Lizards, PowerPoint 1
• Metaphorical statement:
– God must love lizards because she/he created an
enormous number of them (including snakes)!
• Two conflicting tales of evolution:
– Conventional for twenty years:
• Earliest lizards preserve ancient jaw/tongue structures
• More advanced lizards move into a world of smells
– Radically new (and not [yet?] widely accepted):
• Earliest lizards had lost ancient jaw/tongue structures
• Movement into a world of smells begins very early
• Manufacture of disabling toxins is early adaptation
• “Iguanian” lizards are not primitive but are derived
The basic taxonomic question: Does • Tuataras and iguana-type
the skull-kinesis plan define the lizards manipulate food with
most fundamental within-lizards their tongues, which therefore
split, or is it primitive amongst can’t do many other things.
lizards? • If this task were assumed in
part by lips & jaws, then the
tongue could be released for
other functions, such as
• Diagram at left shows a non-
iguana-type mobile skull.
Lizards w/this type of skull
can use tongues to enter “the
world of smells.”
• (Whenever it occurred,
evolution of cranial kinesis–
skull movement– was pre-
requisite to the evolution of
Partial Agreements about Lizards (1 of 4 slides)
• Iguanian Lizards: Today’s main subject, this group is set apart from other
lizards. The iguanians include 3 Families of lizards that tend to be visually oriented,
low-energy ambush predators. Their tongues are involved with food manipulation
and are therefore not available for other purposes. In this iguanians are like tuataras,
the closest living lizard-relatives. But is this condition preserved from ancient
ancestors, or was it re-evolved high in the lizard phylogenetic tree?
• Other Lizards: A subject for later classes, non-iguanian lizards have highly
mobile jaws, and therefore their tongues can be used for purposes other than food
manipulation. (See next slide.) In the conventional taxonomy, these animals are
called Scleroglossan (= “hard-tongued”) lizards. This group includes the snakes.
– Gecko-types (a firm taxonomic group). These animals pursue a number of specialties
(especially nocturnal lifeways) and depart from many of the usual lizard themes.
– “Autarchoglossan lizards.” (This may or may not be an inclusive and coherent group.)
To greater or lesser degree, these lizards use their tongues to gather chemical
information. The group includes:
• Numerous Families of “typical” lizards
• Four Families of (near-) legless wormlizards (amphisbaenians)
• Numerous Families of snakes.
…agreements 2: Lizard evolution in the broader
• No single factor defines lizards, so their ancestry is difficult
to trace in the fossil record.
• About 245-200MYBP, lizard ancestors diverged from the
line that was to become the Archosauria (thecodonts, crocs,
dinosaurs, pterosaurs, and birds).
• Lizards were not a particularly impressive Order during the
earlier Ages of Reptiles, but over time they became the most
successful reptilian group. (Why? See next slide.)
• Furthermore, all major present lineages were established
before or during the Cretaceous (135-65MYBP).
• Cenozoic (post-dinosaur) radiation has been comparable to
that of the perching birds, the other successful tetrapods.
…agreements 3: Lizard evolution in community-
context (think insects).
• The radiations of the lizards should be understood within
the context of the radiation of the arthropods– because that’s
what what most lizards eat.
• Arthropods invade the land about contemporaneously with
tetrapods, but their first major radiation awaits the Jurassic
success of gymnosperm plants (pine trees, etc.).
• The triumph of the angiosperms (flowering plants) during
the Cretaceous is accompanied by an enormous, additional
diversification of arthropods.
• Arthropod radiations also feed on arthropod radiations….
• Among terrestrial vertebrates, only lizards were positioned
to exploit this abundance of potential animal-prey!
…agreements 4: The snakes-versus-lizards non-
• Old-time taxonomists were overly concerned with
distinguishing lizards from snakes:
– General characteristics of Order Squamata (which, of course, fit snakes too):
• epidermal scales
• transverse vent
• paired intromittent organs
• vertebrae usually open-ended toward front
– Characters of some lizards and no snakes:
• four legs (but…)
• external ear openings (but…)
• moveable eyelids (but…)
– Characters of “all lizards” (except of the lizards commonly called snakes):
• in combination, fused mandibles and traces of both girdles
• Nowadays all herpetologists recognize that snakes are
deeply embedded within the lizard tree. In other words,
taxonomically, snakes are lizards.
Dare I consider the classification of Squamates?
• Lizards are a highly complex group with some
experts listing more than 30 Families. (We’ll treat
almost two dozen groups in the next couple of
PowerPoints, & we’ll consider snakes later.)
• Themes to look for on next 4 (complex) slides:
– What is presented as the most basic type of lizard?
– How similar is this most basic type to lizard’s closest
living relatives (tuataras)?
– Where are the snakes placed?
– How many types are presented as having ambiguous
• Iguania is sister to all other
Conventional Classification: lizard groups (i.e., to the
Simplified Version “scleroglossans”).
• Gekkota is sister to all other
“scleroglossans” (i.e., to the
• “Autarchoglossans” are divided
into (at least) skink-forms and
anguid-forms (and others).
• Snakes, dibamids, and
scleroglossan clades of
uncertain affiliation, probably
within the Autarchoglossa.
• Remember: Almost all these
generalizations are now
New Suggested Classification of Lizards
Suggested New Classification:
first major lineage
• Are Iguanians the most ancient lizard type?
