[N] 2006 The glenohumeral joint of the Therizinosaur Neimongosaurus yangi
Burch, S, (2006) The range of motion of the glenohumeral joint of the Therizinosaur Neimongosaurus yangi (Dinosauria: Theropoda) JVP 26(3) Abstracts pp.46
Increasingly the orientation of the glenoid (shoulder socket) has been studied in non-avian theropods to understand what condition was the likely precursor to that of modern birds. The morphology of the glenoid is the prime factor in determining the range of motion of the humerus, which greatly affects the functionality of the forelimb. Elements of the pectoral girdle from a single well-preserved specimen of the therizinosaur Neimongosaurus yangi, including a complete, undistorted furcula, were reconstructed and articulated, and a unique orientation of the glenoid relative to known orientations in other theropods and extant birds was discovered and described. The glenoid was found to be oriented primarily laterally with a slight ventral component. The enlarged scapular and coracoid margins are oriented dorsally and ventrally around the socket instead of anteriorly and posteriorly as in most other non-avian theropod glenoids and those of extant birds.
This reconstruction, along with an associated humerus, was then used to determine the range of motion of the glenohumeral joint. The unusual morphology of the scapular and coracoid margins restricted the overall range of motion in the dorsoventral direction, although the lateral position of the glenoid allowed for a more extensive dorsal excursion of the humerus than has been previously described. The humerus was also found to be capable of considerable anterior protraction. The total dorsoventral motion of the humerus was measured as 72º in anterior view, and the total anterioposterior motion was measured as 110º in dorsal view. The overall range of motion was roughly circular and directed laterally and slightly ventrally, which differs from the more oval and posteroventrally directed ranges of motion that have been described for other theropods.
Such extensive protraction is very different than the flight stroke of extant birds, indicating that this glenoid morphology was most likely not an evolutionary transition to the morphology of modern birds. Therizinosaurs may have used this ability to extend their arms forward considerably for activities such as reaching for and grasping foliage.