10 



E.N. ARNOLD 



subsequent shift back to looser substrates in P. guttatus (Ananjeva & 

 Tuniyev, 1992) and P. przewalskii. 



Another indication that aeolian sand habitats are primitive is that 

 a number of features conferring performance advantage in such 

 environments first appear on the internal branch of the phylogeny on 

 which these habitats are entered, that is the ancestral lineage of the 

 Bufoniceps + Phrynocephalus clade. These are discussed below. 



tion in hearing when lying under the sand. They partly reverse in the 

 P. theobaldi group and perhaps independently in P. axillaris. Cer- 

 tainly the former species do not usually bury directly in the substratum 

 and use permanent burrows instead (K. Autumn, pers. comm.) 



Members of the P. interscapularis group possess a range of 

 features that are rare or absent in other Phrynocephalus (see caption 

 of Figure 15); their functional significance is uncertain. 



Changes in morphological features 



Principal changes in morphology in the history of the Bufoniceps- 

 Phrynocephalus clade are listed in the caption of Figure 15. A high 

 proportion of the characters in the data set (Appendix 1 ) show a 

 single change on the phylogeny. Overt reversals occur in such 

 features as size (in P. euptilopus) and the pattern of arteries arising 

 from the aorta. Simple parallelisms are quite frequent in the remain- 

 ing characters, but few of these are really noisy. 



Body size decreases early in the history of the main lineage of 

 Phrynocephalus. Many features that appear likely to confer per- 

 formance advantage in aeolian sand habitats develop at the base of 

 the Bufoniceps + Phrynocephalus clade and, as noted, are concur- 

 rent with entry into such habitats. These features include: lateral 

 fringes of elongate scales on the digits that prevent the feet sinking 

 into soft surfaces (Carothers, 1986); reduction of the keeling on the 

 digital lamellae, which may be less necessary to reduce heat intake 

 in soft-sand environments (Arnold, 1998); fringes of elongate scales 

 along the edges of the eyelids, countersunk jaws, valvular nostrils, 

 and a U-shaped nasal vestibule consisting of vertically parallel and 

 subequal proximal and distal limbs, all of which features appear to 

 exclude sand (Stebbins, 1943, 1944, 1948), although very long nasal 

 passages may also protect the main nasal cavity from desiccation; 

 skin covering the tympanum that may protect it from damage during 

 burial activity, and lateral prefrontal processes that possibly protect 

 the eyes during the same process. 



Some of these features initially associated with aeolian sand 

 habitats persist in less basal forms that occur on firmer substrata. 

 Thus, toe and eyelid fringes and countersunk jaws occur in all 

 Phrynocephalus, although they are less marked in species that are 

 not found on loose sand. The outer limb of the nasal vestibule is 

 shortened in most firm-ground forms, a shift associated with the 

 changed position of the nostril (p. 5). This feature represents a 

 reversion towards the primitive condition found in other Group 6 

 agamids. It is also associated with increased contact between the 

 maxillary and nasal bones, either directly or via the septomaxilla. 

 These nasal features occur in more terminalPhrynocephalus species 

 on the main lineage of the genus and have developed in parallel in P. 

 maculatus. 



Other changes loosely associated with shift to firmer substrates 

 include reduction in size of the lateral processes of the prefrontal 

 bones, reduction in number of presacral vertebrae, increase in 

 number of scale rows above the upper labial scales, increase in size 

 of the parietal foramen of the skull and reversal in the pattern of the 

 arteries arising from the aorta. 



The high altitude P. theobaldi group is characterised by a number 

 of features, including viviparity, something that often develops in 

 cold conditions (Shine, 1985). Within this group, P. vlangalii devel- 

 ops a nostril structure that is even more reversed than in other 

 firm-ground forms. 



The external and middle ear is heavily modified in the early 

 history of the main Phrynocephalus lineage, the tympanum disap- 

 pearing, the extracolumella decreasing in size and the pharyngeal 

 opening becoming very reduced or absent. These changes may be 

 associated with greater use of subterranean rather than aerial vibra- 



Behaviour 



Phrynocephalus has a number of distinctive behaviour patterns. The 

 appearance of burial by fast lateral oscillation of the flattened body 

 (discussed by Arnold, 1 995 ) is concurrent with entry into aeolian sand 

 habitats at the base of theBufoniceps-Phrynocephalus clade and, like 

 some morphological features already discussed, is likely to be an 

 adaptation to this environment. In line with this, such shimmy burial 

 is best developed in more basal species (e.g. Bufoniceps - Sharma 

 (1978), P. mystaceus, P. interscapularis - Ananjeva & Tuniyev 

 (1992), P. arabicus, P. scutellatus, P. reticulatus (pers. obs.)). Lateral 

 oscillation often persists in species secondarily occurring on harder 

 substrata, for instance in P. maculatus (pers. obs) and/! helioscopus 

 (Ananjeva & Tuniyev, 1992). In such cases this behaviour may be 

 modified and not necessarily always used for burial. 



When sprayed with water, P. helioscopus adopts a distinctive 

 posture in which the hindquarters are raised and the head lowered. 

 Any liquid on the back then moves forward by capillary action in the 

 channels between the scales (and probably by gravity when enough 

 water is present) towards the mouth where it is ingested (Schwenk & 

 Greene, 1987). Presumably, such behaviour permits advantage to be 

 taken of even minor precipitation and condensation, something 

 likely to be a significant benefit in the arid regions where P. 

 helioscopus lives. P. arabicus from the United Arab Emirates re- 

 sponds to spraying very similarly (pers. obs.). As these two species 

 are widely separated on the estimate of phylogeny for 

 Phrynocephalus, this stereotyped behaviour may well be more 

 widespread than presently known. It could not be demonstrated in 

 Trapelus flavimaculatus, also from the United Arab Emirates, so it 

 may be confined to Phrynocephalus and possibly Bufoniceps. 



Phrynocephalus species are also distinctive in using the tail for 

 intraspecific signalling (e.g. Arnold, 1984; Ross, 1989, 1995). For 

 instance, it may be raised, curled upwards in the sagittal plane and 

 wagged laterally. Movements usually expose conspicuous markings 

 on the underside of the tail, such as a dark tip and transverse bars and 

 sometimes areas of bright pigment as well. Tail signalling has been 

 investigated for a number of Central Asian species by Dunayev 

 (1996), who recognises seven distinct ways in which the tail may be 

 used (Dunayev, Figure 3). Of the species considered in the present 

 paper, the following are listed as investigated: P. mystaceus, P. 

 maculatus, P. interscapularis, P. sogdianus, P. reticulatus (as P. 

 ocellatus), P. raddei, P. strauchi, P. helioscopus, P. versicolor and/! 

 guttatus. When data for P. arabicus (Ross, 1995) is incorporated, it 

 is apparent that more basal forms on the main Phrynocephalus 

 lineage have less complex tail displays than the others. When the 

 seven display features are treated as two-state characters (absent or 

 present) and subjected to parsimony analysis on their own, they 

 produce the following consensus tree which is congruent with the 

 estimate of phylogeny based on morphology: (P. mystaceus, P. 

 maculatus (P. arabicus ( all other species))). However, the supposed 

 P. maculatus on which Dunayev's observations were based are from 

 the small area of Tadjikistan where P. golubevi occurs, a species 

 which was previously not separated from P. maculatus. If the 

 animals concerned are in fact P. golubevi, the tree based on tail 

 signalling is no longer congruent with that from morphology. 



