Geckos and their relatives are among the most numerous and widely
distributed of lizards. Though found only in tropical and subtropical regions,
they occur on virtually every qualifying piece of land within those latitudes.
Their small size, hard-shelled eggs, and rapid rate of reproduction have made
geckos and skinks the most successful reptilian colonizers on earth: it is rare
to find a warm enough island that lacks members of one or both families. Not
surprising for such vagile lizards, geckos rank second only to skinks in numbers
of species. The giant of the geckos measures little more than 32 cm/13 inches
overall. Only a very few species of geckos produce live young; most lay 1-2
small, round, brittle-shelled eggs. Almost all geckos can loose the tail and
regrow a rougher replacement.
Geckos are lizards with true voices, and the squeaks made in alarm when we
pick them up may be moderated to serve other communicative purposes. So far,
very little research has been conducted to understand gecko voice communication.
An Australian barking gecko, Underwoodisaurus
milii, a member of the diplodactyline gecko group. This is a medium-sized
member of the large family Gekkonidae. Photo of "Ernie" by Dr. Robert
Sprackland. Click on photo to see antique print of this species.
Geckos are known for their toe pads, which enable them to scale glass or walk
across ceilings. Not all geckos have such pads, and they are entirely wanting
from the eublepharids and pygopods. Excepting the pygopods, all geckos have four
well-developed limbs with 4-5 digits. All geckos, excepting the eublepharids,
lack moveable eyelids, giving them a fixed, snake-like stare. This eye spectacle
is cleaned with the long, blunt-tipped tongue.
Gekkonids lack postorbital and squamosal arches in the skull. The tongue is
broad, flat, and has a tiny nick at the tip.
One of the legless members of the Gekkota, Pygopus
nigriceps, the hooded scaly foot from Australia. The head and voice are
decidedly gecko-like, but the body lacks limbs. Instead, there is a pair of
fleshy flaps near the cloaca, remnants of the legs reduced over evolutionary
history. Photo by Dr. Robert Sprackland.
The legless pygopods have long been held in their own family, but studies
from the 1980s onward support the evolutionary proposal that they belong with
the Australian-region geckos of the subfamily Diplodactylinae.
