Penguin Response to the Eocene Climate and Ecosystem Change in the Northern Antarctic Peninsula Region

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Polar Science 4 (2010) 229e235 http://ees.elsevier.com/polar/

Penguin response to the Eocene climate and ecosystem change in the northern Antarctic Peninsula region

Piotr Jadwiszczak

Institute of Biology, University of Białystok, S´wierkowa 20B, PL-15-950 Białystok, Poland Received 28 October 2009; revised 9 February 2010; accepted 12 March 2010 Available online 25 March 2010

Abstract

Eocene Antarctic penguins are known solely from the La Meseta Formation (Seymour Island, James Ross Basin). They are most numerous and taxonomically diverse (at least ten species present) within strata formed at the end of this epoch, which is concomitant with a signiﬁcant cooling trend and biotic turnover prior to the onset of glaciation. Moreover, all newly appeared taxa were small-bodied, and most probably evolved in situ. Interestingly, some chemical proxies suggest enhanced nutrient upwelling events that coincided with obvious changes in the record of La Meseta penguins. Ó 2010 Elsevier B.V. and NIPR. All rights reserved.

Keywords: West Antarctica; Seymour Island; La Meseta formation (Eocene); Environmental change; Penguins

1. Introduction high latitudes of the Southern Hemisphere to climate deterioration. Penguins (Aves: Sphenisciformes) are The Eocene epoch (55.8e33.9 Ma) witnessed the among the most common and best studied vertebrates warmest interval of the Cenozoic (Early Eocene from the La Meseta Formation. Fifteen species of La Climatic Optimum) followed by a trend toward cooler Meseta penguins have been established since 1905, but conditions (Zachos et al., 2001). Close to the Eocene/ only ten of them have stood a test of time (Jadwiszczak, Oligocene boundary (ca. 34 Ma), Earth’s climate shif- 2006a, 2006b, 2008; Marples, 1953; Myrcha et al., ted from a relatively ice-free world to one with glacial 1990, 2002; Simpson, 1971; Tambussi et al., 2006; conditions on Antarctica characterized by substantial Wiman, 1905a, 1905b; see also Case, 1992). Their ice sheets (Ivany et al., 2006). Such fundamental bones are distributed unevenly within the formation e changes naturally affected whole ecosystems, and can fossils are most numerous in Telm7, the youngest or be observed in the fossil record. uppermost of the seven lithologic units (e.g. Myrcha The richly fossiliferous shallow marine succession et al., 2002). Descriptions of four small-bodied of the early Eocene e latest late Eocene La Meseta (Jadwiszczak, 2001) taxa have been based solely on Formation (Elliot and Trautman, 1982) on Seymour material found within that unit (Myrcha et al., 2002). Island, Antarctic Peninsula (Fig. 1), provides a unique Modern penguins appear to be responsive to climatic opportunity to study the response of organisms from the change, switching diet and altering their range (Emslie et al., 1998). Generally, these highly marine birds are E-mail address: [email protected]. well adapted for survival in a variable environment

