyce in Slack et al. 2006CC10
| `--W. tuatahi Jones, Ando & Fordyce in Slack et al. 2006CC10
`--+--Delphinornis Wiman 1905M09, S46
| |--*D. larsenii Wiman 1905 [=D. larseni]S46
| |--D. arctowskii Myrcha et al. 2002M09
| `--D. gracilis Myrcha et al. 2002M09
`--+--Mesetaornis polaris Myrcha et al. 2002M09
|--Marambiornis exilis Myrcha et al. 2002M09
`--+--+--Eretiscus tonnii (Simpson 1981)M09
| `--SpheniscinaeM09
|--Palaeeudyptes Huxley 1859M09, CC10 [incl. Eosphaeniscus Wiman 1905CC10, EospheniscusS46; PalaeeudyptinaeS46]
| |--*P. antarcticus Huxley 1859S46
| |--P. gunnari (Wiman 1905)S72, A05 [=*Eosphaeniscus gunnariA05]
| |--P. klekowskii Myrcha et al. 1990M09
| `--P. marplesi Brodkorb 1963CC10
`--AnthropornithinaeS46
|--Pachydyptes Oliver 1930S46
| |--*P. ponderosus Oliver 1930 [=Anthropornis ponderosa, A. ponderosus, Pachydyptes ponderosa]CC10
| `--P. simpsoni Jenkins 1974U93
|--Arthrodytes Ameghino 1905S46
| `--*A. grandis (Ameghino 1901) (see below for synonymy)S72
`--Anthropornis Wiman 1905M09, S46
|--*A. nordenskjoeldi Wiman 1905 [=A. nordenskjoeldii]S46
`--A. grandis (Wiman 1905)M09
Spheniscidae incertae sedis:
Duntroonornis Marples 1952CC10
`--*D. parvus Marples 1952CC10
Korora Marples 1952CC10
`--*K. oliveri Marples 1952CC10
Marplesornis Simpson 1972CC10
`--*M. novaezealandiae (Marples 1960) [=Palaeospheniscus novaezealandiae]CC10
Tereingaornis Scarlett 1984CC10
`--*T. moisleyi Scarlett 1984CC10
Archaeospheniscus Marples 1952 [incl. notodyptes Marples 1953]CC10
|--*A. lowei Marples 1952CC10
|--A. lopdelli Marples 1952CC10
`--A. wimani (Marples 1953) [=*Notodyptes wimani]CC10
Platydyptes Marples 1952CC10
|--*P. novaezealandiae (Oliver 1930) [=Pachydyptes novaezealandiae, Pa. novaezelandiae]CC10
|--P. amiesi Marples 1952CC10
`--P. marplesi Simpson 1971 [=P. marplesigi]CC10
Chubutodyptes Simpson 1970S72
`--*C. biloculata Simpson 1970S72
Neculus Ameghino 1905 (n. d.)S72
`--*N. rothi Ameghino 1905 (n. d.)S72
Palaeoapterodytes Ameghino 1905 (n. d.) [=Apterodytes Ameghino 1901 non Hermann 1783]AH10
`--*P. ictus (Ameghino 1901) (n. d.) [=*Apterodytes ictus]AH10
Wimanornis seymourensisS72
Anthropodyptes gilliS72
Orthopteryx Wiman 1905S46
`--*O. gigas Wiman 1905S46
Pachypteryx Wiman 1905S46
`--*P. grandis Wiman 1905S46
Ichthyopteryx Wiman 1905 (n. d.) [=Ichtyopteryx]S46
`--*I. gracilis Wiman 1905 [=*Ichtyopteryx gracilis]S46
Catarractes Brisson 1760 (n. d.)CC10
Penguinus Brünnich 1771 (n. d.)CC10
Madrynornis mirandus Acosta Hospitaleche, Tambussi et al. 2007AH10
Paraptenodytes Ameghino 1891 (see below for synonymy)S72
|--*P. antarcticus (Moreno & Mercerat 1891) (see below for synonymy)S72
|--P. brodkorbi Simpson 1972S72
`--P. robustus (Ameghino 1905) (see below for synonymy)S72
Palaeospheniscus Moreno & Mercerat 1891 (see below for synonymy)S72
|--*P. patagonicus Moreno & Mercerat 1891 (see below for synonymy)S72
