Osteology of Icadyptes Salasi, a Giant Penguin from the Eocene of Peru

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J. Anat. (2008) 213, pp131–147 doi: 10.1111/j.1469-7580.2008.00927.x

OsteologyBlackwell Publishing Ltd of Icadyptes salasi, a giant penguin from the Eocene of Peru Daniel T. Ksepka,1 Julia A. Clarke,1,2,3 Thomas J. DeVries4 and Mario Urbina5 1Department of Marine, Earth and Atmospheric Sciences, and 2Department of Paleontology, North Carolina State University, Raleigh, NC, USA 3Division of Paleontology, American Museum of Natural History, New York, NY, USA 4Burke Museum of Natural History and Culture, University of Washington, Seattle, WA, USA 5Departamento de Paleontologia de Vertebrados, Museo de Historia Natural, Universidad Nacional Mayor de San Marcos, Lima 14, Peru

Abstract

We present the first detailed description of the giant Eocene penguin Icadyptes salasi. The species is characterized by a narrow skull with a hyper-elongate spear-like beak, a robust cervical column and a powerful flipper. The bony beak tip of Icadyptes is formed by fusion of several elements and is unique among penguins, differing markedly from previously described giant penguin beaks. Vascular canal patterning similar to that of boobies, frigatebirds and albatrosses suggests I. salasi may have had a thin, sheet-like rhamphotheca unlike the thick rugose rhamphotheca of modern penguins. Together, these features suggest a novel ecology for I. salasi, most likely involving the capture of larger prey items via spearing. As the first described giant penguin specimen to preserve a complete wing skeleton, the I. salasi holotype yields significant insight into the shape, proportions and orientation of the wing in giant penguins. In articulation, the forelimb of I. salasi is straighter, permitting less manus and antibrachium flexion, than previous depictions of giant penguin wings. Cross-sections of the humerus and ulna reveal a level of osteosclerosis equalling or surpassing that of extant penguins. Based on ontogenetic data from extant penguins and the morphology of the carpometacarpus of I. salasi, we infer the retention of a free alular phalanx in basal penguins. Previously, the status of this element in penguins was disputed. Differences in the proportions of the manual phalanges contribute to a more abruptly tapering wingtip in I. salasi compared with crown penguins. Fossils from Peru, including the I. salasi holotype specimen, document that penguins expanded to nearly the whole of their extant latitudinal range early in their evolutionary history and during one of the warmest intervals in the Cenozoic. Key words alula; body size; fossil; palaeontology; Pisco Basin; Spheniscidae.

salasi includes a nearly complete, well-preserved skull as well Introduction as a partial skeleton including a complete flipper, providing The existence of giant penguins has been recognized since new insight into the morphology of giant Palaeogene the first description of a penguin fossil by Thomas Henry penguins. As the first giant penguin known from equatorial Huxley (1859). However, our understanding of the (~14°) latitudes, I. salasi also has implications for giant pen- anatomy and ecology of these birds has long been hindered guin palaeoecology and early penguin biogeography. by the lack of complete specimens. Most Palaeogene Sphenisciformes first appear in the fossil record in the penguin remains consist of isolated elements (Wiman, 1905; Palaeocene (Tambussi et al. 2005; Slack et al. 2006) and Jadwiszczak, 2006) or a few associated bones (Ameghino, undergo a rapid radiation, attaining high species diversity 1905; Marples, 1952, 1953; Tambussi et al. 2005; Jadwiszczak, and a wide Southern Ocean distribution by the late 2006). Cranial remains in particular have been rare and Eocene. Changes in body size, especially shifts to gigantism, fragmentary (Olson, 1985; Jadwiszczak, 2003, 2006; Ksepka & are some of the most discussed aspects of penguin palae- Bertelli, 2006). The recently discovered holotype of Icadyptes ontology (Simpson, 1946; Jenkins, 1974; Jadwiszczak, 2001; Tambussi et al. 2005; Ksepka et al. 2006). The 17 extant penguin species span a wide range of sizes, from the tiny Correspondence Daniel Ksepka, Department of Marine, Earth and Atmospheric 1-kg Little Blue Penguin (Eudyptula minor) to the Emperor Sciences, North Carolina State University, Campus Box 8208, Raleigh, Penguin (Aptenodytes forsteri), which can reach weights NC 27695, USA. E: [email protected] of 40 kg immediately before the fasting period of its Accepted for publication 29 April 2008 reproductive cycle (Prevost, 1961; Kinsky & Falla, 1976; Article published online 18 June 2008 summarized in Williams, 1995). Fossil penguins overlap the

132 Eocene penguin Icadyptes salasi, D. T. Ksepka et al.

entire size range of living species but also include dramatically fossils that sample a large span of stratigraphic (Eocene– larger forms. The Patagonian fossil Eretiscus tonnii (see Pleistocene) and phylogenetic history. These remains Simpson, 1981) and an unnamed penguin from the Oli- include multiple skulls and skeletons from the crown clade gocene of New Zealand (Fordyce & Jones, 1990) are nearly Neogene fossil species Spheniscus urbinai and Spheniscus identical in size to the extant Little Blue Penguin. Dun- megaramphus, as well as postcranial remains of Spheniscus troonornis parvus and Tereingaornis moisleyi provide examples muizoni, all collected from the Miocene–Pliocene Pisco of mid-sized (Spheniscus and Eudyptes range) species (Marples, Formation (Stucchi, 2002; Stucchi et al. 2003; Göhlich, 2007). 1952; Scarlett, 1983). Giant Eocene and Oligocene species Single bones from early middle Miocene deposits of the are known to have achieved enormous size: Anthropornis Chilcatay Formation have been referred to Palaeospheniscus nordenskjoeldi from Antarctica is estimated to have out- sp. and to an undetermined sphenisciform taxon (Acosta stripped all living penguins by reaching weights of 81.7– Hospitaleche & Stucchi, 2005). Penguins from Palaeogene 97.8 kg and heights of 1.66–1.99 m (Jadwiszczak, 2001). deposits include partial skeletons comprising the holotype Icadyptes salasi, first reported by Clarke et al. (2007), is specimens of I. salasi from the late Eocene Otuma Formation, one of the largest known fossil penguins. Body size impacts and the deeply diverging stem penguin Perudyptes devriesi multiple life-history parameters including thermoregulation, from the middle Eocene Paracas Formation (Clarke et al. 2007). growth strategy, feeding requirements and population struc- The holotype specimen of I. salasi was recovered from ture, and has also been correlated to diving ability in seabirds Otuma Formation deposits (DeVries et al. 2006) cropping (Williams, 1995; Halsey et al. 2006). Until the discovery of out at a site located in the lower Ullujaya valley of the Rio I. salasi, the distribution of giant penguins was restricted to Ica (14°37′S, 75°37′W) (Fig. 1). The Otuma Formation is high latitudes (above 40°S). Because I. salasi occupied equa- part of a Palaeogene marine sedimentary depositional torial waters during the Eocene greenhouse Earth interval, sequence exposed in the Pisco Basin of southern Peru this species may be of particular relevance to investigating between the Paracas Peninsula and the Río Ica (DeVries, the palaeoecology of giant penguins (Clarke et al. 2007) 1998; DeVries et al. 2006). It unconformably overlies and merits further detailed description and analysis. tuffaceous marine siltstone and sandstone of the Paracas Formation and unconformably underlies the basal transgressive sandstone of the uppermost Oligocene to Geological background middle Miocene Chilcatay Formation (DeVries et al. 2006). The Pisco Basin of Peru has been a hotbed of new penguin The base of the Otuma Formation consists of yellow–orange discoveries, in recent years yielding exquisite penguin coarse-grained sandstone that has yielded macroinvertebrate

Fig. 1 Map showing the type locality of Icadyptes salasi (marked by star) in the Pisco Basin and stratigraphic column illustrating early interpretations and current understanding of age of the Otuma Formation and the stratigraphy of the Pisco Basin (after DeVries et al. 2006).

