Lizards, Part 2

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Lizards, Part 2

• Squamate Reptiles in a World of Smells

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Where weve been where were going

• In our last class we considered issues of
  taxonomy.
• The most basic question was whether to place
  Iguanians
• at the root?
• or high on the tree?
• This involved decisions about tongue prehension
  skull kinesis.
• In any case, we considered Iguanians last time,
  and today we should deal with all other lizards.

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The Lizards formerly known as Scleroglossans

• Because the lizard literature still reflects the
  old classification system, I shall organize
  this presentation that way as well.
• Now here come my major generalizations for the
  day
• To some degree (little in some species much more
  in others) these animals show life-history
  patterns that differ from those of iguanians
  (day-active, visual, low-energy ambush
  predators).
• With many exceptions, scleroglossans tend to be
  high-energy patrolling predators that inhabit a
  world of smells.

4
But Lizards are too successful diverse to be
contained within any easy generalizations!

• In scleroglossan evolution, there have been
  many side-tracks. One example is leg-reduction,
  seen in 7 Families (not even to mention the
  snakes)
• Pygopodidae. No front legs back legs tiny flaps
  (all species).
• Teiidae. A few sps. w/tiny front legs stumps
  for back legs.
• Scincidae. Limblessness (or almost) evolves gt 25
  times.
• Cordylidae. Chamaesaurus has many types of limb
  reduction.
• Dibamidae. Females are legless males have flap
  hind legs.
• Anguidae. Some regular legs, some small legs,
  some no legs.
• Aniellidae. Both species are legless.
• Question Why dont iguanians show leg-reduction?

5
The opening of new lifeways

• Remember The development of jaw prehension
  allows a cascade of adaptations.
• The tongue can become specialized for detecting
  chemicals of high molecular weight.
• This sensory modality can free lizards from the
  demands of ambush predation. (They can track
  mobile prey they can find sedentary and hidden
  prey.)
• Therefore, many scleroglossan lizards become
  widely-foraging predators. (No iguanians live
  like that.)
• In some ways the ultimate scleroglossans are
  snakes.

Next we begin our picture-review of these lizards.
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First Family Gekkonidae

• The Family includes c. 100 genera with c.1000
  species mostly tropical.
• Most are nocturnal, but diurnal behavior has
  evolved many times.
• Unusual eyes (next slide).
• Feet for climbing (next slide 1).
• Granular skin is easily torn tails are easily
  broken off.
• Some geckos have voices.
• Some gekkonines are good dispersers (especially
  the parthenogenetic, or all-female species).
• Geckos typically lay multiple clutches of 2 eggs
  each some species have TDSD.

Aeluronyx seychellensis
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More gecko facts
Cosymbotus platyurus

• Except for one relatively small sub-Family,
  geckos lack movable eyelids (like snakes except
  that many geckos lick their eyes).
• Weirdly shaped pupils increase efficiency of
  night vision.
• What do you think about thermoregulation in
  nocturnal geckos?

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Gecko foot (or, how can geckos climb up a
vertical pane of glass?)

• Toe-pads for vertical clinging have arisen
  multiple times in arboreal species of
  subfamilies Gekkoninae Diplodactylinae.
• Toes (left) have rows with thousands of setae
  individual setae divide into many spatulae (for a
  total of about a billion spatulae in G. gecko).
• Flattened spatulae tips are in intimate contact
  with surface and provide attachment by means of
  van der Waals forces.
• Total attachment force for G. gecko could
  approach 600psi.
• When running, geckos reduce local blood pressures
  peel their feet (starting with toe-tips) from
  surface, like tape.

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Eublepharinae

• With 6 genera c. 25 species, these are the most
  primitive geckos. (They have eyelids, their
  feet look normal.)
• They may have been an early (Jurassic) lizard
  response to the increasing abundance of nocturnal
  arthropods.
• Largely terrestrial, the eublepharines have a
  weird geographical distribution (see above next
  slide).

Coleonyx variegatus
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Biogeographical mysteries of the Eublepharinae

• The American radiation the 2 S.E. Asian
  radiations are consistent with the hypothesis of
  a Jurassic Laurasian origin.
• The central Asian radiation apparently rode
  drifting India from Africa.
• But how did ancestors of African and central
  Asian eublepharines get to Africa in the first
  place?
• Any of yall have ideas?
• (Laurasia was the northern Super-continent of
  Europe, Asia, and North America. Jurassic was
  middle-dinosaur times, 215-145MYBP.)