• This lizard-plan is definitely a good one, for iguanians are
hugely successful around the world today.
• The group includes 3 Families and about 1500 species.
General thoughts on Iguanian lifeways
• Iguanian jaws & lips are not typically specialized, so the
tongue retains (regains?) its original manipulation-function,
and iguanians emphasize vision instead of smell.
• Vision is appropriate for real-time detection of prey.
– Iguanidae & Agamidae: detect the slightest motion….
– Chamaeleonidae: detect distant prey….
– (Of course there are iguanian exceptions to this visual emphasis.)
• Thus most iguanians are sit-and-wait predators, and…
– Thus most iguanians can combine thermoregulation with hunting.
– Many are heavy-bodied….
– Most have low to medium metabolic rates….
– Most emphasize burst-speed over endurance.
– Many iguanians are highly cryptic.
– Many iguanians are microhabitat specialists.
– Many are territorial (next slide).
• Typically, females minimize
Typical iguanian territories, & males maximize
territoriality territories. Why?
– Male strategy: inseminate as
many females as possible. But
what are the limiting factors?
– Female strategy: 1 good mating
& put your energy into eggs
(and/or into staying alive).
• Other mating systems:
– Dominance hierarchies
• Should mating-structures be
maintained outside of the
Next: Begin tour of Families…
• About 50 genera with
probably > 1000 species.
• Ranges will be shown when
Family Iguanidae separate subfamilies are
treated below. (These &
other subfamilies might be
promoted to Family level.)
• Small, medium, & large.
• Often brightly colored
(especially males); often w/
crests, dewlaps, etc.
• Thermoregulators and
• Mostly ambush predators.
• Few-egg types & many-egg
• Tail usually long, usually
• 2 genera, c. 12 species
• Most are arid-land or rock-
• Feed on large arthropods or
• All species are sexually
dimorphic, with males
larger than females.
• Females develop orange or
red spots when carrying
• 8 genera & c. 34 species
• Iguanines are medium to
large in size.
• Amblyrhynchus has salt
glands & eats marine algae
• All other genera are hindgut
• Some have unusual
• Most have highly developed
sense of smell (for stuff of
Brachylophus fasciatus low molecular weight).
• 2 genera & 7 species
• Limited to Madagascar.
• Small to medium-large
lizards mostly living in
trees or rocks.
• Most have spiny tails.
• All are thermophilic,
often seeking open sun.
• During breeding season
males show bright
Chalarodon madagascariensis colors & defend
• 10 genera, c. 125 species
• The subfamily is diverse.
• Many are arid-habitat
specialists, and many are
Sceloporus malaciticus somewhat flattened.
• Thermoregulation is often
• Many species are strongly
• Phrynosoma (next slide)
has weird defensive
How lifestyle parameters
of horned lizards are
• They eat ants & little else.
• Ants are small & chitin-covered, hard to digest; thus many
must be consumed & slowly processed.
• So lizard must have large stomach/body ratio.
• Large stomach dictates slow-moving body form.
• So, lizard can’t outrun predators; camouflage & lie low.
• So, lizard can’t thermoregulate well.
• Since lizard doesn’t move much, she won’t have to carry
eggs around very far, so she produces lots of them. Etc.
• 2 or 11 genera,
Iguanidae: depending on whom
Polychrotinae (anoles) you ask; > 440 species
• Usually sexually
dichromatic, with males
• Most are arboreal; some
• Most eat insects; most
are ambush predators or
• 9-12 genera and about 270
“Tropidurinae” • Ecologically diverse, but:
– Most are thermoregulators
(though rainforest types have
– Most rely on crypsis.
– Most are ambush predators.
• Some forms are highly
Plica plica polygynous, with males
breeding many females.
• In some species, dominant
males are distinguished by
• The group is thought by some
to be paraphyletic.
Three additional iguanid subfamilies
(that I do not choose to discuss in any detail)
– 7 genera
– South American
– Many forest animals, most extremely cryptic
– Poorly known South American forest lizards.
– 3 genera, about 12 species.
– 3 genera, about 9 species.
– Basiliscus is semi-aquatic.
• 4-6 genera, c. 130 species
• Highly specialized
Chamaeleo calyptratus arboreal insectivores:
– vertically flattened body
– prehensile tail
– zygodactylous feet
– turret eyes
– changeable color
– projectile tongue
• Often w/ornamentation,
• Foraging techniques:
Chamaeleontidae – They move so slowly; are
(Infraorder Iguania) they stalkers or ambush
– When scanning, eyes send
alternating images to brain
@ about 1-second intervals.
– When ranging, eyes send
simultaneous images; eyes
enlarge image & find range
– Large investment in large
number of small offspring.
– Rather short lifespan.
• About 45 genera w/ about
Physignathus cocincinus 300 species.
• Mostly diurnal; mostly
drab (except some
breeding males); social
commo often by means of
• Many are Old World
• Some highly structured,
• Some large herbivores.
• Some ornamented.
Agamidae (Infraorder • Agamids are medium
to large in size.
Iguania) • Legs are well
• Many agamids are
terrestrial, and the vast
majority are diurnal.
• Except for the genus
agamids lay eggs.
• Southeast Asia’s
Draco (left) is an
Here are other, more representative agamids.
• Note distinct
(left) and horizontal