Geo log i cal Quar terly, 2013, 57 (4): 567–582 DOI: http://dx.doi.org/10.7306/gq.1112

Eocene rel a tives of icefishes (: Notothenioidei) from Sey mour Is land, Antarctica

Ma³gorzata BIEÑKOWSKA-WASILUK1, *, Niels BONDE2, 3, Pe ter Rask MLLER4 and Andrzej GAZDZICKI5

1 Fac ulty of Geol ogy , Uni ver sity of War saw, ¯wirki i Wigury 93, 02-089 Warszawa, Poland 2 In sti tute of Geog ra phy and Geol ogy , Uni ver sity of Co pen ha gen, Voldgade 10, DK-1350 Co pen ha gen K, Den mark 3 Fur Mu seum, Nederby, DK-7884 Fur, Denmark 4 Natu ral His tory Mu seum of Den mark, Uni ver sity of Co pen ha gen, Universitetsparken 15, DK-2100 Co pen ha gen , Den mark 5 In sti tute of Paleobiology, Pol ish Acad emy of Sci ences, Twarda 51/55, 00-818 Warszawa, Poland

Bieñkowska-Wasiluk M., Bonde N., MÝller P.R. and GaŸdzicki A. (2013) Eocene rel a tives of cod icefishes (Perciformes: Notothenioidei) from Sey mour Is land, Antarctica. Geo log i cal Quar terly, 57 (4): 567–582, doi: 10.7306/gq.1112

Fragmen tary skull bones and ver tebra from the Upper Eocene La Meseta Forma tion on Seymour (Marambio) Is land, Ant arc - tic Pen in sula have been de scribed as gadiform fishes, infor mally named “Mesetaichthys”. Here we de scribe jaws as Mesetaichthys jerzmanskae n. gen. and n. sp., and re fer this taxon to the perciform suborder Notothenioidei. This group is al - most un known as fos sils. Sim i lar i ties to the liv ing, “prim i tive” nototheniid Dissostichus eleginoides are in di cated in the dentition. Gadiform evo lu tion in the Paleocene–Eocene is dis cussed, and the pos si bil ity of a corre la tion be tween the ori gin and evo lu tion of notothenioids in con nec tion with the dete ri ora tion of the climate in Antarctica during the Late Eocene–Oligocene is con cluded.

Key words: Notothenioids, cod icefishes, Eocene, Seymour Is land, Antarctica.

INTRODUCTION land in the aus tral sum mer of 1991–1992. The col lec tion com - prises 45 spec i mens and is housed at the In sti tute of Paleo - biology, Polish Acad emy of Sci ences, Warszawa under cat a - Some frag men tary fish fossils from the upper La Meseta logue num ber ZPAL P.V./1–45; all from the lo cal ity ZPAL 3, For ma tion (Up per Eocene) of Seymour Island (Isla Telm7, up per most Eocene (Figs. 2 and 3). Vicecomodoro Marambio), West Antarctica (Fig. 1), have been We pro vide de scrip tions of the jaw frag ments (part den ta - re ferred to Gadiformes by Jerzmañska and Œwidnicki (1992). ries and dermarticulars – “angulars” and premaxillaries), a We in tend to show that these fishes are the al most only known basioccipital and iso lated ver te brae pre vi ously in for mally na - fos sil rep re sen ta tives of cod icefishes’ rel a tives, the perciform med by Jerzmañska and Œwidnicki (1992) as “Mesetaichthys”. suborder Notothenioidei. Large jaw frag ments are described as There are four premaxillae (ZPAL P.V./1–4), 12 den ta ry frag - Mesetaichthys jerzmanskae n. gen. and n. sp. ments (ZPAL P.V./5–16), seven dermarticulars (ZPAL The palaeontological data pro vides new in sights into the P.V./17–23), a basioccipital (ZPAL P.V./24), and 21 ver te brae Ant arc tic Eocene fish com mu ni ties, and the or i gin of cod (ZPAL P.V./25–45). icefishes, and the op por tu nity to re late their evo lu tion to the cli - ma tic changes dur ing the Late Eocene to Pleis to cene, re call ing that this group, to day is found dom i nat ing in the South ern GEOLOGICAL AND STRATIGRAPHICAL Ocean, and is clearly adapted to cold wa ters. SETTING The stud ied spec i mens were col lected by A. GaŸdzicki and A. Tatur dur ing the Ar gen tine-Pol ish Field Party on Seymour Is - The Eocene La Meseta For ma tion, which crops out in the north east ern por tion of Seymour Is land (Fig. 1), is a 720 m thick se quence of richly fossiliferous, shal low-ma rine, deltaic and/or estuarine poorly con sol i dated clastic strata (Figs. 2 and 3), ac- * Corresponding author, e-mail: [email protected] cu mu lated within an in cised val ley (Sadler, 1988; Porêbski, Received: March 8, 2013; accepted: June 3, 2013; first published 1995; Marenssi et al., 1998; Marenssi, 2006; Tatur et al., 2011). online: 8 July, 2013 The for ma tion pre serves an ex cep tional re cord of a shal - 568 Ma³gorzata Bieñkowska-Wasiluk, Niels Bonde, Peter Rask MÝller and Andrzej GaŸdzicki

Fig. 1. Geo log i cal sketch map of the north ern part of Sey mour Is land (sim pli fied from Sadler, 1988) show ing the local ity ZPAL 3 where speci mens Mesetaichthys jerzmanskae n. gen. and n. sp. were collected

