Neuquensaurus, from the Late Cretaceous of Argentina and one of the first dinosaurs described from Patagonia, is one of the most derived sauropod dinosaurs, and its proportions and size place it among the smallest sauropods ever known. In this context, Neuquensaurus is central to understanding late stages of sauropod evolution. This contribution offers a full description of the appendicular skeleton of Neuquensaurus. The anatomical analysis reveals that the appendicular skeleton of Neuquensaurus exhibits unique characteristics only shared with closely related saltasaurine titanosaurs; for example, the laterally directed preacetabular lobe of the ilium, the prominent fibular lateral tuberosity, and the presence of an intermuscular line on the femoral shaft, which is proposed here as a synapomorphy of Saltasaurinae. Neuquensaurus also displays many reversals to primitive character states, such as the presence of a prominent olecranon process of the ulna, a trochanteric shelf, a lesser trochanter and an ischial tuberosity. Additional characters that allow its evaluation in a phylogenetic context are here provided. Among them are the extremely deflected femoral shaft, the elliptical femoral cross-section, and the anterolaterally oriented cnemial crest.
Neuquensaurus (= “Titanosaurus”) australis (Lydekker, 1893) (Fig. 1) is one of the better preserved sauropods from the Upper Cretaceous of Patagonia. It represents, together with Neuquensaurus robustus (Huene, 1929), Saltasaurus loricatus Bonaparte and Powell, 1980, Rocasaurus muniozi Salgado and Azpilicueta, 2000, and Bonatitan reigi Martinelli and Forasiepi, 2004, a member of Saltasaurinae Powell, 1992 (= Saltasaurini Salgado and Bonaparte, 2007). Neuquensaurus is a small sauropod (femoral length 0.75 m) characterized by features in the axial (e.g., posterior caudal centra dorsoventrally flattened) and appendicular skeleton (e.g., fibular lateral tuberosity strong developed), that separate it as a distinctive taxon within Titanosauria (Wilson 2002). The most significant morphological features in the anatomy of Neuquensaurus are present in the appendicular skeleton (Huene 1929; Wilson and Carrano 1999; Wilson 2002; Powell 2003; Salgado et al. 2005; Otero and Vizcaíno 2008), which departs from the typical sauropod limb pattern. Because of its young geological age and anatomical peculiarities, Neuquensaurus figures prominently in discussion of the late stages of sauropod evolution (Wilson and Carrano 1999; Wilson 2005; Salgado et al. 2005).
“Titanosaurus” australis was erected and first described by Lydekker (1893) based on a series of associated caudal vertebrae and some elements of the limbs recovered from Neuquén Province, Patagonia, mostly belonging to the same individual (Lydekker 1893: 4). As noted by Wilson and Upchurch (2003: 139), Lydekker does not specify how many individuals those elements belongs to, and the fragments of the girdles and limbs were not associated with the type caudal vertebrae (Wilson and Upchurch 2003: 139). Huene (1929) later referred to “Laplatasaurus” araukanicus Huene, 1929 some elements previously assigned to “T'. australis by Lydekker and made an extensive description of that material, with the inclusion of numerous elements (mostly belonging to several adult and sub-adult individuals) collected in the early 20th century in the course of fieldwork carried out by the Museo de La Plata, Argentina. The collected bones were discovered intermixed; hence Huene couldn't determine single individuals: “The separation (of the bones) pitifully had to be made by examination; therefore, errors are not excluded” (Huene 1929: 23, translated from the Spanish). Huene made a classification of the limb bones housed at the Museo de La Plata and assigned to the genus Titanosaurus, according to their peculiar shape and relative proportions, recognizing two Patagonian taxa: “Titanosaurus” australis and “Titanosaurus” robustus Huene, 1929. Huene (1929) classified the long bones of “Titanosaurus” australis and “T”. robustus “…without determining or differentiating the vertebral material of each species … Huene (1929) used the name of “Titanosaurus” australis in an arbitrary way to identify the form possessing slender limb bones and creating for the remainder the species “T”. robustus, without taking into account the fact that the type material of the species “T”. australis … consists of