|--P. bergi Moreno & Mercerat 1891AH10 (see below for synonymy)
|--P. biloculata (Simpson 1970)AH10
|--P. gracilis Ameghino 1899AH10 (see below for synonymy)
`--P. wimani (Ameghino 1905) [=*Perispheniscus wimani]S72
Crossvallia unienwillia Tambussi et al. 2005M09
TonniornisM09
|--T. mesetaensis Tambussi et al. 2006M09
`--T. minimum Tambussi et al. 2006M09
Perudyptes devriesi Clarke et al. 2007M09
Icadyptes salsi Clarke et al. 2007M09
*Arthrodytes grandis (Ameghino 1901) [=Paraptenodytes grandis; incl. Paraptenodytes andrewsi Ameghino 1901, Arthrodytes andrewsi]S72
Palaeospheniscus Moreno & Mercerat 1891 [incl. Paraspheniscus Ameghino 1905, Perispheniscus Ameghino 1905, Pseudospheniscus Ameghino 1905; Palaeospheniscinae]S72
Palaeospheniscus bergi Moreno & Mercerat 1891AH10 [=Pal. bergiiS72, *Paraspheniscus bergiS72; incl. Pseudospheniscus concavus Ameghino 1905S72, Ps. convexus Ameghino 1905S72, *Ps. interplanus Ameghino 1905S72, Ps. planus Ameghino 1905S72, Palaeospheniscus planus Ameghino 1905S72, Pal. rothi Ameghino 1905S72]
Palaeospheniscus gracilis Ameghino 1899AH10 [incl. Pal. medianus Ameghino 1905S72, Pal. nereius Ameghino 1901S72, Paraspheniscus nereiusS72]
*Palaeospheniscus patagonicus Moreno & Mercerat 1891 [incl. P. affinis Ameghino 1905, P. intermedius Ameghino 1905, P. interruptus Ameghino 1905, P. menzbieri Moreno & Mercerat 1891]S72
Paraptenodytes Ameghino 1891 [incl. Isotremornis Ameghino 1905, Metancylornis Ameghino 1905, Treleudytes Ameghino 1905; Paraptenodytinae]S72
*Paraptenodytes antarcticus (Moreno & Mercerat 1891) [=Palaeospheniscus antarcticus; incl. *Isotremornis nordenskjoeldi Ameghino 1905]S72
Paraptenodytes robustus (Ameghino 1905) [=Palaeospheniscus robustus, Perispheniscus robustus; incl. *Treleudytes crassa Ameghino 1905, T. crassus, Paraptenodytes curtus Ameghino 1901, *Metancylornis curtus]S72
*Type species of generic name indicated
References
[AH10] Acosta Hospitaleche, C. 2010. Taxonomic status of Apterodytes ictus Ameghino, 1901 (Aves; Sphenisciformes) from the Early Miocene of Patagonia, Argentina. Neues Jahrbuch für Geologie und Paläontologie—Abhandlungen 255 (3): 371–375.
[A05] Ameghino, F. 1905. Enumeración de los Impennes fósiles de Patagonia y de la Isla Seymour. Anales del Museo Nacional de Buenos Aires, serie 3, 6: 97–167, pls 1–8.
[CC10] Checklist Committee (OSNZ). 2010. Checklist of the Birds of New Zealand, Norfolk and Macquarie Islands, and the Ross Dependency, Antarctica, 4th ed. Ornithological Society of New Zealand and Te Papa Press: Wellington.
[M09] Mayr, G. 2009. Paleogene Fossil Birds. Springer.
[S46] Simpson, G. G. 1946. Fossil penguins. Bulletin of the American Museum of Natural History 87 (1): 1–99.
[S72] Simpson, G. G. 1972. Conspectus of Patagonian fossil penguins. American Museum Novitates 2488: 1–37.
[U93] Unwin, D. M. 1993. Aves. In: Benton, M. J. (ed.) The Fossil Record 2 pp. 717–737. Chapman & Hall: London.