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Vertebrates
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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
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Origin of
Tetrapods
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Origin of Tetrapods
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TetrapodsAdvantages of Terrestriality
• 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
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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.
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Tetrapods
Double circulatory system
• 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.
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TetrapodsNasal Openings • 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.
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Tetrapods – General
CharacteristicsBody Density - Limbs
Air is 1000 times less buoyant then water
•counter the effects of gravity
•homologous structures (bones –humerus, ulna and radius).
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Tetrapods – General
CharacteristicsBody Density - Girdles –
• In fish, the pectoral girdle is attached to the skull.
• 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.
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Tetrapods – General
CharacteristicsBody Density -Vertebrae and Ribs –
• Vertebrae have developed zygapophyses.
• The development of ribs can also protect the lungs.
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Tetrapods – General
CharacteristicsBody Density - Skull and Neck
• 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.
• A second vertebrae was then added to allow for a side to side movement.
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Tetrapods – Evolutionary History
1. Fish
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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
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Classification
Phylum: Chordata
Subphylum: Vertebrata
Superclass: Gnathostomata
Class: Amphibia
–Order: Urodela (Salamanders)
–Order: Anurans (Frogs and Toads)
–Order: Apodans (Caecilians)
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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
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Order: Urodela
400 species
Salamanders
Retain their tail as adults
Limbs are at right angles to the body
Carnivorous
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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
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Order: Apodans
150 species
Caecilians
Legless and blind
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Thermoregulation
Ectothermic
Endothermic
Poikilothermic
Homeothermic
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Heat Exchange
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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
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Body
Temp
vs.
Ambient
Temp
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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
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Amphibians and Reptiles
Most are ectothermic
– regulate temperature by behavior
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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
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Temperature Range
Adjustments
Slow changes
–acclimatization (enzymes and membranes)
Fast changes
–heat-shock proteins
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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)
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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
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Amniotes
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Amniotes
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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
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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)
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Reptile
Radiation Synapsids
(therapsids) - led to mammals
Sauropsids
– Anapsids??? (turtles)
– Diapsids (all others)
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Class: Testudines (Chelonia)
Evolved on land and returned to water (lay eggs on land)
Protective Shell
– Carapace
– Plastron
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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?
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Class: Squamata
Lizards
– geckos, iguanas, skinks, chameleons
terrestrial, burrowing, aquatic, arboreal
moveable eyelids
Paired copulatory organs
Lower jaw not attached to skull
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Class: Squamata
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Class: Squamata
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Class: Squamata
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Class: Squamata
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Class: Squamata
Snakes
Lack limbs
Lack moveable eyelids
Jacobson’s organ
Pit Vipers (heat)
Venom
– neurotoxins
– hemolytic enzymes
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Class: Squamata
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Class: Squamata
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Class: Squamata
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Class: Squamata
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Feeding
AdaptationsTeeth curved and pointed inward
Hinged Quadrate bone
Bones of jaw are attached by muscles and ligaments
Moveable palate
Elastic skin
No sternum
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Class: Crocodilia Largest living reptiles
Most closely related to dinosaurs
Complete secondary palate
Four chambered heart
Nest temperature
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Dinosaurs and Pterosaurs
Dinosaurs
– Ornithischian
– Saurischian (closely related to birds)
Pterosaurs
– flying reptiles