a series of caudal vertebrae” (Powell 2003: 43). Though Huene's descriptions were detailed and helpful, they were not extensively comparative with other sauropods yet known. Those taxa received scant attention for some 50 years, until Bonaparte and Gasparini (1978) re-studied limb bones referred by Huene (1929) to “T”. robustus (i.e., left femur, left ulna, right ulna, and left radius). They specified lectotype for those materials, indicating that they may correspond to the same individual (Bonaparte and Gasparini 1978: 397). Powell (2003, adapted from his dissertation written in 1986) also revised the specimens of Titanosaurus and reconsidered the anatomy and validity of both species of the genus. He observed that the Indian type species of the genus Titanosaurus (Titanosaurus indicus Lydekker, 1877) more closely resembles “Laplatasaurus” araukanicus than “T”. australis. Accordingly, the latter was included in a new genus, thus erecting Neuquensaurus australis as a new taxonomic entity with a modified diagnosis (Powell 2003), while N. robustus was regarded as a nomen dubium (Powell 2003; Wilson and Upchurch 2003). Subsequently, McIntosh (1990) tentatively referred “T”. australis and “T”. robustus to the genus Saltasaurus, arguing that the differences between those taxa noted by Bonaparte and Powell (1980) are not of taxonomic importance (McIntosh 1990: 395). Powell (1992) and later Wilson and Upchurch (2003) did not recognize genus-level differences between those species. Salgado et al. (2005) recently described a new specimen of N. australis, adding to information on axial and appendicular elements known for the species, and provided a revised diagnosis. Additionally, Salgado et al. (2005) include in their description of the new specimen other elements that were found associated with the latter and they “…provisionally interpreted [them] as belonging to the same genus” (Salgado et al. 2005: 625). Moreover, other newly discovered material potentially belonging to Neuquensaurus remain undescribed and are included in the present analysis.
The present study is focused on the appendicular anatomy of Neuquensaurus. Bearing in mind its disarticulated condition (which has made a detailed study of its osteology difficult), the new discoveries of the last years, and unpublished new materials, as well as the similarity with Neuquensaurus robustus, a re-assessment and comparative description of all available appendicular material of Neuquensaurus australis and N. robustus is given here.
Institutional abbreviations.—MACN, Museo Argentino de Ciencias Naturales “Bernardino Rivadavia”, Buenos Aires, Argentina; MCS, Museo de Cinco Saltos, Cinco Saltos, Argentina; MPEF, Museo Paleontológico “Egidio Feruglio”, Trelew, Argentina; MLP-Av, Museo de La Plata, Rancho de Ávila Collection, La Plata, Argentina; MLP-CS, Museo de La Plata, Cinco Saltos Collection, La Plata, Argentina; MLP-Ly, Museo de La Plata, Lydekker's Collection, La Plata, Argentina; MPCA-CS, Museo Provincial “Carlos Ameghino”, Cinco Saltos Collection, Cipolletti, Argentina; PVL, Collection of Vertebrate Paleontology of Instituto “Miguel Lillo”, Tucumán, Argentina.
Other abbreviations.—M., muscle; Mm., muscles.
Dinosauria Owen, 1842
Saurischia Seeley, 1887–1888
Sauropodomorpha Huene, 1932
Sauropoda Marsh, 1878
Titanosauria Bonaparte and Coria, 1993
Saltasauridae Bonaparte and Powell, 1980
Saltasaurinae Powell, 1992
(= Saltasaurini Salgado and Bonaparte, 2007)
Genus Neuquensaurus Powell, 1992
Type species: Titanosaurus australis Lydekker, 1893.
Neuquensaurus australis (Lydekker, 1893)
Holotype: MLP-Ly 1/2/3/4/5/6, caudal vertebrae.
Neuquensaurus robustus (Huene, 1929) nomen dubium
Lectotype: Left ulna (MLP-CS 1094), right ulna (MLP-CS 1095), left radius (MLP-CS 1171), left femur (MLP-CS 1480) (Bonaparte and Gasparini 1978).
Remarks.—All currently materials referred to the appendicular skeleton of N. australis mentioned by Lydekker (1893), Huene (1929), Powell (2003), and Salgado et al. (2005) are listed in Appendix 1, as well as those specimens referred by Huene (1929) and Powell (2003) to N. robustus. The new specimens not yet published are also included in Appendix 1. In some cases, the original remains are presumed to be missing, so interpretations were based on illustrations in Huene (1929). In the worst cases, neither material nor drawings were available at all (see Appendix 1 for details).