Eocene penguin Icadyptes salasi, D. T. Ksepka et al. 133

The strata containing the holotype specimen of I. salasi are from a depositional environment further from the palaeoshoreline than those of the Paracas Formation that produced the middle Eocene Perudyptes devriesi holotype specimen. Whereas the former beds contain scales of nearshore and offshore fishes (anchovies, sardine, hake, possibly lanternfish) and pelagic foraminifera and radiolaria (DeVries & Pearcy, 1982; DeVries et al. 2006) deposited in fine-grained sediments below wave-base, the latter beds contain littoral organic remains (Turritella lagunillasensis, Ostrea sp., echinoid spines, barnacle plates, rolled bryozoan- covered bioclastic debris) in coarse-grained and gravelly sandstone deposited a few tens of metres or less above a rugged platform of crystalline basement rock.

Comparative material and taxonomic issues All comparisons with other fossil taxa are based on direct observation unless indicated. Inference of soft tissues associated with osteological structures is based on dissection of specimens of Spheniscus humboldti, Eudyptes chrysocome Fig. 2 Line drawing showing the positions of the elements of the and Pygoscelis adeliae (see Ksepka, 2007). Observations of Icadyptes salasi holotype (MUSM 897) embedded in matrix before musculature are also supplemented by the comprehensive removal. Abbreviations: cm, carpometacarpus; co, coracoid; cv, cervical work of Schreiweis (1982). We follow Clarke et al. (2003) in vertebrae; fu, furcula; h, humerus; m, mandible; ph, phalanges; r, radius; applying the name Spheniscidae to the crown clade of ra, radiale; s, sesamoid; sc, scapula; sk, skull; u, ulna; un, ulnare. penguins, the name Sphenisciformes to all penguins that share the loss of aerial flight, and the name Pansphenisci- remains, while the remainder of the formation consists of formes to the clade including all taxa more closely related tuffaceous fine-grained sandstone with siliceous and to Spheniscidae than any other extant avian lineage. At calcareous microfossils, and macroinvertebrate and present, no volant member of the penguin lineage is vertebrate remains (DeVries et al. 2006). It is from the latter known, so the clade names Pansphenisciformes and deposits that the holotype specimen was collected. Sphenisciformes refer to the same taxa. However, if a basal The partial holotype skeleton was recovered in limited volant member of the penguin lineage were to be discovered, articulation (Fig. 2) about 70 m above an angular unconformity it would be included in Pansphenisciformes but placed that marks the base of the Otuma Formation. Specimens of outside Sphenisciformes. the gastropods Peruchilus culberti and Xenophora carditigera Because of taxonomic complexities, a brief review of the in basal transgressive sandstone beds establish a late middle history of the genus Palaeeudyptes is in order. Palaeeudyptes to late Eocene age for the sequence (Nielsen & DeVries, 2002; antarcticus, the first fossil penguin to be described, was DeVries, 2004), as does a nannofossil assemblage from a based on a partial tarsometatarsus (Huxley, 1859). Due to locality 45 m below the I. salasi holotype that includes difficulties in comparing material to the holotype and a Coccolithus pelagicus, Cribrocentrum reticulatum, Reticu- classification framework in which monophyly was not lofenestra bisectus and Reticulofenestra umbilicus (fide explicitly required, Palaeeudyptes antarcticus later became a Yanina Narváez-Rodriguez, CICESE; DeVries et al. 2006). taxonomic wastebasket for many fossils from New Zealand. Correlation with nearby microfossil-bearing sections Two Antarctic species (Palaeeudyptes gunnari and indicates an age of about 36 Ma for these strata. Ash beds Palaeeudyptes klekowskii) are also generally included collected from near the base of the same depositional in Palaeeudyptes (Simpson, 1971a; Myrcha et al. 1990). sequence across the Río Ica yielded 40Ar–39Ar dates of 37.2 Simpson (1971b) pointed out problems with the taxonomy and 36.5 Ma. An ash bed higher in the section, probably of Palaeeudyptes and considered all New Zealand specimens, correlative with beds above the horizon with the I. salasi save the holotypes of Palaeeudyptes antarcticus and holotype, yielded an age of 35.7 Ma (personal communication, Palaeeudyptes marplesi, as Palaeeudyptes sp. indet. Lawrence Snee, USGS, Denver, 1987; DeVries et al. 2006). Phylogenetic analyses (Clarke et al. 2007; Ksepka, 2007) Stratigraphic relationships in the lower Ullujaya Valley, show that not all Palaeeudyptes specimens, nor even all the lower Ica valley, and the age of the sediments all New Zealand specimens, form a clade. At present, it is not indicate an assignment of the beds of the holotype locality possible to assess which species and specimens may form a to the Otuma Formation (DeVries, 1998, 2004). clade with the holotype individual of Palaeeudyptes

