The most complete arm of Therizinosaurus is represented by the specimen IGM 100/15 which preserves an almost complete right arm except for the left one which is more fragmented.
The right arm covers 2.4 m (7.9 ft) in total length.
The scapula measures 67 cm (670 mm) long with a stocky and flattened dorsal blade, wide acromial process and a very widened ventral surface; the blade seems to be broken at the end though.
Near the anterior edge of the scapular widening and near the scapulocoracoid suture, a foramen is visible; it likely functioned as a channel for blood vessels and nerves when alive.
The posterior edge of the scapula is robust and the acromion is lightly built, likely fused into a cartilaginous system with its periphery in life.
The coracoid measures 36 cm (360 mm) in length, it has a broad and convex lateral surface that forms a slightly inclined concavity near of the scapulocoracoid suture.
This concavity bends down towards the scapular widening.
Near the scapulocoracoid suture, this edge turns very thin and possibly into cartilage along with the periphery of the coracoid in life, as the case of the scapular edge.
A large foramen is also present on the coracoid.
The glenoid is broad and deep, slightly pointing to the outer lateral side.
It has robust, convex crest-like borders.
The supraglenoid thickness is developed in a convex crest-shaped form, it is divided across the top of the scapulocoracoid suture.
The attachment for the biceps muscle is prominently developed by a large tubercle with a stocky top, indicating powerful muscles in life.

The humerus is robustly built, measuring 76 cm (760 mm) long.
It has a broad proximal end.
The deltoid crest is tall and thick, its top is located approximately 1/3 from the upper end, the length of the crest is no less than 2/3 the length of the whole bone element.
The lower end of the humerus is very expanded and flattened in a posterior direction.
The condyles are developed onto the anterior side of the lower expansion while the epicondyles are very broad and project over the limits of the articular areas.
The ulna is measured at 62.02 cm (620.2 mm) and most of its length is occupied by the straight shaft.
The ulnar process is very wide.
The upper articular area can be divided into the inner and outer lateral sides.
The lateral side has a triangular-shaped border and is slightly concave; it is limited in a top view by the fossa for the upper articulation of the radius.
The inner side forms a semilunar-shaped fossa that caps the lunar-shaped condyle of the humerus.
The radius is 55.04 cm (550.4 mm) long and slightly S-curved.
The upper end is flattened in a lateral direction, very wide and the distal end is highly robust.
The most complete arm of Therizinosaurus is represented by the specimen IGM 100/15 which preserves an almost complete right arm except for the left one which is more fragmented. The right arm covers 2.4 m (7.9 ft) in total length. The scapula measures 67 cm (670 mm) long with a stocky and flattened dorsal blade, wide acromial process and a very widened ventral surface; the blade seems to be broken at the end though. Near the anterior edge of the scapular widening and near the scapulocoracoid suture, a foramen is visible; it likely functioned as a channel for blood vessels and nerves when alive. The posterior edge of the scapula is robust and the acromion is lightly built, likely fused into a cartilaginous system with its periphery in life. The coracoid measures 36 cm (360 mm) in length, it has a broad and convex lateral surface that forms a slightly inclined concavity near of the scapulocoracoid suture. This concavity bends down towards the scapular widening. Near the scapulocoracoid suture, this edge turns very thin and possibly into cartilage along with the periphery of the coracoid in life, as the case of the scapular edge. A large foramen is also present on the coracoid. The glenoid is broad and deep, slightly pointing to the outer lateral side. It has robust, convex crest-like borders. The supraglenoid thickness is developed in a convex crest-shaped form, it is divided across the top of the scapulocoracoid suture. The attachment for the biceps muscle is prominently developed by a large tubercle with a stocky top, indicating powerful muscles in life.
The humerus is robustly built, measuring 76 cm (760 mm) long. It has a broad proximal end. The deltoid crest is tall and thick, its top is located approximately 1/3 from the upper end, the length of the crest is no less than 2/3 the length of the whole bone element. The lower end of the humerus is very expanded and flattened in a posterior direction. The condyles are developed onto the anterior side of the lower expansion while the epicondyles are very broad and project over the limits of the articular areas. The ulna is measured at 62.02 cm (620.2 mm) and most of its length is occupied by the straight shaft. The ulnar process is very wide. The upper articular area can be divided into the inner and outer lateral sides. The lateral side has a triangular-shaped border and is slightly concave; it is limited in a top view by the fossa for the upper articulation of the radius. The inner side forms a semilunar-shaped fossa that caps the lunar-shaped condyle of the humerus. The radius is 55.04 cm (550.4 mm) long and slightly S-curved. The upper end is flattened in a lateral direction, very wide and the distal end is highly robust.
Therizinosaurus