Stratigraphic and geographic range.—(Fig. 1A) The holotype and limb elements of “Titanosaurus” australis studied by Lydekker (1893) come from Neuquén. Unfortunately, Lydekker did not give a more precise location of the bones nor the specific stratigraphic position. The materials of “T”. australis and “T”. robustus studied by Huene (1929) come from General Roca and Cinco Saltos (“Gobernación de Río Negro”, currently Río Negro Province), from strata belonging to the “Dinosaurier schichten” (Keidel 1917). Those “Dinosaurs beds” where Neuquensaurus' remains were found correspond to the Anacleto Formation (“Senonense inferior”, Huene 1929: 11). The specimen of N. australis and associated elements cited by Salgado et al. (2005) were recovered from Cinco Saltos, Río Negro Province (top of Anacleto Formation, early Campanian) (Salgado et al. 2005).
It is remarkable that a complete analysis including the axial skeleton of both Neuquensaurus australis and Neuquensaurus robustus is needed to asses the definitive assignment of all the elements to the former valid taxon and to elucidate the taxonomic status of the latter. Such study is, of course, out of the scope of this contribution. I will focus the descriptions primarily on the multiple associated hind limb elements that Huene (1929) referred to “Titanosaurus” australis. Elements previously referred to “Titanosaurus” robustus will be described in each section devoted to the respective element only if there is a reason to believe that they probably represent N. australis. Where they differ in morphology from N. australis, each will appear at the end of the corresponding section, with some comments. Any elements for which referral to N. australis is dubious will be treated in a separate descriptive section as cf. Neuquensaurus.
The phylogenetic relationships of Titanosauria remains obscure, in part, because the fragmentary nature of most genera. To avoid nomenclatural ambiguities, I will follow the phylogenetic definitions for Titanosauria as follows:
Titanosauria Bonaparte and Coria, 1993: Andesaurus delgadoi Clavo and Bonaparte, 1991, Saltasaurus loricatus Bonaparte and Powell, 1980, their most recent common ancestor, and all descendants.
Saltasauridae Bonaparte and Powell, 1980: Opisthocoelicaudia skarzynskii Borsuk-Białynicka, 1977, Saltasaurus loricatus Bonaparte and Powell, 1980, their most recent common ancestor, and all descendants.
Saltasaurinae Powell, 1992 (= Saltasaurini Salgado and Bonaparte, 2005): Neuquensaurus australis (Lydekker, 1893), Saltasaurus loricatus Bonaparte and Powell, 1980, their most recent common ancestor, and all descendants.
Huene (1929) mentioned the existence of thirteen bones of the pectoral girdle of Neuquensaurus. However, of those, eleven are present today in the collections of the Museo de La Plata (Appendix 1). There is also a left coracoid fused to a fragment of scapula (MLP-CS 1298) that was previously described as a fragment of ilium (Huene 1929; Powell 2003) and is re-described herein.
Scapula (Fig. 2A, B).—The description of the scapula is mainly based on MLP-CS 1096 (Fig. 2A) because is the better-preserved specimen. The scapula and coracoid are co-ossified, as in Opisthocoelicaudia (Borsuk-Białynicka 1977). The scapula consists of two well-defined portions, a wide proximal part and a narrow distal, elongated scapular blade. The whole structure has a sigmoid shape in dorsal view and is medially curved. The ventral margin of the scapular blade is straight while the dorsal edge is sigmoid, with its proximal portion narrower than the distal one, which is expanded as in Saltasaurus. The dorsal margin of the proximal portion of the scapula is rugose, at the site where the anterior portion of the M. levator scapulae originated. The acromion is medially curved and laterally concave, as in Saltasaurus. The contact between the latter and the scapular blade is U-shaped. The scapular blade has a longitudinal ridge on its lateral surface (Huene 1929; Salgado et al. 2005). The proximal portion of the scapula is in contact with the coracoid, forming a nearly 90° angle glenoid fossa, resulting in a sub-triangular shape of the fossa. The glenoid is thick and faces ventrolaterally. The glenoid lip of the scapula presumably faced anteroventrally. There is a depression on the proximolateral surface of the scapula, also seen in Saltasaurus, which is interpreted as the supracoracoideal fossa, origin site of the M. deltoides scapularis (M. scapulohumeralis anterior sensu Borsuk-Białynicka 1977). There are also a fragment of right scapula (MLP-CS 1129) and a fragment of left scapula (MLP-CS 1301) that may belong to N. australis. The former was referred by Huene (1929: 36) to probably pertain to the same individual as MLP-CS 1096, which is likely. Both specimens have the same proportions and general outline, and also present a flat, rugose muscular scar posterior to the acromion. On the other hand, the also fragmentary specimen MLP-CS 1301 has the general outline and the medially-curved scapular blade of MLP-CS 1096. As pointed out by Huene (1929), it is highly probable that MLP-CS 1301 belongs to a juvenile specimen of N. australis.
