Paleogene equatorial penguins challenge: biogeography, diversity, and cenozoic climate change

Paleogene equatorial penguins challenge the proposed relationship between biogeography, diversity, and Cenozoic climate change

New penguin fossils from the Eocene of Peru force a reevaluation of previous hypotheses regarding the causal role of climate change in penguin evolution. Repeatedly it has been proposed that penguins originated in high southern latitudes and arrived at equatorial regions relatively recently (e.g., 4 – 8 million years ago), well after the onset of latest Eocene/Oligocene global cooling and increases in polar ice volume. By contrast, new discoveries from the middle and late Eocene of Peru reveal that penguins invaded low latitudes >30 million years earlier than prior data suggested, during one of the warmest intervals of the Cenozoic.

A diverse fauna includes two new species, here reported from two of the best exemplars of Paleogene penguins yet recovered. The most comprehensive phylogenetic analysis of Sphe- nisciformes to date, combining morphological and molecular data, places the new species outside the extant penguin radiation (crown clade: Spheniscidae) and supports two separate dispersals to equa- torial (paleolatitude =14°S) regions during greenhouse earth condi- tions. One new species, Perudyptes devriesi, is among the deepest divergences within Sphenisciformes. The second, Icadyptes salasi, is the most complete giant (>1.5 m standing height) penguin yet described. Both species provide critical information on early penguin cranial osteology, trends in penguin body size, and the evolution of the penguin flipper.

Aves I evolution I Peru I fossil I Bergmann"s rule

Climate has been hypothesized to play a key role in evolu- tionary patterns of both living (1–5) and extinct penguins

(4 –9). Whereas the earliest penguins appear 60 Ma (10), extant lineages were recently proposed to originate in associ- ation with abrupt latest Eocene–Oligocene global cooling (=34 Ma; see refs. 11 and 12) and to undergo a major radiation and range expansion to low latitudes only during later Neogene

presence of at least five penguin taxa (ref. 15 and undescribed specimens). The only other pre-Oligocene penguin fossil from South America is a partial hindlimb from the high-latitude southernmost tip of the continent, equivalent in age to the middle Eocene Peruvian specimens (14). Together, these two records constitute the earliest for penguins on the continent.

Systematic Paleontology

Aves Linnaeus, 1758 (sensu Gauthier, 1986).

Neognathae Pycraft, 1900.

Sphenisciformes Sharpe, 1891 (sensu Clarke et al., 2003).

Perudyptes devriesi. New genus, new species.

Holotype specimen. Museum of San Marcos University, Peru (MUSM) 889, comprising a skull, mandible, cervical vertebrae and ribs, humeri, left carpometacarpus, synsacrum, femora, right tibiotarsus, and left tarsometatarsus (Fig. 1).

Etymology. ""Peru"" references the fossil provenance, and ""dyptes"" is Greek for diver. The species name ""devriesi"" honors Tom DeVries, whose dedicated work and longstanding collaboration in the Pisco Basin of Peru made possible the discovery of the new localities and species.

Locality and age. MUSM 889 is from a coarse-grained, thick-bedded, siliciclastic sandstone exposed at Quebrada Perdida (14°34'S, 75°52'W), Department of Ica, Peru, identified to the basal portion of the middle to late Eocene Paracas Formation (16). The presence of the gastropod Turritella lagunillasensis in correlative sandstone beds confirms the assignment of the holotype locality to the basal Paracas Formation (16, 17), as does the discovery of late middle Eocene radiolarians (Cryptocarpium ornatum, Lithocyclia aristotelis, and Lithocyclia ocellus) in tuffaceous fine-grained sandstones much higher in the section (=42 Ma).kcooling (4). Extant penguin species are broadly considered to be cool-adapted, and even equatorial species are sensitive to sea surface temperature increases associated with El Nin˜o Southern Oscillation events (13).

The new fossils are the first to indicate significant low- latitude penguin diversity over a period characterized by one of the most important climatic shifts in earth history: the transition from peak temperatures in the pre-Oligocene green- house earth to the development of icehouse earth conditions (11, 12). The fossils reveal key data on the poorly known pre-Miocene history of penguins in South America (6, 9, 14). The fauna, from new Eocene localities in Peru, includes the two new species as well as additional material indicating the

Author contributions: J.A.C. and D.T.K. designed research; J.A.C., D.T.K., M.S., M.U., N.G.,

S.B., Y.N., and C.A.B. performed research; J.A.C., D.T.K., M.S., N.G., S.B., Y.N., and C.A.B.

analyzed data; and J.A.C., D.T.K., M.S., N.G., S.B., and C.A.B. wrote the paper. The authors declare no conflict of interest.

This article is a PNAS Direct Submission. R.E.F. is a guest editor invited by the Editorial Board. Abbreviation: MUSM, Museum of San Marcos University, Peru.

dTo whom correspondence should be addressed. E-mail: julia_clarke@ncsu.edu.

kDeVries, T. J., Narva´ ez, Y., Sanfilippo, A., Malumian, N., Tapia, P., XIII Congreso Peruano de Geologi´a, Oct. 17–20, 2006, Lima, Peru´ (ext. abstr.).

This article contains supporting information online at www.pnas.org/cgi/content/full/ 0611099104/DC1.

© 2007 by The National Academy of Sciences of the USA