545 MYA: First vertebrates with a vertebral column emerge.
430 MYA: Evolution of jaws; fishes dominate marine ecosystems.
300 MYA: Vertebrates transition to land, leading to dominance of amphibians.
250 MYA: Evolution of fully terrestrial reptiles which dominate terrestrial life.
65 MYA: Mass extinction event wipes out most reptiles (including dinosaurs), leading to mammals and birds becoming the primary terrestrial vertebrates.
Evolutionary Relationship of Reptiles and Birds
Reptiles share a common ancestor with birds, classified under Archosauria.
Key evolutionary adaptations of reptiles include the development of the amniotic egg and keratinized skin which help in terrestrial living.
Birds exhibit traits common to reptiles but have evolved traits for flight (e.g., feathers).
Major Events Leading to the Rise and Fall of Amphibians
Amphibians transitioned to land around 300-350 MYA and quickly diversified.
By 298 MYA, amphibians had diversified into 34 families mostly residing in tropical swamps.
As the climate became drier (~280 MYA), many amphibians adapted by increasing body size and developing more impermeable skin.
By 248 MYA, reptiles evolved, leading to amphibians' decline and eventual extinction in terrestrial environments by 213 MYA.
Diversity and Habitat of Class Reptilia
Class Reptilia consists of over 10,000 species including snakes, lizards, crocodilians, and extinct dinosaurs.
Reptiles primarily inhabit terrestrial environments; some species return to water.
Key Characteristics of Class Reptilia vs. Amphibians
Amniotic Eggs: Reptiles lay eggs that do not require water, while amphibians lay eggs in water.
Skin: Reptiles possess dry, keratinized skin that conserves water; amphibians have moist skin for cutaneous respiration.
Breathing: Reptiles use thoracic breathing (rib expansion) while amphibians use buccal pumping.
Organ Systems: Reptiles have a more advanced olfactory system (Jacobson's organ) compared to amphibians.
Structure & Function of the Heart
3-Chambered Heart (most reptiles & amphibians): 2 atria, 1 ventricle (partially divided); allows some mixing of oxygenated and deoxygenated blood.
4-Chambered Heart (birds, mammals, crocodilians): Prevents mixing of blood, highly efficient in delivering oxygen.
Synapsids vs. Diapsids
Synapsids: Characterized by one temporal fenestration; early reptiles and gave rise to mammals.
Diapsids: Characterized by two temporal fenestrations; gave rise to birds and most reptiles.
Orders of Reptiles
Order Chelonia (Turtles)
Diversity: 340 species, including aquatic turtles and terrestrial tortoises.
Habitat: Terrestrial, marine, freshwater.
Characteristics: Shell encasing body, lack teeth but have sharp beaks, ribs fused to carapace.
Order Squamata (Lizards and Snakes)
Diversity: 6,200 lizard species and 3,500 snake species.
Characteristics: Highly modified jaws allow for greater feeding efficiency; males have two copulatory organs.
Evolution: Snakes evolved from lizard ancestors, have no limbs and possess movable eyelids.
Order Crocodylia (Crocodiles and Allies)
Diversity: 25 species, including crocodiles, alligators, and caimans.
Habitat: Primarily aquatic and favor subtropical environments.
Characteristics: Carnivorous, nest builders, exhibit more bird-like features than other reptiles, possess a 4-chambered heart.
Evolution of Birds and their Characteristics
Class Aves includes around 10,000 species; diverse in form and habitat.
Key Adaptations for Flight:
Feathers: Modified reptilian scales that provide lift.
Skeleton: Lightweight, thin bones, fused sections for muscle attachment.
Efficient Respiration: Two-cycle respiratory system utilizing air sacs for constant airflow.
Structure and Function of Feathers
Structure: Composed of keratin; features a shaft with a vane of barbs and barbules providing flexibility and strength.
Functions: Insulation, lift during flight, and sexual selection.
Respiration and Circulation in Birds
Unique adaptations include a complete wall dividing the ventricles of the heart, ensuring efficient oxygenated blood delivery to flight muscles.
Birds have a highly efficient respiratory system requiring 2 cycles where air flows continuously through lungs, supported by posterior and anterior air sacs.
Blood circulation is rapid with high heart rates, essential for supporting large flight muscles.