Martinelli et al.—Procolophonians in the German Middle Triassic
upper Permian and Lower Triassic of Madagascar (unpublished data, Meckert, 1995; see Fig. 5). Among the six recognized species of owenettids, only
Owenetta kitchingorum Reisz and Scott, 2002 and Barasaurus besairiei have associated postcranial elements (unpublished data, Meckert, 1995; Reisz and Scott, 2002). Barasaurus has a stout humerus with expanded and twisted proximal and distal ends (unpublished data, Meckert, 1995; Fig. 5), whereas O. kitchingorum has a longer and more slender humerus (Reisz and Scott, 2002). These dissimilar humeral morphologies between these owenettid taxa highlight the diversity within the family. Nonetheless, both taxa lack an entepicondylar foramen, a synapomorphy of the family, unlike in other basal parareptiles (e.g., Millerosaurus; Watson, 1957; Gow, 1972) and procolo- phonids (e.g., Procolophon; deBraga, 2003). Compared to humeri figured and described by Mecker (1995), the humeri here described from Germany are similar in structure (Fig. 5) to Barasaurus, rather than Owenetta. Cisneros (2008, fig. 3D) illustrated, as a comparative figure, a right humerus of Barasaurus besairiei, which has several differences (e.g., presence of an ectepicondylar foramen) when compared to the description and figures of several specimens of B. besairiei studied by Mecker (1995). For that reason, we opted to follow the complete description of Mecker (1995).
Family Procolophonidae Lydekker in Nicholson and Lydekker, 1889
Gen. indet. sp. indet. Figure 3
Referred specimens.—SMNS 91753, left humerus.
Occurrence.—From the Schumann quarry (near the village of Eschenau), Germany. Middle Triassic Erfurt Formation (lower Keuper).
Description.—SMNS 91753 is a small complete left humerus (see Table 1), although it is strongly affected by compression resulting in an extremely thin (almost laminar) fossil, with the deltopectoral crest partially broken off (Fig. 3). The proximal half and most of the entepicondylar area have several small fractures that slightly affect the shape of the bone. The proximal half is not as expanded as the distal end (Fig. 3). The humeral head is reduced and anterodorsally projected. On the dorsolateral edge of the head, a faint crest originates (crest ‘A’ in Fig. 3) that extends distally and delimits the lateral border of the shaft. Just ventrally, there is a proximodistal concave area and another thin and flat crest (crest ‘B’ in Fig. 3). This crest would have been less sharp and thin originally. This crest and the depression would correspond to the process for the insertion of M. brachialis (Angielczyk et al., 2009). Seen in ventral view, the crest ‘B’ forms part of the anterior edge of the proximal half of the humerus and is separated from the base of the deltopectoral crest by a longitudinal concavity, which also would be for insertion of M. brachialis (Angielczyk et al., 2009). The deltopectoral crest is mostly broken off, but judging
from its preserved base, it was more developed than the lesser tuberosity (Fig. 3). As preserved, the deltopectoral crest is apparently projected posteroventrally. In ventral view, the
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bicipital groove for insertion of M. coracobrachialis is well developed proximodorsally between the deltopectoral crest and the lesser tuberosity. The lesser tuberosity forms a thin triangular projection with its most posterior point located below the level of the head. This tuberosity is continuous with the head. The greater tuberosity is indistinguishable, and the bad preservation of this portion of the bone makes its identification difficult. The shaft is narrow and elliptical in cross section but was possibly affected by deformation. On the posteroventral edge of the shaft, there are two tiny foramina. In ventral view, the distal half is extremely flat and fan
shaped (Fig. 3). The widest portion of the distal end represents 48% of the total humeral length. The ectepicondyle is poorly developed, with the main muscular surface facing anterodis- tally. The ectepicondylar foramen is absent, as are the supinator process and ectepicondylar notch. The entepicondyle is proximodistally high and well expanded posteriorly. The entepicondylar foramen is large and elongated, extending obliquely through the entepicondyle and located well away from the posteroproximal edge. There is a substantial entepi- condylar ridge with the foramen through the entepicondyle. The articular condyles are heavily crushed, but on the ventral aspect of the humerus, a rough surface indicates a cartilaginous cover. The larger rough surface is anterior, close to the ectepicondyle, and corresponds to the capitellum (radial condyle; Fig. 3). It is well expanded on the ventral surface of the distal half of the humerus. Continuous with it, there is a reduced rough surface that corresponds to the trochlea (ulnar condyle) posterior to the capitellum. In dorsal view, there is a shallow depression, near the distal edge, which may correspond to an incipient olecranon fossa. The muscle scars are poorly recognized on the humerus.
Comparisons.—The humerus SMNS 91753 is more slender than the humeri described in the preceding (SMNS 92100 and SMNS 92101; Figs. 1, 2). The proximal half is affected by compaction but clearly lacks the stout processes of SMNS 92101. The shape of the deltopectoral crest and the posteriorly placed deep fossa are similar to those of some procolophonids, such as those of the procolophonid Anomoiodon liliensterni von Huene, 1939, from the Lower Triassic of Germany (Säilä, 2008). For example, in the larger procolophonid Procolophon trigoniceps Owen, 1876, this crest and the fossa are better developed (deBraga, 2003). The presence of the entepicondylar foramen in SMNS
91753 is a plesiomorphy widely shared among amniotes (e.g., Romer, 1922, 1956; Romer and Price, 1940; Kennedy, 2010; Nesbitt, 2011). Its position and shape in SMNS 91753 are also reminiscent of that of Anomoiodon (Säilä, 2008) and other nonowenettid procolophonians (e.g., deBraga, 2003; Modesto and Damiani, 2007; Cisneros, 2008). The well-developed entepicondyle was a feature used to characterize ‘horned procolophonids’ (i.e., procolophonines plus leptopleuronines) by Cisneros (2008). The lack of an ectepicondylar foramen or ectepicondylar groove is also a feature of procolophonids (Laurin and Reisz, 1995; Cisneros, 2008). In this way, the combination of features observed in SMNS
91753 resembles the procolophonid condition, having especially close similarity to that of Anomoiodon (Säilä, 2008), and
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