Figure 2. Interpretive drawings of the dorsal skull surface of Pachyrhachis problematicus (HUJ-PAL 3659) illustrating conflicts in interpretation of morphology. 2.1, Haas (1979, figure 3). 2.2, Caldwell and Lee (1997, figure 1a). 2.3, Zaher and Rieppel, 1999b, figure 1). Abbreviations used in figures: Haas, 1979 (ang, angular; atna, atlas neural arch; axna, axis neural arch; com, compound bone; co, coronoid; d, dentary; ect, ectopterygoid; f, frontal; mx, maxilla; p, parietal; pmx, premaxilla; porb, postorbital; prf, prefrontal; ptf, postfrontal; pro, prootic; squ, squamosal; qu, quadrate; socc, supraoccipital; spt, septomaxilla; porb, postorbital; squ, squamosal; st, stapes); Caldwell and Lee 1997 (pm, premaxilla; mx, maxilla; de, dentary; prf, prefrontal; fr, frontal; ju, jugal; pof, postorbitofrontal; pa, parietal; com, compound bone; ec, ectopterygoid; co, coronoid; pro, prootic; sq, squamosal; qa, quadrate; so, supraoccipital; pt, pterygoid; atna, atlas neural arch; axna, axis neural arch; sq, squamosal); Zaher and Rieppel, 1999b at, atlas neural arch; axna, axis neural arch; com, compound bone; co, coronoid; d, dentary; ect, ectopterygoid; f, frontal; mx, maxilla; n, nasal; p, parietal; pm, premaxilla; po, postorbital; prf, prefrontal; q, quadrate; spt, septomaxilla; porb, postorbital; squ, squamosal; st, supratemporal; stp, stapes).