134 Eocene penguin Icadyptes salasi, D. T. Ksepka et al.

antarcticus. Fortunately, a revision of the taxon aided by resulting in the palate being exposed in left lateral view new, associated specimens is currently underway (Tatsuro beneath the orbit. Ando, in progress). In anticipation of this study, we use the The most striking feature of the skull is the long spear-like designations ‘Burnside Palaeeudyptes’ (OM C48:73–81) beak, which makes up more than two-thirds of the total skull and ‘Duntroon Palaeeudyptes’ (OM C47:23 and 47:25) for length (Table 1). Fusion of the premaxillae and the maxillary New Zealand specimens originally assigned to Palaeeudyptes processes of the palatines contributes to the solid construction antarcticus but which cannot be shown to form a clade with of the cylindrical upper beak. Unlike other penguins there the holotype specimen. ‘Palaeeudyptes’ klekowskii and is no ventral separation or visible suturing between the ‘Palaeeudyptes’ gunnari are also referenced. These species posterior facial processes of the left and right premaxillae. appear to be closely related to one another (Myrcha et al. Instead, a flat ventral surface formed these portions of the 2002), but referral to Palaeeudyptes remains provisional premaxillae. It is bounded laterally by low ridges and pending phylogenetic evaluation of Palaeeudyptes presumably includes contributing portions of the maxillae, monophyly. although no sutures are evident. This surface is inscribed Institutional abbreviations: AMNH, American Museum with reticulate vascular impressions reminiscent of those of Natural History, New York, NY, USA; BMNH, Natural History in Sulidae (boobies and gannets) and Fregatidae (friga- Museum, London, UK; CM, Canterbury Museum, Christchurch, tebirds). The beak is straight throughout its length with no New Zealand; MNZS, Museum of New Zealand Te Papa indication of a downturned tip. However, as mentioned Tongarewa, Wellington, New Zealand; IB/P/B, Prof. A. Myrcha above the extreme distal-most tip is missing. It should be University Museum of Nature, University of Bialystok, noted that this morphology does not necessarily rule out Bialystok, Poland; MUSM, Museo de Historia Natural, the possibility of a slightly hooked beak tip, given that Universidad Nacional Mayor de San Marcos, Lima, Peru; OM, bony beak morphology is not completely reflective of Otago Museum, Dunedin, New Zealand; UCMP, University rhamphotheca shape in extant penguins. The dorsal of California Paleontology Museum, Berkeley, CA, USA; surface of the rostrum is mostly smooth with the reticulate USNM, National Museum of Natural History, Smithsonian texturing restricted to the region anterior of the nares. At Institution, Washington, DC, USA. the premaxillae/frontal contact, the skull roof appears to lack a depression associated with nasofrontal flexure and present in extant penguins. However, preservation in this Description region is poor, and additional material is needed to confirm the absence of this feature. Development of the Skull depression varies among species and through ontogeny in The skull (Figs 3 and 4) is nearly complete but partially extant penguins, becoming more developed in adults. deformed. The distal-most tip of the rostrum, left pterygoid, Slit-like external nares extend for approximately half posterior left palatine, vomer, right jugal, right paroccipital the length of the beak. The nares face laterally, with little process and right quadrate are missing. Crushing has or no exposure in dorsal view. In this respect, the nares compressed the cranium mediolaterally posterior to the resemble those of Spheniscus. In other extant penguin midpoint of the orbit, exaggerating the slenderness of taxa, the nares are wide and well exposed in dorsal view. the basicranial region. Some rotation has also occurred, A narrow groove continues anteriorly from each naris,

Table 1 Measurements (mm) from Icadyptes Element Measurement salasi (MUSM 879). The tip of the upper beak is missing, but an estimate of total beak length Skull total length ~318 can be obtained from comparisons with the beak length ~230 mandible Coracoid diameter of scapular cotyle 15.3 Humerus maximum length 167.0 length from head to ulnar condyle 164.0 greatest proximal width 61.7 midshaft width 36.1 midshaft breadth 16.9 Ulna total length 114.5 Radius total length 116.1 Carpmetacarpus total length 97.6 Phalanx II-1 total length 59.5 Phalanx II-2 total length 39.5 Phalanx III-1 total length 40.6

Eocene penguin Icadyptes salasi, D. T. Ksepka et al. 135

Fig. 3 Skull of Icadyptes salasi (MUSM 897) in (A) ventral, (B) dorsal, (C) left lateral, and (D) right lateral views. Scale bar = 5 cm. ending approximately 1/5th of the distance from the tip of large foramen that opens through the lacrimal shaft in the beak. The posterior margin of the naris clearly surpasses most living penguins cannot be determined. The shaft is the anterior margin of the antorbital fenestra. Sutures slightly ventrolaterally deflected, unlike the condition in between the premaxillae and nasals are dorsally obliterated, extant penguins where it is strongly curved, so as to with a short remnant of this contact exposed artificially by appear concave in lateral view. The ventral terminus is crushing in the area of the nasal–frontal hinge. The nasal flared with a sub-triangular and slightly concave facet for is better preserved on the right side of the skull where the contact with the jugal bar. The left jugal is complete while contact with the maxilla is also clearly visible. the right is not preserved. The jugal bar is straight and Both lacrimals are disarticulated from the skull (Fig. 5). mediolaterally compressed. The contact between the jugal The right lacrimal is nearly complete. A thin sheet of bone and maxilla along the bar is obliterated as in extant penguins. representing part of an indeterminate cranial element has On the skull roof, the frontals are hourglass-like in shape, been displaced and is attached to the medial side of the becoming extremely narrow in the interorbital region. lacrimal. Dorsally, the lacrimal expands into a wide, thin Deeply pitted bone texturing along the posterolateral sheet. A small foramen perforates the bone at its postero- margins of the frontals indicates the position of salt gland dorsal corner. However, the presence or absence of the fossae. On both sides of the skull, the frontals are intact

136 Eocene penguin Icadyptes salasi, D. T. Ksepka et al.

Fig. 4 Line drawing of the skull of Icadyptes salasi (MUSM 897) in (A) ventral, (B) dorsal, (C) left lateral and (D) right lateral views. Abbreviations: ao, antorbital fenestra; cp, capping pad on basitemporal plate; gr, groove extending from nares; is, interorbital septum; j, jugal; lp, left palatine; me, mesethmoid; na, narial opening; po, postorbital process; pp, paroccipital process; ps, parasphenoid; rp, right palatine; sc, sagittal crest; sf, salt gland fossa; tf; temporal fossa. Scale bar = 5 cm.

with smooth edges, indicating that these fossae lacked a The basitemporal plate is displaced slightly dorsal to the laterally bounding shelf of bone. The postorbital process is level of the occipital condyle. This condyle is large relative well developed and is ventrally directed. The temporal to skull size compared with extant penguins, a feature also fossae are deep and extend to the midline, meeting at a noted in Paraptenodytes antarcticus and partial Eocene strong sagittal crest. The sagittal crest extends for a significant penguin skulls from Antarctica (Ksepka & Bertelli, 2006; length between the temporal crests and the postorbital Jadwiszczak, 2006). The occipital condyle of I. salasi is processes, giving the temporal fossae squared dorsal more expanded than in any other described fossil penguin borders. In this morphology I. salasi resembles Perudyptes and is nearly equal in width to the distance between the devriesi and Paraptenodytes antarcticus more closely than basal tubera. Anterior to the condyle, a shallow subcondylar the crownward taxon Marplesornis novaezealandiae and fossa is present. The basal tubera are well developed and extant Spheniscus, which possess anteroposteriorly short continuous with a raised platform bounding the basisphe- crests. Spheniscus is the only extant taxon with well-developed noid plate. Anterior to the basal tubera, there is a slight temporal fossae. constriction of this raised area followed by a great expansion