low-ma rine eco sys tem (Feldmann and Woodburne, 1988; Stil- The geochem i cal anal yses made on the fos sil bi valve shells well and Zinsmeister, 1992; GaŸdzicki, 1996, 1998, 2001; Dzik from the La Meseta For ma tion sug gest a cli ma tic cool ing event and GaŸdzicki, 2001; Francis et al., 2006; Uchman and GaŸdzi - dur ing the time of de po si tion of the up per most part of the for ma - cki, 2006; Ivany et al., 2008; GaŸdzicki and Majewski, 2012). tion (GaŸdzicki et al., 1992; Din gle et al., 1998; Ivany et al., Sadler (1988: fig. 1) iden ti fied seven numbered lithological 2006, 2008; Cione et al., 2007; Francis et al., 2009; B³a¿ejowski units (Telm1–Telm7) within the for ma tion, and this sub di vi sion et al., 2010). This is cor re lated with the first Ce no zoic gla ci ation is ac cepted here (Fig. 2). For dif fer ent sub di vi sion schemes and of Antarctica and with the open ing of the Drake Pas sage at the their strati graphi cal cor re la tion see Elliott and Trautman (1982), Eocene-Oligocene bound ary (Zachos et al., 2001; Birkenmajer Marenssi et al. (1998: fig. 4) and Marenssi (2006: fig. 5). The et al., 2005). The up per bound ary of the Telm7 is an un con - Mesetaichthys-bear ing strata rec ognized within Telm7 (Figs. 2 formity with the Late Mio cene Hobbs Gla cier For ma tion and 3) con sists of about 3 m thick fine grained green-gray sand- (Marenssi et al., 2010) or the post-Late Plio cene Weddell Sea stone, mudstone and shell beds. These strata con tain the stud - For ma tion (Fig. 2; GaŸdzicki et al., 2004). ied fish Mesetaichthys, the isocrinid Metacrinus fossilis (Ras - mus sen, 1979; Baumiller and GaŸdzicki, 1996: fig. 2), and the bi valves Hiatella and Mya (Fig. 2). It is prob a bly the same ho ri - NOTOTHENIOIDS FROM THE LA MESETA FORMATION zon in which the fish ver te bra de scribed by Jerzmañska (1988: fig. 1) were found. In this part of the forma tion were also found Notothenioids are the dom i nant and most di verse fishes two large “land-birds” (Case et al., 1987; Tambussi et al., 1994; around Antarctica to day (East man, 2000). One would prob a bly Case, 2006; Cenizo, 2012), nu mer ous bones of pen guins (Sim- expect to find this group in the Paleogene, es pe cially in the pson, 1971; Myrcha et al., 2002; Jadwiszczak, 2006, 2009, Eocene La Meseta For ma tion on Seymour Island, the only 2010, 2012; Jadwiszczak and Mörs, 2011) and whale re mains known ma rine strata with fos sil fishes in Antarctica (Wood ward, (Borsuk-Bia³ynicka, 1988; Mitch ell, 1989; Fostowicz-Frelik, 1908; Welton and Zinsmeister, 1980; Grande and East man, 2003). Myrcha et al. (2002: fig. 2) and Tambussi et al. (2006: ta - 1986; Feldmann and Woodburne, 1988; Jerzmañska, 1988, bles 3, 4) sum ma rized the in ver te brates and ver te brates of the 1991; Ward and Grande, 1991; East man and Grande, 1991; Telm7 (= Submeseta Allomember). Long, 1991, 1992a, b, c; Jerzmañska and Œwidnicki, 1992; The Mesetaichthys-bear ing strata (ZPAL 3: GPS po si tion: Cione et al., 1994, 2001; Crame, 1994; Cione and Reguero, S 64°14’13.197’’, W 56°38’12.014’’, ~157 m a.s.l.; see Fig. 3) 1994, 1995, 1998; Doktor et al., 1988, 1996; Woodburne and can be cor re lated with the Submeseta Allomember Case, 1996; Reguero et al., 2002; Kriwet and GaŸdzicki, 2003; (36.0–34.2 Ma – see Marenssi, 2006: fig. 5) and the Anthro - Kriwet, 2005; Kriwet and Hecht, 2008). Wood ward (1908) iden - pornis nordenskjoeldi Biozone (Tambussi et al., 2006: fig. 2b; ti fied some iso lated ver te brae as , but their cur rent see also Jadwiszczak, 2006). The age of the top of the La tax o nom i cal sta tus re mains un clear (Grande and East man, Meseta Fm. (Telm 7) is dated as 34.2 Ma, close to the Eocene- 1986; East man and Grande, 1989). -Oligocene bound ary (Marenssi, 2006). Eocene relatives of cod icefishes (Perciformes: Notothenioidei) from Seymour Island, Antarctica 569

Fig. 2. Strati graphic col umn of the Eocene La Meseta For ma tion on Seymour Is land show ing li thol ogy and dis tri bu tion of in ver te brate and ver te brate fos sils

As terisk shows the stratigraphic level of the Mesetaichthys jerzmanskae n. gen. and n. sp.; mod i fied from Myrcha et al. (2002: fig. 2) 570 Ma³gorzata Bieñkowska-Wasiluk, Niels Bonde, Peter Rask MÝller and Andrzej GaŸdzicki

and at many of the South Ocean is lands – is known to reach a TL of 215 cm (Duhamel et al., 2005). This is the larg est notothenioid, prob a bly ex ceed ing 100 kg. In ter est ingly, this spe cies has just once been caught off Green land (MÝller et al., 2003; see Fig. 15), and it is the only notothenioid ever found north of the Equa - tor. Most of the notothenioids are much smaller reach ing less than half a metre in length (see Fig. 14). Osteological and phylogen etic studies of living notothe - nioids were pre sented by Balushkin (1984, 1992, 2000) and Voskoboinikova (1994, 1997, 1998), who also stud ied the on - tog eny of the skel eton (Voskoboinikova and Bruce, 2001). Andersen (1984) stud ied the and their clas si fi ca - tion and Iwami (1985) the Channichthyidae. However, pub - lished de tails concern ing the skull anat omy, and teeth are diffi - cult to find (only premaxillaries with teeth are shown by Balu - shkin, 1984). Greg ory (1933) had published quite a few noto - Fig. 3. View of the local ity ZPAL 3 (aster isk), thenioid skulls, in clud ing the primi tive Eleginops that was re- Telm7 (= Submeseta Allomember), Late Eocene ferred by Balushkin (1992) to its own monotypic fam ily. The mo - lec u lar ev i dence for their re la tion ship is dis cussed by Lecointre Pho to graph by A. GaŸdzicki, Feb ru ary 1992 et al. (1997), Ritchie et al. (1997), DettaÎ and Lecointre (2004) and Near (2004) us ing the fossil Proeleginops to cal i brate the The most valid re fer ral of fos sils to the notothenioid group is mo lec u lar clock for notothenioid or i gins. that by Balushkin (1994), who redescribed a part of a skull orig i - nally referred to Gadiformes by East man and Grande (1991), and in cluded it in the prim i tive notothenioid, Eleginopsidae Gill EARLY GADIFORMS (see Balushkin, 1992). It was the first de ter mined fos sil noto - thenioid, which Balushkin (1994) named Proeleginops gran - Tra di tion ally gadiforms are sup posed to have orig i nated in deastmanorum. East man (2000) had been re luc tant to ac cept the north (Svetovidov, 1948). The old est known gadiform and the the mis iden ti fi ca tion, but later he ap par ently ac cepted it (see only Paleocene skel e ton as sign able to this or der is a com plete Claeson et al., 2012). Arratia et al. (2004: p. 48) did not rec og- fish from the Danian of West Greenland (Rosen and Patterson, nize Balushkin’s re vi sion. Proeleginops grandeastma norum 1969; Co hen, 1984). The ear li est di ver si fi ca tion of the gadiforms from local ity RV 8200 in Telm5 (Case, 1992, 2006) which is is re corded by skel e tons from the ear li est Eocene Fur For ma tion Mid dle Eocene, ca. 45 Ma in age (Case, 2006; Marenssi, of Den mark (Bonde, 1987, 1997; Bonde et al., 2008, 2011). In 2006), is the old est known notothenioid, some 10 m.y. older the Lon don Clay (late Early Eocene), there are two taxa of skel e- than the ma te rial de scribed here. tal gadiforms, the merlucciid Rhinocephalus and the merlucciid- Grande and East man (1986) in a re view of all known Ant- like teeth called Trichiurides (Casier, 1966; Rosen and Patter - arc tic ichthyofaunas, dis cussed the like li hood that jaw frag- son, 1969); there are also five otolith spe cies (Casier, 1966). ments and ver te bral centra from Upper Eocene of the La The gadiform otolith re cord is very differ ent from that of the Meseta Fm. could be notothenioids – a pos si bil ity the authors skel e tons (Casier, 1966; Patterson, 1993). From the “Coral nat u rally ex pected. They found no pos i tive in di ca tions, that al- Lime stone” of Faxe (Mid dle Danian, Early Paleocene, Den - lowed “...a de fin i tive di ag no sis of this group...” al though they did mark) a few ju ve nile in de ter mi nate gadiforms are known stress dis tinct sim i lar i ties be tween some of the fos sil ver te brae (Schwarzhans, 2003). In the Dan ish Early Selandian (Middle and those notothenioid Dissostichus. Grande and East man Paleocene) as many as eight spe cies of gadiforms were found: (1986: fig. 5) fig ured two premaxillary frag ments and two denta - three macrourids and five spe cies in four gadoid fami lies. One ry fragments from the Field Mu seum of Natu ral His tory, Chi - Dan ish eulichthyid is known also from the Paleocene–Eocene cago col lec tion (FMNH), and de ter mined the for mer as “...a of the United King dom and Bel gium (Schwarzhans, 2003). Two gadiform type...”, while the den ta ries were de scribed as “...in de - macrourids and two gadoid spe cies were found in Selandian, ter mi nate tele osts...”. The lat ter, how ever, are now called “...de - West Green land (Schwarzhans, 2004). fin i tively Merlucciidae...” by Claeson et al. (2012). In South Aus tra lia and New Zea land the ear li est gadiform oto liths are from the Mid dle Paleocene (Selandian; a macrourid RECENT NOTOTHENIOIDS of the living ge nus Nezumia, Schwarzhans, 1985), and 3 spe - cies are known from Early Eocene (Schwarzhans, 1980). Bregmacerotids and prim i tive Euclichthys-like ga doids were Grande and East man (1986: p. 130) dis cussed the size of found in Late Eocene. Macruronus oto liths are known from the the Eocene fishes based upon the larg est of the ver te brae in the Eocene of South Aus tra lia (Schwarzhans, 1981). Field Mu seum of Natu ral His tory, Chi cago, which is “...gen er ally Kriwet and Hecht (2008) pro vided a re view of early gadi- sim i lar to those of the Re cent nototheniid Dissostichus forms and de scribed a macrourid skull with oto liths in situ from mawsoni...”, the Ant arc tic toothfish. This spec i men is a cau dal La Meseta Fm (Telm3–5), an excep tional pres er va tion. Rattail centrum 4.7 cm in diam eter and 3.3 cm long. Grande and East - skel e tons apart from that skull are un known from the Paleocene man (1986) com pared the size of this ver te brae to size of ver te - and Eocene. Kriwet and Hecht (2008) ac cepted the de ter mi na - brae of D. mawsoni and knowing the size of D. mawsoni they es- tions as gadiforms by East man and Grande (1991) and ti mated that fos sil fish had a stan dard length (SL) of ca. 2 m. That Jerzmañska and Œwidnicki (1992) for jaws from the La Meseta was more than known at that time for D. mawsoni as the larg est For ma tion. Jerzmañska (in Doktor et al., 1996: figs. 11 and 12) notothenioid in the Ant arc tic wa ters. This larg est fish caught by has iden ti fied scales of gadiforms in the lower part of the La East man and DeVries (1981) had a to tal length (TL) of 163 cm. Meseta Fm. (Telm2, Early Eocene). Balushkin’s ar gu ment To day the more north ern spe cies D. eleginoides – which is found (1994), that south ern gadiforms are un likely already in “Late along the coast of south ern South Amer ica from Peru to Uru guay Eocene”, be cause they orig i nated in the north thus is irrevelant. Eocene relatives of cod icefishes (Perciformes: Notothenioidei) from Seymour Island, Antarctica 571

