Lect 11 Flashcards
Lepidosauria
lepisma, “scale” + sauros, “lizard” Tuatara, lizards, and snakes.
Lepidosauria within Amniota
Within Leo is squamata and rhynchocephalia
Sister Clade to archosauria
Clades within Lepidosauria
• Order Sphenodontia/Rhynchocephalia: tuatara (more distal)
• Order Squamata: lizards, including snakes
Lepidosaur characters
Scales and growth
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)
Lepidosaur characters
Tail and reproductive parts
• 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
Lepidosaur characters
Skull
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
Rhynchocephalia/Sphenodontia
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)
Squamata
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
Limb loss in squamates
• 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)
Snake form and function
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
Snake locomotion
• 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)
Feeding
• 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
Protective mechanisms
Colouration
• Cryptic: blending in with surroundings
• Aposematic: having bright, recognizable colours or patterns that predators can learn to avoid
Can get mimics of apo
Protective mechanisms
Predator deterrents
• 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
Protective mechanisms
Predator evasion
• Autotomy
• Dropping tail
• Shedding skin or scales (big chunks of skin can come off so they can run away)
Social behaviour and reproduction
Communication
• 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
Parental care
• 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
Mode of reproduction
• 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)
Sex determination
• 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)
Lepidosaur conservation
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
Key Concepts
• 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.
