120


Journal of Paleontology 90(1):102–132


such that the exterior–facing part of each metacarpal will be called anterior, and the interior–facing part (the palmar surface) will be called posterior. Metacarpal I is elongate (length/midshaft breadth =9.0;


Table 2) with a straight medial border and curved lateral border (Fig. 16). The proximal end is D-shaped, with subequal anteroposterior and transverse dimensions, unlike the transver- sely compressed proximal end of metacarpal I in Venenosaurus (Fig. 17). The midshaft is rounded in cross section and bears a flat boss about two-thirds of the way up the shaft on its posterior side, as in the metacarpals of many sauropods (e.g., Camarasaurus, Ostrom and McIntosh, 1966; Veneno- saurus, Fig. 17). Distally, metacarpal I is subrectangular, undivided, and its articular face is orthogonal to the long axis of the bone. The posterior side of the distal end is weakly divided into medial and lateral condyles. Metacarpal II does not appear to be as gracile as metacarpal I (Table 2). Its proximal end forms an elongate triangle, whereas its distal end is


subrectangular with two posteriorly projecting condyles (Fig. 16). As in other sauropods, the medial condyle (i.e., that facing metacarpal I) is better developed. The proximal and distal ends are subequal in area to those of metacarpal I. Little is preserved of metacarpal III; its proximal end is teardrop-shaped with a flat anterior face and pointed posterior face. Metacarpal IV is strongly damaged proximally. It tapers towards a narrow midshaft, and widens distally. As in the other metacarpals, the distal end has weakly divided condyles posteriorly, but is undivided distally (Fig. 16).


Ilium.—The left ilium is preserved as several fragments (ASDM 500-30, -371, -372, -373, -379; (Fig. 18) that do not fit together with complete precision. The preacetabular process flares laterally and is strongly expanded anterodorsally. All that is preserved of the right ilium is a 34 cm–long segment of the pubic peduncle, whose distal end measures an estimated 21cm transversely (ca. 18cm preserved) by 10cm anteroposteriorly. Though the medial face is not completely preserved, it is clear that Sonorasaurus possessed the titanosauriform condition, in which the iliac peduncle is anteroposteriorly narrow and trans- versely broad (D’Emic, 2012). Considering the left and right ilia together indicates that the pubic peduncle was very tall, resem- bling that of Giraffatitan (Janensch, 1961:pl. 198; Fig. 18). None of the many broken surfaces of the ilium reveal pneumaticity.


Tibia.—The right tibia is poorly preserved and is missing much of its proximal and distal ends (Fig. 19). It measures at least 95.5cm long, and its midshaft is D-shaped and measures 13.8cm × 8.0 cm, with a circumference of 34.8 cm. Its distal end is expanded transversely relative to its midshaft, but this may be an artefact of crushing of the latter. Little else can be said about its morphology due to damage.


Figure 18. Holotypic ilia of Sonorasaurus thompsoni (ASDM 500) from the mid-Cretaceous Turney Ranch Formation of Arizona, USA: (1) partial left ilium in lateral view; (2) pubic peduncle of right ilium in lateral view; (3) same in anterior view; (4) same in posterior view; (5) same in distal view.


Figure 19. Holotypic right tibia of Sonorasaurus thompsoni (ASDM 500) from the mid-Cretaceous Turney Ranch Formation of Arizona, USA: (1) lateral; (2) medial; (3) anterior views, with schematic cross section depicted between (2) and (3).


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