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Gekko gecko

• Gekkoninae. Found in around S.E. Asian houses,
  G. gecko marks territory by calling, often
  choosing perches that amplify its voice. Its a
  good hunter cockroaches beware!!!!!

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More gekkonine lifeways

• Heavily calcified, gekkonine eggshells harden on
  exposure to air. Such eggs are almost impervious
  to drying and raft well, aiding gecko dispersal
  (palm trees, hurricanes).
• Several species (e.g., Hemidactylus garnotii,
  above) are parthenogenetic. (Why are such
  all-female clones so successful? Why dont they
  rule the lizard world?)
• Consider the re-evolution of diurnal lifeways
• The Neotropical Sphaerodactylus (etc.) are tiny
  leaf-litter lizards, mostly in areas w/o
  microteiids.
• On Madagascar in other isolated places with
  depauperate lizard faunas, many geckos (e.g.,
  Phelsuma guimbeaui, left) are diurnal.

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Pygopodinae

• 8 genera c. 36 species.
• Tail is typically long and fragile no front
  legs back legs almost invisible flaps.
• Some pygopodines are burrowing sand-swimmers
  others are grass-swimmers.
• Most eat invertebrates, but hinged teeth of
  Lialis are for snake-like feeding on skinks.
• Lialis burtoni (remember?) imitates venomous
  snakes.

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Diplodactylinae

• 14 genera c. 115 species many are convergent
  w/gekkonines.
• One of the few non-flying vertebrates to inhabit
  New Zealand.
• Largely xeric-adapted in Australia.
• On isolated New Caledonia, Rhacodactylus (to 28cm
  SVL) is top terrestrial predator.

Diplodactylus intermedius
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The Autarchoglossan Grand Lineage
?

• Many iguanians (previous presentation) are
  diurnal, visual ambush predators using tongues to
  manipulate prey.
• Many geckos (above) are nocturnal ambush
  predators, eco-cognates of iguanians. Jaws show
  scleroglossan hinges, but geckos use tongues to
  manipulate prey to clean eyes.
• Remember, most autarchoglossan lizards use
  tongues to detect chemical cues about
  environment. Thus they begin the reptilian
  invasion of the world of smells.
• Is this the most successful terrestrial
  vertebrate lifeway? (See also concluding slide
  on community structure.)

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Thinking about differences between scincomorphs
and anguimorphs

• Scincomorphs tend to be active predators working
  within relatively high-energy ecosystems.
• Anguimorphs tend to be adapted to relatively
  low-energy systems such as deserts and cool
  places. (Many are less frenetic than most
  scincomorphs.)
• Many exceptions to these trends exist!

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The Scincomorpha, or skink lineage

• Lacertids (Old World) teiids gymnophthalmids
  (New World) are dominant, active lizards in open
  terrestrial habitats. (Xantusiids are something
  of a mystery.)
• Scincids, gerrhosaurids, and cordylids have some
  scales underlain by bone. Many are deliberate,
  cruising foragers, less frantically active than
  lacertids, etc.

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Family Teiidae

• 9 genera, c. 105 species.
• Teiids are in constant motion, watching for
  predators as they forage.
• High body temps typically support active
  foraging.
• Teiids often form size-graded communities of
  morphologically similar species.
• These often dominate high-sun neotropical
  terrestrial habitats (though rainforest species
  are common too).

Dracaenea guianensis
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Teiidae

• Body is often stout but is also streamlined.
  Head is usually pointed. Rear legs are long
  strong.
• Colors often are subdued blacks, browns, or
  greens, frequently with yellow mixed in stripes
  are common (fast moving).
• Larger species convergent w/Old-World varanids.
• The complex genus Cnemidophorus (c. 56 species)
  includes several parthenogenetic varieties such
  as C. tesselatus, left.

some are called race-runners, with good reason
Cnemidophorus tesselatus
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Family Gymnophthalmidae (smaller version of
teiids)

• C. 36 genera, 160 sps.
• Often called micro-teiids, these have
  transparent membranes in lower eyelids.
• These are dominant lizards in scaled down teiid
  habitats (but at lower body temps).
• Sympatric species are usually microhabitat
  specialists (as opposed to being size-graded).
• Parthenogenesis may be widespread.
• Bachia is almost legless.

Proctoporus ventrimaculatus
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Family Lacertidae

• 27-29 genera, about 220 species
• Most are terrestrial or rock-dwelling.
• Most are active-foraging, Old World teiid
  cognates. (Consider a thermophilic clade of
  scorpion-eaters in the Namib Desert)
• A few are sit-and-wait. (Consider cross-over
  depredation.)
• 5 parthenogenetic species are known.