Fig. 4. Left den ta ry, ZPAL P.V./5, holotype of Mesetaichthys jerzmanskae n. gen. and n. sp., dusted with am mo nium

A – lat eral, B – me dial, C – dorsal, D – ven tral view; photo graphs by G. Dziewiñska

SYSTEMATIC PALAEONTOLOGY

Or der Perciformes Suborder Notothenioidei Fam ily incertae sedis Ge nus Mesetaichthys nov. Type specie s. – Mesetaichthys jerzmanskae sp. nov., only known spe cies. La Meseta For ma tion, Late Eocene, Sey mour Is land, Ant arc tic Pen in sula. Der i va tion of name. – From the La Meseta Fm. and Greek ichthys means fish. The name was used in for mally by Jerzmañska and Œwidnicki (1992: p. 246). Diagnosis. – As for the type and only spe cies. Strati graphic and geo graphic range. – La Meseta For ma tion (Telm7), Late Eocene, Seymour Is land, Antarctica.

Mesetaichthys jerzmanskae sp. nov. (Figs. 4–11) Holotype. – ZPAL P.V./5, a large frag men tary, but nearly com plete den ta ry (Figs. 4, 5 and 6F). Paratypes. – ZPAL P.V./1 and 2, proxi mal fragments of premaxillae (Fig. 7). Material. – Re ferred mate ri als are dis cussed be low af - ter the rel e vant de scrip tions. Fig. 5. Left den ta ry, ZPAL P.V./5, holotype of Mesetaichthys Type horizon. – Telm7 of the La Meseta For ma tion, jerzmanskae n. gen. and n. sp. Late Eocene. Type locality. – ZPAL 3, Seymour Island, Antarc tic A – lat eral, B – me dial, C – dorsal view; Pen in sula (Figs. 1 and 3). drawings from Jerzmañska and Œwinicki (1992) Der i va tion of names. – Named in honour of the late Pol ish palaeoichthyologist Prof. Dr. Anna Jerzmañska (see dle of the den ta ry. Wide open groove for the man dib ular sen - El¿anowski, 2003). sory canal (Figs. 4–6F). Diagnosis. – The most char ac ter is tic fea ture is the Description. dentition with strong, con i cal, slightly bent and pointed teeth stand ing on large bony pedicles (Figs. 4–8). Teeth mostly with Holotype (The large denta ry) . The larg est den ta ry frag- an in ter nal cav ity with lon gi tu di nal ridges mir ror ing the ex ter nal ment (ZPAL P.V./5; Figs. 4–6F) is about 10 cm long, and a few ridges and fis sures in the “enameloid” at the base of the teeth centi metre are miss ing from the pos te rior end of the den tal proper. Teeth in one row, fang-like teeth in the premaxilla at the edge and the ven tral branch. The bone is about 1 cm wide at the symphysis, but teeth di min ish ing back wards. Small teeth at the dental edge where strong, con i cal teeth are fused to high, bony den ta ry symphysis, but very large “ca nines” at least in the mid - pedi cles in a shal low groove (see Moy-Thomas, 1934; Fink, 572 Ma³gorzata Bieñkowska-Wasiluk, Niels Bonde, Peter Rask MÝller and Andrzej GaŸdzicki