Fig. 1. Location map of units of the La Meseta Formation on Seymour Island (according to Sadler, 1988) and main penguin localities. unless they are affected by localized events such as into seven major lithologic units Telm1e7 and this unpredictable long-term or considerable fluctuations system is adopted here (Fig. 1). in the food availability (Davis and Renner, 2003; Williams, 1995). Here, I outline the penguin response 3. Age of the La Meseta Formation to drastic environmental changes in the northern Antarctic Peninsula during Eocene time. 87Sr/86Sr ratios from mollusk shells have been widely used to determine the ages of units forming the La 2. Geologic setting, sedimentology and Meseta Formation. Data presented by Dutton et al. stratigraphy (2002) suggest early (50.5 Ma), middle (>44.5 and <47.4 Ma) and late Eocene (34.7, 35.0 and 36.1 Ma) Seymour Island is located off the north-eastern tip of ages for samples from Telm2, 5 and 7, respectively. Data the Antarctic Peninsula at 64170S, 56450W(Fig. 1). reported by Marenssi (2006) place the base of the La Importantly, it is completely free of ice. The Eocene La Meseta Formation at 56 Ma (close to the Paleocene/ Meseta Formation (Elliot and Trautman, 1982)is Eocene boundary), and those for Telm5 and 7 at 49 Ma exposed in the north-eastern part of Seymour Island (early/middle Eocene transition) and 36 Ma (late (Fig. 1). It comprises mostly poorly consolidated sili- Eocene), respectively. Ivany et al. (2008) suggested that ciclastic fine-grained sediments (ca. 800 m thick and deposition of the lower part of the formation (Telm2e5) richly fossiliferous at numerous horizons) deposited in had taken place in the early Eocene, whereas specimens deltaic, estuarine and shallow marine environments. The from Telm7 and most of Telm6 were late middle to late formation is a shelf-valley geometrically compound fill. Eocene in age. Two major hiatuses have been suggested Por˛ebski (2000) demonstrated that local subsidence within the La Meseta Formation: the first one between along fault-controlled valley margins and associated Telm3 and 4 (e.g. Por˛ebski, 2000), and another one amplified tidal circulation can be a major factor between Telm5 and 6 (Ivany et al., 2008). The former contributing to geometric and genetic complexity of lasted no more than two million years, the latter e such fills. According to Marenssi (2006), however, roughly five million years (Ivany et al., 2008). a period of tectonic quiescence and a lull in volcanism The age of the topmost few meters of the La Meseta allowed sedimentation to be controlled mostly by sea- Formation was estimated by Dingle and Lavelle (1998) level changes. Sadler (1988) subdivided the formation to be 34.2 Ma (late late Eocene). However, the youngest P. Jadwiszczak / Polar Science 4 (2010) 229e235 231 documented ages from the formation are those reported 2001: Fig. 2; Bohaty and Zachos, 2003: Fig. 2). The by Ivany et al. (2006): 33.6e34.8 Ma (based on lower part of Telm6 recorded another episode of 87Sr/86Sr ratios of bivalves from the highest shell- considerable warming in Antarctic Peninsula shelf bearing marine bed). This may indicate the earliest waters (likely related to the Middle Eocene Climatic Oligocene age for the uppermost levels of the formation. Optimum or MECO, ca. 41.5 Ma; see Bohaty and Zachos, 2003: Fig. 2) followed by a drop in tempera- 4. Eocene climate change in the northern ture to some 5 C by ca. 37 Ma. Ivany et al. (2008) Antarctic Peninsula proposed the possibility of winter sea-ice formation in the region of Antarctic Peninsula during the late middle Several lines of evidence indicate that the northern Eocene (ca. 37 Ma). Alpine glaciers were present in the Antarctic Peninsula experienced generally warm and region even earlier (45e41 Ma; Birkenmajer et al., ice-free climates during the earliest part of the Eocene 2005). One more transient warming (of 2e3 C) took followed by gradual cooling (Francis et al., 2008). This place in the upper Telm7 or late Eocene (Ivany et al., trend was not monotonic, however. It followed a some- 2008; see also Bohaty and Zachos, 2003: Fig. 2). what step-like pattern with several reversals (Fig. 2; Unpublished data obtained by Feldmann and Marenssi Ivany et al., 2008). Sea surface temperatures, average (after Francis et al., 2008) show a drop of 1.5 Cin values for each Telm based on d18O data, were estimated seawater temperature during 35e34 Ma (late late by Dutton et al. (2002) to range from 14.5 to 15.5 Cin Eocene). Interestingly, Scher and Martin (2006) repor- the early and middle Eocene to 10.5 C in the late ted a strong line of evidence, based on Neodymium Eocene (see also Cione et al., 2007). Their compilation isotope records, for the late Eocene establishment of of climate proxy data derived from the La Meseta fossil a complete circum-Antarctic pathway. Its evolution record yielded estimates ranging from 2.0 to 13.5 C began ca. 41 Ma (Scher and Martin, 2006) and coincided (Gaz´dzicki et al., 1992) to 8.0e17.0 C(Dutton et al., with some of the climate reversals mentioned above (see 2002). Recently, Ivany et al. (2008) provided d18O also Ivany et al., 2008). To be precise, this age corre- data testifying to temperatures of ca. 15 C near the base sponds to the best inferred age for the uppermost of Telm3, at least 4e5 C warmer than those inferred horizon of Telm6 (see Ivany et al., 2008: Table 2). from earlier or later (through the end of Telm5) samples. According to Dutton et al. (2002), amplitude of Most probably this event corresponds to the Early temperature variation was considerably larger in the Eocene Climatic Optimum (EECO; see Zachos et al., early and middle Eocene (ca. 4e9 C) and dropped to 2.5 C in the late Eocene. Dingle et al. (1998) suggested a strongly seasonal climate solely for the ca. 47e42 Ma time period (i.e. a large part of the middle Eocene). Sediments located just above the highest shell-bearing marine bed of the La Meseta Formation (so-called unit b, at or very close to the Eocene/Oligocene boundary) indicate the transition to glacial marine deposition. This suggests the existence of a regionally extensive West Antarctica ice sheet (Ivany et al., 2006).