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Lacertidae

• Lacertids typically have slender bodies, stout
  legs, long fragile tails.
• Head scales are enlarged fold of skin between
  chest throat scales.
• Some species are sexually dichromatic females
  brownish males greenish.
• Some actively foraging lacertids include fruit in
  the diet.
• Takydromus is a grass swimmer from SEA.

Takydromus sexlineatus
(Total length may be gt 600 of snout-vent length.)
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Family Xantusiidae

• 3 genera, c. 17 species
• Taxonomic placement within Scincomorpha is
  uncertain (perhaps closer to geckos spectacles
  over eyes).
• Most are adapted to arid habitats.
• May be nocturnal or work crevasses in daytime.
• Viviparous w/ placentation some are
  parthenogenetic.

Xantusia vigilis
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Xantusiidae (cont.)

• Most xantusiids are small dull-colored
  w/disruptive patterns.
• Demographics may reflect low TBs (body temps)
  slow metabolism
• Slow-maturing long-lived.
• Populations sometimes dense.
• Usually insectivores one species eats seeds.
• Diurnal foraging nocturnal sociality?

Xantusia henshawi
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Family Scincidae
Note Every autarchoglossan adaptation has arisen
at least once among the skinks!

• Perhaps 120 genera w/ c. 1400 species (but only 5
  New World genera, 4 with Old World species).
• Great diversity
• Size
• Food
• Habitat
• Body form
• Reproduction
• Sociality.
• Skinks defy stereotyping.

Tiliqua rugosa
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Non-Typical Examples of Skink Diversity
Acontias
Chalcides chalcides
Tribolonotus gracilis
Corucea zebrata
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A more typical scincid (Genus Eumeces)

• In most scincids, head is not distinct from neck
  scales are overlapping, polished, and underlain
  by multiple small interconnected bones (against
  snake predators?).
• Most skinks are diurnal but secretive.
• Multiple evolution of
• Body forms (leglessness, eyes, scale patterns).
• Repro strategies
• Eggs to various levels of placentation (Mabuya
  heathi)
• Maternal care
• Many- and few-young strategists
• Note on tail autonomy do some return re-ingest
  lost tails??

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The two pictures shown below illustrate the
common skink evolutionary tendency towards
elongated bodies small legs.
Lygosoma bowringii
Riopa sp.
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Biogeography of New World Scincids

• The 2 most important genera are medium-sized
• Mabuya, a placental reproducer, rafted across the
  Atlantic into South America.
• Eumeces, which is viviparous or tends eggs,
  invaded North America by way of Beringia.
• Competition w/ teiids in direct-sun versus cool
  and deep-shade habitats (led to specialization
  in reproductive foraging strategies).
• The smaller genera are successful only in
  habitats from which gymnophthalmids are absent
• Is this because the micro-teiids can spread out
  their eggs???
• Tiny Southeast Asian forest skinks have converged
  in body shape with South American gymnophthalmids.

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Family Gerrhosauridae

• 6 genera, about 30 species.
• Scales are underlain by bone are arranged in
  transverse rows.
• These lizards look like scale-banded, long-tailed
  skinks.
• These African plated lizards are slow-cruising
  foragers.

Tracheloptychus petersi
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Family Cordylidae

• 4 genera, about 42 species
• Scales are in transverse rings are often spiny.
• Most are viviparous.
• Most are territorial, diurnal sit--wait
  insectivores, behaviorally convergent w/
  iguanians.
• One genus nearly legless.

Cordylus giganteus
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Cordylidae (cont.)

• Many cordylids are crevasse-dwellers that
  thermoregulate by exposing sides of bodies
  spines help protect these lizards while in rocks.
• Males sometimes colorful, marking territories by
  visual displays.
• Platysaurus can be densely colonial inhabits
  kopjes isolated as Kalahari sands drifted east
  during Plio-Pleistocene. (Why is this the only
  oviparous genus?)

Cordylus cataphractus
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The Anguimorph Lineage

• The next dozen slides display representatives of
  a loosely-connected set of autarchoglossan
  lizards called the anguimorph lineage.
• These animals exhibit a vast array of body forms,
  ranging from stout legs to leglessness, from thin
  tails to the fattest tails of any lizards.
• Perhaps they are united in their expression of
  the autarchoglossan lifeway these are largely
  creatures of smell.
• Many herpetologists believe the evolutionary
  origins of snakes should be sought in this
  diverse group.

