Early Modern Human from Tianyuan Cave, China

C h a p t e r 9The Tianyuan 1 Upper Limb Remains

96 C h a p t e r 9 The Tianyuan 1 Upper Limb Remains THE UPPER limb skeletons of Tianyuan 1 are reasonably well represented. The fossil preserves portions of both scapulae, both humeri, an ulna, both radii, three carpal bones, three proximal manual phalanges, a middle manual phalanx , and a distal manual phalanx (see Figure 3-2). In addition, it is possible to estimate reliably the original lengths of the left humerus and radius. But only the hand bones are largely complete. The preserved arm articulations consist of only one scapular glenoid fossa and one distal humerus; therefore, most of the comparisons are diaphyseal. Given evidence for marked asymmetry, especially in the humeral diaphyses, of the Tianyuan 1 upper limb and those of most other Late Pleistocene partial skeletons (Trinkaus et al., 1994; Churchill and Formicola, 1997; Trinkaus, 2006b), with the apparent exception of the Minatogawa ones (Baba and Endo, 1982), most of the comparisons for the shoulder and arm bones are made only to bones of the same side. Scapulae The scapulae provide information on both lateral spines and acromion processes and for the left glenoid fossa, coracoid process, infraglenoid tubercle, and cranial axillary border. Given the incomplete natures of these scapulae, there are limited osteometrics for them (Table 9-1), and several areas of interest are not in evidence. Spines and Acromion Processes The scapular spines (Figure 9-1) are relatively smooth with little rugosity for the attachments of deltoideus and trapezius. Near the middle of each spine is the THE TIANYUAN 1 UPPER LIMB REMAINS 97 caudal expansion over the infraspinatus surface, which is rounded on both spines but more projecting on the right side. It forms more of an inferiorly directed lip of bone on the right side, whereas it is mostly a thickening of the spine on the left side. This difference, as well as the general asymmetry reflected in the minimum spine thicknesses, is evident in the larger right side thickness values (Table 9-1). These values provide asymmetry indices of 13.4 and 22.2, respectively. The acromion processes are similar in terms of their breadths, but the right one projects ~5 mm farther than the left one. Both of the acromion processes nonetheless have normal facets for the distal clavicle, moderate levels of rugosity dorsally, and a series of fine pits on their ventral surfaces. Figure 9-1. Left to right: Dorsal view of the Tianyuan 1 right and left scapular spines and acromion processes. Scale in centimeters. CHAPTER 9 98 Coracoid Process Tianyuan 1 is one of the few Late Pleistocene specimens with a complete coracoid process (Figure 9-2). At its proximal, or dorsomedial, end it projects slightly over the supraspinatus surface, forming a hollow between itself and the lateral end of the supraspinatus surface. It is moderately rugose on its dorsocranial surface, but it is not possible to discern distinct attachments for the muscles and ligaments that attach to it, including the biceps brachii short head origin and the coracoacromial arch attachment. Glenoid Fossa The right glenoid fossa is completely absent, but the left one is intact and has sustained only trivial damage to its inferior margin (Figure 9-2). The left glenoid fossa is strongly pyriform. Its caudal two-thirds closely approximate a circle, or a portion of a sphere given its concavity. The dorsal margin continues as an evenly convex curve up to the supraglenoid tubercle. The ventral margin becomes slightly concave as it approaches the inferior root of the coracoid process, and then convex up to the supraglenoid tubercle. While the inferior two-thirds are strongly concave , the superior portion is only slightly so. The glenoid margin has a slight lipping, or ossification into the glenoid labrum, along the entire ventral margin. Dorsally it forms a rounded right angle onto the Table 9-1. Osteometric dimensions of theTianyuan 1 scapulae, in millimeters Right Left Glenoid maximum height (M-12) — 39.2 Glenoid maximum breadth (M-13) — 29.7 Glenoid articular height1 — 35.5 Glenoid articular breadth1 — 27.8 Coracoid thickness — 7.9 Coracoid length2 — 43.9 Spine mid maximum thickness3 12.7 11.1 Spine lateral minimum thickness4 9.0 7.2 Acromial base maximum thickness (M-9) 26.9 27.0 Acromial projection5 58.1 53.0 1 Diameters of the subchondral bone surface, not including the glenoid labrum attachment area (Churchill and Trinkaus, 1990). 2 Length from the angle to...