The general aspect of the scapula of N. australis resembles that of other Titanosauria, such as Saltasaurus, Opisthocoelicaudia (Borsuk-Białynicka 1977), Lirainosaurus (Sanz et al. 1999), and Alamosaurus (Gilmore 1922). However, the scapula of the Patagonian specimen differs from these titanosaurs in having a glenoid lip that ends in a right angle.
Coracoid (Fig. 2A–C).—There are three preserved coracoids (MLP-CS 1096, MLP-CS 1298, and MLP-Ly 14). Two of them (MLP-CS 1096 and MLP-CS 1298) are co-ossified with the respective scapula. The coracoid corresponds in size to the proximal portion of the scapula. It is stout and firmly fused to the scapula along its posterior surface although the suture is not evident. The ventral margin of the element contacts the anterior margin in a nearly 90° angle, giving the coracoid a quadrangular outline, resembling that of Saltasaurus (Wilson 2002; Powell 2003). The glenoid (ventral) portion is notably rugose and thick, particularly the infraglenoid lip. The medial surface is flat, while the lateral surface presents a concavity, origin site of M. supracoracoideus. There is a slight ridge anterior to the concavity, perpendicular to the dorsal margin, which Huene (1929: 37) referred to as the attachment site of pectoral musculature. It may actually correspond to the M. coracobrachialis. In MLP-CS 1096 and MLP-CS 1298 the coracoid foramen is not evident, although there is a slender non-perforated hole close to the margin of the scapular contact.
The general quadrangular outline of the coracoid is similar to that of other saltasaurines (i.e., Saltasaurus) and several Titanosauria (e.g., Lirainosaurus, Sanz et al. 1999), but differs from others (e.g., Opisthocoelicaudia, Borsuk-Białynicka 1977; Rapetosaurus, Curry Rogers and Forster 2001; Curry Rogers 2009; and Isisaurus, Jain and Bandyopadhyay 1997) in which the outline is roughly oval. The lateral ridge present in MLP-CS 1096 is also present in Saltasaurus (PVL 4017-92, Powell 2003: 35).
Sternal plates (Fig. 2D, E).—There are two sternal plates mentioned by Huene (1929) as belonging to Neuquensaurus australis (MLP-CS 1104 and MLP-CS 1260). The general outline of the sternal plate is crescentic as in other Titanosauria (Salgado et al. 1997; Wilson 2002; Curry Rogers 2005), with lateral margins strongly concave. The anterior portion is robust and becomes thinner towards its lateral and posterior borders. The anteroventral region has a stout crest which runs anteroposteriorly, and was the origin site of M. pectoralis (Huene 1929; Borsuk-Białynicka 1977). The crest is ventrolaterally oriented. The dorsal surface is almost flat. The right sternal MLP-CS 1104 and the left sternal MLP-CS 1260 are very similar in size and general proportions, so that they are symmetrically equal. As pointed out by Huene (1929: 36), it is very probable that pertain to a single individual.
Crescentic sternal plates are also present in Rapetosaurus (Curry Rogers 2009); Alamosaurus (Lucas and Hunt 1989), Opisthocoelicaudia (Borsuk-Białynicka 1977) and Saltasaurus (Powell 2003). Nonetheless, the most interesting features of the sternal plates present in N. australis are their large size and the presence of the large anteroventral ridge. A similar ridge is present in Saltasaurus (Powell 2003: pl. 39b), although it is much less developed than in the Patagonian specimens.
There is also a right sternal plate (MLP-CS 1295) referred by Huene (1929) and Powell (2003) as a left sternal of N. robustus. I consider these as belonging to N. australis due to their close resemblance, general outline, and the presence of the well developed anteroventral crest (contra Huene 1929: 36).
