878


Journal of Paleontology 89(5):870–881


fragmentary fish dentary bone with a strong and conical tooth and a piece of a second tooth. The tooth is slightly bent back- wards and has its internal cavity exposed at the tip. The tooth surface is weathered, but a pedicle is developed at its base, and the tooth is inserted in a shallow longitudinal groove. Based on its gross morphology, the specimen may probably be assigned to the cod-icefish Mesetaichthys jerzmanskae Bieñkowska- Wasiluk, Bonde, Moller and Gazdzicki, 2013, a Notothenioidei (Perciformes) recently described (Bieñkowska-Wasiluk et al., 2013) for the Submeseta Formation (middle/late Eocene). The specimen in question (MLP 83-V-30-2) is not referable to Aves, much less Pelagornithidae.


Discussion and conclusions


Regarding their affinities, both morphotypes recognized for Antarctic pelagornithids share with the late Paleocene/early Eocene Dasornis the presence of several possible plesiomorphic characters (i.e., humerus: deep concavities for the musculus extensor carpi ulnaris surrounded by a thick and smooth ridge; rostral end of the beak: slightly down-curved, absence of transverse sulcus; narial region of the rostrum: well-defined dorsolateral constriction and dorsal ridge, palatal ridge slightly prominent, and with a marked medial sulcus; tarsometatarsus: corpus mediolaterally narrower with square cross section, nar- row and poorly excavated trochlea II, proximally positioned trochlea II with a processus medioplantaris, narrow dorsal opening of foramen vasculare distale). However, a number of characters also remind the more derived condition typical of the Neogene Pelagornis (i.e., humerus: flattened diaphysis, well- developed epicondylus dorsalis, vertically positioned and proxi- mally extended tuberculumsupracondylare ventrale; narial region of the rostrum: longitudinal sulcus more dorsally positioned; tar- sometatarsus: recessed and more distally located plantar opening of the foramen vasculare distale, slight plantar projection of tro- chlea II, wider and lower dorsal surface of trochlea III). A com- bination of plesiomorphic and derived character states, showing an ‘intermediate’ condition between Dasornis and Pelagornis was already reported in post-early Eocene and pre-late Oligocene specimens. Taxa showing such combination include the middle Eocene L. tethyensis from Ukraine (Mayr and Zvonok, 2011, 2012), Gigantornis eaglesomei Andrews, 1916 from Nigeria (Harrison andWalker, 1976;Mayr et al., 2008), Togo specimens referred to Gigantornis (Bourdon and Cappetta, 2012), and some other remains from Belgium tentatively assigned by Mayr and Smith (2010) to D. emuinus and Macrodontopteryx oweni Harrison and Walker 1976 (although they probably correspond to Gigantornis and Lutetodontopteryx, respectively; Mayr and Zvonok, 2012; see alsoBourdon et al., 2010).The late Eocene and ?early Oligocene materials from Oregon described by Goedert (1989) also seems to fit in this intermediate morphology (Mayr et al., 2013). A valuable element in order to recognize plesiomorphic-


derived conditions is probably represented by the tarsome- tatarsus. The progressive increase in the distal projection of the trochlea metatarsi II, and the reduction of its plantar extension are consistent with the rise of the more modern taxa studied (Fig. 5). The distal end of tarsometatarsus UCR 22176 from the middle Eocene of Seymour Island is morphologically more


similar to the middle Eocene L. tethyensis and the probably late Oligocene P. “Palaeochenoides” mioceanus than to any other pseudo-toothed birds. UCR 22176 belonged to a huge bird similar to P. “Palaeochenoides” mioceanus (Table 1) and markedly larger than L. tethyensis (similar in size to D. toliapica).


Pelagornithid size-types.—Otherwise, considering the world- wide pelagornithid record and according to the estimated wingspan, four approximate size-ranges were identified (Fig. 7). The small gannet-sized Dasornis abdoun Bourdon et al., 2010 (1.5–1.7m wingspan; Bourdon et al., 2010), the medium albatross-sized D. toliapica and L. tethyensis (2–3m wingspan; Bourdon et al., 2010), the large D. emuinus (3.5–4.5m wing- span; Mayr, 2009; Bourdon et al., 2010), and finally, the giant middle/late Eocene and Neogene Pelagornis-related taxa (5–6m wingspan; Olson, 1985; Mayr, 2009; Mayr and Rubilar Rogers, 2010; Boessenecker and Smith, 2011; Ksepka, 2014). The Antarctic material assigned to morphotype 1 (middle


