166 



E.N. ARNOLD 



squamosal 



extracolumella 



depressor 

 mandibulae 

 muscle 



quadrate 



pars superior 



extracolumella 



pars inferior 



tympanum 



foot plate 



Fig. 1 General structure of the ear in Iguania. a. Lateral view of left ear. tympanum stippled, b. Transverse section of left ear. Figures based on those of 

 Baird(1970). 



Australian agamids 



(Fig. 2) 



Among Australian agamids of Group 3 (Moody, 1980), ear modifi- 

 cation has occurred independently in Ctenophorus maculosus 

 (Mitchell, 1948) and in all the species of Tympanocryptis Peters, 

 1863, except T. adelaidensis and T. diemensis (data from Cogger, 

 1992). In Ctenophorus maculosus and the Tympanocryptis parviceps 

 Storr, 1964 group the ear is covered with scaly skin but the tympa- 

 num is present just beneath it (Greer, 1989). In the Tympanocryptis 

 lineata group (species examined: T. lineata Peters, 1863, T. intima 

 Mitchell, 1 948 and T. cephalus Gunther, 1 867) further reduction has 

 occurred. The anterior slip of the m. depressor mandibulae, has 

 moved forwards beneath the skin to cover the tympanic area, the 

 columella is more robust, no clear tympanum exists, the 

 extracolumella is reduced to a small projection, and the dorsal and 

 internal processes are robust and sometimes ossified. The middle ear 

 opens broadly into the buccal cavity in T. lineata and T. intima, but 

 more narrowly in T cephalus. 



Arboreal agamids of the Oriental region 



(Fig. 2) 



Among mainly arboreal agamids of the Oriental region which 

 constitute Group 4 (Moody, 1980), a fully exposed tympanum is 

 lacking in some or all members of the following apparent clades 

 (relationships based on the weighted and unweighted Wagner tree 

 analyses of Moody, 1980) 1. Gonocephalus Kaup, 1805 (partly 

 obscured in G. miotympanum (Gunther, 1872)); 2. Japalura Gray, 

 1853 (some species); 3. Phoxophrys Hubrecht, 1881, 4. Otocryptis 

 Wagler, 1830; 5. Draco Linnaeus, 1758 (some species); 6. 

 Ptycholaemus Peters, 1864; 7. Aphionotis Peters, 1864, Ceratophora 

 Gray, 1834, Cophotis Peters, 1861 and Lyriocephalus Merrem, 

 1820; and 8. Oriocalotes Gunther, 1864 (some individuals). 



The tympanum consequently may have become obscured at least 

 eight times in the Oriental assemblage (although Phoxophrys and 



Otocryptis could represent a single origin if reversal occurred in 

 Sitana, the apparent sister group of the latter genus). In groups 

 where members vary in the degree to which the tympanum is 

 obscured, such as Draco, Japalura and Oriocalotes, it is apparent 

 that covering of the external ear has taken place by development of 

 scales on the tympanic surface (Fig. 5). Although most of the 

 Oriental taxa with hidden tympana lack the extensive modifica- 

 tions found in some Tympanocryptis, there may be less extreme 

 changes. Draco for instance has a thick columella, the stem of the 

 extracolumella is angled relative to this, and the air-filled space in 

 the middle ear is restricted; there is also a substantial loss of 

 sensitivity (Wever, 1978) 



Only in the clade made up of Aphaniotis, Cophotis, Lyriocephalus 

 and Ceratophora has the process of ear modification gone further. 

 The relationships of this group (based on Moody, 1980) are shown 

 in Fig. 2. In this assemblage, the basal Aphionotis has the tympanum 

 covered (Fig. 5c), but little other change is apparent, apart from the 

 columella being robust and the exposure of the extracolumella on 

 the tympanum large (checked in A. acutirostris Modigliani, 1 889, A. 

 fusca (Peters, 1864) and A. ornata Lidth de Jeude, 1893). In the 

 sister genera Cophotis and Lyriocephalus, the tympanum has disap- 

 peared and this area is covered by the anterior slip of the m. 

 depressor mandibulae. The pars superior of the extracolumella is 

 absent, the pars inferior is small and projects laterally, and the dorsal 

 and internal processes are robust and ossified, the former attaching 

 substantially to the paroccipital process. The quadrate itself is more 

 or less straight and without an auditory cup, while the middle ear 

 cavity extends laterally as far as the tympanic area and has a quite 

 large opening to the buccal cavity. In Ceratophora, the ear is 

 essentially similar (illustrated by Wever, 1978) but there are no 

 openings from the buccal cavity to a distinct middle ear cavity 

 (checked on C. aspera Gunther, 1 864, C. stoddarti Gray, 1 834 and 

 C. tennentii Gunther, 1861). 



Smith (1938) erroneously attributed a highly modified middle ear 

 structure to Aphaniotis and also incorrectly described the middle ear 

 openings to the buccal cavity of this genus, Cophotis and 

 Lyriocephalus as being strongly reduced. 



