Do lizards give evidence to an intelligent design? One of the problems
in answering that question stems from the fact that lizards can be quite
diverse no accepted classification system exists among creationists to
identify those groups which have a common ancestry.
The general lizard body plan is not as specialized as that of many other
reptiles. A number of groups bear a superficial resemblance to lizards
such as the earliest anapsid reptiles, the earliest diapsid reptiles,
and even advanced amphibians. Because of this similarity, the first lizards
do not seem to have required a supernatural design but rather a modification
of ancestral reptiles which were already lizard-like in their overall
form. The first lizards were small, less than 10 cm in length, and were
probably insectivorous. Upper Permian and Lower Triassic lizards are more
primitive than later forms in that they possessed unfused proximal tarsal
bones in the foot, poorly developed fenestration of limb girdles, and
Lizards are quite diverse. Modern lizards range from the equator to New
Zealand and north of the Arctic circle and inhabit ecosystems from sea
level to 5,000 meters in elevation. The sizes of chameleons can vary from
less than 2.5 cm to more than 50 cm. The modern Komodo dragon reaches
3 meters and the extinct Megalania that reached twice this size. Australia's
fossil fauna included a lizard (goanna) which reached 4 to 5 meters in
length (Dawson, 1995). Extinct mosasaurs reached 10 meters.
Although most lizards move on four limbs, some groups have significantly
modified this ancestral "design". Some lizards have reduced
their limbs to the point that they are vestigial stubs or are completely
absent. This is true of all species of the limbless family Anniellidae,
the family Pygopodidae (which have lost their front legs and whose hind
legs are vestigial), and Dibamidae (in which males retain vestiges of
hind legs). In other families, only some members of the family have legs
which are reduced or absent. This is true in the family Teiidae (in which
some South American species of the genus Bachia possess small arms and
vestigial leg stubs), Scincidae (in which some species have reduced legs,
some are missing front legs, and some are completely legless), Cordylidae
(in which some species possess small arms and vestigial leg stubs), and
Anguidae (in which limbs can be reduced or absent in some species). (Mattison,
1989; Halliday, 1987; Pough, 1998).
There are 4 families of lizards known as amphisbaenids. In this group,
the species of three families lack any trace of limbs or limb girdles.
The fourth family has not only retained its arms, but the hands have grown
to considerable size.
The fossil record indicates that one early group of lizards significantly
reduced its limbs.
Other significant variations exist as well. Some iguanids, igamids, and
monitor lizards are capable of bipedal locomotion (even running across
the surface of water in the South American basilisk) and standing. Some
species of Crotaphytidae are bipedal while jumping. Species of the family
Corytophanidae can run bipedally. When threatened, Gould's monitor stands
on its hind legs (Halliday, 1987; Pough, 1998).
Some geckos can glide through the air using skin flaps between their limbs
and webbed digits. In the agamid genus Draco, elongated ribs allow a skin
flap between the limbs to be used in gliding (Mattison, 1989). A separate
lineage of fossil lizards (Kuehnosaurus) also possessed expanded their
ribs for gliding.
The lizard genus Helodermoides possessed armor (Carroll, 1988).
Within the family Agamidae, individual species can possess neck frills,
throat fans, spines along their backs, and modified head structures. Some
chameleons have horns. Extensive skull casquing in known in the family
Polychrotidae. Many groups developed a firmer tooth attachment and one
extinct group possessed deep sockets for its teeth. The Gila Monster is
poisonous (Pough, 1998).
Some lizard scales are thick enough to serve as armor while others (such
as those of gecko feet) are covered with microscopic bristles which allow
them to climb smooth surfaces. Some defend themselves through bluffing,
inflating their body, hissing, extending a neck ruff to appear larger,
and even squirting blood out of their eyes (in Phrynosoma; blood can be
squirted up to four feet). Some lizards can change their coloration in
response to the background of the environment, a threat from a predator,
or in courtship/territorial displays (Mattison, 1989).
Most lizards depend primarily on vision, although eyes are often reduced
(or even vestigial) in burrowing lizards. Some lizards (geckos, pygopodids,
and xantusids) have fused their eyelids to form a protective brille over
the eye, just as in snakes. Chameleon eyes are capable of independent
movement. Most lizards possess an external ear opening and some make sounds
which serve in intra-specific communication. The Bornean earless monitor
lacks both an outer and middle ear cavity. (Mattison, 1989).
Lizard tails can be used for a variety of purposes ranging from balance
in bipedal locomotion, a fat reserve, a prehensile grasping structure,
and the source of noxious secretions which deter predators. A number of
lizards have modified their tail so that it is prehensile, including species
of the families Chamaeleonidae, Agamidae, Gekkonidae, Polychrotidae, and
Scincidae (Halliday, 1987; Pough, 1998). Tails are adapated to break in
at least some species of 11 of the 16 families of modern lizards (Halliday,
Many lizards reproduce through live birth and this adaptation has arisen
many times within different groups. Both egg-laying and live-bearing species
are known in the families Agamidae, Chamaeleonidae, Phrynosomatidae, Tropiduridae,
Gekkonidae, Eublepharidae, Lacertidae, and Scincidae. Some species brood
over their eggs and others (such as the Great Plains skink, the desert
night lizard, and the California alligator lizard) offer maternal care
after birth. Live birth seems to have evolved separately in skinks more
than 20 times. Parthenogenesis (all-female populations which reproduce
by giving birth to clones of themselves) is known in some in rock lizards,
geckos, whiptails, and racerunners. The number of eggs laid per clutch
can vary significantly in a family. For example, clutch size can vary
from 4 to 70 in diverse chameleon species.
The lizard body form has been modified for a diversity of habitats. While
most lizards are terrestrial, adaptations for arboreal life have evolved
in some species of the families Iguanidae, Phrynosomatidae, Tropiduridae,
and Teiidae. A number of groups have adapted to burrowing such as glass
lizards, blind lizards, snake lizards, and many skinks. Amphisbaenans
are unusual in that the group is exclusively subterranean in its habits.
Some Teiid lizards are semi-aquatic and the extinct mosasaurs were highly
specialized for marine life. Fossil lizards of the family Aigialosauridae
were semiaquatic and were transitional between varanoids and mosasaurs.
Most lizards prey on other animals. While many feed on a variety of
prey, some have become more specialized such as the Caiman lizard whose
teeth are modified to crush snail shells and the Komodo dragon whose teeth
are modified to cause lethal infections and can bring down water buffaloes.
About two percent of lizard species are herbivores including iguanas,
the Egyptian spiny-tailed lizard (an agamid), some girdle-tailed lizards,
and some Australian skinks.
Not only can lizards in different groups vary in their habits, lifestyle
can vary significantly within a family. Many iguanas are terrestrial,
many are arboreal, and the marine iguana have become adapted for swimming
in the coastal ocean. While many iguanas feed primarily on insects, others
are herbivores, and the marine iguana feeds on algae. Diet can vary considerably
in the family Tropiduridae. While most species are generalists which prey
on insects, some are herbivores and others eat only ants.