Reptiles

Novel adaptations:

• amniotic egg

• Thick, scaly, waxy skin with scales

  • Scales contains keratin and waxy lipids

  • Reduces water loss from skin in terrestrial environment

• Keratinized epidermal structures which are often defining characteristics:

  • Scales, claws, horns, feather

• Respiration occurs in lungs only

  • Lungs are larger (metabolic needs)

  • Costal breathing- pulling air into lungs by expanding ribs/lungs

  • Negative pressure breathing

• Stronger jaws, larger teeth than amphibians

• Brain has larger cerebrum and cerebellum compared to amphibians

  • Larger cerebellum correlated with increased sensory system and better control of muscles associated with movement

  • Most reptiles have excellent, full color vision

• Continuous lifetime growth

  • Shed their skin periodically to grow and remove ectoparasites

    • Snakes shed skin completely ALL AT ONCE

    • Other reptiles shed in patches

• Ectotherms (homeothermic)

  • Body heat comes from environment

  • Reptiles can live on 10% of the calories required by similar size endotherm

Reptile Circulatory System:

• Minimal blood mixing

• 3 Chambered heart

• 2 Atria 1 ventricle

• Double circuit

• Deox→right atrium → ventricle → lungs (reoxygenated) → left atrium → ventricle. Mostly oxygenated blood is pushed to the aorta and out of the body. Ventricle contains both oxygenated and deoxygenated blood, partial septum and pressure difference.

• Higher blood pressure

• Alligators and crocodiles have a 4 chamber heart

Crocodilia- Alligators, caimans, gharials, and crocodiles

• Share common ancestor with dinosaurs

• Carnivorous homeotherms

• Typical reptilian diapsid skull

  • Elongated skull, strong jaw musculature

  • Bite force is one of the strongest of all animals

  • Meant more to close than to open their jaws

• Adapted to aquatic habitats

  • Eyes and nostrils at tops of their head

• Sensory system- well developed sight and hearing

  • Vocalize during mating season

  • Can see color, underwater, and at night

    • Transparent lens protects eyes underwater, limits sight

  • Nearly 180 degree vision

  • Very thick eyelids, can pull eyes into skull

• Primitive 4 chambered heart

• True pallet in mouth

Reproduction Crocodilia:

• Internal fertilization

• Females dig/build nests to lay eggs (30-100)

• Females guard nest

• Shells are harder/thicker than other reptiles

• Young vocalize during hatching

  • Mom comes to help excavate eggs and carry hatchlings to water

  • Guards them for several months

• Sex is temperature dependent

  • Cooler temp: female

  • Warmer temp: male

  • Between: mix of both

Sphenodontia: Tuataras

• Only one surviving species

• Typical reptilian diapsid skull, no external ears, very primitive hearing (bone conduction)

• When young, they have a parietal (third) eye on their forehead (skin covers as they mature)

• Carnivorous

• Defining characteristic: Upper jaw has two rows of teeth, lower jaw has one row of teeth that sit between the upper rows when mouth is shut.

Sphenodontia Reproduction:

• Internal fertilization

  • Slow to sexually mature (~25 years old)

• Males do not have penis, cloacas are rubbed together

• Females can store sperm for up to a year

• Females are oviparous

• Eggs incubate 7-12 months

  • Warmer, faster

• No parental care

• Temperature dependent sex determination:

  • Cooler temp: female

  • Warmer: male

  • Between: 50/50 chance

Squamata (Lizards and snakes)-

• Have waxy/scaled skin

• Most nonavian reptiles are lizards or snakes

• Lizards appeared first, snakes diverged after

  • Snakes share a common ancestor with Gila monsters, monitors, iguanas

• Found on all continents except Antarctica

• Ectotherms, homeothermic

• Have a kinetic skull with moveable joints

  • Diversification

• Some squamates are viviparous (not seen in any other order)

Lizards:

• Almost exclusively tetrapods with four limbs

  • Glass lizard is exception

• Almost exclusively carnivorous

  • Use sticky tongue to catch prey

  • Few species are herbivorous (Iguanas)

  • Several species are venemous (Gila monster)