Several elements of the forelimb are represented, including well preserved right and left humeri, ulnae and radii; however many others elements described by Huene (1929) are missing.
Humerus (Fig. 3).—Nine humeri are preserved in total. The humerus is a robust bone, as in other Titanosauria (robustness index, RI = 0.305–0.339, Appendix 2A), but more slender than that of Opisthocoelicaudia (RI = 0.37, Wilson and Upchurch 2003). The proximal and distal portions are expanded, particularly the former, reaching in some cases (e.g., MLP-CS 1050) 50% of the total length of the bone. The proximal portion is slightly medially oriented with respect to the distal end, as in Saltasaurus (Powell 2003). It is mediolaterally expanded and anteriorly concave. The humeral head is rounded and well developed. The lateral margin of the diaphysis is also concave. The proximal surface has its greater robustness in the central part, corresponding to the humeral head, being more slender on its lateral and medial margins. The dorsal edge of the proximal end is straight and forms a 90° angle with the lateral margin, as in Saltasaurus and Opisthocoelicaudia (Borsuk-Białynicka 1977: fig. 7B). The most notable features of the proximal portion are the above-mentioned mediolateral expansion and the robust deltopectoral crest, which runs down the lateral edge of the anterior face of the proximal half of the bone: this is longitudinally oriented, and slightly medially twisted. This structure has a rugose surface, which was the site for the attachment of the abductor musculature (i.e., M. pectoralis, M. dorsalis scapulae, and M. deltoides scapularis). There is a deep surface on the anteroproximal portion of the humerus, medial to the deltopectoral crest, which is interpreted as the site of insertion of the M. coracobrachialis (“coracobraquial breve” sensu Huene 1929; see also Powell 2003). The posterior surface has a tuberosity placed posteroventrally to the deltopectoral crest. This structure is also seen in Opisthocoelicaudia (Borsuk-Białynicka 1977: fig. 7D) and Saltasaurus, although it is less developed in these taxa than in Neuquensaurus. This tuberosity was the site of insertion of M. latissimus dorsi, not the “braquial inferior” (contra Huene 1929).
The humeral shaft is mediolaterally expanded and its cross section is approximately elliptical, with its anteroposterior length 70% of the mediolateral breadth (eccentricity index, ECC index= 1.3–1.45, Appendix 2A). The posterior surface of the proximal portion of the humerus has a longitudinally oriented convex area flanked by two depressions, which correspond to the origin site of the humeral heads of M. anconeus. The distal end of the humerus is less expanded than the proximal one. The condyles are asymmetrical, being the lateral condyle the more robust. They are separated by the cuboid fossa, which is well developed in saltasaurines.
A proximal portion of a right humerus (MLP-CS 1019) was referred by Huene (1929) to “Titanosaurus” robustus. As he pointed out, this bone lacks the acute angle between the dorsal and lateral edges seen on the other humeri. However, that portion of the bone is not well preserved and shows abrasion marks as well as the periosteum damaged. In other respects, the bone presents similar proportions and a robust and elongated deltopectoral crest of those seen in Neuquensaurus australis. Despite the fact that it is difficult to assess a definitively taxonomic identity to that bone, I find no reason to consider MLP-CS 1019 as different from N. australis.
The most notable features of Neuquensaurus humeri are their robustness and the mediolateral development of the proximal portion, as well as the almost right angle between the dorsal and lateral margins of the proximal portion, also seen in other Titanosauria, such as Saltasaurus (PVL 4017-92, Powell 1992), Opisthocoelicaudia (Borsuk-Białynicka 1977), Alamosaurus (Lucas and Hunt 1989), and Magyarosaurus (McIntosh 1990: fig. 16.10).
There is also a left humerus (MLP-Ly 25) that Lydekker (1893: pl. 4: 2) assigned to Microcoelus patagonicus Lydekker, 1893. Huene (1929) described that bone together with those of “Titanosaurus” australis due to their close resemblance. Also, Powell (2003: 45) regarded Microcoelus patagonicus as a nomen dubium because of the lack of diagnostic features. I agree with Huene (1929) in the fact that the humerus referred by Lydekker to M. patagonicus must be considered as belonging to Neuquensaurus australis because of their similar size and proportions, the well developed and distally expanded deltopectoral crest, and the almost right angle between the lateral and dorsal margin.