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Family Anguidae

• 15 genera, 102 species
• Sub-scale osteoderms provide somewhat separate
  dorsal ventral armor.
• Anguids include New World alligator lizards
  (w/legs) plus Ophisaurus types (legless)
  skink-like neotropical galliwasps (short legs
  left).

Diploglossus monotropis
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More about anguids

• Opening of the Atlantic Ocean (c. 100MYBP) split
  the Laurasian distribution of ancestral anguids
• Gerrhonotine alligator lizards evolved in New
  World they probably share ancestors with
  diploglossines.
• Legless anguines evolved in Old World.
• The anguine genus Ophisaurus (left) invaded North
  America via Beringia.
• Some herpetologists propose a different
  biogeographical scenario.

Ophisaurus ventralis, a South Carolina lizard
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Family Anniellidae

• 1 genus, c. 2 species
• Evolved in New World.
• Included in Anguidae by many herpetologists.
• Shovel-snouted sand-swimmers w/ blunt tails.

Anniella pulchra
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Family Xenosauridae

• 1 genus and c. 12 species
• Knob-scaled crevasse-dwellers converging w/
  cordylids.
• Adapted to operate at TBs as low as 22oC.
• All are viviparous maternal care may be
  extensive.

Xenosaurus grandis
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Xenosauridae (cont.)

• This Mexican Family is not well known and may be
  lumped with the Chinese Shinisauridae (next
  slide).
• Although some inhabit xeric regions, most prefer
  moist microhabitats.
• Most are largely diurnal.
• Most are insectivores.

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Family Shinisauridae

• 1 genus, 1 species
• This lizard is semi-aquatic, inhabiting limestone
  streams in moist southeastern China.
• It eats mostly invertebrates but may sometimes be
  a tadpole specialist, even foraging underwater.

Shinisaurus crocodilurus
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Family Helodermatidae

• 1 genus, 2 species
• The only living venomous lizards.
• Venom glands very different from those of snakes
• In lower jaw
• Not muscularized
• Usually operate _at_ lower TBs than most other
  lizards.
• Studded dorsal skin resembles a beaded purse.

Heloderma horridum
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More about the Helodermatidae

• Helodermatids probably spend gt 95 of year in
  underground refuges.
• They live in regions where a short, intense
  rainy season provides a time-concentrated
  supply of clumped prey such as eggs, nestlings,
  etc., which are hunted by smell.
• Long fasts are tolerated!
• Helodermatids are legally protected throughout
  their range.

H. suspectum (Gila monster)
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Family Lanthanotidae

• 1 genus, 1 species
• This lizard occurs only in Sarawak (in Borneo).
• Adult length is c. 42-43cm.
• The lizard is thought to swim burrow
  prehensile tail suggests climbing
• Perhaps it eats earthworms.
• The natural history of this earless monitor is
  basically unknown.

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A tiny bit more about the little-known
Lanthanotidae

• The legs are small.
• There are 3-4 rows of enlarged scales along the
  back and tail.
• Some snake-like aspects
• Braincase is relatively solid.
• Skin is shed in one piece.
• Teeth on palatine and pterygoid bones.
• Hinge in lower jaw.
• No external ears.
• (Translucent lower eyelids)
• Gobi fossils of presumed lanthanotids suggest
  little change since Cretaceous.

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Family Varanidae (monitors)

• 1 living genus and about 50 species.
• Varanids forked tongues are edge-detectors!
• Varanids are active widely foraging predators.
• They vary greatly in size
• V. brevicauda (left) 20cm mass lt 20g
• V. komodoensis (next slide) 3m mass to 150kg
• Extinct Megalina prisca (26-19KYBP) 6m mass gt
  600kg
• Varanids are particularly speciose in Australia,
  where communities are often size-graded.

Varanus brevicauda
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More about the Varanidae(V. komodoensis, the
Komodo Dragon, is shown below.)

• Usually browns or grays body cylindrical neck
  tail long. Head long narrow jaws strong.
  Forked tongue acute vomeronasal sensing.
• Monitors swallow large prey.
• Monitors have more aerobic capacity higher
  potential metabolism than other lizards.
• Retaining heat overnight, large monitors are
  thermally (and behaviorally) convergent with
  mammalian predators.
• Monitors are often considered to be intelligent.
• Varanids are usually the top predators on the far
  side of Wallaces Line (e.g., in Australia).

