Aeolosaurus sp.

Garcia, Rodolfo A. & Salgado, Leonardo, 2013, The titanosaur sauropods from the late Campanian-early Maastrichtian Allen Formation of Salitral Moreno, Río Negro, Argentina, Acta Palaeontologica Polonica 58 (2), pp. 269-284 : 270-274

Aeolosaurus sp.

Figs. 2–4 , 5A .

Material.— A single specimen (MPCA−Pv 27174) represented by three anterior caudal vertebrae, one mid−caudal, one mid−posterior caudal, right ulna, left radius, metacarpal III, left pubis, and right ischium. A second specimen (MPCA−Pv 27175) is represented only by a left ulna. Salgado and Coria (1993) provided a brief description of most of these elements. In this work, we re−describe the already published material and describe for the first time other material very probably belonging to a third specimen, a left ulna, MPCA−Pv 27180. Besides, there is a lot of material of Aeolosaurus sp. that could belong to any of these three specimens: a left humerus (MPCA−Pv 27176), a left femur (MPCA−Pv 27177), a metatarsal I (MPCA−Pv 27178), and a haemal arch (MPCA−Pv 27179). In addition, there is a partial sacrum, assigned to the specimen MPCA−Pv 27174 by Salgado et al. (1997), that clearly comes from a much smaller sauropod. All from Salitral Moreno locality, Rio Negro, Argentina, Campanian– Maastrichtian, Upper Cretaceous .

Description

Anterior (1 st and 2 nd?) caudal vertebra.— Salgado and Coria (1993) mentioned but did not describe two large, anterior caudal vertebrae, which confidently belong to the specimen MPCA−Pv 27174. These elements are incomplete and badly crushed, but some characters are easily distinguishable. The wide centrum is only slightly procoelous; its lateral faces are anteroposteriorly concave and dorsoventrally plane; in lateral view, the robust articulations for the haemapophyses are prominent. The neural arch is robust and the neural canal is wide. The small and slender transverse processes are clearly observed ( Fig. 2A ). The neural spine is not preserved.

Anterior (3 rd?) caudal vertebra.—Unlike the elements previously described, the centrum of this vertebra is strongly procoelous, with broad articular surfaces ( Salgado and Coria 1993). Its lateral faces are anteroposteriorly concave and dorsoventraly plane. The ventral face is only slightly anteroposteriorly concave.

The base of the neural arch occupies all the anteroposterior length of the centrum. The transverse processes are placed on the neural arch, just above the centrum−arch boundary. These are robust and directed posterolaterally ( Fig. 2B , Supplementary Online Material: SOM 1 available at http://app.pan.pl/ SOM/app58−Garcia_Salgado_SOM.pdf)

As described by Salgado and Coria (1993), the prezygapophyses are robust, anterodorsally projected at an angle of nearly 60 ° above the floor of the neural canal. The articular facets of the prezygapophyses are broad, ellipsoid, with their greater axes anteroposteriorly oriented, and their articular surfaces almost vertical. The postzygapophyses are equidistant from the anterior and posterior borders of the centrum; these are short and are, like the prezygapophyses, substantial. The articular surfaces of the postzygapophyses are broad and kidney−shaped, with their greater axes dorsocaudally oriented. The neural spine is not preserved.

Mid (5 th?) caudal vertebra.—The centrum has broad, high lateral faces, which are anteroposteriorly concave and dorsoventrally plane. The ventral face is narrow, with the articulations for the haemapophyses well developed, enclosing a deep furrow between them. In lateral view ( Fig. 2C ), the ventral border of the centrum is very concave.

The transverse processes are robust and posterolateraly projected. They are ventral to the postzygapophyses, rather below the position in the anterior caudals ( Fig. 2A–C ). The neural arch is on the anterior−mid part of the centrum, more anterior than in the anterior caudals, and it is more anteriorly inclined.

The prezygapophyses are more elongate and more anteroventrally inclined than in the anterior caudals; they form an angle of 40 ° to the base of the neural canal. The articular facets are subcircular and subvertical. The pre− and postzygapophyses are horizontal and level, a condition that changes towards the posterior caudals; obviously, this is explained by the different curvatures of the successive portions of the tail.

