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LIGABUESAURUS LEANZAI BONAPARTE, GONZÁLEZ RIGA & APESTEGUÍA, 2006 Type species and etymology The name of the type species was erected in honour of geologist Dr Héctor Leanza, who reported about the presence of fossils at Cerro de los Leones, Picún Leufú, Neuquén Province, Argentina. Holotype MCF-PVPH-233 (Fig. 4A): a single, large-sized, incomplete and disarticulated sauropod specimen represented by ten maxillary teeth (MCF-PVPH-233/ 01), a posterior cervical vertebra (MCF-PVPH-233/02), an anterior dorsal vertebra (MCF-PVPH- 233 / 03), two articulated midposterior dorsal vertebrae (MCF-PVPH-233/04 and MCF-PVPH- 233 / 05), two articulated posterior dorsal vertebrae (MCF-PVPH-233/06 and MCF-PVPH-233/07), both scapulae (MCF-PVPH-233/08 and MCF-PVPH-233/09), a left humerus (MCF-PVPH-233/10), a proximal and distal epiphysis of the right humerus (MCF-PVPH-233/11 and MCF-PVPH-233/12), a right metacarpal II (MCF-PVPH- 233/13), a right metacarpal III (MCF-PVPH- 233/ 14), a distal epiphysis of the left metacarpal II (MCF-PVPH-233/15), a distal epiphysis of the left metacarpal IV (MCF-PVPH-233/16), a right femur (MCF-PVPH-233/17), a right tibia (MCF-PVPH-233/18), a right fibula (MCF-PVPH-233/19), a right astragalus (MCF-PVPH-233/20) and a nearly complete and articulated right pes, with five metatarsals and three phalanges (MCF-PVPH-233/21–MCF-PVPH-233/28). Referred specimens MCF-PVPH-261 (Fig. 4A): several postcranial elements from the type quarry no. 4 of Ligabuesaurus, consisting of a mid-cervical vertebra (MCF-PVPH-261/16), two posterior cervical vertebrae (MCF-PVPH-261/01 and MCF-PVPH-261/02), an anterior caudal vertebra (MCF-PVPH-261/15), an incomplete dorsal rib (MCF-PVPH-261/17), both coracoids (MCF-PVPH-261/05 and MCF-PVPH-261/06), a distal half of left radius(?) (MCF-PVPH-261/07), a partial left ilium (MCF-PVPH-261/08), both pubes (MCF-PVPH-261/09–MCF-PVPH-261/11), a left femur (MCF-PVPH-261/12), a proximal epiphysis of the left tibia (MCF-PVPH-261/13) and a proximal epiphysis of the left fibula (MCF-PVPH-261/14). MCF-PVPH-228 and MCF-PVPH-908 (Fig. 4B), a single, large-sized and incomplete sauropod specimen from quarry no. 3, represented by the following associated bones: two articulated posterior cervical vertebrae (MCF-PVPH- 228 / 01 and MCF-PVPH-261/02), an anterior dorsal vertebra (MCF-PVPH-908), two articulated mid-posterior dorsal vertebrae (MCF-PVPH-228/03 and MCF-PVPH-228/04), six incomplete dorsal ribs (MCF-PVPH-228/05–MCF-PVPH-261/10) and a right scapula (MCF-PVPH-228/11). MCF-PVPH-744 (Fig. 4B), one isolated, almost complete tooth. See the Supporting Information (Table S1 and Section 1.1.2 ‘Comments on referred specimens of Ligabuesaurus ’) for considerations about the composition of the type material of Ligabuesaurus. Locality and horizon The fossil remains of Ligabuesaurus come from the Cerro de los Leones locality, a hill located ~ 10 km to the southwest of Picún Leufú city, southern Neuquén Province, Patagonia, Argentina (Fig. 1A, B). The fluvial deposits outcropping in this area were referred to the lower section of the Cullin Grande Member (Martinelli et al., 2007), the upper member of the Lohan Cura Formation (Bajada del Agrio Group, Lower Cretaceous, Albian). The type quarry (no. 4) was opened in the fossiliferous level no. 2 (sensu Martinelli et al., 2007) in the southern flank of the Cerro de los Leones (Fig. 1C) and 40 m to the east of quarry no. 3, where part of the referred specimen was found (Supporting Information, Table S1). The sauropod remains were found in laminate mudstones with interbedded fine- to very fine-grained sandstones. These fluvial deposits were dated as Albian and are considered to have