Ulna (Fig. 4).—Ten ulnae were mentioned by Huene (1929), although only eight of those can be located, one of those of dubious affinities. The proximal portion of the ulna is wide and is formed by three structures. Two conspicuous ridges anteromedially and anterolaterally directed, respectively, frame the olecranon on both sides: the anterolateral (AL), and the anteromedial (AM) processes (Bonnan 2003: 607). The third structure is the olecranon process, which is placed posterolaterally and was the insertion site of the tendons of M. anconeus. It is a well defined structure, although it does not protrude above the articular surface. Those three elements (the olecranon plus the two processes) define a triradiate proximal cross-section. The radial (anterior) and medial surfaces are concave. There is a longitudinal ridge on the radial surface that corresponded to the origin site of M. pronator quadratus (Huene 1929; Meers 2003). There are also two left ulnae (MLP-CS 1053 and MLP-CS 2004) which Huene (1929: 39) and Powell (2003: 39) both referred to N. australis. However, those bones does not resemble the slender appearance of the ulna of N. australis, but have the stout look and extremely developed ulnae of N. robustus (MLP-CS 1094 and MLP-CS 1095), which constitute part of the lectotype designed by Bonaparte and Gasparini (1978). The olecranon process of MLP-CS 1053 (Huene 1929: pl. 11: 2), MLP-CS 2004, MLP-CS 1094, and MLP-CS 1095 are strongly developed, projecting above the proximal articulation (contra Curry Rogers 2005: 85). I consider MLP-CS 1053 and MLP-CS 2004 as belonging to N. robustus.
A well defined but not projecting olecranon process is also present in other Titanosauria, such as Rapetosaurus (Curry Rogers 2009: fig. 37) and Magyarosaurus (McIntosh 1990: fig. 16.11 L). An olecranon process that project above the articular surface, as seen in N. robustus, is also present in the camarasaurid Janenschia (Upchurch 1995: fig. 14 B) and in the titanosaurs Saltasaurus (PVL 4017-74), Opisthocoelicaudia (Borsuk-Białynicka 1977: fig. 8A) and Malawisaurus (Gomani 2005: 22).
Radius (Fig. 5).—Five radii of Neuquensaurus are preserved. There are two additional radii with dubious affinities. The radius is a rather bent bone. Its proximal end is more expanded than the distal one; it is roughly oval in proximal view and its dorsal margin is straight, with rugosities on the proximal and distal ends. The proximal portion is medially expanded. The anti-ulnar (anterior) face is straight, while the ulnar (posterior) face is convex. On the latter there is a furrow flanked by two ridges oriented obliquely from the anteromedial to the posterolateral side of the diaphysis (“interosseous ridge”, Curry Rogers 2009). The medial ridge could correspond to the insertion site of the M. pronator teres (see also Huene 1929; Borsuk-Białynicka 1977). The distal surface of the bone is elliptical and its distal margin is oriented obliquely with respect to the long axis of the diaphysis, from the ventromedial to the dorsolateral side.
A well developed interosseous ridge is also observed in Saltasaurus (PVL 4017-92, contra Curry Rogers 2005: 87), Aeolosaurus (Salgado and Coria 1993: fig. 6), Opisthocoelicaudia (Borsuk-Białynicka 1977), and Rapetosaurus (Curry Rogers 2009).
Huene (1929) referred to “Titanosaurus” australis several radii (MLP-CS 1176, MLP-CS 1172, MLP-CS 1169, and MLP-CS 1175), which differ from MLP-CS 1167 and MLP-CS 1174. The formers are more robust (see Appendix 2C), have the proximal and distal ends more expanded and the interosseous ridge more developed. In this sense, those materials close resembles the lectotype of N. robustus (MLP-CS 1171). I consider MLP-CS 1172, MLP-CS 1175, and MLP-CS 1169 as belonging to N. robustus. On the other hand, MLP-CS 1176 is longer than the lectotype of N. robustus and has less expanded proximal and distal ends: hence, its assignation to N. australis is probably correct.
Carpus and manus (Fig. 6).—The only carpal (MLP-CS 1234) tentatively assigned to “T”. australis by Huene (1929: pl. 12: 1) is missing. The overall shape is rounded although its proximal surface is almost pyramidal. No other anatomical details can be gleaned from Huene's drawing.