The postzygapophyses are at the base of the neural spine, on the middle of the vertebral centrum, dorsal to the anterior portion of the transverse processes. The articular surface of the postzygapophysis is subtriangular, slightly concave dorsoventrally, and smaller than the articular surface of the prezygapophyses. The spinopostzygapophyseal lamina is well developed.

The neural spine is anterodorsally inclined at 80 ° to the base of the neural canal, and at 40 ° to the prezygapophyses; it is lateromedially compressed, mostly in its mid portion. The distal end of the neural spine surpasses the anterior border of the centrum. On the right lateral side of the neural spine, where the bone is damaged, it is not possible to observe pneumatic tissue. The spinoprezygapophyseal lamina and spinopostzygapophyseal lamina are preserved only on the left side of the neural spine: these laminae contact the neural spine with the pre− and postzygapophyses, respectively.

Mid−posterior (10 th?) caudal vertebra.—The centrum ( Fig. 2D ) is similar to that of the mid caudal, except for the articular condyle, which is less pronounced and more dorsally pointing. The lateral sides of the centrum are somewhat less concave than in the mid caudal, and the ventral face is broader. The articulations for the haemapophysis, although incompletely preserved, are well developed, more than in the anterior and mid caudal.

http://dx.doi.org/10.4202/app.2011.0055

The well−developed prezygapophyses are robust, anteriorly projected, and placed just above the centrum−neural arch boundary. The articular surfaces of these apophyses are slightly convex, and their planes are practically vertical. The postzygapophyses are placed at a higher level than the prezygapophyses, unlike the condition in the anterior and mid caudals. The articular surface of the postzygapophysis is concave, being in the vertical plane, mostly its lower half. The neural spine is low and notably compressed lateromedially, more than in the mid caudal; it is anteriorly directed, but not as much as in the caudal vertebrae already described.

Chevron.—A complete, probably mid−distal haemal arch (MPCA−Pv−27179) is well preserved. This element ( Fig. 2E ) was not previously described. The haemal spine is very short; the haemal canal is wide, and, in lateral view, the haemal peduncles are angled 40 ° posteriorly, with respect to the haemal spine. The articular surfaces for the vertebral centrum are well developed. The right process has a protuberance, probably a deformation or a scar.

Humerus.—A left humerus is preserved, and is described here for the first time ( Fig. 3A ). The humeral head and deltopectoral crest are partially preserved; however, it is possible to infer that the proximal portion of the bone was expanded lateromedially, much like the humerus of Aeolosaurus from the Los Alamitos Formation described by Salgado et al. (1997a). In anterior view, the medial margin is markedly concave, much more than the lateral margin, which is straighter ( Fig. 3A 1 , A 2 ), but not as concave as in Neuquensaurus ( Salgado et al. 2005; Otero 2010). The deltopectoral crest, although partially preserved, is robust and presents a protuberance on its lateral margin. In posterior view ( Fig. 3A 4 ), the cuboid fossa or intra−condylar furrow on the distal end of the bone is broader than that of the humerus of the titanosaur described below (MPCA−Pv 88/A) and other titanosaurs. The ratio between the minimum shaft diameter and the length of the bone is 0.17 (14 cm / 81.5 cm) (see SOM 1). This value shows that this element is robust when compared with the same bone of the Titanosauria gen. et sp. indet. 2 (MPCA−Pv 88/A) described below.

Ulna.—Three basically similar ulnae ( Fig. 3C, D ), one right (MPCA−Pv 27174), belonging to the same specimen as the other pieces, and two left, one of a greater size (MPCA−Pv 27175) and the other one, smaller (MPCA−Pv 271780), are relatively well preserved, although the anterolateral process of the MPCA−Pv 27175, and the olecranon process of the MPCA−Pv 271780) are incomplete (see SOM 1). The morphology of the ulnae is similar to that of Aeolosaurus rionegrinus . The bone has three main structures, which in proximal view are easily observed. There are two conspicuous processes, the anteromedial and anterolateral, which run longitudinally, becoming less developed to the distal end, and the olecranon process, which is placed posterolaterally at the most proximal end of the bone.

