2; Weishampel, 1997). We divide these into four general (and not mutually exclusive) classes: defense, communication, thermoregulation and sensory

function. These features can be attributed to repulsion of predators and to conspecifics of the same sex in agonistic behaviors (non-exclusively). Notable examples are the horns and frills of ceratopsians, the plates and spikes of stegosaurs, the scutes and tail club of ankylosaurs and the domes of pachycephalosaurs. Weishampel (1981) tested the possibility of a defensive function of lambeosaurine crests and concluded that the bone was too thin to have been of any use in this regard. Ankylosaurs would seem to pose the least controversial example of a defensive function for bizarre structures, in this case the dermal scutes (traditionally and tellingly called ‘armor’) and tail ‘club’ (in ankylosaurids only: Carpenter, 1997, 2001; Vickaryous, Maryanska EPZ-6438 molecular weight & Weishampel, 2004). Scutes cover the skull, the neck, the back, and much of the tail, but there is great variety in their size, form and extent among ankylosaurs

(Carpenter, 1997). This suggests that there was no ‘optimal’ pattern of scute form and distribution, and therefore it is difficult to propose that a defensive function was successively ‘improved’ in ankylosaurs. However, consideration of their outgroups shows that ankylosaurs had more extensive dermal ossifications than the basal thyreophorans Scutellosaurus and Scelidosaurus (the latter often considered an ankylosaur), not to mention the stegosaurs, which lost all but the parasagittal rows (Main et al., Alvelestat ic50 2005). This pattern points to defense as a plausible

basal function of ankylosaur scutes, and suggests that whatever the variations in scute form and distribution, they were ‘good enough’ to serve an adequate defensive function. Yet, as Carpenter (1997: p. 315, fig. 22.6) notes, the variation in scute form, and notably in the more conspicuous long neck spikes, suggests no obvious defensive strategy (see also Scheyer & Sander, 2004), and may instead medchemexpress be primarily related to display. Sexual dimorphism has not been established, so sexual selection has no support, but social selection (Hieronymus et al., 2009) could be investigated further. Several evolutionary strategies may have been involved here. The enlarged and fused scutes at the end of the ankylosaurid tail, preceded by a series of fused caudal vertebrae, have often been invoked as a weapon, and this seems to be supported by the enlarged areas of muscle attachment on the pelvis, hindlimbs and transverse processes of the anterior caudal vertebrae, despite some limits in vertical mobility (Vickaryous et al., 2004). Most attributions of defense to the frills of neoceratopsians have focused on Triceratops (Fig. 3).