Lizards, PowerPoint 1

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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

2
The basic taxonomic question Does the
skull-kinesis plan define the most fundamental
within-lizards split, or is it primitive amongst
lizards?

• Tuataras and iguana-type lizards manipulate food
  with their tongues, which therefore cant do many
  other things.
• If this task were assumed in part by lips jaws,
  then the tongue could be released for other
  functions, such as smelling.
• 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 snakes swallowing adaptations.)

3
Partial Agreements about Lizards (1 of 4 slides)

• Iguanian Lizards Todays 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.

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agreements 2 Lizard evolution in the broader
reptilian context.

• 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.

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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 thats 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!

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agreements 4 The snakes-versus-lizards
non-issue.

• 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.

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Dare I consider the classification of Squamates?

• Lizards are a highly complex group with some
  experts listing more than 30 Families. (Well
  treat almost two dozen groups in the next couple
  of PowerPoints, well 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 lizards
  closest living relatives (tuataras)?
• Where are the snakes placed?
• How many types are presented as having ambiguous
  affiliations?

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Conventional classification of lizards
Next slide simplifies
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Conventional ClassificationSimplified Version

• Iguania is sister to all other lizard groups
  (i.e., to the scleroglossans).
• Gekkota is sister to all other scleroglossans
  (i.e., to the autarchoglossans).
• Autarchoglossans are divided into (at least)
  skink-forms and anguid-forms (and others).
• Snakes, dibamids, and wormlizards form
  scleroglossan clades of uncertain affiliation,
  probably within the Autarchoglossa.
• Remember Almost all these generalizations are
  now under question.

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New Suggested Classification of Lizards
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Suggested New ClassificationSimplified version
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Considering the Iguaniansour 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.

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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).

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Typical iguanian territoriality

• Typically, females minimize territories, males
  maximize 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
• Promiscuity
• Monogamy
• Dominance hierarchies
• Should mating-structures be maintained outside of
  the breeding season?

Next Begin tour of Families
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Family Iguanidae

• About 50 genera with probably gt 1000 species.
• Ranges will be shown when 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 thermal conformers.
• Mostly ambush predators.
• Few-egg types many-egg types.
• Tail usually long, usually autonomous.

Basiliscus plumifrons
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Iguanidae Crotaphytinae

• 2 genera, c. 12 species
• Most are arid-land or rock-outcrop specialists.
• Feed on large arthropods or other lizards.
• All species are sexually dimorphic, with males
  larger than females.
• Females develop orange or red spots when carrying
  eggs. (Why???)

Crotaphytus bicinctores
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Iguanidae Iguaninae

• 8 genera c. 34 species
• Iguanines are medium to large in size.
• Amblyrhynchus has salt glands eats marine algae
  in Galapagos.
• All other genera are hindgut cellulose
  fermenters.
• Some have unusual thermoregulation strategies.
• Most have highly developed sense of smell (for
  stuff of low molecular weight).

Brachylophus fasciatus
Fiji Islands
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Iguanidae Oplurinae

• 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 colors
  defend territories.

Chalarodon madagascariensis
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Iguanidae Phrynosomatinae

• 10 genera, c. 125 species
• The subfamily is diverse.
• Many are arid-habitat specialists, and many are
  somewhat flattened.
• Thermoregulation is often precise.
• Many species are strongly sexually dichromatic.
• Phrynosoma (next slide) has weird defensive
  behaviors.

Sceloporus malaciticus
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Phrynosomatinae (cont.) How lifestyle parameters
of horned lizards are linked together.

• 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 cant outrun predators camouflage
  lie low.
• So, lizard cant thermoregulate well.
• Since lizard doesnt move much, she wont have to
  carry eggs around very far, so she produces lots
  of them. Etc.

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Iguanidae Polychrotinae (anoles)

• 2 or 11 genera, depending on whom you ask gt 440
  species
• Usually sexually dichromatic, with males
  possessing bright, extendable throat-flaps
  (dewlaps).
• Most are arboreal some converge w/chameleons,
  others w/geckos.
• Most eat insects most are ambush predators or
  visual stalkers.

Anolis conspersus
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Iguanidae Tropidurinae

• 9-12 genera and about 270 species
• Ecologically diverse, but
• Most are thermoregulators (though rainforest
  types have difficulties).
• Most rely on crypsis.
• Most are ambush predators.
• Some forms are highly polygynous, with males
  breeding many females.
• In some species, dominant males are distinguished
  by coloration.
• The group is thought by some to be paraphyletic.

Plica plica
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Three additional iguanid subfamilies(that I do
not choose to discuss in any detail)

• Leiosaurinae
• 7 genera
• South American
• Many forest animals, most extremely cryptic
• Hoplocercinae
• Poorly known South American forest lizards.
• 3 genera, about 12 species.
• Corytophaninae
• 3 genera, about 9 species.
• Basiliscus is semi-aquatic.

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Family Chamaeleontidae

• 4-6 genera, c. 130 species
• Highly specialized arboreal insectivores
• vertically flattened body
• prehensile tail
• zygodactylous feet
• turret eyes
• changeable color
• projectile tongue
• Often w/ornamentation, sometimes sexually
  dimorphic.

Chamaeleo calyptratus
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Chamaeleontidae (Infraorder Iguania)

• Foraging techniques
• They move so slowly are they stalkers or ambush
  predators?
• When scanning, eyes send alternating images to
  brain _at_ about 1-second intervals.
• When ranging, eyes send simultaneous images eyes
  enlarge image find range by focusing.
• Demography
• Large investment in large number of small
  offspring.
• Rather short lifespan.

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Family Agamidae

• About 45 genera w/ about 300 species.
• Mostly diurnal mostly drab (except some breeding
  males) social commo often by means of shape.
• Many are Old World iguanid cognates.
• Some highly structured, dense colonies.
• Some large herbivores.
• Some ornamented.

Physignathus cocincinus
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Agamidae (Infraorder Iguania)

• Agamids are medium to large in size.
• Legs are well developed.
• Many agamids are terrestrial, and the vast
  majority are diurnal.
• Except for the genus Phrynocephalus, all agamids
  lay eggs.
• Southeast Asias Draco (left) is an accomplished
  glider.

Draco volans
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Here are other, more representative agamids.

• Note distinct shapes vertical compression in
  arboreal species (left) and horizontal
  compression in terrestrial species (above).