Posteriorly, the ulna has a broad, concave surface that reaches the mid portion of the bone: from there up to the distal condyle, the bone surface is plane. In lateral view ( Fig. 3C 1 ), on the radial face, the three specimens show a notable anterolateral process (in the largest ulna this process is only represented by its base), which runs along the length of the bone, dividing two surfaces, one broader than the other, the first one being that that for articulation with the radius.

Near the most proximal anteromedial process, on the broader surface, an osseous protuberance (scar) is observed, probably for muscular attachment. Proximally, as noted by Salgado and Coria (1993), the ulna is triradiate and the olecranon is prominent, as is common in titanosaurs ( Fig. 3C 2 , C 3 ). The distal articulation is semicircular ( Fig. 3C 4 ). The greater axis of the distal epiphysis (articular surface) is perpendicular to the greater axis of the proximal epiphysis (articular surface).

Radius.—A left radius is preserved (MPCA−Pv 27174). This bone matches perfectly with the right ulna MPCA−Pv 27174 ( Salgado and Coria 1993), and these probably belong to the same individual (see SOM 1). It is a slightly curved bone, lateromedially compressed, with its epiphyses (distal and proximal) expanded, the proximal epiphysis being more expanded than the distal one ( Fig. 3E ). The lateral margin is slightly concave, while the medial is straight. Distally on its lateral face, a rugose, very developed prominence is present; this is perhaps for the insertion of M. flexor carpi radialis ( Borsuk−Białynicka 1977). In posterior or ulnar view, the interosseous ridge runs from the proximomedial portion three−quarters of the way along the bone, but it is not so developed as in other titanosaurs such as Rapetosaurus ( Curry Rogers 2009) and Neuquensaurus ( Otero 2010) . The width of the proximal expansion practically doubles the narrowest portion of the diaphysis, and its proximal margin is oriented perpendicular to the long axis of the diaphysis, while the distal margin is oblique to the long axis.

Metacarpal.—The only bone of the metacarpus that is preserved is a third metacarpal ( Salgado and Coria 1993). It is straight and robust; however, it is less robust than the metacarpal reassigned to Neuquensaurus robustus by Otero (2010). At mid−shaft the section of the bone is elliptic, and its ends are only slightly expanded ( Fig. 3B , SOM 1). The proximal articular surface is markedly wider than the distal articular end, and has a triangular contour in proximal view. Distally, the articular surface is elliptical. The metacarpal/radius ratio is 0.73, the highest value in a sauropod, which raises doubts about the association of the two elements. Likewise, the metacarpal is 73.3% of the radius, much higher than the values in Camarasaurus (47%), and in the titanosaurs Opisthocoelicaudia (46%) and Alamosaurus sanjuanensis (51%) ( Apesteguía 2005).

Pubis.—A left pubis (MPCA−Pv 27174) is preserved. Compared with the pubis of other titanosaurs (e.g., Neuquensaurus ) it is a robust bone ( Fig. 4B ). Its distal end is practically complete, except for the distalmost portion, which appears not to have been strongly expanded. It is wide dorsolatero−ventromedially, and its lateroventral face bears a longitudinal crest (“ventral crest” of Powell 2003 and Otero 2010) that divides two surfaces, much like the crest observed in other titanosaurs, such as Uberabatitan ( Salgado and Carvalho 2008) . At its mid part, the pubis has a nearly elliptical cross−section. The laterodorsal margin of the pubis is concave, whereas the medioventral margin is irregular, in part due to its poor preservation. The articular surface for the ischium is the thickest portion of the bone, becoming abruptly laminar and thin towards its ventral portion. The articulation with the ilium is not completely preserved. The obturator foramen is placed near the puboischiatic contact.

Ischium.—The right ischium is practically complete ( Fig. 4C ). The iliac peduncle is relatively short, and significantly less robust than in the holotype of Aeolosaurus rionegrinus . The acetabular border is short, notably less extensive than in the holotype. The distal process is laminar, narrow at its mid portion, and distally expanded: it is not possible to appreciate the ischial tuberosity, as in Neuquensaurus australis ( Otero 2010) . The caudal margin of the ischium is less concave than in Aeolosaurus rionegrinus . The pubic peduncle is proximally wide; it is the thickest portion of the bone, as is the articular surface for the ischium of the pubis, which indicates a robust contact. Ventrally, the pubic peduncle becomes thin, becoming only a few millimetres thick ( Fig. 4C , SOM 1).

