Martinelli et al.—Procolophonians in the German Middle Triassic The deltopectoral crest is extremely reduced and stands
apart from the head as an anteriorly projected triangular process, on the same plane as that of the ectepicondyle (Fig. 1). The anterodistal edge of the deltopectoral crest extends distally to contact the anterodorsal edge of the ectepicondyle. The trajectory of this crest is unusual because in most amniote humeri with twisted proximal and distal ends and a short shaft (e.g., some procolophonids, synapsids; Romer, 1922; Jenkins, 1971; deBraga, 2003), the distal border of the deltopectoral crest extends distally to merge with the ventral surface of the entepicondyle (and not the anterodorsal edge of the ectepicon- dyle). In dorsal view, there is a concave triangular surface and a deep groove on the deltopectoral crest with scars, which would indicate the origin area of M. brachialis and part of M. supracoracoideus (in the deep proximal groove; Romer, 1956; Holmes, 1977; Angielczyk et al., 2009; Figs. 1, 4). The insertion of M. deltoideus would be restricted to the anterodorsal edge of the deltopectoral crest. In ventral view, the deltopectoral crest bears a transverse elevation at its middle point, whichwould correspond to the insertion area of M. pectoralis (Romer, 1956; Holmes, 1977). Distal to it, there is also a longitudinal concave area that extends distally, extending parallel to the anterior border of the shaft.We are not confident that this depression corresponds to a muscle attachment area, but perhaps the most proximal portion would have also been part of the insertion area of M. pectoralis (Romer, 1956; Angielczyk et al., 2009). The transverse elevation on the ventral surface of the
deltopectoral crest also delimits the laterodistal border of a large semicircular concave area (Fig. 1). This area is widely extended and faces anteroventrally, with randomly distributed vascular foramina and conspicuous scars, which would correspond to the insertion area of M. coracobrachialis. One of the most conspicuous processes on the proximal
half of the humerus is the lesser tuberosity (Fig. 1). It is stout and, contrary to most tetrapods (e.g., Romer, 1956), greatly extended posteroventrally as in the procolophonian Barasaurus (unpublished data, Meckert, 1995; hypertrophied in turtles; e.g., Romer, 1956). The lesser tuberosity is as wide as the humeral head, and its proximal tip is positioned below the level of the humeral head, almost at the same level as the deltopectoral crest. In addition, its proximal portion forms a rough surface from which a thin crest descends onto the dorsoposterior aspect of the tuberosity. The lesser tuberosity also has a ventral surface with muscle scars. The most proximal portion of the lesser tuberosity would correspond to the insertion of M. subcoracoscapularis and more distally (on the posterodorsal and posteroventral margins) of M. latissumus dorsi. Of note, on the ventral side, at the distal base of the lesser tuberosity, there is a prominent buttress that is not developed in the same way as in other amniotes (e.g., Romer, 1922, 1956; Jenkins, 1971). This process would correspond to the insertion area of M. coracobrachialis longus (Angielczyk et al., 2009). The narrowest portion of the shaft has a subtriangular cross
section with a flat surface in the dorsal aspect and a concave apex in the medial aspect, which correspond to the bridge linking the distal base of the lesser tuberosity and the proximal base of the supinator process (Fig. 1). The distal width of the humerus is slightly more expanded than the proximal width, representing about one-half (0.47) of
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the proximodistal length. The entepicondyle is proximodistally tall, well developed posteriorly, with a straight lateral edge, forming a right angle with the distal articular end. The posterior surface of the entepicondyle has a longitudinal, gently concave
groove with shallow rugosities and pits for the origin of the flexor muscles of the forearm (Holmes, 1977; Angielczyk et al., 2009; Fig. 4). There is no evidence of an entepicondylar foramen on either side, and both the dorsal and ventral sides of the entepicondyle are gently concave (Fig. 1). The ectepicon- dyle is also well developed, with its anterior edge semicircular in outline. This area of the ectepicondyle, for the attachment of extensor muscles of the forearm (Holmes, 1977; Angielczyk et al., 2009), is not as rough as the opposite area of the entepicondyle. On the ventral surface, there is a stout supinator process. This process delimits the proximal edge of the entepicondylar notch, which is open anterodistally. The entepicondylar notch encloses the groove for nerves and veins extending dorsoproximally-ventrodistally (Fig. 1). The ectepi- condylar notch is positioned well distally, similar to the condition in some procolophonians (Barasaurus; unpublished data, Meckert, 1995), some basal synapsids (e.g., Dimetrodon; Romer and Price, 1940) and some archosauromorphs (e.g., Trilophosaurus buettneri Case, 1928 and Otischalkia elderae Hunt and Lucas, 1991; Spielmann et al., 2008). The distal articular surface is characterized by a prominent
semispherical capitellum (radial condyle) positioned on the lateral half of the distal end, close to the ectepicondyle and ectepicondylar notch. The articular surface of the capitellum is mainly developed on the ventral and distal aspects of the humerus, without a contribution to the dorsal surface. Most of the surfaces of the capitellum have a rough texture indicative of a cartilaginous cover. The trochlea (ulnar condyle) is medial to the capitellum, almost at the middle of the distal end, but it is poorly developed, almost flat. In addition, there is no evidence of an olecranon fossa. Consequently, the dorsal aspect of the distal half of the humerus is gently concave without remarkable features.
SMNS 92100.—This specimen is a right humerus with a par- tially preserved proximal articular surface, capitellum, and most of the distal portion of the distal end, lacking most of the supi- nator process in the ectepicondylar region (Fig. 2). This element has the same morphological pattern (i.e., shape of the processes and crests, relationships of the areas for muscle origin/insertion, lack of an entepicondylar foramen) as the already described humerus SMNS 92101 (Fig. 1). For such reason, it is described in less detail than is SMNS 92101. The main differences are the development of the scars for the muscles and the twisted angle between the proximal and distal ends. The more robust scars in SMNS 92100 are consistent with the larger size of this specimen (see Table 1). The difference in the angle of the proximal and distal ends, and the shape of the lesser tuberosity (more gently quadrangular than in SMNS 92101), is explained by tapho- nomic deformation: SMNS 92100 has evidence of strong flat- tening all over the bone. Due to the flattening, the major axis of the proximal end is on the same plane as the major axis of the distal end, considerably deforming the lesser tuberosity. Consequently, the lesser tuberosity of SMNS 92100 is more posteriorly (in almost the same plane as the entepicondyle) than
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