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

Origin of Tetrapods

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

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

• The double circulation system allows for higher pressure with one circuit going to the lungs and another going to the body.

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.

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).

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.

Tetrapods – General

CharacteristicsBody Density -Vertebrae and Ribs –

• Vertebrae have developed zygapophyses.

• The development of ribs can also protect the lungs.

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.

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

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

Class: Squamata

Class: Squamata

Class: Squamata

Class: Squamata

Snakes

Lack limbs

Lack moveable eyelids

Jacobson’s organ

Pit Vipers (heat)

Venom

– neurotoxins

– hemolytic enzymes

Class: Squamata

Class: Squamata

Class: Squamata

Class: Squamata

Feeding

AdaptationsTeeth 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