Piksi barbarulna Varricchio, 2002

Agnolin, Federico L. & Varricchio, David, 2012, Systematic reinterpretation of Piksi barbarulna Varricchio, 2002 from the Two Medicine Formation (Upper Cretaceous) of Western USA (Montana) as a pterosaur rather than a bird, Geodiversitas 34 (4), pp. 883-894 : 888

Piksi barbarulna Varricchio, 2002

HOLOTYPE. — MOR 1113 ; distal end of right humerus, proximal half of right radius, proximal half and distal end of right ulna. The bones have some distortions due to compression; however, main anatomical details of the specimens are clearly discernible (for detailed discussion of pterosaurian taphonomical bias see Kellner 2010).

EMENDED DIAGNOSIS. — Piksi barbarulna is a minute pterosaur diagnosable by the following autapomorphies: 1) distal margin of humerus oblique relative to the main axis of the shaft, with trochlea strongly distally extended; 2) trochlea bulbous and subspherical; 3) acute and well defined transverse crest connecting the entepicondyle and the lateral ridge that delimitates the olecranal fossa, in posterior view. COMMENTS

The only named pterosaur from the Two Medicine Formation is Montanazhdarcho minor Padian, de Ricqles & Horner, 1995 ( Padian et al. 1995; McGowan et al. 2002). Piksi differs from the latter in having a less distally expanded humerus, a more anteroposteriorly compressed humerus, distal end of the humerus with its external margin longer than the internal one (diagnostic trait of Ornithocheiroidea ), more bulbous and larger ectepicondyle, and capitulum shorter and smaller (see additional features in Piksi ’s generic diagnosis) ( Fig. 2 ).

Based on the transversal expansion of the distal humerus of Piksi , compared with that of Anhanguera spielbergi Veldmeijer, 2003 and A. piscator Kellner & Tomida, 2000 ( Kellner &Tomida 2000; Veldmeijer 2003) we calculated a wing span of approximately one metre, which posits Piksi as a very small pterodactyloid pterosaur (see also Costa & Kellner 2009).

Figures

FIG. 2. — Right distal humerus of selected birds and pterosaurs in anterior (top),and distal (bottom) views:A, Azhdarcho Nessov,1984 modified from Averianov (2010); B, Dsungaripterus Young, 1964 modified from Young (1964); C, Piksi Varricchio, 2002 modified from Varricchio (2002); D, Ornithocheiroidea indet.,modified from Averianov et al. (2005);E, Anhanguera Campos & Kellner, 1985, modified from Veldmeijer (2003); F, Montanazhdarcho Padian, de Ricqles & Horner, 1995, modified from McGowen et al. (2002); G, Enantiornithes indet., modified from Hope (2002); H, Ichthyornis dispar Marsh, 1872, modified from Clarke (2004); I, Anas platyrhynchos Linnaeus,1758; J, Limenavis, modified from Clarke & Chiappe (2001). Abbreviations: br, brachial depression; cap, capitulum; dc, dorsal condyle; ent, entepicondyle; pn, pneumatic foramen; tr, trochlea; vc, ventral condyle. Not to scale.