Fig. 6 Quadrate of Icadyptes salasi (MUSM 897) in (A) medial and (B) lateral views. Abbreviations: am, tubercle for m. adductor mandibulae externus pars profunda; fb, fossa basiorbitalis; lc, lateral condyle; mc, Fig. 5 Cranial elements of Icadyptes salasi (MUSM 897). Right lacrimal medial condyle; oc, otic capitulum; or, orbital process; pc, pterygoid in (A) lateral view and right pterygoid in ventral (B) and dorsal (C) views. condyle; qc, quadratojugal cotyle; sc, squamosal capitulum; tu, tubercle Scale bars = 1 cm. Abbreviations: fl, foot of lacrimal; fpa, articular facet (see text). Scale bar = 1 cm. for parasphenoid; fpt, articular facet for pterygoid; fq, articular facet for quadrate; p, tab-like process; sk, attached fragment of skull. The right pterygoid was freed during preparation (Fig. 5). The bone is rod-like, lacking the fan-shaped ante- marking the lateral basitemporal process. The development rior expansion of extant penguins. As in Paraptenodytes of the lateral basitemporal process varies in extant penguins, antarcticus but unlike extant penguins, a tab-like process but no living or fossil species shows the degree of expansion projects medially. At the posterior end, a shallow concave present in I. salasi. In the only known skull of Parapteno- cotyle for articulation with the quadrate is bordered by a dytes antarcticus (AMNH 3338), the ventral margins of the short, square, lateral expansion. The dorsal surface of the lateral basitemporal processes are incomplete, but show anterior end bears a semicircular articular facet for the expansion at their bases (Bertelli et al. 2006). The lateral parasphenoid rostrum and the ventral surface bears a basitemporal process of Marplesornis novaezealandiae small projection for articulation with the left pterygoid. (CM zfa16527) is less developed and resembles extant Spheniscus. The opening of cranial nerve IX is visible just Quadrate dorsal to the basal tubera. The left paroccipital process is undeformed, showing that there is only a short gap The quadrate (Fig. 6) is stout and apneumatic. The orbital between the paroccipital process and the occipital condyle. process is significantly longer than the main body of the An elongate parasphenoid rostrum extends from the quadrate (i.e. from the mandibular articulation through the basitemporal plate. The rostrum expands near the level of dorsal tip of the otic process), as in Paraptenodytes antarcticus the pterygoid/palatine contact, though to a lesser degree but unlike in extant penguins. The medial surface of the than in Perudyptes devriesi. At this point a pair of ventral orbital process is strongly concave, and the lateral surface ridge arises. These ridges are present in extant penguins, bears a dorsal tubercle continuous with a slight ventral but they are more pronounced in I. salasi. ridge. We observed a similar tubercle in a few individuals Much of the delicate mesethmoid is preserved. The of Spheniscus humboldti, although the associated ridge was posterior border of the mesethmoid is intact and continu- absent in these specimens. A wide, deep incision separates ous with the anterior wall of the braincase. The thin anterior the otic and squamosal capitula of the quadrate and a walls of the braincase have been compressed into a single rounded fossa indents the posterior face of the quadrate flat surface by post-mortem deformation. On the right shaft directly ventral to the otic capitula. On the lateral side, the anteroventral rim of the mesethmoid is partially side of the otic process, a strong tubercle for attachment intact. At the ventral contact with the parasphenoid rostrum, of pars profunda of m. adductor mandibulae externus is the mesethmoid thickens significantly mediolaterally. developed. The tubercle is contiguous with the squamosal The right palatine is largely intact, but its morphology is capitulum as in Paraptenodytes antarcticus and Marplesornis obscured by rotation and overlying elements. Some novaezealandiae, whereas it is separate in extant penguins. degree of posterior expansion of the element is present, The quadratojugal cotyla is a deep, round socket. although its full extent is not known. A small facet on the posterodorsal palatine is identified as a sliding articulation Mandible for the parasphenoid rostrum. This facet is located on a prominent medial flange in extant penguins that is only The mandible (Fig. 7) is straight and of similar depth for very weakly developed in I. salasi. Near the nares, the maxillary much of its length before tapering anteriorly. The symphysis process of the palatine fuses with the premaxilla. is extensive, a feature also seen in Waimanu tuatahi (see Slack

Fig. 7 Mandible of Icadyptes salasi (MUSM 897) in (A) dorsal view. Scale bar = 1 cm. Image (B) shows a close up of the broken rostral tip in cross- section and is not to scale. Abbreviations: ao, anterior ossification underlying symphysis; ld, left dentary; rd, right dentary.

et al. 2006) and Archaeospheniscus lowei (see Discussion). The anterior and posterior margins of the lateral mandibular Comparison of the mandible with the upper jaw reveals cotyla are more sharply projected than in extant penguins that approximately 40 mm of the mandibular tip is missing, and in this respect are similar to those in Paraptenodytes indicating the symphysis was significantly longer than antarcticus. The medial and retroarticular processes are the preserved segment. The splenial is large, extending not clearly separated. I. salasi also lacks the hooked medial posteriorly to the caudal mandibular fossa and closely process developed in extant penguins. The retroarticular approaching or taking part in the mandibular symphysis. fossa is a deep, concave cup similar to the fossa in extant Whether the splenial actually reached the symphysis is Pygoscelis and some isolated Eocene mandibular frag- unclear due to preservation. Vascular foramina cover the ments from Seymour Island (Ksepka & Bertelli, 2006) but external surface of the tip of the mandible, a condition much deeper than in other extant penguins. A caudal typical of penguins. A narrow, subcylindrical spur of bone mandibular fossa is present distally on the medial face of is present on the ventral surface of the mandible at the the mandible, but damage precludes determining if a cau- symphysis, a feature hitherto unknown in penguins. Because dal mandibular fenestra perforated the bone. If a fenestra the anterior tip of the mandible is missing in I. salasi, it was present, the opening must have been diminutive. The cannot be discerned if this feature is a projection of the coronoid process is represented by a small raised scar, dentaries separated posteriorly by deep grooves or a with a smaller roughened muscle insertion scar probably separate ossification. A posterior projection of the dentaries representing another branch of m. adductor mandibulae is present in the Suloidea (well developed in Sula nebouxii, located slightly posteriorly. Morus capensis and Phalacrocorax magellanicus, vestigial in Anhinga anhinga) and some Procellariiformes (Diomedei- Cervical vertebrae dae: Diomedea immutabilis, Diomedea nigripes, Diomedea epomophora, Phoebastria nigripes). This projection is absent The axis and nine additional cervical vertebrae are preserved in other surveyed Procellariiformes (Puffinus griseus, Fulmarus (Fig. 8 and Table 2). Compared with extant penguins, the glacialis, Pterodroma lessoni, Daption capensis, Macronectes cervical vertebrae are disproportionately more robust, and giganteus, Oceanites oceanicus, Oceanodroma leucorhoa, the skull is narrower. For example, the maximum width of Hydrobates pelagicus). the mid-series cervicals of I. salasi closely approaches the

Table 2 Vertebral measurements (mm) from Vertebra Length of Maximum width at Maximum width at Icadyptes salasi (MUSM 879). Position in the number centrum prezygapophyses postzygapophyses vertebral column was estimated by comparison with extant penguins. Length was measured −− cervical 5 49.8 from the anteriormost ventral edge of the −− cervical 6 50.8 centrum to the posteriormost ventral edge of − cervical 7 51.2 41.5 the centrum, except in the specimens marked cervical 8 50.2 39.0 44.2 with an asterisk, where the ventral edge was cervical 9 45.7* 53.1 47.7 broken and measurement was made to the − cervical 10 43.2 52.6 dorsal edge of the centrum cervical 11 43.0* 54.2 41.9

