EAR REDUCTION IN IGUANIAN LIZARDS 



169 



d 



Fig. 6 Stages in reduction of external ear in the clade containing Phrynocephalus. a. Tympanum superficial and fully exposed, Pseudoirapelus sinaitus 

 (BMNH 1953.1.7.9); b. tympanum sunk and external opening of meatus so formed reduced, Trapelus agilis (BMNH 94.1 1.13.4); c. tympanum deeply 

 sunk and meatus and external opening very narrow, Bufoniceps laungwalaensis (BMNH 1975. 1592); d. meatus totally closed Phrynocephalus maculatus 

 (BMNH 1973.2038). 



4. In P. maculatus the tympanum is reduced to a delicate membrane 

 and, while smaller than in P. mystaceus, the extracolumella still 

 overlies the quadrate; the buccal opening to the middle ear is 

 reduced in size, its greatest dimension being about 15-20% of the 

 head length. P. arabicus is similar but the buccal opening is rather 

 smaller. 



5. In most of the other species of Phrynocephalus which form a 

 large terminal clade, the extracolumella is very small or absent 

 and, if present, does not overlap the quadrate or only slightly. The 

 buccal opening to the middle ear is also minute or absent. 



6. The only exceptions to this arrangement within the large terminal 

 clade of Phrynocephalus are P. roborowski, P. theobaldi, P. 

 vlangali and P. axillaris. These are generally similar to P. 

 maculatus and P. arabicus, but the entrance to the middle ear is 

 smaller, not extending beyond the spheno-occipital tubercle of 

 the basi-occipital bone, the greatest dimension being about 10- 

 14% of the head length. Relationships within Phrynocephalus 

 suggest that the condition found in these species results from 

 evolutionary reversal with the extracolumella increasing in size 

 and the buccal entrance of the middle ear re-evolving or at least 

 enlarging. Reversal may have occurred twice: in the common 

 ancestor of the first three species and perhaps independently in P. 

 axillaris. 



Some variation also exists within Phrynocephalus in the extent to 

 which the anterior slip of the m. depressor mandibulae extends over 



the quadrate bone and whether the dorsal and internal processes are 

 ossified, although this does not constitute a regular phylogenetic 

 pattern. 



Chameleons 



In chameleons, the skin over the quadrate region is more or less like 

 that covering surrounding areas, the tympanum has disappeared and 

 the m. depressor mandibulae runs close to the quadrate which is 

 straight; the columella is short, and the extracolumella elongate, 

 with a superior ligament attached to it. 



Variation exists, for instance in the form of the pars inferior of the 

 extracolumella and the extent to which this is embedded in the m. 

 depressor mandibulae (Wever, 1968). There is an anterior process 

 extending to the flattened posterior section of the pterygoid in 

 Chamaeleo quilenis Bocage, 1866. C. senegalensis Daudin, 1802 

 and C. chamaeleon (Linnaeus, 1758) (Wever, 1978) and in C. dilepis 

 Leach, 1819 and Bradypodion ventrale (Gray, 1845) (personal 

 observations). This is lacking in Chamaeleo elliotti Giinther, 1895, 

 C.fischeri tavetanus Steindachner, 1891, C. hoehnelii Steindachner, 

 1891 and C. jacksoni Boulenger, 1896 (Wever, 1968), in the 

 Madagascan C. brevicornis Giinther, 1879 and C. lateralis Gray, 

 1831 (referred to Calumna Gray, 1865 and Furcifer Fitzinger, 1843 

 respectively by Klaver & Bohme, 1986), and in the dwarf 

 Rhampholeon brevicaudata (Matschie, 1 892) and Brookesia stumpfii 

 Bottger, 1894 (personal observations). 



