Simplified Classification of Lizards

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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
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
                                      snakes’ swallowing
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
                 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.
   …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
of lizards

   Next slide
                               • 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
                                 “wormlizards” form
                                 scleroglossan clades of
                                 uncertain affiliation, probably
                                 within the Autarchoglossa.
                               • Remember: Almost all these
                                 generalizations are now
                                 under question.
New Suggested Classification of Lizards
Suggested New Classification:
     Simplified version
  Considering the
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:
                      – Promiscuity
                      – Monogamy
                      – Dominance hierarchies
                   • Should mating-structures be
                     maintained outside of the
                     breeding season?
                      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
                          thermal conformers.
                        • Mostly ambush predators.
                        • Few-egg types & many-egg
                        • Tail usually long, usually
Basiliscus plumifrons

                          • 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
                         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
Brachylophus fasciatus     low molecular weight).
    Fiji Islands
            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
Chalarodon madagascariensis     colors & defend
            Iguanidae: Phrynosomatinae
                         • 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
                           sexually dichromatic.
                         • Phrynosoma (next slide)
                           has weird defensive
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 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
                                possessing bright,
                                extendable throat-flaps
                              • Most are arboreal; some
          Anolis conspersus
                                converge w/chameleons,
                                others w/geckos.
                              • Most eat insects; most
                                are ambush predators or
                                visual stalkers.
                 • 9-12 genera and about 270
 Iguanidae         species
“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)
• 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.
Family Chamaeleontidae

                                • 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,
                                  sometimes sexually
                       • 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
                            by focusing.
                       • Demography:
                          – Large investment in large
                            number of small offspring.
                          – Rather short lifespan.
   Family Agamidae

                          • 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
                            iguanid cognates.
                          • Some highly structured,
                            dense colonies.
                          • 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
                          Phrynocephalus, all
                          agamids lay eggs.
                        • Southeast Asia’s
                          Draco (left) is an
                          accomplished glider.

Draco volans
Here are other, more representative agamids.

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

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