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Lineage(s) of Uncertain Status

• The relationships among amphisbaenians are
  reasonably clear.
• The relationships between snakes, amphisbaenians,
  and dibamids and between those groups and all
  other scleroglossans are unclear (see later
  slides).

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Squamates that dont fit well.

• The next 7 slides show three clades of lizards
  that are difficult to mesh within most
  classification schemes.
• Dibamidae
• These are among the strangest least-known of
  lizards.
• They may be related to wormlizards (below) or to
  skinks.
• The 4 wormlizard Families
• These have conventionally been considered a
  squamate Suborder.
• May be related to gekkotans, to skinks, to
  teiids, or to anguids.
• Snakes (roughly 20 Families)
• These have conventionally been considered a
  squamate Suborder.
• They may be related to dibamids or to
  wormlizards, but many modern herpetologists
  suggest a varanoid affiliation.
• Snakes will get days of their own, but since they
  are lizards.
• Remember, a clade is a group of all organisms
  sharing a common ancestor.

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Dibamidae (Scleroglossan, but beyond that, who
knows)

• 10-11 species e. Mexico (1 species) Southeast
  Asia.
• Taxonomic affiliations unknown. Once assumed
  skink-like now thought closer to snakes or
  (other) anguimorphs.
• Plate-like scales on heads body worm-like eyes
  under skin ears covered by scales. No front
  legs rear legs are peg-like in males absent
  in females.
• These are mostly burrowers.

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Amphisbaenians

• So different from other squamates, wormlizards
  have been considered a separate Suborder (of
  co-equal rank with lizards snakes).
• Many differences may reflect adaptation for
  digging (rather than separate ancient ancestry).
• Skulls are strongly ossified highly modified
  for digging (tunneling, not swimming).
• Skin can moves independently of underlying trunk
  muscles.
• No right lung (snakes lack left).

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Amphisbaenidae (a wormlizard Family)

• C. 19 genera 140 species.
• 2 digging systems, reflecting head shape
• Vertical keel move head left right to pack
  walls less powerful muscles than...
• Horizontal spade scrape down and then lift up,
  compressing soil into roof of tunnel.
• 2 Fierce underground predators, eating anything
  they can catch.

Amphisbaena fuliginosa
51
Trogonophidae (a wormlizard Family)

• About 4 genera 6 species spotty Afro-Arabian
  distribution.
• Appears to screw-burrow its way by oscillation
  through less-compressible soils.
• Head shifts back forth while rotating dirt is
  scraped from front and sides.
• The animal uses its pointed tail and short,
  stout body to keep up continuous forward pressure.

Agamodon angeliceps
52
Rhineuridae (a wormlizard Family)

• 1 species only U.S. amphisbaenian (North
  Florida) fossils are more widely spread.
• As with other wormlizards, lower jaw is
  counter-sunk to keep out sand.
• Burrows up-down like horizontal-spade
  amphisbaenids, but has different bone structure.
• More common than usually thought.

Rhineura floridana
53
Bipedidae (a wormlizard Family)

• Baja, California.
• Two front legs only lagartijas con orejas.
• Thrust head forward use legs to scrape away
  loosened sand.
• A sand-burrowing animal, usually found near old
  wood, where it probably collects termites.

Bipes bipes
54
SERPENTES (Scleroglossan for sure, but beyond
that)

• Snakes (gt 2500 sps) are traditionally classified
  as a full Suborder in our course they will have
  a few days of their own.
• However, in evolutionary terms
• they are another lizard offshoot (an extreme
  expression of general scleroglossan themes)
• they are the most successful lizard offshoot
  can do things most (other) lizards cannot.

55
The impact of autarchoglossan radiations on the
taxonomic constitution of lizard communities

• Autarchoglossan impact on gekkotans
• In general, gekkotans were driven into the trees
  and into the night.
• In Australia, gekkotans also driven to converge
  w/colubroids (generalized harmless snakes), which
  are largely absent from Australia.
• Autarchoglossan impact on iguanians
• Generalist iguanians were often out-competed, but
  iguanian microhabitat specialists were largely
  unaffected.
• Autarchoglossans often hold terrestrial
  thermally favorable niches while iguanians tend
  to be arboreal and/or shade-lizards.
• Consider radiations of S. Andean Liolaemus
  Caribbean Anolis.
• Whats the evolutionary role of non-squamate
  competitors?????
• The place of snakes in lizard communities
• Consider snakes as cooled-down varnoids
  specialized for swallow-whole consumption of
  large prey.