Femur.—The preserved left femur of this specimen was not

http://dx.doi.org/10.4202/app.2011.0055

described by Salgado and Coria (1993); it is straight, with its lateral and medial margins being virtually parallel ( Fig. 4A ). It is anteroposterioly compressed, and mediolaterally wide (mediolateral/anteroposterior index is 2.08). The lateral bulge that characterizes the femora of titanosauriformes is somewhat less developed than in other titanosaurs (e.g., Neuquensaurus [ Otero 2010]; Rocasaurus [ Salgado and Azpilicueta 2000]; Titanosauria indet. here described). The greater trochanter is developed at the intersection of the virtual extension of the dorsal surface of the femoral head with the virtual extension of the line that contains the most lateral point of the lateral bulge. The angle formed by these two straight lines is 114 °, which is less than in Rocasaurus and Titanosauria gen. et sp. indet. (MPCA−Pv 33/2) ( Fig. 5 ). The ratio between the minimum shaft width and the bone length, the so−called robustness index, is 0.19 (see SOM 1). The distal end of the femur, including the tibial and fibular condyles, seems to be somewhat less expanded than in other taxa ( Fig. 5 ). The posterior intercondylar groove is shallow, and reaches dorsally only 15% of total femur length.

Metatarsal.—The bone (MPCA−Pv 21778), here interpreted as a metatarsal I, was found associated with the other elements above described. It is short, with expanded proximal and distal ends ( Fig. 4D ). The proximal and distal articulations have elliptical contours, and form an angle of 90 °. This rotation is the main difference between this bone and the same bone in Rapetosaurus ( Curry Rogers 2009) .

Saltasaurinae Powell, 1992b

Genus Rocasaurus Salgado and Azpilicueta, 2000

Type species: Rocasaurus muniozi ; Salitral Moreno locality, Campanian–Maastrichtian.

Figures

Fig. 2. Titanosaur sauropod Aeolosaurus sp. (MPCA−Pv 27174) from Salitral Moreno locality, Rio Negro, Argentina, Campanian–Maastrichtian, Upper Cretaceous. A. First? anterior caudal vertebrae, in right lateral view. B. Third? anterior caudal vertebrate, in right lateral view. C. Fifth? anterior caudal vertebrae, in left lateral view. D. Tenth? anterior caudal vertebrae, in left lateral view. E. Haemal arch, in anterior view.

Fig. 3. Titanosaur sauropod Aeolosaurus sp., forelimb from Salitral Moreno locality, Rio Negro, Argentina, Campanian–Maastrichtian, Upper Cretaceous. A. Left humerus (MPCA−Pv 27176), in anterior (A1), posterior (A2), proximal (A3), and distal (A4) views. B. Metacarpal III (MPCA−Pv 27174), in anterior view. C. Right ulna (MPCA−Pv 27174), in lateral (C1), posterior (C2), proximal (C3), and distal (C4) views. D. Left ulna (MPCA−Pv 27180), in lateral view. E. Left radius (MPCA−Pv 27174), in posterior view.

Fig. 4. Titanosaur sauropod Aeolosaurus sp. from Salitral Moreno locality, Rio Negro, Argentina, Campanian–Maastrichtian, Upper Cretaceous. A. Left femur (MPCA−Pv 27177), in posterior (A1) and distal (A2) views. B. Left pubis (MPCA−Pv 27174), in anterolateral view. C. Right ischium (MPCA−Pv 27174), in lateral (C1) and pubis articular surface (C2) views. D. Metatarsal I (MPCA−Pv 27178), in medial (D1) and proximal (D2) views.

Fig. 5. Femora of titanosaurs from Salitral Moreno locality, Rio Negro, Argentina, Campanian–Maastrichtian, Upper Cretaceous, showing the greater trochanter angle. A. Aeolosaurus sp. (MPCA−Pv 27174). B. Rocasaurus muniozi Salgado and Azpilicueta, 2000 (MPCA−Pv 46/6). C. Titanosaurus sp. (MPCA−Pv 33/2).

Fig. 1. Site map showing the geographical location of Salitral Moreno, where specimens of titanosaurs were collected.