168 



E.N. ARNOLD 



a 



b 









. 



















-''^iJSfcfa 





^§2*P^iP 



fe. m ^— r 







ifc.'^v — 



, *^ t -^ 





^^^ i^^^ 





Fig. 5 Stages in reduction of the external ear in Oriental agamids. a. Tympanum superficial and exposed, Japalura dymondi, BMNH 1914.3.2.2.; 



tympanum indicated by a depression but covered with scales, Japalura polgyonata ishikagiensis, BMNH 1913.3.10.9; tympanic area scarcely sunk and 

 covered with unmodified skin, Aphaniotis fusca, BMNH 1886.12.28.12-13. 



Phrynocephalus and its relatives 



(Fig. 3) 



Moody (1980), on the basis of his morphological study of the 

 Agamidae, regarded Phrynocephalus as the sister group of Laudakia 

 plus Acanthocercus and a relationship to Laudakia has also been 

 supported by immunological evidence (Joger, 1991). However, a 

 more detailed anatomical investigation (in progress) suggests that 

 Phrynocephalus is the sister group of Bufoniceps Arnold, 1992 (a 

 new generic allocation for Phrynocephalus laungwalaensis Sharma, 

 1978) and successively more distant relatives are Trapelus, 

 Pseudotrapelus, various African taxa the relationships of which are 

 yet to be fully resolved including Agama, Xenagama and species 

 assigned to Acanthocercus, and then Laudakia (Fig. 3) This hypoth- 

 esis of relationships is used in the following reconstruction of the 

 history of earreduction in the group. However, even if Phrynocephalus 

 plus Bufoniceps is regarded as the sister group of Laudakia, only 

 evidence for the initial changes in stage 1 below would be lost. 



An estimate of Phrynocephalus phylogeny based on morphology 

 (Arnold, 1999) suggests that successive branches on the main 

 lineage are: P. mystaceus; P. maculatus; P. arabicus; the P. 

 interscapularis group (P. interscapulars, P. sogdianus, P. ornatus, 

 P. clarkorum, P. luteoguttatus and P. euptilopus); P. scutellatus; P. 

 golubevi: P. reticulatus; P. raddei; there is then a large clade made up 



of most of the remaining species. Within the latter assemblage, little 

 robust phylogenetic structure is apparent but P. roborowski, P. 

 theobaldi and P. vlangali are clearly closely related to each other and 

 perhaps more distantly to P. forsythi. 



1 . In some Trapelus, the anterior slip of the m. depressor mandibulae 

 moves anteriorly to partly obscure the tympanum, producing a 

 short meatus with a small opening (Fig. 6b; at the same time the 

 bar-like, superficial part of the extracolumella becomes more 

 horizontal. 



2. In Bufoniceps, the tympanum is directed more posteriorly, the m. 

 depressor mandibulae moves further forward and the meatus and 

 its surface opening become very narrow (Fig. 6c), so that its 

 depth is several times the width of the latter. 



3. In all Phrynocephalus, the tympanic area is entirely covered by 

 skin (Fig. 6d) and substantially by the m. depressor mandibulae. 

 In P. mystaceus, there is still a well defined tympanum incorpo- 

 rating a extracolumella which lacks the pars superior, but the pars 

 inferior is large and overlaps the conch of the quadrate. The 

 dorsal process is long and joins the intercalary cartilage, and the 

 internal process is quite slender. The buccal opening to the 

 middle ear is large and extends from the back of the basisphenoid 

 process well beyond the spheno-occipital tubercle of the basi- 

 occipital bone; its greatest dimension is over 25% of the head 

 length in small specimens. 