Fig. 8 Cervical vertebrae of Icadyptes salasi (MUSM 897). The top two rows show elements in lateral view (axis in lateral and posterior view), the bottom two rows show elements in dorsal view. Numbers correspond to position of each vertebra in the cervical column as estimated from partial articulation and comparison with extant penguins (see text). The lateral views of axis, cervical vertebra 7 and cervical vertebra 8 are mirrored to facilitate comparison. Scale bar = 1 cm. diameter of the cranium. In extant taxa, the width of these and slightly expanded, but not disc-like. Strong plate- vertebrae may commonly be one-third skull diameter. like expansion is also present in Sulidae. A broken edge The neural spine of the axis is sail-like. The base of the indicates a midline ridge was present on the ventral face spine is much longer anteroposteriorly than in extant of the plate in I. salasi, although the degree of projection penguins and has a strongly arcate dorsal margin bounded of this ridge remains uncertain. The tip of the hypapophysis by a slight ridge. This crest and the associated ridge are is the site of origin for m. rectus capitis ventralis, and the related to development of the m. splenius capitus. The ridge probably marks an attachment surface for that muscle. lateral surfaces of the centra are depressed to form shallow Several of the nine additional cervical vertebrae elements ovoid fossae. In these morphologies the axis is more similar were preserved in partial articulation with each other, but to that of Sulidae than extant penguins. The odontoid process none was articulated with the axis. Thus, their positions is completely flat dorsally (unlike Sula) and presents a cannot be known with certainty. These vertebrae are here prominent hemispherical articular surface ventrally. The identified as cervical vertebrae 4–11, plus one centrum of centrum is elongate and slender, although mediolateral undetermined position, based on comparisons with extant compression has exaggerated the thinness. A disc-like plate penguins. with raised edges terminates the elongate hypapophysis. Cervical vertebra 4 is represented by a left postzygapo- This feature was a proposed autapomorphy of I. salasi in physis preserved in articulation with cervical vertebra 5. the original description (Clarke et al. 2007), but examination The postzygapophysis has an anteriorly arising hypapophysis. of a wider pool of extant penguin skeletons reveals that Although the relevant area is not intact in cervical vertebra some individuals of Aptenodytes forsteri may also show a 4, transverse foramina are present in all more posterior disc-like plate, albeit a smaller one. In other extant penguins, vertebrae. The centra of cervical vertebrae 5–8 are slender the ventral surface of the hypapophysis is typically rugose and elongate, while more posterior vertebrae become

increasingly broad and anteroposteriorly abbreviated. There are no hypapophyses in cervical vertebrae 5–8, and this structure was probably also absent in vertebra 9 although damage partially obscures the relevant region. Cervical vertebra 4 is represented by a large portion of the centrum as well as a left postzygapophysis that is attached to the left prezygapophysis of cervical vertebra 5. A well- developed epipophysis is developed on this postzygapophysis, but does not overhang its posterior edge. Remnants of narrow costal processes are preserved on the right side of the centrum. Cervical vertebra 5 preserves the base of a short dorsal midline ridge or spinus process. An epipophysis is preserved on the right side and overhangs the posterior edge of the postzygapophysis. On cervical vertebra 6, the flange-like epipophyses are displaced anteriorly, and do not overhang the posterior margins of the postzygopophyses. Dorsally, there is low central ridge along the midline. Remnants of narrow costal processes are preserved on the right side. Cervical vertebra 7 bears a central ridge on the dorsal midline. This ridge is larger than that of the preceding vertebrae, although the distal edge is broken. The preserved bases of the epipophyses indicate they were in the same position as in cervical vertebra 6, but their degree of development (projection) cannot be ascertained. Cervical vertebrae 8–11 bear low central ridges on the dorsal midline. In cervical vertebra 8 this ridge extends nearly the entire length of the neural arch. Cervical vertebra 9 has a notably shorter centrum than the preceding three vertebrae. The articular surfaces of the centrum are broader mediolaterally in cervical vertebra 9 and 10 than in preceding vertebrae. A groove marks the lateral face of the small, knob-like transverse process. The epipophyses Fig. 9 Omal portion of the furcula (left side) of Icadyptes salasi (MUSM are very strongly developed, anteriorly displaced and 897) in (A) medial and (B) lateral view. Coracoid in (C) ventral and more tuberculate than in preceding vertebrae. They do (D) dorsal view. Omal end of scapula in (E) ventral and (F) dorsal view. Abbreviations: ac, acromion; f, fossa; gl, glenoid facet; sc, scapular not overhang the postzygapophyses. Cervical vertebra 10 cotyle. Scale bar = 1 cm. preserves the base of a robust hypopophysis. The dorsal ridge is posteriorly displaced. Cervical vertebra 11 also than in extant penguins. The coracoid tubercle is developed preserves the base of a robust hypopophysis. In contrast to as a hemispherical projection. Between the tubercle and cervical vertebrae 10, the dorsal ridge is anteriorly displaced. the acromion process there is a pronounced depression on One additional poorly preserved centrum may represent the lateral surface of the scapula. The glenoid surface is cervical 12 or 13. The base of a strong dorsal ridge is well defined and extends further over the lateral surface preserved, but the remaining vertebra are too damaged to of the scapula than in extant penguins. Approximately discern most morphological features. half of the glenoid facet lies in the plane of the scapular shaft in I. salasi. It is less ventrally deflected than in extant penguins, where nearly the entire facet lies ventral to the Furcula axis of the shaft. The scapular blade is not preserved. Fragments of the left and right omal ends of the furcula indicate mediolaterally compressed rami with thickened Coracoid anterior margins (Fig. 9). Unfortunately, the rest of the furcula has been lost and no further comment is possible. The omal ends of both coracoids are preserved. A deep, circular scapular cotyle is contiguous with a flat, oblong glenoid facet (Fig. 9). The ligamentous attachment site for Scapula the furcula at the tip of the acrocoracoid process is a deep The proximal end of the left scapula (Fig. 9) is well preserved. concave scar as opposed to the flattened surface in living The acromion process is subtriangular and is less slender penguins. This surface is also more medially orientated in

the fossil, while extant penguins show a more dorsal that in living penguins. A broken edge indicates the level orientation. An unusually deep ovoid fossa is present on of the procoracoid process, but the shaft is not complete the ventral face of the acrocoracoid process. This feature enough to reveal whether the procoracoid process parti- was reported as an autapomorphy of I. salasi by Clarke cipated in completely enclosing a coracoidal fenestra (Zusi, et al. (2007). The ovoid fossa is absent in extant penguins, 1975). The broken proximal edges of both coracoids reveal in which the ventral face of the acrocoracoid process is flat extremely thick cortical bone (~4.3 mm on the left side). or slightly indented. The ovoid fossa is also absent in other The centre of the shaft is filled with dense trabecular bone. fossil penguins examined in the present study, including isolated giant penguin coracoids from Seymour Island Humerus (UCMP uncataloged specimens), as well as Seymour Island coracoids assigned to Palaeeudyptes gunnari by Jadwiszczak Articulated skeletal remains are rare for fossil penguins, (2006). However, a similar fossa is present in IB/P/B-0454, a and I. salasi is the first described stem taxon to preserve coracoid assigned by Jadwiszczak (2006) to Anthropornis the entire wing. When articulated, the wing is quite grandis (personal communication, Piotr Jadwiszczak, 2008). straight. The angle between the humerus and radius/ulna It remains difficult to assign isolated elements to individual is significantly lower than portrayed in reconstructions of species of Seymour Island penguins, as all holotypes from other giant penguins (Marples, 1952: fig. 3; Jenkins, 1974: this locality are based on the tarsometatarsus and very few fig. 2). Interestingly, the angle between the humerus and articulated specimens have been reported. Regardless, distal forelimb in I. salasi is lower than would be predicted I. salasi does not form a clade with any of the Seymour from simply the orientation of the distal condyles of the Island taxa (Ksepka, 2007; Clarke et al. 2007), so the most humerus. The relative lengths of the humerus, ulna and parsimonious interpretation is that the ovoid fossa is a carpometacarpus are virtually identical to that seen in local autapomorphy of I. salasi that was acquired conver- ‘Duntroon Palaeeudyptes’. gently in the taxon represented by IB/P/B-0454. The The humerus (Fig. 10) is robust and osteosclerotic, with acrocoracohumerale ligament scar in I. salasi is similar to a square-shaped head and wide, straight shaft. In anterior