Ypresian), including the humerus MLP 12-I-20-4 and the humeral shaft USNM 494035 (Jones et al., 2000) correspond to the large size-type (i.e., equivalent in size to D. emuinus, Table 1). The material assigned to morphotype 2 (Bartonian/? Priabonian, including the humerus recently described by Rubilar-Rogers et al., 2011) correspond to the giant size-type. As stated previously (see also Tonni, 1980; Cenizo, 2012), they may belong to birds larger than the huge Neogene taxa (i.e., P. chilensis; similar-sized to P. sandersi; Table 1), constituting one of the largest pelagornithid known so far. In this sense, two Antarctic morphotypes were recognized


by previous authors. However, it was thought that both morphs coexisted during the middle/late Eocene of Seymour Island (Tonni and Tambussi, 1985; Cenizo, 2012). This idea was conceived from the finding of the mandible MLP 83-V-30-1 assigned—at that time—to a pelagornithid. Its removal from pelagornithids implies that only giant pseudo-tooth birds (i.e., morphotype 2) are known for the Bartonian/?Priabonian strata of the Submeseta Formation. Across the world, a large diversity of body sizes of


pelagornithids has been recorded between the late Paleocene and middle Eocene (Mayr, 2009). Since the middle/late Eocene, only giant pelagornithids are known. These forms (more than 5m wingspan) show a trend toward acquiring huge sizes, reaching a maximum specialization during the late Neogene (Fig. 7). Even taking into account the incompleteness of the fossil record, it seems that large, medium, and small taxa (Fig. 7) become extinct after middle Eocene times. An ecological competition for food or breeding sites could be the main cause (Mayr, 2009). A large list of candidates for such a competition may include the oldest Procellariformes (Noriega and Tambussi, 1996; Tambussi and Acosta Hospitaleche, 2007; Tambussi and Degrange, 2013; Reguero et al., 2013) described for the Cucullaea II Allomember (Ypresian/Lutetian), and the extre- mely diversified and widely extended early penguin fauna (Acosta Hospitaleche and Reguero, 2010; and references therein). The onset and diversification of giant forms occurred at the same time both in penguins (Clarke et al., 2007; Ksepka and Clarke, 2010), and pseudo-toothed birds. Giant penguins are recorded until the latest Eocene/earliest Oligocene


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68  |  Page 69  |  Page 70  |  Page 71  |  Page 72  |  Page 73  |  Page 74  |  Page 75  |  Page 76  |  Page 77  |  Page 78  |  Page 79  |  Page 80  |  Page 81  |  Page 82  |  Page 83  |  Page 84  |  Page 85  |  Page 86  |  Page 87  |  Page 88  |  Page 89  |  Page 90  |  Page 91  |  Page 92  |  Page 93  |  Page 94  |  Page 95  |  Page 96  |  Page 97  |  Page 98  |  Page 99  |  Page 100  |  Page 101  |  Page 102  |  Page 103  |  Page 104  |  Page 105  |  Page 106  |  Page 107  |  Page 108  |  Page 109  |  Page 110  |  Page 111  |  Page 112  |  Page 113  |  Page 114  |  Page 115  |  Page 116  |  Page 117  |  Page 118  |  Page 119  |  Page 120  |  Page 121  |  Page 122  |  Page 123  |  Page 124  |  Page 125  |  Page 126  |  Page 127  |  Page 128  |  Page 129  |  Page 130  |  Page 131  |  Page 132  |  Page 133  |  Page 134  |  Page 135  |  Page 136  |  Page 137  |  Page 138  |  Page 139  |  Page 140  |  Page 141  |  Page 142  |  Page 143  |  Page 144  |  Page 145  |  Page 146  |  Page 147  |  Page 148  |  Page 149  |  Page 150  |  Page 151  |  Page 152  |  Page 153  |  Page 154  |  Page 155  |  Page 156  |  Page 157  |  Page 158  |  Page 159  |  Page 160  |  Page 161  |  Page 162  |  Page 163  |  Page 164  |  Page 165  |  Page 166  |  Page 167  |  Page 168  |  Page 169  |  Page 170  |  Page 171  |  Page 172  |  Page 173  |  Page 174  |  Page 175  |  Page 176  |  Page 177  |  Page 178  |  Page 179  |  Page 180  |  Page 181  |  Page 182  |  Page 183  |  Page 184  |  Page 185  |  Page 186  |  Page 187  |  Page 188  |  Page 189  |  Page 190  |  Page 191  |  Page 192  |  Page 193  |  Page 194  |  Page 195  |  Page 196  |  Page 197  |  Page 198  |  Page 199  |  Page 200  |  Page 201  |  Page 202  |  Page 203  |  Page 204  |  Page 205  |  Page 206  |  Page 207  |  Page 208  |  Page 209  |  Page 210  |  Page 211  |  Page 212