Lect 11

Question 1

Lepidosauria

Answer 1

lepisma, “scale” + sauros, “lizard” Tuatara, lizards, and snakes.

Lepidosauria within Amniota

Within Leo is squamata and rhynchocephalia

Sister Clade to archosauria

Question 2

Clades within Lepidosauria

Answer 2

• Order Sphenodontia/Rhynchocephalia: tuatara (more distal)

• Order Squamata: lizards, including snakes

Question 3

Lepidosaur characters

Scales and growth

Answer 3

what makes them unique

Comp and structure of scales and most scale don’t have any bony tissue

• Overlapping keratinous scales

• Skin grows over scales and is shed
- Snakes shed whole skin; other lizards shed in patches
(Diff from fish scale, scales grow through epidermis)

• Determinate growth: skeletal growth stops at a genetically controlled point, does not continue throughout life (diff than archosaurs with indeterminate growth, relatively somewhat to fact are small)

Question 4

Lepidosaur characters

Tail and reproductive parts

Answer 4

• Transverse cloacal opening (goes across body side to side)
- Other vertebrates with cloacae have longitudinal openings

• Bilateral penis called a hemipene (forked)

• Planes of caudal autotomy in caudal vertebrae
- How lizards “drop” their tails
- Lost in most snakes

Note between vertebrae, plane between them and breaks there in the vertebrae.
Many able to regress, if between vert would not be able to regrow but don’t grow same way again, new break needs to be before the break

Question 5

Lepidosaur characters

Skull

Answer 5

Kinetic skulls
• Skulls have joints in addition to jaw joint

• One joint on top of skull between front and back parts of skull roof

• One between quadrate and rest of skull

• Snakes have three joints around their lower jaws alone

• Trade-off between mobility and bite force

Most lepido have weak bite or don’t active chew or bite bits off food items

Some 2ndaryly lost this mobility - stronger bite force

Question 6

Rhynchocephalia/Sphenodontia

Answer 6

rhynchos, “beak” + cephalos “head”/ sphen, “wedge” + dont, “tooth”

• Tuatara is the only living species

• Inhabits islands around New Zealand

• Nocturnal and tend to have cool body temperatures (6-16°C)

• Live around seabird colonies
- Occasionally eat birds, but prefer the insects that the bird colonies attract

Dis-did skull
Are amniotes
Sprawled posture (wide)

Question 7

Squamata

Answer 7

squamatus, “having scales”

• Over 11,000 species of lizards and snakes

• Live in wide range of habitats

• Determinate growth allows many species to sustain themselves on insects alone
- 80% of squamates never grow bigger than 20 grams (b/c are still lepidos. Don’t have high energy requirements)

• Large species include Komodo dragon and reticulated python

Question 8

Limb loss in squamates

Answer 8

• Limb reduction/loss has evolved in more than 60 taxa (recurring trend independently)

• Serpentes (snakes) is just the most successful legless clade

• Some legless taxa are fossorial (burrowers) and have more compact bodies (which is useful for this lifestyle and more strength to build and fit in burrows)

• Others live above ground and tend to be more elongated (allows to grip more surface)

Question 9

Snake form and function

Answer 9

Often relates to environment

• Variety within snake proportions

• Vipers tend to be shorter for their width (on ground and in cracks, compact and muscular, faster movement for striking)

• Arboreal taxa tend to narrow and elongated (more surface area to grip, weigh a little less)

• Fossorial taxa also tend to be slim, but with very smooth scales

• Sea snakes tend to be laterally compressed
(Completely in water or most of time and little bit of a caudal tail, anguilliform swimming)

1 snake —> flare out skin to glide between trees

Question 10

Snake locomotion

Answer 10

• Snakes utilize four mode of locomotion

1) Lateral undulations
• Requires objects/texture to push against

2) Concertina locomotion
• In narrow spaces (live in burrows)

3) Rectilinear locomotion
• Alternating ventral scutes (go across belly)

4) Sidewinding
• ”walking” with loops of body (hot/dessert enviro)

Question 11

Feeding

Answer 11

• Squamates have a variety of diets

• Among carnivorous species, there are two main strategies
1) Sit-and-wait: choose a location, then wait to ambush prey (more blotchy colouration)
2) Widely foraging: roam over an area to find prey

• Snake venom evolved as a mechanism to immobilize prey
B/c nothing to Archie to prey. Also a protective mechanism

Question 12

Protective mechanisms

Colouration

Answer 12

• Cryptic: blending in with surroundings

• Aposematic: having bright, recognizable colours or patterns that predators can learn to avoid

Can get mimics of apo

Question 13

Protective mechanisms

Predator deterrents

Answer 13

• Spines
- Modified scales

• Awareness signals
- “I see you, and I will try to defend myself” (seen as random bright colourations)

• Spraying behaviour
- Spitting cobra venom
- Sticky, bad-smelling secretions
- blood out of eyes

Question 14

Protective mechanisms

Predator evasion

Answer 14

• Autotomy
• Dropping tail
• Shedding skin or scales (big chunks of skin can come off so they can run away)

Question 15

Social behaviour and reproduction

Communication

Answer 15

• Correlation between foraging mode and main form of communication among lizards

• Sit-and-wait taxa tend to rely more on visual communication
- Territorial

• Widely foraging taxa tend to rely more on olfactory communication

• Snakes generally rely on olfaction

Question 16

Parental care

Answer 16

• Not universal, but not rare either

• Some snakes and lizards guard their nests of eggs

• Newborn rattle snakes stay with their mother for two weeks

Question 17

Mode of reproduction

Answer 17

• Oviparity is ancestral

• Viviparity has evolved in 20% of squamates (independently)
- Viviparity reduces number of offspring a female can produce

• Growing at mother’s body temperature speeds development (more developed and able to defend self, less mortality)

Question 18

Sex determination

Answer 18

• Genetics play some degree of a role in all squamate sex determination

• Environmental sex determination a factor for geckos, skinks, chameleons, and some iguanas
(Like temp. Lizards more than snakes)

• Environmental sex determination can also have an impact on some viviparous species
(Based on envrio female is in)

Question 19

Lepidosaur conservation

Answer 19

Climate change
• Lepidosaurs are heterothermic ectotherms (don’t produce own body temp, temp depends on enviro)

• As temperatures rise, they are having increasing difficulty regulating their temperature (to where they can function most efficiently)

• They must spend more time hiding from sun’s heat

• Less time for foraging, mating
(Therefore have to change their behaviour)

This could lead to extinction to some groups

Question 20

Key Concepts

Answer 20

• Lepidosauria includes tuatara, lizards, and snakes and its members are united by having overlapping, keratinous scales and hemipenes.

• Limbs have been reduced or lost in many squamate lineages, and snakes are the most successful group of legless squamates.

• Squamates have numerous methods of protecting themselves, from their colouration patterns to dropping their tails.

• Due to the diversity of Squamata, modes of reproduction and sex determination are varied, but parental care, viviparity, and environmental sex determination are employed by some taxa.