Fig. 10 Humerus of Icadyptes salasi (MUSM 897) in (A) posterior, (B) anterior, (C) proximal and (D) distal views. Abbreviations: atr, anterior trochlear ridge; cp, coracobrachialis posterior scar; dt, dorsal tubercle; fp, fossa for pectoralis insertion; ld, latissimus dorsi scar; mtr, middle trochlear ridge; ptr, posterior trochlear ridge; px, preaxial angle; rc, radial condyle; sc, m. supracoracoideus scar; sm, sesamoid of m. scapulotriceps tendon; tf, tricipital fossa; ts, transverse ligament sulcus; uc, ulnar condyle. Scale bars = 2 cm.

view, the proximal apex is placed near the middle of the distally. The anterior trochlear ridge projects further ventrally head, unlike the more ‘conical’ head of extant penguins, than the other two trochlear ridges. where the apex is displaced towards the ventral border. In Prior to repair, we were able to examine the cross-section proximal view, the head is reniform, but less strongly so of the humerus along a break. The cortical bone is osteo- than in extant penguins. The dorsal tubercle projects far sclerotic and there appears to be no true marrow cavity. proximally, but does not reach the same level as the apex Additionally, the area of densely meshed trabecular bone of the head. A deep transverse ligament groove incises the at the centre of the shaft is barely discernible. This gross humerus immediately distal to the head. The tricipital structure is most similar to that described for Aptenodytes fossa is apneumatic, single and has a small volume com- forsteri by Meister (1962) and more solid than observed in pared with shaft size as in large other Eocene penguins stem penguin fossils from the Eocene La Meseta Formation (Marples, 1952). A small area of the humerus is damaged, (Ksepka, 2007). Although examination of thin section samples obscuring the area of the capital incisure. is desirable for further study, the details observable support The shaft is stout and robust. Greatest width occurs the interpretation of the holotype individual as an adult directly distal to the tricipital fossa and the shaft narrows and also confirm that I. salasi had attained a degree of distally. Relative width and thickness exceeds that of all osteosclerosis comparable with that in extant penguins. known penguins except for Pachydyptes ponderosus, Platydyptes (P. novaezealandiae, P. marplesi and P. amesi) Sesamoid and Paraptenodytes robustus. A deep, oblong fossa on the anterior face of the shaft marks the insertion of m. pectoralis. An ovoid disc-shaped sesamoid for the tendon of m. On the posterior face, three prominent muscle insertion scapulotriceps is preserved in articulation with the humerus, scars are discernable. The m. supracoracoideus (pectoralis contacting the trochlea formed by the posterior and middle secondus of Marples, 1952) scar is proximally–distally elongate trochlear ridges. The sesamoid of this tendon is well devel- and orientated parallel to the long axis of the humerus. A oped in extant penguins. In extant penguins, a second smaller raised circular scar for insertion of m. latissimus dorsi arises sesamoid is also present for the tendon of m. humerotriceps. near the midpoint of the ventral edge of the humerus. The m. It is uncertain if this second sesamoid was absent in I. salasi coracobrachialis posterior (pectoralis tertius of Marples, or was lost from the holotype. The Pliocene taxon ‘Pygoscelis’ 1952) scar is wide and is orientated at an approximately tyreei (CM zfa22631) preserves both sesamoids in articula- 45° angle to the long axis of the shaft, nearly identical to tion with the humerus, and they are similar in shape to those the conformation in Pachydyptes ponderosus (MNZS of extant penguins. The number and morphology of wing 1450). This scar is orientated at a higher angle in the Burn- sesamoids remains poorly known in other fossil penguins. side Palaeeudyptes specimen (OM C48:73-81) and in one specimen of Palaeeudyptes gunnari (UCMP 321826) we Ulna examined. In Platydyptes amesi (OM C50:61) and a specimen referable to Palaeeudyptes klekowskii (UCMP 321023) the Like the humerus, the ulna (Fig. 11) is strongly compressed, orientation is similar to I. salasi. However, some intraspecific widened and shows marked osteosclerosis. The olecranon variation in the orientation of this muscle insertion does process is tab-like and strongly projected. Distally, the ventral occur, so its taxonomic utility is questionable. The preaxial condyle projects beyond the dorsal condyle. No quill knob angle is distinct, but not especially prominent. impressions or other demarcations of the attachment Two profoundly developed subcircular scars just proximal points for secondary feathers are preserved on the ulna. In to articular condyles on the anterior surface of the humerus some extant penguins, pit-like depressions mark these mark the entepicondylar ligament insertions. On the posterior attachment points along the ulnar shaft (Mayr, 2004). The surface the insertions of the ectepicondylar ligaments are anterior margin of the ulna is thick, unlike the narrow less strongly marked by three contiguous but discernible margin of extant penguins. Overall, the ulna of I. salasi scars. In anterior view, the radial and ulnar condyles are bears a strong resemblance to that of other giant Eocene orientated at a low angle to the main axis of the shaft. penguins, particularly Antarctic fossils assigned to Anthro- Although this arrangement suggests a high angle between pornis nordenskjoeldi and Palaeeudyptes klekowskii the humerus and distal forelimb, this is not the case when (Jadwiszczak, 2006) and the Burnside Palaeeudyptes speci- the wing bones are articulated. Distally, the ulnar condyle men from New Zealand. The olecranon in the Duntroon forms a prominent hemispherical articulation. Adjacent to Palaeeudyptes specimens is more distally placed and has a this condyle, a wide flat shelf, nearly equal to the width of more squared proximal corner. A foramen perforating the condyle at its base is present. Three well-developed the olecranon process is sometimes present in penguins, trochlear ridges form the borders of the trochlea for but no such foramen is discernible in I. salasi. Presence of the tendons of m. scapulotriceps and m. humerotriceps. this foramen is variable in extant penguins and has also The posterior trochlear ridge is directed ventrally while the been shown to be variable within at least one species of middle and anterior trochlear ridges are directed ventro- fossil penguin (Jadwiszczak, 2006).

