Patagosaurus fariasi Bonaparte 1979

Patagosaurus fariasi Bonaparte, 1979 HOLOTYPE. — PVL 4170, consisting of several anterior, middle and posterior cervical vertebrae (PVL 4170 [1]-[9]); anterior, mid- and posterior dorsals (PVL 4170 [10]-[17]); anterior caudals (PVL 4170 [19]-[25]) and middle to posterior caudals (PVL 4170 [26]-[32]); sacrum (PVL 4170 [18]); fused ischia (PVL 4170 [36]); right ilium (PVL 4170 [34]); right pubis (PVL 4170 [35]); and right femur (PVL 4170 [37]). See Tables 1 and 2 for vertebral measurements, and Table 3 for appendicular measurements. The holotype was said to also contain a scapula and coracoid (Bonaparte 1986a), but these could unfortunately not be located in the collections. In the collections of the MACN we found two elements labelled as MACN-CH 1986 scapula ‘A’ and coracoid ‘B’, which might be these holotypic elements; however, at present the association of these bones with the holotype is uncertain, and the association with another Patagosaurus specimen, MACN-CH 935, is also likely, due to close association of these elements with MACN-CH 935 on the excavation map. A large humerus is also indicated in the original quarry map for the holotype, however, the only large humerus retrieved from the PVL collections is from another locality,Cerro Cóndor South.Originally, associated teeth with typical eusauropod wrinkled enamel were mentioned (Bonaparte 1986b). However, no directly associated teeth or tooth-bearing bones are known for the holotype specimen, so that these teeth are not regarded as part of the holotype here and were not used in the diagnosis, even though some are ascribed to Patagosaurus (Holwerda et al. 2015). Ribs and chevrons appear on the quarry map of the holotype, but are mixed in with ribs and chevrons of other Patagosaurus specimens, and will therefore be omitted from the holotype description. ORIGINAL DIAGNOSIS (Bonaparte 1986b). — Cetiosaurid of large size, with tall dorsal vertebrae; posterior dorsals with elevated neural arches and well-developed neural spines, formed from 4 divergent laminae and with a massive dorsal region; dorsoventrally-oriented neural spine cavities, more expanded than in Barapasaurus. Anterior and lateral regions of the neural arch similar to that of Cetiosaurus and Barapasaurus. Sacrum with 5 vertebrae, elevated neural spines, and a large dilation of the neural canal forming a neural cavity. Pelvis with pubis showing distal and proximolateral expansions, more developed than in Barapasaurus, and a less expanded pubic symphysis than in Amygdalodon Cabrera, 1947. Ischium slightly transversely compressed, with a ventromedial ridge of sublaminar type, and with a clear distal expansion. Ratio of tibia-femur lengths from 1: 1.5 in juveniles, reaching 1: 1.7 in adults. Mandible with weak medial torsion. Spatulate teeth with occlusal traces. EMENDED DIAGNOSIS. — Patagosaurus fariasi is a non-neosauropodan eusauropod dinosaur that can be diagnosed on the basis of the following morphological features, and the following combination of characters (features with * are tentatively considered autapomorphies): 1) cervical and anterior dorsal vertebrae with marked pleurocoel, which is deep in cervicals but shallower in dorsals. In cervical vertebrae, the pleurocoel is deeper anteriorly with well defined margins, but becomes shallow posteriorly and has only well defined dorsal and ventral margins; 2) in several cervicals, a faint oblique accessory lamina is present, dividing the pleurocoel into an anterior deeper part and a posteriorly shallower part; 3) the cervicals have a relatively high neural spine, accompanied by high dorsal placement of postzygapophyses, which results in a high angle between the postzygodiapophyseal and posterior centrodiapophyseal laminae of about 55°; 4) Posterior dorsal neural arches with a centrodiapopohyseal fossa that extends internally as a pneumatic structure, which is separated by the mirroring structure by a thin septum, and both of which connect into a ventral, oval shaped internal pneumatic chamber, which is dorsal to and well separated from the neural canal*; 5) posterior dorsals with small round excavations on the posterior side of the distal extremity of the diapophyses*; 6) posteriormost dorsals have rudimentary aliform processes; 7) all dorsals display an absence of the spinodiapophyseal lamina in all dorsals, with a contact between the lateral spol and podl in posterior-most dorsals instead; 8) sacrals with dorsoventrally high neural spine; 9) ilium with round dorsal rim, hooks-shaped anterior lobe and dorsoventrally elongated pubic peduncle; 10) fused distal ischia with the paired distal shafts creating an angle of 110° to the horizontal; 11) pubis with torsion and kidney-shaped pubic foramen; 12) femur with posteromedially placed fourth trochanter, and laterally convex surface of femoral shaft. HORIZON, LOCALITY AND AGE. — Patagosaurus fariasi was found in what are now considered latest Early to early Middle Jurassic beds of the Cañadón Asfálto