rior surface al most in tact, about 15 mm high, and slightly bent inwards, in di cat ing that the angle be tween the two denta ries must have been a very obtuse one. This in di cates a very blunt and rounded snout with out any fusion be tween the two bones, but rather a thin car ti lage. The lat - eral sur face of the bone shows a weak “bulge” or con vexity below the interspace be tween teeth num ber four and five, and fur ther an te ri orly there is a slight de pres - sion be low the three an te rior teeth (Figs. 4A and 5A). The sur face of this part and the strong lat eral ridge has a fine and some what ir - reg ular or nament of thin grooves and ridges be com ing a lit tle coarser and straighter on the pos te rior part of the lat- eral ridge (Fig. 4A). This or na ment, not shown in the draw ing (Fig. 5A), is the rea - son for as sum ing that the bones de - scribed here, e.g. the premaxillaries and dermarticulars are prob ably from the same spe cies. The or na ment is not well- de vel oped on the in side of the den ta ry (Fig. 4B), where there are only very faint and al most straight lon gi tu di nal grooves and ridges. The exter nal face of the ven - tral lamina is or na mented by much stron- ger and more reg u lar lon gi tu di nal gro oves and ridges (Figs. 4A and 5A). The open groove for the man dib ular sen sory canal Fig. 6. Den ta ry frag ments of Mesetaichthys jerzmanskae n. gen. and n. sp is quite smooth and rounded, it is deep est A–E – dusted with ammo nium; A–C – ZPAL P.V./9 in lat eral, me dial and dor sal views; D, E – at the poste rior margin of the den ta ry and ZPAL P.V./11 in lat eral and dorsal views; F – ZPAL P.V./5, the holotype in pos terior view to seems to dis appear into a fora men near show the large in ternal cav ity and the open sensory canal; pho to graphs by P.R. MÝller the an te rior margin of the den ta ry (Fig. 4D). The lat eral wall of this groove is formed by the thick ridge. There are nerve 1981). Along the mid dle part of the lat eral face of the bone a fo ram ina for the sen sory “buds” in the ca nal at the top of the open very strong, broad ridge is run ning smoothly into the strong groove (Fig. 4D), at least four can be seen (they are mislead ingly symphyseal re gion, mak ing the bone al most 2 cm wide be low called “...ven tral sen sory ca nal pores...” in Claeson et al., 2012: the last pre served tooth. Above this ridge along the laterodorsal fig. 4). mar gin there is a broad, dis tinct but rather shal low groove end - The three pos te rior large and very robust teeth pre served ing near the symphysis of the den ta ry, at two nerve fo ram ina, are widely spaced. Be tween them are dis tinct de pres sions from be low the stron gest ca nine tooth. The first nerve fo ra men is ca. teeth hav ing fallen out. Prob a bly two teeth are miss ing be tween 1 mm in di am e ter, just pos te rior to and be low the pos te rior face the two ante rior large teeth. Each tooth is con i cal, bent in wards of this tooth, and the sec ond is 2 mm in di am e ter, be low the an - and it is con tin u ing the shape of its bony pedicle. The tooth's te rior margin of the tooth, it is run ning into a forwardly di rected “shin ing” enamel-like cover has an or na ment of fine and thin ca nal (the mental fo ra men). The pos te rior end of this groove is grooves at the base dis appear ing to wards the tip of the tooth. lo cated at the lat eral in ci sion (Fig. 5A), the dor sal rim of which These fine grooves were de scribed by Jerzmañska and seems to be the nat ural thin edge of the bone (that tightly cov- Œwidnicki (1992: p. 245) as “...ra di at ing from the tip to half or at ered the miss ing dermarticular’s ante rior pro cess), while the an - least 1/3 height of the tooth...”, be cause ap par ently they did not te rior and ven tral edges of this in ci sion are bro ken. The lat eral rec og nize the base as a “bony pedicle” like de scribed here (and lamina bend ing up at the pedicle below the large tooth is slightly by Moy-Thomas, 1934; Fink, 1981). There does seem to be a more frag mented now, when com par ing Fig ure 4A with Fig ure clearly marked dis tinc tion be tween these pedi cles and the teeth 5A (from Jerzmañska and Œwidnicki, 1992), and like wise the in - proper with a dif fer ence of the sur face struc ture, as is clearly in- te rior dor sal flange of the dor sal branch has a dam aged ven tral di cated in drawings (Fig. 5) by Jerzmañska and Œwidnicki edge slightly above the wide in ter nal in ci sion (see Figs. 4B and (1992). There are four teeth also on pedi cles be ing closely 5B). The ven tral edge of the den ta ry (Fig. 4D) is very thin and spaced near the symphysis with bases a lit tle more oval. One is al most straight and forms the in ter nal wall of a deep, open of “in ter me di ate” size, the three an te rior ones are small, their groove for the man dib ular sen sory canal. Seen from be hind tips are also in clined in wards, and at least three of them show (Fig. 6F) it is clear that the bone wall is quite thin around a wide the same orna ment at their bases. These basal pedi cles all man dib u lar (Meckelian) ca nal. along are al most about the same height as the teeth proper. The in ter nal face of the den ta ry is almost smooth and plane, The tips of most of the teeth are slightly damaged by post- only bending very slightly inwards at the ven tral edge in the mid - -mor tem breaks expos ing the thin outer and shiny layer be ing a dle of the bone (Figs. 4B, D and 5B). Be low the an te rior small lit tle lighter col oured than the al most black in te rior, but none is teeth there is a shal low depres sion, pre sum ably for a mus cle or bro ken at a level dis pos ing the in ter nal cav ity. In the interspaces lig ament near the symphysis. The lat ter seems to have its an te - be tween the teeth the shal low groove shows ir reg u lar “spongy” Eocene relatives of cod icefishes (Perciformes: Notothenioidei) from Seymour Island, Antarctica 573 bone structure. No traces of re place ment teeth are seen. There and Œwi dnicki (1992: fig. 1; here Fig. 7), both from the left side might perhaps have been two teeth between the fourth symphy- with the proxi mal and ar tic u lar head of the bone, both here se - seal one and the an te rior large tooth, which in that case would be lected as paratypes. We fea ture in some de tail spec i men ZPAL po si tion sev enth. Marks on this tooth (Fig. 4B) are from sam pling P.V./1 with two ante rior “fangs” be ing pre served (Fig. 7A, C, for iso tope anal y sis (see B³a¿ejowski et al., 2010). E–G). The short rounded as cend ing pro cess is well-pre served This al most com plete left denta ry (Figs. 4–6F) is slightly big- and shows an exter nal or nament simi lar to that of the lat eral ger than that of the large Dissostichus (~180 cm long, ~70 kg; face of the den ta ries. This rather thin and flat pro cess has an in - MÝller et al., 2003) from Green land. Hence it in di cates a fish of ter nal face (Fig. 7F) with a coarse or na ment of straight, thin about 2 m length.