5. Eocene biotic turnover in the northern Antarctic Peninsula

It seems obvious that the Telm5/Telm6 transition with accompanying radical temperature change Fig. 2. Distribution of Eocene penguin bones within the La Meseta dramatically affected both marine and coastal ecosys- Formation based on the pooled data from the Polish (Jadwiszczak, tems. Representative examples (Case, 2006; Fostowicz- 2006a, 2006b; Myrcha et al., 2002) and Argentine (Bargo and Frelik, 2003; Francis et al., 2008; Gaz´dzicki and Dzik, Reguero, 1998) collections. Asterisks mark the horizons from 2001; Jadwiszczak et al., 2008; Kriwet [personal which bones of four species of the smallest penguins (see text) were communication], 2010; Kriwet and Gaz´dzicki, 2003; collected. Accompanying paleotemperature curves are based on global deep-sea stable oxygen isotope record (dashed line; Zachos Kriwet and Hecht, 2008; Myrcha et al., 2002; Reguero et al., 2001) and stable oxygen isotope values of La Meseta and Gasparini, 2006; Werner et al., 2004; Stilwell and Formation bivalves (solid line; Ivany et al., 2006, 2008). Zinsmeister, 1992) follow. 232 P. Jadwiszczak / Polar Science 4 (2010) 229e235

The last occurrence of truly warm-water organisms and 2 closely resemble their geologically younger in Antarctica is exemplified by the presence of scarce counterparts assigned to P. gunnari (Jadwiszczak, nautiloid remains in Telm6. These invertebrates were 2006b). A number of specimens are known from more abundant in older units. Generally, a sharp Telm4 and even more from Telm5 and 6, but the fossil decrease in molluscan fauna diversity is conspicuous record is decidedly most abundant within Telm7 (Fig. 2; near the Telm5/Telm6 boundary. For example, Jadwiszczak, 2006a; Myrcha et al., 2002). Telm7 is not gastropod genera that are architecturally well defended homogenous in this respect, however. The fossils are against durophagous predators are not present in Telm6 commonest in the middle and lower levels of this unit and 7. The Telm5 unit contains the bulk of the fossil (Fig. 2; Case, 1996; Jadwiszczak, 2006b: Fig. 2; Myrcha shark localities. There are no shark remains known from et al., 2002: Fig. 2). Telm6 and 7. On the other hand, teleostean gadiforms I repeatedly suggested that ten species sorted into are relatively abundant in the upper parts of the La six genera were a minimum reliable estimate of the late Meseta Formation, though one group (macrourids) is Eocene Antarctic penguin diversity (Jadwiszczak, known solely from earlier units. The majority of land 2006a, 2006b; Myrcha et al., 2002). The following mammal material comes from Telm5 (e.g. ‘‘Mammal distinct taxa are known from Telm7 (some of them also Site’’), whereas marine mammals (whales) are known from earlier units): Anthropornis grandis (Wiman, from younger strata. The only reptile found in the La 1905a,b), A. nordenskjoeldi Wiman, 1905a,b, Archae- Meseta Formation (a Cryptodira turtle) comes from the ospheniscus wimani (Marples, 1953), Delphinornis Telm5 unit. Among the terrestrial birds, two large- arctowskii Myrcha et al., 2002, Delphinornis gracilis bodied flightless forms and one volant bird were Myrcha et al., 2002, Delphinornis larseni Wiman, discovered in Telm6 and 7, whereas Telm5 yielded 1905a,b, Marambiornis exilis Myrcha et al., 2002, remains of individuals from three taxa of volant birds. Mesetaornis polaris Myrcha et al., 2002, P. gunnari The record of penguins is presented in the next section. (Wiman, 1905a,b) and Palaeeudyptes klekowskii The La Meseta Formation yielded plant material from Myrcha et al., 1990. The presence of undescribed taxa most of its column. The flora from Telm5 as well as is highly probable (Jadwiszczak, 2006a, 2008). those from Telm6 and 7 are dominated by Nothofagus According to Case (1996) and Tambussi et al. (2006) (the southern beech), and are most similar to modern there has been little effect of time-averaging within cool- to cold-temperate Valdivian and Magellanic Telm7. This suggests that most, if not all, of the La rainforests from Chile. Middle Eocene Nothofagus Meseta penguin species may have co-existed in the leaves were found to be within the 7.5e12.5 cm length West Antarctic during the late Eocene epoch, just prior category, and their size decreased during the late Eocene to the final break-up of Gondwana and the rapid (a signal of climate change). expansion of continental ice sheets near the Eocene/ Oligocene boundary (see also Case, 1992; 6. Record of Eocene Antarctic penguins Jadwiszczak, 2006a; Simpson, 1975).

