Aspects of diversity in early Antarctic penguins PIOTR JADWISZCZAK and THOMAS MÖRS Jadwiszczak, P. and Mörs, T. 2011. Aspects of diversity in early Antarctic penguins. Acta Palaeontologica Polonica 56 (2): 269–277. Penguin bones from the Eocene La Meseta Formation (Seymour Island, Antarctic Peninsula) constitute the only exten− sive fossil record of Antarctic Sphenisciformes. Here, we synonymize some of the recognized genera (Anthropornis with Orthopteryx, Delphinornis with Ichtyopteryx) and species (Anthropornis nordenskjoeldi with Orthopteryx gigas, Delphi− nornis gracilis with Ichtyopteryx gracilis). Moreover, we suggest that Antarctic species of Anthropornis and Pala− eeudyptes, so−called giant penguins, may in fact comprise only one species each instead of two, based on evidence of well−marked sexual dimorphism. We also present new estimates of body mass based on femora testifying to the impres− sive scope of interspecific body−size variation in Eocene Antarctic penguins. Key words: Aves, Sphenisciformes, systematics, sexual dimorphism, body mass, Eocene, Antarctic Peninsula. Piotr Jadwiszczak [[email protected]], Instytut Biologii, Uniwersytet w Białymstoku, ul. Świerkowa 20B, PL−15−950 Białystok, Poland; Thomas Mörs [[email protected]], Department of Palaeozoology, Swedish Museum of Natural History, P.O. Box 50007, SE−104 05 Stockholm, Sweden. Received 19 August 2009, accepted 8 October 2010, available online 11 October 2010. Introduction gunnari (Wiman, 1905), and Palaeeudyptes klekowskii Myr− cha, Tatur, and del Valle, 1990 (see also Jadwiszczak 2008). Penguins (Aves: Sphenisciformes) are highly marine sea− Their type specimens are tarsometatarsi, bones from the hind− birds confined in their distribution to the Southern Hemi− limb skeleton (Wiman 1905a, b; Marples 1953; Simpson 1971; sphere. The oldest record of penguins is represented by a par− Myrcha et al. 1990, 2002; see also Walsh et al. 2007). Other tial skeleton from the late early Paleocene of New Zealand named species were based either on very fragmentary material (Slack et al. 2006). The earliest known Antarctic sphenisci− (Ichtyopteryx gracilis Wiman, 1905) or on non−tarsometatarsal form is late Paleocene in age, and its remains are much less features (e.g., Orthopteryx gigas Wiman, 1905). Interestingly, complete—just three poorly preserved bones found within most (if not all) of the above−mentioned species were probably the Cross Valley Formation of Seymour Island, Antarctic synchronous (and surely sympatric) during the late Eocene Peninsula (Tambussi et al. 2005). In contrast, thousands of time period (Simpson 1975; Case 1996; Jadwiszczak 2006a), bones have been recovered from the Eocene La Meseta For− an unusual situation (in terms of taxonomic diversity) com− mation of Seymour Island, and this is the oldest record of pared to “recent standards” (e.g., Case 1992). Such a situation high diversity in Sphenisciformes. occurred twice more in fossil penguins from younger epochs Based on collections acquired from the La Meseta Forma− (Jadwiszczak 2009). Moreover, estimated body−size parame− tion, fifteen species assigned to ten genera have been erected ters (body mass and total length) indicate that individuals from since 1905 (Wiman 1905a, b; Marples 1953; Simpson 1971; at least four (distinct) species were larger than extant Emperor Myrcha et al. 1990, 2002; Jadwiszczak 2006a, 2008, 2009; Penguins (Aptenodytes forsteri Gray, 1844) (Livezey 1989; Tambussi et al. 2006; and references cited therein), but only Jadwiszczak 2001). six genera and ten species seem to be taxonomically distinct Here, we investigate three aspects of diversity of early (Simpson 1971; Myrcha et al. 2002; Jadwiszczak 2006b). Antarctic penguins: systematics of the smallest and largest These are: Anthropornis grandis (Wiman, 1905), Anthropornis representatives of these birds, body mass, and sexual size di− nordenskjoeldi Wiman, 1905, Archaeospheniscus wimani morphism in “giant” species (from the genera Palaeeudyptes (Marples, 1953), Delphinornis arctowskii Myrcha, Jadwisz− and Anthropornis). This work aims to refresh the list of dis− czak, Tambussi, Noriega, Gaździcki, Tatur, and del Valle, tinct taxa and to review, using samples from wider taxo− 2002, Delphinornis gracilis Myrcha, Jadwiszczak, Tambussi, nomic ranges, unexplored (by students of Eocene sphenisci− Noriega, Gaździcki, Tatur, and del Valle, 2002, Delphinornis forms) models corresponding to the relations between femo− larseni Wiman, 1905, Marambiornis exilis Myrcha, Jadwisz− ral diameter and circumference, and body mass. The cross− czak, Tambussi, Noriega, Gaździcki, Tatur, and del Valle, sectional measurements of the femur (a bone sensitive to 2002, Mesetaornis polaris Myrcha, Jadwiszczak, Tambussi, mass−related