Fig. 11 Wing elements of Icadyptes salasi (MUSM 897). Left radius in (A) dorsal and (B) ventral views, left ulna in (C) dorsal and (D) ventral views, left ulnare in (E) dorsal and (F) ventral views, and left radiale in (G) proximal and (H) distal views. Abbreviations: br, insertion of m. brachialis; ela, groove for tendon of extensor longus alulae; emr, impression from tendon of m. extensor metacarpi radialis; ol, olecranon; sup, insertion of m. supinator. Scale bars = 2 cm.

penguin from the Eocene of Seymour Island shows fan-like Radius expansion but does not preserve the distal angle (Marples, The radius (Fig. 11) is flattened and anteriorly bowed as in 1953). all other Sphenisciformes. Proximally, a roughened surface extending onto both the dorsal and the ventral faces of Carpometacarpus the radius marks the insertion of m. brachialis. The anterior edge of the radius curves smoothly to meet the proximal The carpometacarpus (Fig. 12) is completely intact. border, as in Duntroon Palaeeudyptes and Marplesornis Metacarpal II is strongly flattened and its anterior margin novaezealandiae. In Palaeospheniscus patagonicus and is gently bowed. A faint, raised scar is developed in the Platydyptes amesi, a shallow notch bounded by a proximally location of the pisiform process. The spatum intermetacar- directed spine is developed at the proximal part of the pale is long and slit-like. Metacarpals II and III are subequal anterior edge. In extant penguins, the development of the in distal extent, as in Waimanu tuatahi (see Slack et al. spine shows some intraspecific variation, but it is typically 2006), Perudyptes devriesi, Pachydyptes ponderosus and absent in Aptenodytes and present in other taxa. On the most other birds. Metacarpal III projects markedly distal to dorsal side of the radius, a shallow depression running metacarpal II in more crownward penguins including the length of the anterior border marks the course of the Duntroon Palaeeudyptes, Platydyptes marplesi and Palae- tendon of m. extensor metacarpi radialis, indicating a path ospheniscus patagonicus, as well as in Spheniscidae. At the for this tendon similar to that seen in extant penguins. proximoventral end of metacarpal III, a small but deep Distally, a deep groove incises the dorsal surface of the subcircular fossa is developed. This area is flat in extant bone near the midline. In extant penguins, m. extensor penguins, but a similar fossa is present in Pachydyptes longus alulae creates this groove as it traverses the radius ponderosus, Duntroon Palaeeudyptes and also in a large to insert on the anterior edge of the proximal end of the carpometacarpus assigned to Anthropornis nordenskjoeldi carpometacarpus. by Simpson (1971a). The distal articular surfaces of metacarpals II and III are suboval. Metacarpal III expands slightly over the distal third of its length. The course of flexor digitorum Carpals minoris can be traced on the ventral surface of metacarpal The ulnare (Fig. 11) is a subtriangular element exhibiting III continuing into a groove on the posterior surface of the the fan-like expansion of extant penguins. The anterior bone distally. Demarcation of the insertion of this muscle angle of the ulnare fits wedged between the intercondylar on phalanx III-1 is also preserved. sulcus of the ulna and the proximal end of the carpomet- The most striking feature of the carpometacarpus is the acarpus. The anterior angle and the proximal angle are similar presence of a distinct subtriangular facet-like surface at to those in extant penguins. The distal angle, however, is the distal end of metacarpal I. Although this facet would much more blunt and less projected. The radiale (Fig. 11) suggest the retention of a free alular phalanx, no such element is shaped like an irregular disc. The proximal and distal faces was found with the specimen. We originally attributed the are gently concave. The carpals are unknown for most other lack of a preserved alular phalanx to true absence (Clarke fossil penguins, although Marplesornis novaezealandiae et al. 2007). However, given additional ontogenetic data possesses carpals essentially identical to those of crown we now suspect an alular phalanx was originally present, penguins. A broken ulnare belonging to a very large but lost post-mortem (see below).

Fig. 12 Carpometacarpus and phalanges of Icadyptes salasi (MUSM 897) in (A) dorsal and (B) ventral views. Abbreviations: af, articular facet for alular phalanx; dp, depression (see text); fdIII, groove for flexor digitorum III; II-1, phalanx II-1; II-2, phalanx II-2; III-1, phalanx III-1. Scale bar = 2 cm.

prey items. The robust cervical column, narrow skull and hyper-elongate beak of I. salasi provide the most compelling morphological evidence to date for a spear-diving ecology for giant penguins. Presumably, the inferred powerful cervical musculature would facilitate striking prey and would also resist forces of impact and struggling prey. Extant penguins have thick, solid rhamphotheca that give them more robust beaks than would be apparent from the skull alone (Fig. 14). While the rhamphotheca remains unknown for fossil penguins, the texture of the Fig. 13 Phalanx II-2 of Icadyptes salasi (MUSM 897) in ventral view. bony beak may provide insight into the nature of the Abbreviation: ol, ossified ligament. Scale bar = 1 cm. overlying soft tissue. Extant penguins have a beak tip marked by numerous neurovascular foramina. However, the pronounced reticulate vascular texturing on the beak Phalanges of I. salasi is unknown in any other penguin. In extant Digit II comprises two phalanges and digit III a single seabirds that show this texturing, such as Fregata (frigate- phalanx. Phalanx II-1 is rectangular with a convex dorsal birds) and Sula (boobies), the rhamphotheca is very thin face and flat ventral face. Phalanx II-2 is shorter, slightly and is made up of multiple layers closely applied to the posteriorly curved and tapers to a point. A small portion of bone (Fig. 14). Diomedea and Phoebastria (albatrosses) the ossified flexor digitorum minoris ligament is preserved show a similar but less pronounced vascular texturing on the ventral side of this phalanx (Fig. 13). Phalanx III-1 along parts of the upper beak. We propose that I. salasi lacks the proximally projected tubercle developed in extant may have had a thin rhamphotheca tightly fitted to the penguins. Phalanx III-1 is much shorter than phalanx II-1, bony beak based on these observations. the typical avian condition. However, in extant penguins Giant penguin beaks have previously been reported these phalanges are nearly equal in length. Phalangeal from the Eocene of Seymour Island, Antarctica (Olson, 1985; proportions remain unknown in other stem penguins. Myrcha et al. 1990; Jadwiszczak, 2003), and New Zealand Together with the less projected metacarpal III, the short (Fordyce & Jones, 1990). The beak in USNM 244152, the phalanx III-I gives the wingtip of I. salasi a more tapered specimen described by Olson (1985), is clearly elongate shape than that of extant penguins. and straight, although its exact proportions are unknown because it is incomplete posteriorly. Descriptions of another Seymour Island specimen (IB/P/B-0167) by Myrcha et al. Discussion (1990) and Jadwiszczak (2003) correspond to the morphology of USNM 244152. Although elongate and tapering, these Beak structure and feeding ecology Antarctic specimens exhibit a less solid and spear-like Following the discovery of giant penguin beak remains in construction than seen in I. salasi. For example, the pre- Antarctica (Olson, 1985), the feeding ecology of these maxillae are not ankylosed ventrally for the anterior half of forms has been the subject of much interest. Olson (1985) their lengths at least in USNM 244152. We were not able and Myrcha et al. (1990, 2002) considered the long, straight to examine IB/P/B-0167 directly, but the external nares morphology of these beaks to be suited for spearing large extend much further anteriorly in both IB/P/B-0167 and

Fig. 14 Skulls of the sulid Morus capensis (A, C) and the penguin Spheniscus humboldti (B, D) with rhamphotheca attached (A, C) and removed (B, D).

