Animal Diversity Web

This wide­spread and di­verse group of lizards is often re­ferred to as the old world iguanids. They are wide­spread through­out the pa­le­otrop­ics and Palearc­tic, though their range does not ex­tend far into Eu­rope and they seem to have been re­cently in­tro­duced to Mada­gas­car. Agami­dae con­tains two sub­fam­i­lies, ap­prox­i­mately 52 gen­era, and more than 350 species.

Agamids have ex­pe­ri­enced in­de­pen­dent ra­di­a­tions of form and size on each of Africa, Asia, and Aus­tralia. All agamids have well-de­vel­oped limbs, and many have keeled scales, mid­dor­sal crests, and throat flaps or fans. They range in size from tiny (14 mm snout-vent length in Pog­ona mi­crolepi­dota) to quite large (145 cm total length in the water dragon Hy­drosaurus am­boinen­sis). Di­ag­nos­tic fea­tures for the group are in con­tention, but may in­clude paired, en­larged ster­nal fontanelles. Like the chameleons, but un­like other igua­ni­ans, agamids have acrodont teeth. Sev­eral ad­di­tional char­ac­ters are shared with chameleons, in­clud­ing retic­u­lar lin­gual papil­lae, re­duced post­frontals, the ex­pan­sion of the den­tary onto labial face of the coro­noid, short­ened spe­nial, loss of ptery­goid teeth, and the an­te­rior suran­gu­lar fora­men ven­tral to the pos­te­rior ex­trem­ity of the den­tary.

The agamids are a di­verse group of lizards that rep­re­sent a va­ri­ety of life his­tory strate­gies. Among their ranks are ter­res­trial, trop­i­cal for­est dwellers; ter­res­trial desert dwellers; and semi­aquatic forms that use water as a refuge. Some agamids dig bur­rows (e.g. Leiolepis, Uro­mastyx); oth­ers have mod­i­fied foot scales that allow them to run bipedally across the sur­face of water (Hy­drosaurus). The heav­ily spined Moloch hor­ridus (thorny devil) can in­flate it­self with air when stressed. Draco has mod­i­fied ribs cov­ered in thin skin that acts as an aero­foil, and these lizards glide to safety as an es­cape re­sponse. Many Agama species live in colonies, re­plete with ter­ri­to­r­ial bor­ders and so­cial hi­er­ar­chies. Phryno­cephalus is live-bear­ing, but the re­main­ing agamids are oviparous. Agamids are di­ur­nal and vi­su­ally-ori­ented, and at least some species can dis­tin­guish be­tween col­ors in the vi­sual spec­trum, as well as in ul­tra­vi­o­let wave­lengths. In Agama agama, males de­velop bright breed­ing col­oration, and fe­males re­spond with arched back and el­e­vated tail only to brightly col­ored males. In Ctenopho­rus mac­u­lo­sus, male dis­play col­oration is cor­re­lated with dom­i­nance. Sev­eral species of agamids are pop­u­lar in the pet trade.

Agamids are un­am­bigu­ously placed in the Igua­nia, a group that is sis­ter to all other squa­mates (lizards and snakes). Within the Igua­nia, how­ever, re­la­tion­ships are hotly con­tested. Fol­low­ing a new phy­lo­ge­netic analy­sis, Frost and Etheridge (1989) re­cently split the large fam­ily Iguanidae into eight fam­i­lies (in­clud­ing Iguanidae sensu stricto). Most re­searchers agree that the only iguan­ian fam­i­lies that were not pre­vi­ously mem­bers of Iguanidae -- Agami­dae and Chamaeleonidae -- form the mono­phyletic group Acrodonta, which is sis­ter to the re­main­ing fam­i­lies (equiv­a­lent to Iguanidae sensu lato). Frost and Etheridge's (1989) analy­sis found Agami­dae pa­ra­phyletic with re­spect to Chamaeleonidae, al­though in one topol­ogy this is based solely on the ques­tion­able iden­ti­fi­ca­tion of the fos­sil Priscagama as an agamid. They argue that the two agamid sub­fam­i­lies should be sub­sumed within a larger Chamaeleonidae, but the lit­er­a­ture con­tin­ues to re­flect the tra­di­tional clas­si­fi­ca­tion. Con­trary to an Acrodonta clade, some re­search sug­gests that Iguanidae sensu lato is pa­ra­phyletic with re­spect to Agami­dae. Fi­nally, much work has been done on in­ter-agamid sys­tem­at­ics, the broad­est find­ing being that the two sub­fam­i­lies are sis­ter to one an­other (but see Macey, et al. 1997).

In ad­di­tion to the pu­ta­tive fos­sil agamid Priscagama, one ex­tinct agamid genus, Mimeosaurus, is known from the Cre­ta­ceous.

Cog­ger, H. G., and R. G. Zweifel, ed­i­tors. 1998. En­cy­clo­pe­dia of Rep­tiles and Am­phib­ians, 2nd edi­tion. Aca­d­e­mic Press, San Diego.

Cooper, W. E. Jr. and N. Green­berg. 1992. Rep­til­ian col­oration and be­hav­ior. Pages 298-422 in C. Gans and D. Crews, ed­i­tors. Hor­mones, Brain, and Beahv­ior: Bi­ol­ogy of the Rep­tilia, vol­ume 18, Phys­i­ol­ogy E. Uni­ver­sity of Chicago Press, Chicago.

Frost, D. R., and R. Etheridge. 1989. A phy­lo­ge­netic analy­sis and tax­on­omy of Iguan­ian lizards (Rep­tilia: Squa­mata). Uni­ver­sity of Kansas Mu­seum of Nat­ural His­tory, Mis­cel­la­neous pub­li­ca­tions 81:1-65.

Frost, D. R., and R. Etheridge. 1993. A con­sid­er­a­tion of iguan­ian lizards and the ob­jec­tives of sys­tem­at­ics: a reply to Lazell. Her­peto­log­i­cal Re­view 24:50-54.

Lazell, J. D. 1992. The fam­ily Iguanidae: Dis­agree­ment with Frost and Etheridge (1989). Her­peto­log­i­cal Re­view 23:109-112.

Macey, J. R., A. Lar­son, N. B. Anan­jeva, and T. J. Pa­pen­fuss. 1997. Evo­lu­tion­ary shifts in three major struc­tural fea­tures of the mi­to­chon­dr­ial genome among iguan­ian lizards. Jour­nal of Mol­e­c­u­lar Evo­lu­tion 44:660-674.

Pi­anka, E. R. 2001. Aus­tralia's Thorny Devil. Web­site at http://​uts.​cc.​utexas.​edu/​~varanus/moloch.​html

Pough, F. H., R. M. An­drews, J. E. Cadle, M. L. Crump, A. H. Sav­itzky, and K. D. Wells. 1998. Her­petol­ogy. Pren­tice-Hall, Inc., Upper Sad­dle River, NJ.

Schwenk, K. 1994. Sys­tem­at­ics and sub­jec­tiv­ity: the phy­logeny and clas­si­fi­ca­tion of iguan­ian lizards re­vis­ited. Her­peto­log­i­cal Re­view 25:53-57.

Uetz, P., and M. Bartz. 1996. EMBL Rep­tile Data­base: Agami­dae. (Web­site.)

Zug, G. R. 1993. Her­petol­ogy: an in­tro­duc­tory bi­ol­ogy of am­phib­ians and rep­tiles. Aca­d­e­mic Press, San Diego.

Con­trib­u­tors

Heather Hey­ing (au­thor).