Other den ta ries. Jerzmañska and Œwidnicki (1992: fig. 4) described a small fragment (ZPAL P.V./6) from the poste rior end of the den tal ridge with 3–4 closely set and dimin ish ing teeth of which the larger one clearly has a bony pedicle (their fig. 4). This is ac cepted here as prob a bly rep re sent ing Mesetaichthys jerzma nskae. There are two other well-pre served den ta ries (ZPAL P.V./9 and 11; Fig. 6A–E) showing the symphyseal re gion. Both are from the left side and are 30 mm long and very close to 15 mm high at the symphysis as ZPAL P.V./5, but they are slightly shal- lower than the lat ter pos te ri orly to the symphysis. ZPAL P.V./9 (Fig. 6A–C) is the better pre served end ing at a clear and nearly ver ti cal cut through the bony base of a tooth cor re spond ing to the 6th or 7th po si tion in ZPAL P.V./5, which repre sents the an - te rior large tooth. Spec i men ZPAL P.V./11 al though more bro ken (Fig. 6D, E), rep re sents an te rior part of den ta ry and is lack ing part of the me - dial sur face. It has seven tooth-po si tions pre served, the last ir - reg u larly bro ken bony pedicle cor re spond ing to the an te rior big one of spec i men ZPAL P.V./5 (Fig. 4). Its small an te rior tooth is miss ing from its po si tion very close to the me dial face di rectly pos te rior to the symphysis, but teeth num bers two to four are pre served as bony pedi cles cut near tops of pendicles, and teeth two and four are showing traces of the in ter nal cav i ties (Fig. 6E). The fifth tooth has left a deep, round groove, while the rather strong sixth is cut al most ver ti cally through the mid dle of its high bony pedicle and its in ter nal cav ity. The lat ter, as well as the base of the cav ity of sev enth tooth, shows weak traces of in ter nal, ver - ti cal ridges and fur rows, and the same is the case in the basal cav ity of the bony pedicle of one of the pos te rior pre served tooth in spec i men ZPAL P.V./9. The lat ter is lack ing the small sec ond tooth, and all teeth be tween the third and pos te rior pre served tooth, all leav ing deeper or shal lower pits, which show no traces of the in te rior cav i ties (Fig. 6C). Teeth num ber one and three clearly show fine ridges and fur rows at the base of the tooth proper, and when approach ing the large pos te rior tooth the lat- eral edge of the dental groove is as cend ing like in spec i men ZPAL P.V./5. First tooth is the only tooth of M. jerzmanskae pre - serv ing the al most com plete tip, clearly with out a sharp “cap”. Spec i men ZPAL P.V./9 ex hib its the an te rior end of the large man dib u lar (Meckelian) ca nal, the an te rior 22 mm of the smooth groove for the man dib ular sen sory canal, and the large, lat eral fo ra men be low the large pos te rior tooth. The bony sur- face shows the same or namen ta tion as speci men ZPAL P.V./5, al though slightly stron ger lon gi tu di nal ridges mark the pos te rior part of the me dial sur face of the frag ment (Fig. 6A). There is no rea son to doubt that these two den ta ry frag ments rep re sent M. jerzmanskae. Very im por tantly, they show the in ter - nal cav i ties of the bony pedicles with their faint ridges and fur - Fig. 7. Symphyseal re gions of premaxillaries rows. The re main ing den ta ries, spec i mens ZPAL P.V./6–16 also of Mesetaichthys jerzmanskae n. gen. and n. sp. seem to be long to this spe cies, but are more frag men tary. A, C – ZPAL P.V./1 in left lat eral and ven tral views; B, D – ZPAL P.V./2 in me dial and left lat eral views; E–G – ZPAL P.V./1 in left lat - Premaxillae. The better pre served premaxillae are spec i - eral, me dial and latero-ven tral views; A–D – drawings from mens ZPAL P.V./1, 2, de scribed and fig ured by Jerzmañska Jerzma ñska and Œwidnicki (1992); photo graphs by P.R. MÝller 574 Ma³gorzata Bieñkowska-Wasiluk, Niels Bonde, Peter Rask MÝller and Andrzej GaŸdzicki ridges ra di at ing out from the me dial cav ity between the as cend - ing and ar tic u lar pro cesses. This me dial cav ity also has 2–3 nerve fo ram ina “ra di at ing” in the same di rec tion as ridges of the as cend ing pro cess (also seen in ZPAL P.V./2; Fig. 7B). The as - cend ing pro cess is about 7–8 mm thick at its ba sis, but very thin, al most sharp at the dor sal edge. Only the ante rior part of the strong ar tic u lar pro cess is pre served (Fig. 7A, E, F). Spec i - men ZPAL P.V./2 shows the en tire ar tic u lar pro cess which is about the same size as the as cend ing pro cess, but stron ger and slightly more nar row (Fig. 7B, D). It shows a lat eral, verti cal ridge in the mid dle of the pro cess, pre sum ably indi cat ing how far for ward the ar tic ular head of the maxilla would have cov ered the premaxilla. Only a small part of the dentigerous branch of the bone is pre served in ZPAL P.V./2 cor re spond ing roughly to four tooth po si tions but only the bony pedicle of the large ante - rior “fang” is pre served. In ZPAL P.V./1 the dentigerous branch of the bone is cor re spond ing to three ante rior teeth (Fig. 7E–G). Spec i men ZPAL P.V./1 has the two an te rior teeth and pedi cles partly pre served, the sec ond one bro ken in the pedicle show ing traces of the in ter nal cav ity. The an te rior tooth is a very strong, con i cal and in wardly bent “fang” with the tip bro ken off to dis - close a large in ter nal cav ity (Fig. 7F). Includ ing nearly 15 mm as a bony pedicle, the tooth it self with strong, closely set ridges at the base is about 7 mm high as preserved, and re stored with the point would have been at least 2.5 cm high. The width of its Fig. 8. Sup posed more dis tal right premaxillary frag ment of Mesetaichthys jerzmanskae n. gen. and n. sp. (ZPAL P.V./4) base is about 8 mm, and the “enameloid” of the tooth has a light brown col our, as op posed to the much darker bone and the A – ven tral view; B, C – drawings from Jerzmañska dentine in te rior of the tooth which is nearly black (Fig. 7F). The and Œwidnicki (1992) in me dial and ven tral views; pos te rior wall to wards the next tooth is slightly concave giv ing it pho to graph by P.R. MÝller in fact a sub-tri an gular base (Fig. 7C, E, G). The sec ond tooth is bro ken at the top of the bony pedicle and as pre served is ca. in force ment along the dor sal edge. On the in side there is a 12 mm high, also bent in wards, and with the in ter nal cav ity small cav ity up behind the down-turned ar tic u lar sur face, and mostly filled by spongy bone. Its base is 6 mm wide, but slightly there are two nar row cav i ties an te rior to the ar tic u lar sur face. wider per pen dic u lar to the jaw giv ing it an “ovaloid” shape, but There is a large cav ity in the bone between the strong lat eral with a nearly flat front wall. The pos te rior wall is a lit tle con cave, ridge (lat eral wall) and the me dial wall (Fig. 9E, F). appar ently worn by the next and now miss ing tooth, which has Spec i men ZPAL P.V./17 (Fig. 9A, B) from the left side is left only a shal low cav ity (Fig. 7C, G). So the teeth are very from a much big ger an i mal and is 4 cm long and al most 2 cm closely set, de creas ing in size back wards, and or na mented like mea sur ing across the ar tic ular sur face, and part of the bone is the den ta ry teeth. They must have formed an “over hang ing” up - bro ken off ante ri orly. Its post-ar tic ular pro cess is 25 mm high, per jaw oppos ing the small teeth at the symphysis of the den ta - and a tiny bit may be miss ing at the sharp ven tral edge. Rough ry (Figs. 4 and 5). Spec i men ZPAL P.V./3 may also be from this and pit ted lat eral sur face shows where the miss ing retroarti - spe cies. Grande and East man (1986) fig ured sim i lar frag ments cular was su tured (Fig. 9A). The ven tral part of the bone below mostly with miss ing teeth. the wide open groove for the sen sory canal is much higher than Spec i men ZPAL P.V./4 is a slim dis tal part of a premaxilla pre served in spec i men ZPAL P.V./18, and the ven tral edge with three teeth and in ter ven ing shal low grooves of four miss ing seems bro ken and in com plete. The same three cav i ties or ones (Fig. 8; as sum ing that this fish is much too ad vanced to pock ets are seen be hind and in front of the smooth me dial have a toothed maxilla). Only the bony pedi cles are preserved “tongue” of the ar tic u lar sur face (Fig. 9B). The dor sal edge of the teeth, and they have dark spongy bone in the inte rior and slant ing up wards is not pre served. The lat eral sur face of the no cav ity. On its dor sal mar gin is a shal low groove which may bones (Fig. 9A, C) has a struc ture rem i nis cent of that of the have ac com mo dated the ventral edge of the maxilla. We as - den ta ries (Figs. 4 and 6). Both bones are very incom plete in sume that all premaxillaries be long to M. jerzmanskae. front with the pre sum ably long and pointed process for ar tic u la- tion with the den ta ry broken off. We as sume that the de scribed Jaw ar tic u la tion. Sev eral strong dermarticulars were (ZPAL P.V./17, 18) and the re main ing five dermarticulars found, and the two best pre served ones (ZPAL P.V./17, 18) are (ZPAL P.V./19, 23) be long to M. jerzmanskae. fig ured by Jerzma ñska and Œwidnicki (1992). The an a tom i cally more com plete frag ment (ZPAL P.V./18; Fig. 9C–F) is from the Basioccipital. This sin gle bone (ZPAL P.V./24; Fig. 10) is right side, ca. 3.5 cm long showing the ar tic ular sur face, which 26 mm wide and 21 mm high at the con cave ar tic u lar facet, extends much fur ther down the me dial face than on the lat eral and it is 45 mm long at the midline, but bro ken at the front mar - face. The length of the ar tic u lar or glenoid cavity is ca. 15 mm gin. There are two deep ex ca va tions in the ven tral sur face mea sured across to the tip of the post-artic ular pro cess. The (Fig. 10F) for thick pos te rior prongs of the parasphenoid with a strong post-ar tic u lar pro cess is ca. 13 mm high, and the ven tral strong ridge and in front a nearly 1 cm high, ver ti cal wall be - edge is in com plete where the retroarticular is missing. Below tween them (Fig. 10A). The dor sal in te rior sur face has a blunt the ar tic u lar sur face on the lat eral side is a wide open groove for ridge in the midline on top of the men tioned wall, and the bone the man dib ular sen sory canal which has a small ridge over - has a flat slop ing sur face dip ping about 20° to wards the lat eral hanging it from the strong lat eral ridge of the der mal com ponent edge (Fig. 10A, D). The lat ter is broken at both sides (Fig. 10A, (Fig. 9C, D). The ar tic ular sur face con tin ues for ward by the dor - B), but rather thin, and the bone may not have been much sal as cend ing part of the bone at an an gle of about 30o with re - wider than about 3 cm. Com par ing with many skulls fig ured by Eocene relatives of cod icefishes (Perciformes: Notothenioidei) from Seymour Island, Antarctica 575