  • Some omnivorous

• Sensory system: Moveable eyelids, external ears, Jacobson’s organ (chemoreceptor)

  • Can focus eyes by changing shape of the lens

  • Have color vision

  • External ear (hearing unimportant)

• Most species have spines/crests/frills

  • Used for defense and to attract mates

  • Some have chromatophores in skin for color changing

• Reproduction: Sexual with internal fertilization

  • Males have 1-2 penises, transfer sperm internally (hemipenes)

  • In most species, female is oviparous

  • Lay eggs, no parental care

  • Eggs are leathery soft

• CHROMOSOMAL SEX DETERMINATION

• A few species are ovoviviparous

  • Females give birth to fully developed young, with young obtaining nourishment from egg yolk

• Parthenogenesis observed in a number of species

  • Reproduce asexually by combining a polar body with an egg

Snakes:

• Defining characteristic:

  • Secondarily legless

    • Boidae (boas) and Pythonidae (phythons) have vestigial rear “limbs”

  • Flexible skull with 8 joints, lower jaw has no bony or ligamentous attachment to upper jaw

  • In addition, the two halves of lower jaw are joined by muscle only

  • Teeth are curved backwards

    • Allows snakes to swallow large prey

  • More vertebrae which are shorter and wider than most tetrapods

    • Fast, undulated motion

    • VERY flexible skull

• Sensory System:

  • Snakes do not have moveable eyelids or external ears

  • Have Jacobson’s organ

    • most have poor vision

      • other senses more important

      • However, arboreal (tree) snakes have excellent vision

  • No external ear, internal ear only

  • Use tongue to bring environmental chemicals to Jacobson’s organ on roof of mouth

  • Boids and pit vipers have heat sensing pits along jawline to sense infrared heat

• Carnivorous:

  • Kill prey through constriction

  • Many species have venom injected through fangs

    • Even harmless snakes have ancestral trait of mildly toxic saliva

  • Venomous snakes have specialized in greater toxicity:

    • Neurotoxins which act on nervous system

    • hemotoxins which destroy red blood cells and blood vessels

    • All venom contains enzymes that speed digestion

• Snake movement:

  1) Concertina: allows snake to move in narrow passages

  • Braces S-loops against side of passage

  • Trees, vertical crawl, exaggerated

  2) Lateral undulation: Snakes move in an S shape

  • Most common type of movement

  3) Side winding: Allows movement across sand

  • Minimal contact with sand

  • Snake throws body forward in loops

  4) Rectilinear: Areas of the body remain in contact with the ground, other sections are lifted and moved forward

  • Slow movement, heavy-bodied snakes

  • Inchworm like

• Reproduction:

  • Same as lizards except:

    • No parental care besides female pythons

Testudines- turtles, tortoises, terrapins

• Appeared before other reptilian orders

• Secondarily lost temporal fenestrae, anapsid (evolutionary diaspids)

• Defining characteristics:

  • All species have bony shells that are their skeleton

    • Shell overlaid with large scales

    • Dorsal shell is called carapace, includes the backbone and ribs

      • Broadening of the ribs was the first evolutionary step towards a shell

    • Ventral shell is called plastron

    • Carapace and plastron are connected by a bridge, bones between the front and back legs (pelvic girdle)

    • Some can draw head and legs into carapace, sea turtles can’t

• Their mouth has adapted to a beak without teeth

  • Evolutionary adaptation

  • Keratinized plates for biting

  • Diet is species specific

    • Snapping turtles are carnivorous

    • Green turtles are herbivorous

    • Red-eared sliders are omnivorous

• Cannot expand ribs to pull air into lungs (concious)

  • Inhalation: Use abdominal muscles to pull air in

  • Exhalation: Pull back limbs into shell to force air out

  • Overall movement of the limbs helps them to breathe

• Sexual reproduction via internal fertilization

  • Males have penis

  • Females are oviparous

  • Lay eggs on land

  • No parental care

  • Young turtles hatch fully formed

• Sex is temperature dependent DIFFERENT THAN OTHERS:

  • Cooler: male

  • Warmer: female

  • In between: 50/50