Ch 15 Lepidosaurs Flashcards
snakes share a common ancestor with…
a group of lizards
Clade Lepidosauria
1 tuatara, 7000 lizards, 4000 snakes;
snakes monophyletic, but also part of lizard clade;
“lizard” by itself is a grade (paraphyletic)
lepidosaur synapomorphy
keratinous overlapping scales, transverse cloacal slit, tail autotomy
tail autotomy
ability to cause tail to fall off to escape predators, breaks at fracture plane of a caudal vertebra and can later regrow with a cartilagenous rod replacing tail vertebrae
earliest known reptiles with tail autotomy lived in…
early Permian
other lepidosaur characteristics
mainly terrestrial, many groups have reduced or lost limbs
tuatara
diverse group during Mesozoic,
only extant species left,
lives in New Zealand,
nocturnal, has lowest optimal body temp of any reptile, primarily insectivorous, unique dentition, bony beak formed from fused snout bones
unique dentition of tuatara
2 rows of teeth on upper jaw, 1 row on bottom jaw, for shearing food, structure of jaw joint allows bottom teeth to slide between upper teeth after mouth closes
tuatara reproduction
slow growing, takes 10-20 years to reach sexual maturity, females mate every 4 years, lay 5-19 eggs, gestation period is about 8 months, incubation period in egg outside body is 11-16 months, no external genitalia, evidence suggests ancestor had a penis
squamate synapomorphies
includes all lizards and snakes:
determinant growth, hemipenes
determinant growth
growth occurs for a genetically determined period of time,
smaller size enables insectivory, in turtles and crocodiles
hemipenes
paired copulatory organs (single or absent in all other amniotes),
stored in tail (males have longer tails), everted during copulation, only use one at a time, extravagantly ornamented, species-specific designs
squamate anti-predator behavior
crypsis/camouflage, aposematic coloration, Batesian mimicry, playing dead
crypsis/camouflage
blending into surroundings, solor-changing in anoles and chameleons, visual and behavioral, stripes to appear motionless while moving through vegetation
aposematic coloration
bright coloring to advertise toxicity
ex. venomous snakes
batesian mimicry
harmless species mimics the warning coloration of a toxic species to reduce predation
ex. scarlet king snake mimics coral snake
playing dead
hog snake technique to avoid predation
sexual dimorphism
common social behavior in “lizards”, males typically bigger
visual cues
common social behavior used by iguanas and anoles,
ex. anole dewlaps and behavioral displays (head-bobbing, tail-wagging, etc.)
dewlap
species-specific throat fan, in anoles
pheromones
chemicals released by many lizards and snakes to attract mates
vocalizations
social behavior common to geckos
squamate reproduction
oviparity, viviparity, parthenogenesis
oviparity in squamates
probably ancestral, most common
viviparity in squamates
20% of squamates, associated with cooler climates, pregnant lizards more vulnerable to predation
parthenogenesis in squamates
in 6 families of lizards and 1 snake species, create all-female populations genetically identical to mother,
higher reproductive potential (important in frequently disturbed habitats)
iguanas
can grow to large size, terrestrial or arboreal, primarily herbivorous, use short bursts of movement to escape threats, good swimmers
chameleons
typically diurnal, primarily insectivorous, specialized arboreal lizard, zygodactylous feet, and prehensile tail, body laterally compressed, slow-moving, specialized tongue and hyoid apparatus allow tongue projection, independently mobile eyes and binocular vision for hunting prey
geckos
large well-developed eyes, no eyelids, toe pads with setae allow dry adhesion to vertical and upside down surfaces
setae
projections of highly modified scales on toe pads of geckos, so tiny that they form molecular bonds with surfaces
amphisbaenians
“double walk”, fossorial features, large median upper tooth fits between 2 lower teeth to act as sharp forcepts
fossorial
burrowing
fossorial features
limbless (or reduced limbs), heavily ossified skull for digging tunnels, eyes often reduced, elongate body, short tails, reduce right lung due to elongation of body, skin is loose and moves independently of skeleton
telescoping
skin moves independently of skeleton
helodermatids
5 living species, SW US to Guatemala,
stout, flat head, blunt tail, venomous (no muscles around venom glands);
eat mammals, birds, eggs, lizards, insects
monitors
in Africa, Asia, and Australia;
fast-moving, active predators, use gular pumping, varied carnivorous diet, forked tongue used to smell
gular pumping
monitors can inflate/deflate their throat
Komodo dragon
type of monitor, largest living lizard, two glands in lower jaw secrete toxic proteins
snakes
limbless (earlier fossils had legs), elongated body, short tail, left lung reduced or absent, right kidney in front of left, about 120+ precloacal vertebrae, lack eyelids, have clear scale near eyes for protection, diverse diet (some venomous), wide range of habitats
snake reproduction
oviparous or viviparous, little sexual dimorphism
snake sensory systems
sight is limited, forked tongue aids in chemoreception, lack external and middle ear, have internal ears with receptors, many have one or more infrared-detecting pit organs
snake feeding
highly kinetic skulls and jaws to eat prey larger than head, swallow slow and head first, eat mostly live prey, kinetic skull is very fragile; methods include constriction, envenomation, and oophagy
constriction in snakes
grab with jaws, coil around prey, tighten coils;
short vertebrae for tight coiling, short trunk muscles for strong contractions, morphology limits speed
envenomation in snakes
use venom to kill prey, safer for snake, venom secreted by gland in upper jaw, muscles squeeze out venom, venom consists of complex mix of proteins and other molecules that differ among species
oophagy in snakes
egg eating, very mobile jaws, vertebrae have ventral projections that press into egg and crack it, reduction in number of teeth