Formation in west-central Chubut, Patagonia, South Argentina (Cúneo et al. 2013). The Cañadón Asfálto Formation is a continental unit, consisting mainly of lacustrine deposits. Patagosaurus was found in the Cerro Cóndor area. The type locality of the holotype of Patagosaurus fariasi is Cerro Cóndor North, which lies approximately 2 km north-east of the first discovery site of Patagosaurus remains: Cerro Cóndor South, close to the village of Cerro Cóndor, near the Chubut river, not far from the town of Paso de Indios (Fig. 1). GEOLOGICAL SETTING The Cañadon Asfálto Formation (west-central Chubut province, Patagonia, Argentina, see Fig. 1) was first studied by Piatnitzky (1936), after which it was formally described and named by Stipanicic et al. (1968) and further described by Nullo (1983). It is part of the sedimentary infill of the eponymous Cañadón Asfalto Basin, which consists of different subunits of Lower Jurassic to Upper Cretaceous sediments. The Cañadon Asfálto Formation is the uppermost unit of the lower megasequence of the Cañadón Asfalto basin, which has sedimentary infill of the Lower Jurassic(Figari et al. 2015). This unit is exposed between the Chubut province towns of Paso del Sapo and Paso de Indios (Olivera et al. 2015). The early Middle Jurassic (Toarcian-Bajocian, possibly earliest Bathonian) Cañadón Asfalto Formation conformably overlies the Early Jurassic (Pliensbachian-early Toarcian; Cúneo et al. 2013; Figari et al. 2015; Volkheimer et al. 2015) Lonco Trapial Formation. It has been the subject of numerous geological studies in recent years to determine its sedimentology and age, since the age of the Cañadón Asfálto Formation has long been considered to be Callovian-Oxfordian (and thus the South American equivalent of several other Jurassic beds worldwide, such as the Oxford Clay; Frenguelli 1949; Bonaparte 1979; Bonaparte 1986a; Rauhut 2003a). However, a recent detailed chronostratigraphic study showed otherwise, using zircon grains from several tuff samples from the Cañadón Asfálto Formation (Cúneo et al. 2013). These were pre-treated by the chemical abrasion, or CA-TIMS technique, in order to constrain radiation-induced Pb loss. This method (using U/ PB isotopes) is considered to be one of the most precise dating methods (Mattinson 2005). The U/Pb isotope ratios show a latest Early (early-mid Toarcian), to early Middle Jurassic age range (Aalenian or Bajocian, Cúneo et al. 2013), although the youngest radiometric age for this formation has been given as Bajocian-Bathonian (Cabaleri et al. 2010). This much older age of the formation is also consistent with palynological and other radiometric studies (e.g. Volkheimer et al. 2008; Cabaleri et al. 2010; Zavattieri et al. 2010; Olivera et al. 2015; Hauser et al. 2017). Moreover, this new age also puts the vertebrate fossils found in the Cañadón Asfálto Formation in a new light. Since its discovery, over twenty species of different taxonomic groups (including sauropod, theropod, and ornithischian dinosaurs, pterosaurs, sphenodontians, mammals, fishes, frogs, turtles and crocodiles) have been discovered (e.g., Escapa et al. 2008; Sterli & de la Fuente 2010; Olivera et al. 2015). This makes it an important unit for the study of Middle Jurassic tetrapods, and the diversification of Middle Jurassic dinosaurs in particular. The outcrops of the Cañadón Asfálto Formation are dominated by microbial limestones, often tuffaceous mudstones and shales with conchostracans, and conglomeratic intercalations (Silva Nieto et al. 2002; Tasch & Volkheimer 1970). They provide mainly disarticulated dinosaur remains, as well as a few articulated skeletons, as shown in the quarry map of the sauropod bonebed of Cerro Cóndor North (Fig. 1). The Cañadón Asfálto Formation shows evidence of both folding and faulting, which makes correlation of the different localities impossible, until further study is performed. The region was dominated by a warm and relatively humid climate in the Middle Jurassic, evidenced by palynology (Volkheimer et al. 2001) and by macrofloral remains (e.g. Cheirolepidiaceae and Araucariaceae; Volkheimer et al. 2008, Volkheimer et al. 2015). Lacustrine sedimentation cycles found in paleolakes in the Cañadón Asfálto Formation provide evidence of climatic fluctuations and cyclicity (Cabaleri & Armella 2005; Cabaleri et al. 2005). José Bonaparte started excavations in the Cañadón Asfálto Formation with a team of scientists and preparators, and with funding from the National Geographic Society, in 1977. They found bones, on the Farias farm estate close to the river Chubut. After this, in 1978, they found a sauropod skeleton 4-5 km north of Cerro Condor. This site was then dubbed Cerro Cóndor Norte (North), and the original site Cerro Cóndor Sur (South). The Cerro Cóndor North site was excavated until 1982; in 1980, however, most material was uncovered and visible, as demonstrated in the quarry map of Fig. 1. From this site, the holotype PVL 41

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