Vertebrates

The Origin of Tetrapods  The first vertebrates on land were amphibians in the Devonian (400 mya)  May have arose from the rhipidistian (features).  Arose in coastal or brackish marine environment

Origin of Tetrapods

Tetrapods Advantages of Terrestriality An increase in metabolism and development due to higher body temperature. An increase in metabolism and development due to higher body temperature. Energy – An increase of 10 degrees Celsius (from 20 degrees (water temp) to 30 degrees (air temp) would allow for a doubling of their metabolic rates Energy – An increase of 10 degrees Celsius (from 20 degrees (water temp) to 30 degrees (air temp) would allow for a doubling of their metabolic rates

Tetrapods Lungs – To breath air, it required an increased vascularization of the air-filled cavity (a pouch from the posterior pharynx similar to the swim bladder), with a rich capillary network to form a lung.

Tetrapods Double circulatory system Fish have a single circuit system – low blood pressure Fish have a single circuit system – low blood pressure The double circulation system allows for higher pressure with one circuit going to the lungs and another going to the body. The double circulation system allows for higher pressure with one circuit going to the lungs and another going to the body.

Tetrapods Nasal Openings Bony fish have 4 external nares (2 on each side) which allows water to run across the olfactory tissue. Bony fish have 4 external nares (2 on each side) which allows water to run across the olfactory tissue. Tetrapods have two external and two internal nares in the palate. This allows air to be drawn in through the nose. Tetrapods have two external and two internal nares in the palate. This allows air to be drawn in through the nose.

Tetrapods – General Characteristics Body Density - Limbs Air is 1000 times less buoyant then water counter the effects of gravity homologous structures (bones – humerus, ulna and radius).

Tetrapods – General Characteristics Body Density - Girdles – In fish, the pectoral girdle is attached to the skull. In fish, the pectoral girdle is attached to the skull. Early tetrapods developed a stronger shoulder girdle, bulky limb bones and well developed muscles. Early tetrapods developed a stronger shoulder girdle, bulky limb bones and well developed muscles. The pelvic girdle is fused to the backbone to increase the force that can be generated by the hind legs. The pelvic girdle is fused to the backbone to increase the force that can be generated by the hind legs.

Tetrapods – General Characteristics Body Density - Vertebrae and Ribs – Vertebrae have developed zygapophyses. Vertebrae have developed zygapophyses. The development of ribs can also protect the lungs. The development of ribs can also protect the lungs.

Tetrapods – General Characteristics Body Density - Skull and Neck The skull has been shortened and the snout elongated. The skull has been shortened and the snout elongated. The head becomes separated from the body by a neck (a cervical vertebrae) that allows the head to be lifted. The head becomes separated from the body by a neck (a cervical vertebrae) that allows the head to be lifted. A second vertebrae was then added to allow for a side to side movement. A second vertebrae was then added to allow for a side to side movement.

Tetrapods – Evolutionary History 1. Fish

Tetrapods – Evolutionary History  “Fishapod” – Tiktaalik (375 mya)  A fish with tetrapod features, this animal probably could not walk on land but could lift itself out of the water. 1. Fish Characteristics –Scales –Fins –Gills and lungs 2. Tetrapod Characteristics –Neck –Ribs –Fin skeleton –Flat skull –Eyes on top of skull

Classification  Phylum: Chordata  Subphylum: Vertebrata  Superclass: Gnathostomata  Class: Amphibia –Order: Urodela (Salamanders) –Order: Anurans (Frogs and Toads) –Order: Apodans (Caecilians)

Class: Amphibia  Two lives –refers to metamorphosis of many frogs  Skin smooth, moist (cutaneous respiration), and glandular (toxins)  Three chambered heart with a double circulation system  Mesolecithal eggs with jelly-like membrane

Order: Urodela  400 species  Salamanders  Retain their tail as adults  Limbs are at right angles to the body  Carnivorous

Order: Anurans  3500 species  Frogs and Toads  Lose their tail as adults  Hind limbs are adapted for jumping  Tongue connected to front of mouth  Secrete mucus

Order: Apodans  150 species  Caecilians  Legless and blind

Thermoregulation  Ectothermic  Endothermic  Poikilothermic  Homeothermic

Heat Exchange

 Conduction - direct transfer of heat  Convection - transfer of heat by the movement of air or water across a surface  Radiation - emission of electromagnetic waves  Evaporation - loss of heat from changing a liquid into a gas

Body Temp vs. Ambient Temp

Thermoregulation Adjustments  Adjusting the rate of heat exchange –vasodilation/vasoconstiction –countercurrent heat exchange  Cooling by evaporation  Behavioral responses  Changing the rate of metabolic heat production

Amphibians and Reptiles  Most are ectothermic –regulate temperature by behavior

Feedback Mechanisms  High body temperature –hypothalamus activates skin blood vessels to dilate and the sweat glands to produce sweat  Low body temperature –hypothalamus activates skin blood vessels to constrict and the skeletal muscles to shiver

Temperature Range Adjustments  Slow changes –acclimatization (enzymes and membranes)  Fast changes –heat-shock proteins

Evolution of the Amniotic Egg  Allows animals to complete their entire life cycle on land  Has shell that retains water (or is lost when kept inside mammals)  Specialized extraembryonic membranes (not part of the animal)

Evolution of the Amniotic Egg  Amnion - Protects from dehydration and mechanical shock  Yolk Sac - Nutrient storage  Albumin - Nutrient storage  Allantois - stores waste, gas exchange  Chorion - gas exchange

Amniotes

Amniotes

How Reptiles differ from Amphibians  Tough, dry skin  Amniotic egg  Crushing or gripping jaws  Copulatory organs  More efficient circulatory system with a higher blood pressure  More developed lungs (thoracic breathing)  Better water conservation  Better body support and limbs  Better nervous system

Classification  Phylum: Chordata  Subphylum: Vertebrata  Superclass: Gnathostomata  Class: Reptilia (not real) –Class: Testudines (Turtles and Tortoises) –Class: Spenodontia (Tuataras) –Class: Squamata (Lizards and Snakes) –Class: Crocodilia (Crocodiles and Alligators)

Reptile Radiation  Synapsids (therapsids) - led to mammals  Sauropsids –Anapsids??? (turtles) –Diapsids (all others)

Class: Testudines (Chelonia)  Evolved on land and returned to water (lay eggs on land)  Protective Shell –Carapace –Plastron

Class: Sphenodontia  Tuataras –Two living species (New Zealand) –Not a True Lizard (no external ears) –Very Primitive (similar to mesozoic reptiles –Well developed eye below skin?

Class: Squamata  Lizards –geckos, iguanas, skinks, chameleons  terrestrial, burrowing, aquatic, arboreal  moveable eyelids  Paired copulatory organs  Lower jaw not attached to skull

Class: Squamata

 Snakes  Lack limbs  Lack moveable eyelids  Jacobson’s organ  Pit Vipers (heat)  Venom –neurotoxins –hemolytic enzymes

Class: Squamata

Feeding Adaptations  Teeth curved and pointed inward  Hinged Quadrate bone  Bones of jaw are attached by muscles and ligaments  Moveable palate  Elastic skin  No sternum

Class: Crocodilia  Largest living reptiles  Most closely related to dinosaurs  Complete secondary palate  Four chambered heart  Nest temperature

Dinosaurs and Pterosaurs  Dinosaurs –Ornithischian –Saurischian (closely related to birds)  Pterosaurs –flying reptiles