D’Emic et al.—Revision of the sauropod dinosaur Sonorasaurus


Table 2. Measurements of limb bones of Sonorasaurus thompsoni from the middle Cretaceous of Arizona, USA Length Proximal a-p or d-v Proximal trv Midshaft a-p or d-v Mid trv


rt ulna


rt humerus —— — 99.8 —— 90.5 96


rt radius lt radius mc I


mc II mc III mc IV rt tibia


mt II


mt IV mt V ph I.1 ph II.1


?ph III.1 or IV.1 ph II.2


rt fibula mt I


50.2 — —


>39


19.4 24.2 26.1 22.1 7.7 8.5 7.3 5.3


95.2i —— 97e


19.6 20.5 11.3 12.4 11.1 11.3


18.5i 12.3 15.4 6.8 5.7


6.8e 8


5.4i 5.4


10.1 8.1


9i


11.2 13.5 8.8


14.7 12 9


12.2 — 9


8e


6.8 —— 8.8 9.8 —— — 5.6 —— 8.4 —


5.4


8.2e 5.8


7.5


9.2i —— — 8.6 —— — 8.1 —— —


8.6 5.7 6.7 4.7 3.2 —


— 7


9.2 —


8.7 4.5 5.7 4.1


7.5 —— — — — —


18.5 11.9 8.7i 9.4 4.3


9.1i 7.8 6.3


8.1 —


6.2


Measurements are in centimeters. a-p, anteroposterior; d-v, dorsoventral; d, distorted measurement; e, estimated measurement; i, incomplete; lt, left; Min Circ, minimum circumference; mc, meta- carpal; mt, metatarsal; rt, right; rv, travel.


16.8 —


115


Distal a-p or d-v 24


13.2 21.5 16


Distal trv Min Circ 40.1


19.2 14.3 17


11.4 12.5 —


27.5e 11


10.1 6.6


47.5 33.2 26.2 26.5 18


— 21.1


17.7e 35.1d 25.3 24e


20.2 17.2


12.6e


Figure 13. Comparison of distal humerus shape in various neosauropods. Bones are scaled to the same transverse width and are oriented with their anterior faces towards the top of the page. Note the posterior projection of the ulnar condyle (highlighted by the thin horizontal line that runs along the posterior part of the opposite condyle) in Sonorasaurus and deeply nested titanosaurs. Specimen numbers for depicted humeri are: Apatosaurus, NMST–PV 20375 (drawn from Upchurch et al., 2004b); Camarasaurus, YPM 1901 (drawn from Ostrom and McIntosh, 1966); Sonorasaurus, ASDM 500; Ligabuesaurus, MCF–PHV 233; Rapetosaurus (FMNH PR 2209; reversed and drawn from Curry Rogers, 2009); Neuquensaurus, MCS–8.


The distal articular condyles are undivided when viewed in anteroposterior views (Fig. 13.1, 8), restricted to the distal face of the bone, and have a coarse crenulated texture indicative of a cartilaginous covering. There is a deep supracondylar fossa on the posterior face of the distal end of the humerus as in many other sauropods (Fig. 13.2).


Ulna.—A right ulna is preserved in four segments that roughly articulate with one another and is mostly complete, only missing its anteromedial arm proximally (Fig. 14). The ulna is elongate with a slightly raised olecranon process and a slightly poster- iorly expanded distal end. The cross-sectional shape of the ulna varies along its length; near the proximal end, it is a ‘pinched’ triangle, with fossae on the anterior, posteromedial, and posterolateral faces, though these fossae are exaggerated by crushing (Fig. 14). More distally, these fossae shallow and the cross-section becomes subtriangular. A well-developed ridge for ligamentous attachment to the radius is present obliquely along the anterior face of the bone. The distal end of the ulna is D-shaped, with a gentle concavity anteriorly for reception of the radius, a pointed lateral edge, and a gently rounded medial edge.


Radius.—Both left and right radii were recovered from the Sonorasaurus quarry; the right (Fig. 15) is better preserved. The left radius appears to be slightly longer than the right (ca. 96cm versus 90.2), though this seems to be an artifact of crushing and too much reconstruction along the shaft of the left radius. The other dimensions of the left and right radii are nearly identical (Table 2). The radius is very gracile with relatively unexpanded proximal and distal ends. The proximal end is D–shaped as in other sauropods, with an anterior pointed end, flat medial face, and rounded lateral face. Each radius bears a sharp ridge that extends obliquely along its length and a parallel, rounder ridge that extends for only part of its midshaft (Fig. 10); these ridges mark the ligaments for attachment of, and bound the articulation site for, the ulna (Borsuk–Bialynicka, 1977). The midshaft of the radius is oval and about 1.2 times broader than wide. The distal end of the radius is orthogonal to the long axis of the bone, unlike the condition in deeply nested titanosaurs (Wilson, 2002). The distal end is roughly oval in shape, with a small embayment on the posteromedial margin (accentuated by damage), as in most sauropods (e.g., Camarasaurus, Ostrom and McIntosh, 1966).


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