Altogether several thousand penguin bones were 7. Ecology of late Eocene Antarctic penguins collected from the La Meseta Formation (Fig. 1; Jadwiszczak, 2006a; Myrcha et al., 2002; Tambussi There are several factors that can potentially shape et al., 2006). They are almost exclusively isolated ecological niches of penguins (and other animals): skeletal elements (but see Tambussi et al., 2006: p. 146), breeding chronology, foraging range and behavior, and often incomplete and/or abraded. The oldest penguin life-history tactics (e.g. Trivelpiece et al., 1987). remains from the formation come from its lowermost Unfortunately, the very nature of fossil record imposes unit (Telm1; Myrcha et al., 2002). These are two partial some limitations with respect to such considerations. humeri and an incomplete tibiotarsus. Although they are A surprisingly high taxonomic diversity of sphenisci- probably not allochtonous in their origin, the earliest forms from the uppermost unit of the La Meseta obviously in situ findings (14 specimens) are known Formation seems to be obvious (see above) and from the ZPAL 8 locality (Telm2s sensu Sadler (1988); considerably exceeds that known for any locality in the see Jadwiszczak, 2006b). present-day world (e.g. Case, 1992). Four (or five e The oldest bone (tarsometatarsus) assigned to see Jadwiszczak, 2008) species known solely from a species, Palaeeudyptes gunnari (Wiman, 1905a,b)to Telm7, D. arctowskii, D. gracilis, M. exilis and M. be precise, comes from the upper part of Telm3 (Myrcha polaris, are represented by the smallest Eocene et al., 2002). Interestingly, humeral heads from Telm1 penguins. The remaining taxa include either birds P. Jadwiszczak / Polar Science 4 (2010) 229e235 233 approaching the largest extant Sphenisciformes or so- foragers. As a consequence, where many species of called giant penguins (Jadwiszczak, 2001), and are sphenisciforms breed sympatrically, their diets are quite known also from older units. Without doubt, the similar. Some penguins avoid competition due to interspecific body-size range observed in the La differences in timing of breeding and foraging ranges. Meseta penguins is intriguing. There are, however, localities where sphenisciforms are High variation in body sizes amongst sympatric ‘‘truly’’ segregated trophically preying largely on species appears to promote coexistence in communities e different species (see Davis and Renner, 2003 and competition strength tends to increase when the body references cited therein). Croxall et al. (1999) suggested masses become more similar (e.g. Leyequień et al., 2007). that dietary segregation may have resulted from inter- If we assume that all/most of discussed penguins co- specific competition when food is in short supply. existed during the deposition of at least a part of Telm7 Additionally, Trivelpiece et al. (1987) proposed that (its middle subunit [see previous section and Fig. 2] with ultimate factors responsible for segregation may be localities ZPAL3 and 4, DPV 13/84 and 14/84 [Myrcha unrelated to such proximate factors as those mentioned et al., 2002: Fig. 2, Table 2]), the roots of observed size- above. They stressed the importance of adaptation to related and taxonomic diversity seem to be obvious. The conditions in the center of distributions of sympatric sudden appearance of at least four species could have been species. likely related to filling unoccupied ecospace e maybe We know that representatives of at least one a result of the late Eocene establishment of a complete large-bodied species (A. nordenskjoeldi or P. kle- circum-Antarctic