It is pos si ble that the basioccipital (ZPAL P.V./24) be longs to M. jerzmanskae, but this is un cer tain.

Ver te brae. The de scribed col lec - tion com prises 21 ver te brae with short centra (ZPAL P.V./25–45; Jerz - mañ ska and Œwidnicki, 1992). The centra were measured by Jerz- mañska and Œwidnicki (1992: ta ble 2). Some have quite strong parapo - physes (Fig. 11A–D), as also in some nothenioids and many gado ids. Many of the centra show several lat eral bony lamellae (Fig. 11B, F; like their figs. 7 and 8 of ZPAL P.V./31, 32), a fea ture found in both some notothenioids (Fig. 12E) and some gadiforms. Spec i mens (ZPAL P.V./29; Fig. 12C, D and ZPAL P.V./30) hav ing large, lat eral cav i ties for ribs, could be from dif fer ent spe cies than the oth ers. They are unlikely to be noto thenioids, as these have weak or miss ing ribs (Grande and East man, 1986: p. 128). Such centra were men tioned by Jerz- mañska (1988: p. 425) and spe cial sim i lar ity was found with the mer lucciid Macruronus. Some of the cen tra (ZPAL P.V./34–42) have been de ter - mined as some thing more spe cific by Jerzmañska (dated 1992 on the la - Fig. 9. Dermarticulars of Mesetaichthys jerzmanskae n. gen. and n. sp. bels), namely “Macruronus” (see Fig. 12A, B). Jerzmañska (1988: figs. 7, 8) A, B – ZPAL P.V./17, left side, lat eral and me dial views; C–F – ZPAL P.V./18, right side il lus trated very sim i lar centra and de - in lat eral (C, D) and medial (E, F) views; pho to graphs (A, C, E) by P.R. MÝller; scribed them as gadiforms. drawings (B, D, F) from Jerzmañska and Œwidnicki (1992) Gadiform ver te brae are not usu - ally short, but rather equally long and high. Sev eral of the centra are from Balushkin (1984) the lat eral wall may have been rather low, quite large fishes, prob a bly over one metre long. The ver te brae and there fore not much ap pears to be miss ing. Grande and can not with cer tainty be re ferred to M. jerzmanskae, but large East man (1986) un for tu nately did not de scribe the size might in di cate, that some of them are quite likely from this basioccipital of the fos sil skull. taxon. Just in front of the dor sal edge of the facet for ar tic u la tion Occurrence. – La Meseta For ma tion (Telm7), Late (Fig. 10C, E) is a sub-hor i zon tal ir reg u lar sutural sur face for the Eocene. exoccipitals (Fig. 10D), in di cat ing that these were in a pos te rior po si tion at the level with the facet, and they met each other above the facet. This sutural sur face also has paired and rather COMPARISONS deep, blunt cav i ties which are 4 mm long and 3 mm wide, and in front and be low from those there are two much broader cav i ties 1 cm across still filled with matrix, and form ing the pos te rior wall Grande and East man (1986) dis cussed the pos si bil ity that of the ven tral part of the brain cav ity (Fig. 10A, D). upper and lower jaw frag ments they illus trated from the La This ar range ment does not look at all like that in Meseta Fm. were notothenioids, and they decided that the gadiforms, were the exoccipital ar tic u la tions are placed much premaxillaries were prob a bly from gadiforms, and the den ta ries fur ther an te ri orly, and those two bones do not meet in the were in de ter mi nate like the ver te brae. This opin ion was changed midline (see Greg ory, 1933; Svetovidov, 1948; Mujib, 1967; con cern ing den ta ries (Claeson et al., 2012) when de scrib ing a Rosen and Patterson, 1969). This criti cism was made by poorly preserved bone with frag men tary dentition, and the de ter - Balushkin (1994) con cern ing the exoccipital-basioccipital po- mi na tion be came much more pre cise as “merlucciids”, fol low ing si tions in the skull orig i nally descri bed by East man and Jerzmañska and Œwidnicki (1992). Clearly these jaw frag ments Grande (1991) as a “gadiform”, but shown by Balu shkin are of the same sort as the more well-pre served ones de scribed (1994) to be a noto thenioid. It is likely that in a fish of this size, here, just from much smaller fishes. in di cated by the iso lated basioccipital, the exoccipitals and The jaw frag ments de scribed by Jerzmañska and Œwidnicki basioccipital would be fused to gether in a gadi form, while (1992) were only compared with gadoid fishes (8 spp. from 3–4 notothenioids tend to os sify very late (Voskobo inikova, 1994). fam i lies). Seven fea tures were used (two from premaxillae, 576 Ma³gorzata Bieñkowska-Wasiluk, Niels Bonde, Peter Rask MÝller and Andrzej GaŸdzicki

