Cenizo et al.—Pseudo-toothed birds from Eocene of Antarctica
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Figure 7. Temporal distribution, phylogenetic affinities, and size-types in selected pelagornithid species (modified from Mayr et al., 2013). The internal nodes are supported by the following presumable derived features (Mayr et al., 2013, and present work): Clade 1 (humerus with ventral portion of proximal end narrow and tuberculum dorsale strongly projected, ulna with very short olecranon, trochlea metatarsi II at the same level or slightly more plantarly projected than the trochlea IV); Clade 3 (femur with trochlea fibularis lacking sulcus). The Clade 2 is still uncertain, but according to general similarities it considered by Mayr et al. (2013) as Pelagornis s.l. (a presumable derived character noted here is the presence of the transverse furrow near the tip of the rostrum). The size-types represent the wingspan inferred by extrapolated dimensions of the known elements in incomplete specimens compared with the homologous elements in the P. chilensis holotype, the most completely known pelagornithid specimen. The gray areas indicate possible cladogenetic event. (Af) Africa, (E) Europe, (NA) North America, (Ant) Antarctica, (NZ) New Zealand, (SA) South America, (Au) Australia.
in Antarctica (Acosta Hospitaleche, 2013, 2015; Acosta Hospitaleche and Reguero, 2015), and the late Oligocene in New Zealand (Ksepka and Ando, 2011). After that, giant penguins disappear from the fossil record, suggesting an important ecological segregation favoring medium and small penguins, in contrast with pseudo-toothed birds, in which giant size was maintained until their extinction in the late Neogene.
Highlights in pelagornithid evolution.—The phylogenetic affi- nities within Pelagornithidae are not well understood, and thus, reliable conclusions are difficult to assess. The following inferences about the evolutionary history of the group should be considered as
the younger Mio/Pliocene taxa in a highly specialized group of forms (Clade 3, Fig. 7), that probably constituted the third and more recent evolutionary event in pelagornithids.
Acknowledgments
preliminary, and must be confirmed with new and more complete findings. On this basis, and having in mind that the pelagornithid record is patchy, three main evolutionary events can be recognized. MLP 12-I-20-4, assigned to morphotype 1, is the oldest
pseudo-toothed birds from Antarctica, and is more derived than Dasornis in several features. It indicates in the middle Ypresian, the presence of a more specialized ‘clade’ than that of Dasornis. This first event probably includes the disappearance of Dasornis and would be the starting point of the dominance of more advanced forms (“Clade” 1, Fig. 7) with a trend toward the extreme specialization of soaring capacity. The second event would be linked to the origin of the
Pelagornis s.l. species (hypothetical Clade 2, Fig. 7; see Mayr et al., 2013). It would have occurred during the early Oligocene, although unfortunately, the fossil record of pseudo-toothed birds is very scarce for that time. Finally, Mayr et al. (2013) recognized some presumable synapomorphies that allow to join
We thank the logistic support of the Dirección Nacional del Antártico and Fuerza Aérea Argentina during field work in Antarctica. Especially to Cecilia Deschamps and Federico Agnolin for their assistance with English version. The sugges- tions and comments provided by the associate editor Daniel Ksepka, Estelle Bourdon and an anonymous reviewer improved the quality of the manuscript and are appreciated. The Instituto Antártico Argentino supported this project along with grants from the Consejo Nacional de Investigaciones Científicas y Técnicas, Agencia Nacional de Promoción Científica y Tecno- lógica, and Universidad Nacional de La Plata.
References
Acosta Hospitaleche, C, 2015, New penguin giant bones from Antarctica: systematic and paleobiological significance: Comptes Rendus Palevol, v. 13, p. 555–560.
Acosta Hospitaleche, C., and Haidr, N., 2011, Penguin (Aves, Sphenisciformes) cranial remains from the La Meseta Formation (Eocene) of Antarctic Peninsula (Antarctica): Antarctic Sciences, v. 23, p. 369–378.
Acosta Hospitaleche, C., and Reguero, M., 2010, Taxonomic notes about Ich- tyopteryx gracilis Wiman, 1905 and Orthopteryx gigas Wiman, 1905 (Aves, Spheniscidae): Alcheringa, v. 35, p. 463–466.
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