been formed in a distal floodplain in semi-arid climatic conditions (Martinelli et al., 2007). Comments on original diagnosis In the original description of Ligabuesaurus, Bonaparte et al. (2006) identified four autapomorphies. The first three are listed below with the numbers (1), (2) and (3). The fourth autapomorphy, listed by Bonaparte et al. (2006) as (4) rudimentary prespinal lamina (prsl) on the posterior cervical and anterior dorsal vertebrae, is not used here for the following reasons: in the posterior cervical vertebra MCF-PVPH-233/02 the prsl is not present (Fig. 5L), whereas in the anterior dorsal vertebra MCF-PVPH-233/03 there is a reduced lamina on the dorsalmost portion of the anterior face of the neural spine (Fig. 5M). However, in the anterior dorsal vertebra MCF-PVPH-908 the prsl is not rudimentary but represented by a narrow and prominent lamina, well developed from the base to the apex of the neural spine (Fig. 5N). Therefore, we consider that the rudimentary prsl on the posterior cervical and anterior dorsal vertebrae is not a pertinent autapomorphy for Ligabuesaurus and exclude it from the diagnosis. Revised diagnosis Ligabuesaurus leanzai is characterized by the following autapomorphies: (1) laminar and anteroposteriorly compressed neural spines on posterior cervical and anterior dorsal vertebrae that are rhomboid in shape and wider than the vertebral centra; (2) spinoprezygapophyseal laminae in posterior cervical vertebrae forked to form two pairs of laminae: the medial pair unites them towards the top of the neural spine, and the lateral pair form the lateral border of the neural spine; (3) posterior cervical and anterior dorsal vertebrae with low neural arch pedicels, less than onethird of the height of the anterior articular surface; (4) humeral head expanded posteriorly (D’Emic, 2012); (5) quadrangular ventral half of the coracoid in lateral view (Fig. 5A); (6) fossae on proximoventral faces of metatarsals II and III (D’Emic, 2012); and (7) deep pit on ventrodistal face of pedal phalanx II-1 (modified from D’Emic, 2012). With regard to (4), (6) and (7), in the extended contribution on the early evolution of Titanosauriformes, D’Emic (2012; appendix 4) also provided a diagnosis for Ligabuesaurus, identifying five autapomorphies, some of which are not included in the diagnosis to represent morphological features with a wide distribution within Sauropoda. In this sense, the distal scapular blade with rounded dorsal expansion (autapomorphy 1; D’Emic, 2012) is a condition that Ligabuesaurus shares with several Titanosauriformes (e.g. Brachiosaurus Riggs, 1903, Brontomerus Taylor, Wedel & Cifelli, 2011, Euhelopus Romer, 1956, Giraffatitan Paul, 1988, Rukwatitan Gorscak et al., 2014), hence it is excluded from the diagnosis. Likewise, the gracile humerus of Ligabuesaurus (autapomorphy 3; D’Emic, 2012) is a plesiomorphic condition that is also present in several sauropods, such as Alamosaurus Gilmore, 1922, Chubutisaurus Del Corro, 1975, Europasaurus Mateus et al. in Sander et al., 2006, Giraffatitan, Patagosaurus Bonaparte, 1979, Rinconsaurus Calvo & González Riga, 2003 and Wintonotitan Hocknull et al., 2009. In contrast, we agree with D’Emic that the deep pit on the ventrodistal face of the pedal phalanx represents an autapomorphy of Ligabuesaurus (autapomorphy 5; D’Emic, 2012), but we have reconsidered the pedal element (MCF-PVPH-233/28) as a phalanx II-1 and not a I-1 (contra D’Emic, 2012). However, also in the phalanx I-1 (MCF-PVPH-233/26) there is a ventrodistal vascular foramen, but it is small and poorly preserved, hence it is not included in the present diagnosis. Minimum number of individuals Body mass estimation Axial skeleton Appendicular skeleton |