Fig. 10. Basioccipital, sup pos edly from Mesetaichthys jerzmanskae n. gen. and n. sp. (ZPAL P.V./24)

A – ante rior, B – right lat eral, C – pos te rior, D – dorsal, E – pos terior, F – ven tral view; pho to graph by M. Dziewiñski, dusted with am mo nium (A) and by P.R. MÝller (B–D); drawings (E–F) from Jerzmañska and Œwidnicki (1992) three from den ta ries and two from dermarticulars), and of these The dentition of the gadoid Mer luccius (see Figs. 13 and traits six were sim ilar in Merluccius, while the rest (in clud ing the 14C, D) with sharp, pointed, rather strong teeth in two rows is merlucciid Melanonus) only matched one or two charac ters. not sim i lar to the dentition of Mesetaichthys: the teeth are slim The con clu sion was “gadiform” re la tion ship for the fos sils, al - and smooth (also in side) and there are no “fangs”, they are though the match with the major ity of the ma te rial was poor, and about the same size all along the jaws. They also have a small they in di cated (Jerzmañska and Œwidnicki, 1992: p. 248) that sharp “cap” (Fig. 14G, H) on each tooth, which ad mit tedly could the dentitions are quite differ ent. Claeson et al. (2012) took the have been bro ken off in the Mesetaichthys jaws showing only de ter mi na tion a step fur ther as “merlucciid” (al though very lit tle one of the small symphyseal teeth with the point pre served. The sim i lar ity with Melanonus), and they tried to in voke also the only sim i lar ity be tween the dentition of Mesetaichthys and dentition as an ar gument. We find espe cially the lat ter en tirely Merluccius is that the teeth are bent in wards (Figs. 5C, 7F and un con vinc ing, be cause Merluccius has very dif fer ent dentition. 13) and some are hol low (Fig. 14H). Notothenioids like Chaenocephalus (Fig. 14E) have pre - One fea ture which could be a gadi form one is the large, maxillary ascend ing and ar tic u lar pro cesses not un like those of open groove for the man dib ular sen sory canal (Figs. 4A, D; 5A the fos sils which like in most gadiforms are low and rounded, and 6F), as also stressed by Claeson et al. (2012). Most not with the as cend ing pro cess higher and slim mer than the ar - gadiforms have such open grooves (Fig. 14D), while this is very tic u lar pro cess, as is the case in by far most perciforms and also rare in perciforms (ex cep tions e.g., per coids-like Howellidae; nototheniids like Dissostichus (Fig. 15D; see also Balushkin, see Prokofiev, 2007), and we have seen none in notothenioids, 1984: fig. 15; Greg ory, 1933). The “trend of de vel op ment” in nei ther in our few skel etons (Fig. 14) nor our X-rays (Fig. 15). notothenioids is the re duc tion in rel a tive size of the as cend ing The open sen sory mandib ular ca nals are un known in noto - pro cess of pre maxilla (Balushkin and Voskoboinikova, 1995). thenioids (ac cord ing to per sonal in for ma tion from Dr. Balu - We rec og nize that the fos sil den ta ries in di cate a broad and shkin, April 2012; see also Claeson et al., 2012). We are, how - rounded snout. The dentition is very unlike that of gadi forms, as ever, struck by some detailed simi lar ity in the dentition of these none of those have “fangs” at the front of the premaxillary, nei - fos sils and liv ing notothenioids, spe cif i cally that of the huge ther gadi forms have small teeth at the den ta ry symphysis. Dissosti chus (Fig. 15). Mesetaichthys has two strik ing sim i lar i- Eocene relatives of cod icefishes (Perciformes: Notothenioidei) from Seymour Island, Antarctica 577

Fig. 11. Verte brae of ?Mesetaichthys jerzmanskae n. gen. and n. sp.

A–D – ZPAL P.V./31 in an te rior, right lat eral, ven tral and pos te rior views; E–H – ZPAL P.V./32 in an te rior, right lat eral, ven tral and pos te rior views; photo graphs by P.R. MÝller (C–D) and by M. Dziewiñski (G–H, ammo nium dusted); drawings (A, B, E, F) from Jerzmañska and Œwidnicki (1992)

Fig. 12. Verte brae A, B – ab dom i nal of so-called “Macruronus”, ZPAL P.V./35, ?an terior and ven tral views; C, D – ZPAL P.V./29, ante rior abdom i nal with large, deep rib cav ity from Teleostei indet; E, F – ab- dom i nal ver te bra of re cent Noto thenia; G–J – Wood ward’s so-called Noto- thenia sp., foremost ver tebral cen trum in an te rior, pos te rior, left lat eral and ven tral views (from Wood ward, 1908); pho to graphs by P.R. MÝller (A, B) and by M. Dziewiñski (C, D dusted with am- mo nium) 578 Ma³gorzata Bieñkowska-Wasiluk, Niels Bonde, Peter Rask MÝller and Andrzej GaŸdzicki

Fig. 13. Merluccius merluccius (Jrn. 215, dry skel e ton), gape show ing the strong, slim, pointed teeth with glit ter ing acrodin caps in two rows in the jaws (and strong vomerine teeth are barely vis i ble)