USNM 244152 than in I. salasi, contributing to a less solid morphology. Although the Seymour Island beaks cannot be assigned with confidence to particular species, the morphology of the beaks of Perudyptes devriesi and Waimanu tuatahi suggests that an elongate beak is primitive for penguins and was retained for a long phylogenetic interval of early penguin evolution (Clarke et al. 2007). Nevertheless, the solid spear-like construction in I. salasi is here reaffirmed as apomorphic. A partial mandible found with the holotype of Archae- ospheniscus lowei (OM C 47:20) was considered to belong to a non-sphenisciform bird by Marples (1952). Marples’s Fig. 15 Carpometacarpus of immature Spheniscus magellanicus concern stemmed from the elongate symphysis of the (AMNH 10898) illustrating the incompletely fused components of this element. Abbreviations: I-1, alular phalanx 1; mcI, metacarpal I. mandible, which was unlike any penguin known at the Scale bar = 1 cm. time. A furcula was also collected with OM C 47:20, and was assigned to a small albatross by Marples (1946), although Olson (1985) considered this assignment to be carpometacarpus, extending nearly to the distal end of doubtful. Regardless of the status of the furcula, no pro- the bone. Later in ontogeny, the alular phalanx fuses to cellariiform possesses a mandible with a greatly elongated metacarpal II, contributing to the smoothly curving anterior symphysis, and the mandible was not referred to an border of the bone. albatross by Marples (1946). New discoveries including In light of ontogenetic information, the presence of a I. salasi and Waimanu tuatahi reveal that an extensive man- distal facet on metacarpal I in I. salasi suggests a free alular dibular symphysis occurred in stem penguins, and appears phalanx was present in this species. In agreement with this to have been widely distributed (Slack et al. 2006; Clarke hypothesis, the anterior border of metacarpal II is thick as et al. 2007). Given this new knowledge of fossil penguin in most non-sphenisciform birds, rather than showing the anatomy, and the match in size, style of preservation and sharp edge formed by the fused alular phalanx in extant colour between the partial mandible and the remaining penguins. Unfortunately, no trace of the alular phalanx elements of OM C 47:20, the mandible may be considered was recovered during preparation. It is probable this deli- to belong to the holotype individual of Archaeospheniscus cate bone was displaced from the slightly disarticulated lowei. specimen. A similar morphology of the carpometacarpus is seen in Waimanu tuatahi (see Slack et al. 2006) and Burn- side ‘Palaeeudyptes’, suggesting these taxa also retained a The alular phalanx of penguins free alular phalanx. Accounts of the fate of the alular phalanx in penguins In several extant diving birds, the alula is employed during have varied. Watson (1883: 35) considered the alular underwater locomotion. Loons, although primarily foot- phalanx to be absent in extant penguins. Pycraft (1907) propelled divers, are known to use the alula as a stabilizer reported the alular phalanx to be free embryonically but while turning (Barr, 1996). The alula is extended (although fused to metacarpal II in the adult. O’Hara (1989: 50) the primaries remain tightly held against the body) by considered the alular phalanx to be completely fused to diving ducks of the genus Melanitta (Books, 1965). Whether the proximal phalanx of digit II. Examination of a juvenile a free alula retained any active role in manoeuvring in early specimen of Spheniscus magellanicus shows that Pycraft penguins is unclear. A full appreciation of any potential (1907) was correct. Early in ontogeny, the alular phalanx is functional significance of a free alular phalanx would present as an elongate, thin tapering element (Fig. 15). require knowledge of the feathers anchored to this bone, This element is proportionally very long relative to the but no fossil penguin with integumentary remains has yet

been reported. It is also possible that this diminutive spear-like beaks. Convincing explanations for the extinction element was essentially vestigial in basal penguins. of giant penguins remain elusive. Giant species persisted well into the Oligocene, at least in New Zealand where the large Archaeospheniscus lopdelli and Duntroon Pal- Giant penguin evolution aeeudyptes occur in late Oligocene deposits (Marples, 1952; Giant penguins were quite widely distributed throughout Fordyce & Jones, 1990). Giant forms possibly cross the the Palaeocene. In addition to I. salasi from approximately Eocene–Oligocene boundary in southern South America as 14°S, a few bones of the very large penguin Arthrodytes well, although this hinges on whether the age of Arthrodytes andrewsi have been described from higher latitudes andrewsi is late Eocene or early Oligocene (Acosta Hospi- (~50°S) on the Atlantic coast of South America (Ameghino, taleche, 2005). In Antarctica and Australia, the penguin 1901, 1905; Acosta Hospitaleche, 2005). Giant forms are record is too discontinuous to estimate the last occurrence also known from the Antarctic Peninsula (Wiman, 1905; of giant forms. Given the late survival of giant penguins in Marples, 1953; Simpson, 1971a; Myrcha et al. 2002), the at least some localities, their disappearance cannot be linked North and South Islands of New Zealand (Marples, 1952; to abrupt Eocene/Oligocene global cooling (Clarke et al. Simpson, 1971b; Fordyce & Jones, 1990; Fordyce, 1991) and 2007). One intriguing possibility (Simpson, 1976; Olson, the southern coast of Australia (Simpson, 1957; Jenkins, 1974). 1985) is that competition from cetaceans factored into the Phylogenetic analyses do not support a single clade of extirpation of the largest penguins. Testing this hypothesis giant penguins, but instead recover a paraphyletic grade would require increased understanding of the ecological of stem sphenisciforms that includes all giant taxa (Clarke niche of giant penguins and the timing of their disappearance et al. 2007). Large size is presently optimized as having from all continents. evolved deep in the penguin tree, and retained over a large part of penguin phylogeny. Depending on how polytomies are resolved, the topology is consistent with at Acknowledgements least one reversal to smaller size. This pattern reflects our Discussions with Marcelo Stucchi were instrumental in improving current understanding of trends in penguin body size, but this manuscript and are noted with much appreciation. This paper may be partially shaped by artefacts of the fossil record. also benefited from careful reviews by R. Ewan Fordyce and Piotr The dearth of well-known smaller Palaeogene penguins Jadwiszczak. We gratefully acknowledge Rodolfo Salas, Niels may reflect a real rarity or be preservation driven. Some Valencia, Dan Omura, Julia Tejada, Walter Aguirre and Eusebio Díaz small taxa currently known with certainty only from single of the Museo de Historia Natural, Universidad Nacional Mayor de bones (e.g., Korora oliveri and Duntroonornis parvus) co- San Marcos, Leonard Brand of Loma Linda University and Cesar Aguirre for contributions to fieldwork. We thank Sue Heath (OM), occur with giant penguins, but cannot be reliably placed Alan Tennyson (MNZS), Paul Scofield (CM), Joel Cracraft, Paul phylogenetically. These taxa have the potential to alter Sweet and Peter Capainolo (AMNH), Mark Florence and Storrs our interpretations should new material be discovered. Olson (USNM), and Pat Holroyd (UCMP) for access to comparative It remains uncertain whether I. salasi inhabited equa- specimens, and R. Ewan Fordyce and Tatsuro Ando (Otago University) torial regions throughout the year or journeyed to low for generous access to published and unpublished material. Support latitudes seasonally, perhaps for breeding. Some extant for this project from the National Geographic Society Expeditions penguin species (e.g. Megadyptes antipodes, Spheniscus Council, National Science Foundation Office of International Science and Engineering and North Carolina State University to J.A.C. and mendiculus) are sedentary, returning to shore each night, from the Frank M. Chapman Memorial Fund, Doris O. and Samuel while others (e.g. Aptenodytes forsteri) range over vast P. Welles Fund, and AMNH Division of Paleontology to D.T.K. is areas of the oceans over the course of the year. The single gratefully acknowledged. known specimen of I. salasi provides only one data point to be brought to bear on distribution patterns. 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