There are three metacarpals (MLP-CS 1197, MLP-CS 1189, and MLP-CS 1238, Fig. 6) that were erroneously assigned by Huene (1929) as metatarsals of “Titanosaurus” robustus (Powell 2003). Metacarpal II (MLP-CS 1197, Fig. 2A) is columnar, with expanded ends. The proximal portion is rugose and has a triangular outline, with the apex on the palmar side. The medial side of the triangle is convex and articulated with the concave surface of metacarpal I (Apesteguía 2005). On the proximomedial side there is a short, longitudinal ridge facing downward, which is the articulation area for metacarpal I. The lateral and anteroproximal sides of the bone are flat. However, there is a longitudinal ridge that extends from the middle of the shaft to the distal portion, close to the distal end. The distal part of metacarpal II is quadrangular in outline and bears rugosities.
Metacarpal III (MLP-CS 1189, Fig. 2B) is similar to metacarpal II in general outline. Its proximal portion has a triangular shape, with slight convex sides. The diaphysis is columnar with a triangular cross-section, while the distal end is quadrangular in cross section. Rugosities are present on the proximal and distal portions and the anterior side of the shaft is flat. The lateral side has a ridge flanked by rugosities.
Metacarpal IV (MLP-CS 1238, Fig. 2C) has a characteristic subrectangular cross-section in proximal view (Apesteguía 2005). The lateral and medial sides are concave for articulation with metacarpals V and III, respectively. The anterior surface is almost flat and the palmar side is broader proximally. On the lateral and medial sides of the proximal end there are two ridges flanking both sides that probably correspond to attachment sites for tendons (Huene 1929).
Some pedal phalanges (MLP-CS 1202, 1204, 1206, 1222, 1223, 1224) were erroneously drawn as belonging to the manus by Huene (1929: pl. 12: 13–15) and will be described accordingly below.
As in other neosauropods (e.g., Diplodocus, Camarasaurus, Brachiosaurus, Rapetosaurus, Opishocoelicaudia), the proximal end of metacarpals II and III form triangular wedges in proximal views. Metacarpal IV of Neuquensaurus shares with other titanosaurs the presence of a subrectangular proximal end with concave sides for articulation with metacarpals III and V (Apesteguía 2005).
Several ilia, ischia and pubes were previously described (Lydekker 1893; Huene 1929; Powell 2003; Salgado et al. 2005). Eleven incomplete ilia of Neuquensaurus australis and materials referred to Neuquensaurus robustus were described by Lydekker (1893) and Huene (1929); seven of those could be located in the MLP collection (MLP-CS 1056, MLP-CS 1057, MLP-CS 1258, MLP-CS 1259, MLP-CS 2008, MLP-Ly 17, and MLP-Av 2069). Salgado et al. (2005) assigned to N. australis an almost complete pair of ilia (MCS-5/16) fused to the sacrum, and a fragment of ischium (MCS-5/24). There is also a fragment of ischium that probably pertains to the genus that has not previously been described (MPCA-CS 001) and is described here for the first time.
Ilium (Fig. 7).—The description of the ilium is based on the original material described by Lydekker (1893) (MLP-Ly 17), a fragment of left ilium described by Huene (1929) (MLP-Av 2069) as belonging to “Titanosaurus” robustus, which I consider more probably that of N. australis, and those elements described by Salgado et al. (2005) (MCS5/16). The ilium has both expanded preacetabular and postacetabular portions. The preacetabular lobe of MCS-5/16 (Fig. 7A) is subhorizontally oriented and projects laterally, as in others titanosaurs (Borsuk-Białynicka 1977; Salgado et al. 1997, 2005; Jain and Bandyopadhyay 1997; Upchurch 1998). The whole iliac blade has a “twisted” configuration, so that the outside surface of the preacetabular lobe faces upward, whereas the outside surface of the postacetabular lobe faces downward (Salgado et al. 2005). The pubic peduncle is transversely expanded and anteroventrally directed, and its ventral (distal) surface has a triangular shape, with one of the vertices pointing inwards. The ischiadic peduncle is poorly developed, as in other sauropods (Wilson 2002). The shape of the preacetabular lobe is semicircular and it faces anterodorsally when the ilium is oriented with the ischial and pubic peduncles in the same plane (Salgado et al. 1997). The fragment of left ilium described by Huene (1929) (MLP-Av 2069) as belonging to “T”. robustus, I consider more closely similar to that of N. australis because of its general proportions, the mediolaterlal development of the pubic peduncle and the same angle between the preacetabular lobe and the pubic peduncle.