forces) are closely related to body mass in liv− Noriega, Gaździcki, Tatur, and del Valle, 2002, Palaeeudyptes ing terrestrial vertebrates (Anderson et al. 1985) and can also Acta Palaeontol. Pol. 56 (2): 269–277, 2011 doi:10.4202/app. 2009.1107 270 ACTA PALAEONTOLOGICA POLONICA 56 (2), 2011 North Section Weddell Sea Penguins of Białystok, Białystok, Poland; MLP, Museo de La Plata, (Sadler 1988) Formation and other Ciudad de La Plata, Argentina; NRM−PZ, Department of m vertebrates Telm 80 Palaeozoology, Swedish Museum of Natural History, Stock− holm, Sweden; NRM−VE, Department of Vertebrate Zool− ogy, Swedish Museum of Natural History, Stockholm, Swe− 7 den; SAMA, South Australian Museum, Adelaide, Australia. 70 Other abbreviations.—CV, coefficient of variation; N, num− ber of specimens; P, P−value, a measure of the strength of ev− 6–7 6 idence against the null hypothesis; SSD, sexual size dimor− phism (skeletal sexual dimorphism). 5 4 shells 60 pebbles Material and methods 3 sand silt + sand A total of 41 tarsometatarsi, 30 femora and three synsacra of the location of the oldest in situ 50 Eocene Antarctic penguins from Seymour Island (Antarctic penguin bones Peninsula) were used for this study (Appendix 1). They are housed at the IB/P/B, MLP and NRM−PZ. Morphology of LA MESETA FORMATION 100 m bones from the IB/P/B and NRM were studied directly. Data 2 for femora from the IB/P/B and tarsometatarsi from the 40 IB/P/B (except two measurement categories, see below) and 0 MLP were taken from Jadwiszczak 2006a and Myrcha et al. 1 2002, respectively, whereas measurements for bones from the NRM (tarsometatarsi, femora and synsacra) and selected measurements (distal width and thickness of shaft) for tarso− 30 metatarsi from the IB/P/B were taken by PJ (using digital Occurrence of penguin bones within Telm7 callipers with an accuracy of 0.1 mm). Taxonomic assign− ment of bones from the IB/P/B and MLP follows that of rare Myrcha et al. (2002) and Jadwiszczak (2006a), the systemat− frequent ics of specimens from the NRM (Wiman 1905a, b; Marples numerous 20 1953; Simpson 1971) was revised by PJ (based on size abundant and/or morphology; see below). The material consists solely of isolated skeletal elements. Symmetry of distribution (skewness = 0) was tested by fossil wood means of classical Student’s t−tests, whereas testing for nor− pebbles and cobbles 10 mality was performed using Shapiro−Wilk’s W test. Elonga− boulders tion indices were compared by means of a two−sided ran− sand domization test (10000 randomizations). The coefficient of bioturbated sandy mudstone variation (CV), a standardized measure of variation, was ex− sand-mud heterolith pressed in a form of the standard deviation as a percentage of 0 shell bed the mean. CVs for extant penguins were calculated using data from Livezey (1989). The scaling model of Campbell Fig. 1. The rock column of the La Meseta Formation (Seymour Island, and Marcus (1992), used for body mass estimation, was de− Antarctica) showing the concentration of penguin bones in Telm7 and the rived from the logarithmic relationship between selected oldest penguin locality in situ (modified from Myrcha et al. 2002: fig. 2). skeletal measurements and body masses of birds (89 fami− lies). Here, we utilized data only for the “Swimmers” sub− be treated as approximate measures of body size in birds group (including, but not limited to, Spheniscidae or pen− (e.g., Campbell and Marcus 1992). Moreover, due to the re− guins). Another model we used, that of Cubo and Casinos cent advances in the study of osteology and systematics of (1997), was based on the long−bone allometry, and resulted early Antarctic penguins (assignment of isolated bones to in regressions with body mass as the independent variable taxa or groups of taxa; Jadwiszczak 2006a) as well as the size (so inverse prediction was needed). Unlike the previous ap− of the studied sample, such data can be used to verify proach, this one concentrated mainly on Palaeognathiformes previous estimates (see above). (running birds) and penguins, although several non−flying Institutional abbreviations.—BMNH, Natural History Mu− species from other orders were also considered (Cubo and seum, London, UK; IB/P/B, Institute of Biology, University Casinos 1997). JADWISZCZAK AND MÖRS—DIVERSITY OF EARLY ANTARCTIC PENGUINS 271 Tambussi, Noriega, Gaździcki, Tatur, and del Valle, 2002), Geological and stratigraphical IB/P/B−0492 (incomplete left tarsometatarsus), IB/P/B−0549 setting (incomplete left tarsometatarsus), IB/P/B−0408 (incomplete left tibiotarsus) and IB/P/B−0130 (incomplete right femur). The La Meseta Formation (Elliot and Trautman 1982) is an Emended diagnosis.—Tarsometatarsus small and slender unconformity−bounded unit exposed in the north−eastern