Tetrapods & Amniotes Amphibians + Reptiles

Tetrapods (gnathostomes that have limbs)= amphibians, reptiles, birds, and mammals Derived from the lung-fish branch of lobe-finned fish Characteristics of Tetrapods: 2 pairs of limbs WITH DIGITS – Support weight, provide mobility on land

Amphibians: --Reproduction is tied to water --Activity is restricted to aqueous or humid/damp/moist environments 3 clades: Urodeles = salamanders Anurans = frogs and toads Apoda = ceacilians – Legless, almost blind, – Look segmented like earthworm (but with distinct head) – Live in soil (tropical) – From legged ancestor

Amphibian: common characteristics damp habitats External fertilization in most Eggs require moisture (sometimes retained) – Susceptible to drying out Lungs + Skin for gas exchange – Positive pressure/buccal breathing 3 chambered heart with double circulation

Gas Exchange Lungs: Infoldings with many pockets – Localized w/in body  circulatory system – Thin layer of tissue between blood and air SKIN Significant contribution to gas exchange Permeable to gas (good) = permeable to water (bad) Very vascular Relative importance of skin varies with activity/O2 demand of individual.

Ventilation (i.e., breathing) Inhalation: 1. Oral Cavity Expansion w/ nares open – “sucks” air into oral cavity 2. Oral cavity contracts w/ nares closed – Air “pumped”/pushed into lungs Exhalation 1.Elastic recoil of lungs + compression of muscles of body wall – Air pushed out

Double Circulation Two circuits/loops of blood pumped by a single heart – Lungs (pulmonary) Picks up O2, removes CO2 – Rest of body (systemic) Delivers O2, picks up CO2 Single pump ensures ‘evenness’ of both circuits Repressurizes blood after it has picked up O2 in the pulmonary circuit

Amphibians: Heart and Blood Flow 3 Chambered heart = 2 atria + 1 ventricle R atrium = venous blood from muscle and organs/systemic L atrium = venous blood from lungs and skin (pulmocutaneous circuit) – Ventricle pressurizes blood/pumps out Ridge (spiral valve) in ventricles prevents most mixing of blood. Blood flow to lungs “stops” during diving

Osmoregulation: Freshwater Net gain of water Large quantities of dilute urine water can be re-absorbed across the urinary bladder wall.

Amniotic Egg Amnion: encloses embryo in fluid that cushions/protects, Chorion: gas exchange Yolk sac: stores/transfers nutrients Allantois—waste storage and some gas exchange These are extraembryonic (i.e., not part of the embryonic tissue)

Amniotes Amniotic Egg – Egg can be retained – Egg can be retained and no shell, but still has 4 layers Also ribs that assist in negative pressure breathing

Reptile Clade: Tuataras, lizards, snakes, turtles, crocodilians, & birds Scales w/ keratin (makes skin relatively impermeable) Shelled, amniotic eggs Internal fertilization Clawed Mostly ectothermic – Regulate body temp – 10% of the calories required by endotherms Birds are endothermic

3 Clades TURTLES: Shell (carpace + plastron), fused to ribs and clavicles Can breath through GI tract LEPIDOSAURS (tuataras + lizards + snakes, later two are squamates) Crocodilians (alligators, crocodiles, and caimen) Breath air through upturned nostrils Warm regions

Reptile Heart Double Circulation Typically 2 atria + 1 partially divided ventricle – Very little mixing of blood In crocodiles ventricle is completely divided – aorta are joined by a passageway – allows blood to be shunted/bypass pulmonary circuit when diving

Ventilation Negative pressure Expansion of ribcage