An anteroventrally directed pubic peduncle is also reported in Opisthocoelicaudia (Borsuk-Białynicka 1977: fig. 12). The most noteworthy feature of the ilium of Neuquensaurus is the lateral projection of the preacetabular lobe with respect to the long axis of the ilium (Salgado et al. 2005). This condition is related to the great development of the hind limb extensor musculature (Otero and Vizcaíno 2008). This condition is also present in other saltasaurines, such as Saltasaurus (PVL 4017-92) and Rocasaurus (MPCA-Pv 46), and non-titanosaur sauropods, such as Camarasaurus (Osborn and Mook 1921: figs. 49, 87).
Ischium (Fig. 8).—The description of the ischium is based on MCS-5/24 and a hitherto undescribed, well preserved but incomplete right ischium (MPC A-CS 001). Additionally, Huene (1929: 40, pl. 14: 3) mentioned the existence of a fragment of a left ischium (MLP-CS 1261) that resembles MCS-5/24. The ischium is, as in other titanosaurs (see Salgado et al. 1997: fig. 5), a short bone with a relatively broad blade. This could be related to the development of the site of origin of the adductor musculature (Otero and Vizcaíno 2008). MCS-5/24 is slender, more so than MPCA-CS 001. The latter is a robust bone, showing thickened articular surfaces. The iliac peduncle is well developed and stout, and is separated from the main body of the ischium (Curry Rogers 2005: character 332), as in Saltasaurus and Rocasaurus. The pubic peduncle, only preserved in MPCA-CS 001, is extensive, as in other titanosaurs. In MPCA-CS 001 there is a protuberance on the lateral surface of the posterior margin, over the line of the pubic contact, also reported in MLP-CS 1261 (Huene 1929: 41). This is the ischial tuberosity, an elongated process with rugosities over the surface, which was the site of origin of the M. flexor tibialis internus 3 (Borsuk-Białynicka 1977; Hutchinson 2001a, 2002). The posterior margin is similar to that of Saltasaurus, and differs from Rocasaurus in being less concave.
The assignment of MPCA-CS 001 to Neuquensaurus australis is mainly based on the presence of the ischial tuberosity, which is mentioned by Huene (1929: 41). This tuberosity can not be seen in MCS-5/24 because the ischial blade is damaged. The ischial tuberosity is also reported in other Titanosauria, such as Opisthocoelicaudia (Borsuk-Białynicka 1977), Rapetosaurus (Curry Rogers 2009), Rocasaurus (MPCS-Pv 46), and Saltasaurus (PVL 4017-99).
The ischium of Neuquensaurus has a similar morphology to that of other Titanosauria (e.g., Saltasaurus, Rocasaurus, Aeolosaurus, Isisaurus, Alamosaurus) in which the whole structure has a semilunate shape with a distally expanded blade.
Pubis (Fig. 9).—Five incomplete pubes of Neuquensaurus are preserved. Only MLP-CS 1102 has a relatively well-preserved shaft. The pubis is an expanded bone with thick proximal and distal margins. The proximal end is wider than the entire shaft, while the distal end is as wide as the shaft. There is a longitudinal crest on the ventral surface of the bone, close to the lateral margin (“ventral crest”, Powell 2003: fig. 43: lb). The presence of the longitudinal crest determinates two parallel areas, which were the sites of origin of the M. puboischiofemoralis externus 1 and 2 (Borsuk-Białynicka 1977; Otero and Vizcaíno 2008). The dorsal surface of the pubis is flat. The obturator foramen is only partially preserved in MLP-CS 1102 and is placed near the puboischiatic contact. The posteromedial margin of the pubic blade is becomes thinner close to the contralateral pubis.
The crest on the ventral surface of the pubis is also present in other titanosaurs such as Saltasaurus (PVL 4017-95), Isisaurus (Jain and Bandyopadhyay 1997: fig. 24B), Opisthocoelicaudia (Borsuk-Białynicka 1977: fig. 12) and Aeolosaurus (Salgado and Coria 1993: fig. 8), although it is more weakly developed than in N. australis.