Pho to graph by P.R. MÝller ties to this living rather prim i tive nototheniid in the pat tern of the dentition and in the de tailed struc ture of the teeth. Dissostichus also has fanglike teeth at the pre maxillary symphysis, very small teeth at the denta ry symphysis, fanglike teeth in the mid - dle of den ta ry, and the sin gle teeth fur rowed on the base at the pedicle, and the cav ity is ridged to corre spond to the exter nal striation. There is only lit tle over lap in basioccipital (Fig. 10) and the skull roof and neurocranium of the notothenioid (Middle Eocene) from the La Meseta For ma tion, Proeleginops grande - a st manorum Balushkin (1994), but, in fact, the latter has a basio ccipital which is not re ally like a gadiform one. There fore we do not know if the two taxa could be synon y mous, and in that case the skull roof only a few cm long would clearly be from a ju - ve nile spec i men. Iso lated centra from Seymour Is land were de scribed by Wood ward (1908: fig. 5) and re ferred to Notothenia (Fig. 12G–J). It seems cer tain that there is more than one type of ver - te brae pre vi ously re ferred to “Mesetaichthys” and ac cord ingly much doubt about which centra may belong to the skull bones of M. jerzmanskae, and this raises doubt also about the re fer ral of the basioccipital. It seems quite likely that some centra are Fig. 14. Dry bones of recent fishes notothenioid, and that the larger ones could be long to M. A, B – Notothenia microlepidota (ZMUC uncat., 7495 – jerzmanskae. dry skel e ton), left lower jaw and right premaxilla, both in lat eral view; C, D – Merluccius merluccius (fish shop, Co pen ha gen, ZMUC uncat.), views as above; E, F – NOTOTHENIOID EVOLUTION AND Chaenocephalus aceratus (ZMUC uncat., 7741 – dry DETERIORATION OF CLIMATE skel eton), left lower jaw and premaxilla; G, H – Mer - luccius merluccius tooth, SEM photo show ing smooth pulp cav ity, cutting edge, also on the dis tinct cap/tip The old est rep re sen ta tives of notothenioids, P. grande - (uncat. spec i men); pho to graphs by P.R. MÝller (A–F) eastmanorum Balushkin, 1994, (Telm5) and M. jerzman- and C. Bonde (G–H) skae n. gen. and n. sp. (Telm7) are rec ognized in the La Meseta For ma tion. In the for ma tion a grad ual de te ri o ra tion of cli mate is recorded, with the ev i dence of de creas ing tem per a - the notothenioids is linked to this cli ma tic event, as was hy- tures through the later Eocene cul mi nat ing with the first Ant - poth e sized al ready by Regan (1914) and men tioned by arc tic glaciations at the Eocene-Oligocene bound ary (GaŸdzi - Grande and East man (1986: p. 134). cki et al., 1992; Din gle et al., 1998; Birkenmajer et al., 2005; The ear li est di ver si fi ca tion of notothenioids with anti-freeze Ivany et al., 2006, 2008; Tatur et al., 2006; Fran cis et al., 2009; liq uids in the blood (AFGP of Near, 2004) ac cord ing to the mo- see also Cantrill and Poole, 2012). Most pos si bly, the or i gin of lec u lar bi ol o gists took place in the ear li est Mio cene (~24 Ma; Eocene relatives of cod icefishes (Perciformes: Notothenioidei) from Seymour Island, Antarctica 579

Fig. 15A–C – large teeth from the middle of left den ta ry and near the premaxillary symphysis of the huge Dissostichus eleginoides (ZMUC P632150, 180 cm, 70 kg, wet speci men) in lateral view show ing fis sures and the pedicle like base, in section showing the “ridged” soft in te rior pulp, and from the base look ing into the cavity with ridges on the wall; D – X-ray of the snout and jaws of a small D. eleginoides ex posing large fangs near the premaxillary symphysis and in middle part of the den ta ry, which has smaller teeth at the symphysis (ZMUC P6341, 28 cm SL); E – jaws of Dissostichus eleginoides (ZMUC P632150, 180 cm) show ing distri bu tion and size of teeth

Pho to graphs by P.R. MÝller

Near, 2004). The prim i tive nototheniid branch with Dissostichus The most well-preserved lower jaw frag ment (Figs. 4, 5 and has a min i mum age of about 14 Ma (Near, 2004), so that the 6F) was se lected as the holotype for Mesetaichthys jerzman- 35 Ma old Mesetaichthys could be in a stemgroup po si tion to skae n. gen. and n. sp., a notothenioid incertae sedis – with the AFGP notothenioids. premaxillary tooth bearing frag ments as pararatypes. The di ag - nos tic features are pres ent in the dentition (which is re mark ably sim i lar to that of the big, pre daceous nototheniid Dissostichus) CONCLUSIONS in com bi na tion with the open groove for the sen sory canal. The Mesetaichthys jerzmanskae n. gen. and n. sp. de scribed here as notothenioid and a 10 m.y. older skull of Proeleginops Jaw frag ments of tele ost ean fishes and pos si bly a grandeastmanorum Balushkin, 1994 de scribed ear lier also basioccipital and some ver te brae from the Late Eocene of the from the La Meseta For ma tion are the only fossil notothenioids La Meseta For ma tion (Telm7) of Seymour Island are con sid - rec og nized up to now. ered to be notothenioids (cod icefishes rel a tives among perciforms). Pos tu lated “gadiform” fea tures are shown to be du - COMPARATIVE MATERIAL bi ous, apart from the open groove for the sen sory canal in the lower jaw. This fea ture is seen in a few perciforms, but is not known in any living notothenioid. Re cent Notothenioids, Nat ural His tory Museum of Den - mark, Uni ver sity of Co pen ha gen, SNM. 580 Ma³gorzata Bieñkowska-Wasiluk, Niels Bonde, Peter Rask MÝller and Andrzej GaŸdzicki

Nototheniidae: Notothenia microlepidota ZMUC uncat. Moridae: Antimora rostrata ZMUC uncat. (Ingolf exp.), Mora (7495 – dry skel eton; Figs. 12E, F and 14A, B); Dissostichus mora Jrn. 76. elegino ides ZMUC P632150 (155 cm SL; Fig. 15; MÝller et al., Macrouridae: Coryphaenoides rupestris ZMUC uncat. 2003: fig. 1), ZMUC P6341 (28 cm SL, X-ray; Fig. 15). (Skagerrak), Macrourus berglax Jrn. 15, Trachyrincus murrayi Chaenichthyidae: Chaenocephalus aceratus ZMUC ZMUC P375081. uncat. (7741 – dry skel e ton; Fig. 14E, F). Re cent Lophiiforms. Lophiidae: Lophius piscatorius ZMUC Eleginopsidae: Eleginops maclovinus ZMUC P63275 Jrn. 62. (84 mm SL, clear and stain); ZMUC CN 2 (365 mm SL, X-ray). Re cent Gadiforms (skel e tons in Nat u ral His tory Mu seum Ac knowl edg ements. Discus sions with Dr. A.V. Balushkin of Den mark, Uni ver sity of Co pen ha gen, SNM). (St. Pe ters burg) and Dr. J. Niel sen (Co penha gen) on the anat - Merlucciidae: Merluccius merluccius Jrn. 215–217 (Figs. omy on notothenioids are very much ap pre ci ated. We are very 13 and 14C, D, G, H). grate ful to re view ers Prof. J. Kriwet (Vi enna) and Dr. Gadidae: Arctogadus glacialis ZMUC P371663, Boreoga - P. Jadwiszczak (Bia³ystok) whose com ments have led to im - dus saisa CN 16, Brosme brosme Jrn. 28, morhua prove ments of the manu script. NB are very thankful to the Fur ZMUC P374478, P372971, Lota lota Jrn. 30 x, Melano - Mu seum for fi nancial sup port to study-trips to the In sti tute of grammus aeglefinus Jrn. 301, Merlangus merlangus Jrn. 348, Paleobiology PAS, Warszawa. AG wishes to acknowl edge the Molva molva Jrn. 58, Jrn. 835, Triso- lo gis tic sup port of the Instituto Antártico Argentino and Fuerza pterus esmarkii ZMUC P3711, Trisopterus luscus Jrn. 9. Aérea Ar gentina dur ing the field work in Antarctica. Prof. A. Phycidae: Phycis blennoides Jrn. 41, Urophycis brasilien - Tatur (Warszawa) ac com pa nied AG dur ing field col lec tion ac - sis Jrn. 30(I). tiv i ties. K. Gre gersen, Zoo log i cal Mu seum (Co pen ha gen) made skel e tons of the notothenioids.

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