pathway and the formation of the Scotia kowskii) had elongated, dagger-like bills, maybe Arc, the ‘‘fertile crescent’’ of the Southern Ocean evolved as an adaptation to spear large fish and/or (Kooyman, 2002; Scher and Martin, 2006). According to squid (Jadwiszczak, 2003; Myrcha et al., 1990; Kooyman (2002), this chain of islands and the West Wind Olson, 1985; see also Zusi, 1975: p. 79). Further- Drift (the dominant circulation feature of the Southern more, the shape of a partial mandible (belonging to Ocean enabled by opening of the Drake Passage and A. wimani or a small individual of P. gunnari; Tasmanian Gateway e see Scher and Martin, 2006) Jadwiszczak, 2006a: p. 40, Fig. 18a) suggests ‘‘must have been central to the radiation of penguins’’. a shallow bill, not suitable for being too dependent Interestingly, changes in Al/Ti ratios and organic carbon on small shoaling crustaceans (see Zusi, 1975). burial in sediments suggesting enhanced nutrient Abundant fish remains (gadiforms) are present in the upwelling in the Atlantic sector of the Southern Ocean lower and middle part of the Telm7 unit (e.g. yielded high values centered at 39 Ma (late middle Myrcha et al., 2002; Kriwet and Hecht, 2008). Eocene; maybe an artifact) as well as 36.5 and 34.6e Fishes undoubtedly constituted an important compo- 33.6 Ma (late Eocene), which coincided with a post- nent of penguin diets. Additionally, the presence of MECO cooling, speculated changes in circulation toothed whales (Fostowicz-Frelik, 2003) in the upper (Scher and Martin, 2006, and references cited therein) and La Meseta Formation suggests the existence of the obvious changes in the fossil record of Antarctic penguins resource-based competition and/or prey-predator (Fig. 2; Case, 1992; Jadwiszczak, 2003, 2006a, 2008; relationship between those warm-blooded animals. Myrcha et al., 1990, 2002; Tambussi et al., 2006). Of There were, however, short periods of adverse course, whether newly appeared penguins migrated from trophic conditions for marine animals during late other regions, expanded their ranges or evolved in situ (i.e. Eocene time. Such periods are best documented for in the Antarctic Peninsula) remains obscure. The last those foraging on skeleton-breaking fish (and deca- possibility seems to be the most probable one, though. pods), but those conditions were so far suggested (by First, small-bodied genera mentioned above (unlike other ‘‘limited ecological evidence’’) to occur solely within taxa of this rank) are known solely from the La Meseta the uppermost Telm7 (Aronson et al., 1997; Aronson Formation. Second, D. larseni (a larger congener of D. and Blake, 2001). Theoretically, such fishes could arctowskii and D. gracilis, and a potential ancestor of all have been a source of food for some Eocene sphe- small-sized penguins from Telm7) is known from older nisciforms, but penguins were already very rare during units (and Telm7) and is more basal than Marambiornis this time period (Case, 1996; Jadwiszczak, 2006b: and Mesetaornis (according to cladogram by Clarke et al. Fig. 2; Myrcha et al., 2002: Fig. 2). If periodic, but stable (2007)). long enough, food deficiency conditions were also In present-day penguins, even though the diets may present within the lower two thirds of Telm7, then they be locally and/or temporarily dominated by single would be a reasonable alternative explanation for species of prey, these birds are rather opportunistic penguin species diversity observed in this unit (the 234 P. Jadwiszczak / Polar Science 4 (2010) 229e235

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