Unit 25 Vertebrates

25.1 Vertebrate Origins

KEY CONCEPT All vertebrates share common characteristics.


hollow nerve cord

tail

notochord

pharyngeal slits

The phylum Chordata contains all vertebrates and some invertebrates. • Chordates share four features at some stage of

development.– notochord– hollow nerve cord – pharyngeal slits– tail


hollow nerve cordtail

notochord

pharyngeal slits

• Most chordates lose some or all of these characteristics in adulthood.

Tunicates (Sea Squirts) only have these characteristics as larva. Once they settle into their sessile filter-feeding adults, none of these are visible.


All vertebrates share common features.

• An endoskeleton allows vertebrates to grow to large sizes.– internal– made of bone or cartilage


• An endoskeleton can be divided into four parts.

– braincase (cranium) braincase

vertebrae

bones

– gill arches (in fish and some amphibians)

– bones

– vertebrae


• There are seven classes of vertebrates.

– Agnatha are jawless fish, such as hagfish.– Cartilaginous fish (Chondrichthyes) include the sharks

and rays– Bony fish (Osteichthyes) obviously have bones.– Amphibians are characterized by the presence of four

limbs and water permeable skin.– Reptiles, birds, and mammals are characterized by the

presence of an amnion and water-tight skin.– Birds are characterized by the presence of feathers.– Mammals are characterized by the presence of hair.


Agnatha Chondrichthyes Osteichthyes Amphibia Aves Mammalia

JAWSJaws helped vertebrates to become successful predators.

VERTEBRAEVertebrates have a segmented backbone.

FOUR LIMBSFour limbs let animals move from the water to life on land.

FEATHERSFeathers insulate birds from the cold and allow for flight.

HAIRHair helps mammals to maintain constant body temperatures by roviding insulation from the cold.

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What group seems to be missing from this slide?


Fossil evidence sheds light on the origins of vertebrates.

• Tunicates may be the closest relatives to vertebrates.• The first recognizable vertebrates were jawless fish.• Two groups of jawless fish still exist today.

– hagfish

– lampreys


KEY CONCEPT The dominant aquatic vertebrates are fish.

http://upload.wikimedia.org/wikipedia/commons/2/23/Georgia_Aquarium_-_Giant_Grouper_edit.jpg


Fish are vertebrates with gills and paired fins. • Fish use specialized organs called gills to breathe

underwater.– sheets of thick, frilly tissue filled with capillaries – take in dissolved oxygen from water, release carbon

dioxide

waterflow


• Countercurrent flow is the opposite movement of water against the flow of blood in the fish’s gills.


• Fins are surfaces that project from a fish’s body.

dorsal fin

caudal fin

anal finpectoral fin pelvic fin

– keep fish stable– redirect water around fish as it swims– help fish maneuver in water


Jaws evolved from gill supports.

• Jaws developed from gill arches located around the pharynx.

cranium

mouth gill arches

cranium

mouth

cranium

mouth

• Jaws gave vertebrates a huge advantage as predators.


Only two groups of jawed fish still exist. • Cartilaginous fish such as sharks and rays (970 species).

• Cartilaginous fish have skeletons made of cartilage.• Bony fish make up the vast majority vertebrates at over

29,000 species!


• Cartilaginous fish include the Holocephali and Elasmobranchs.

– Holocephali include ratfish, a small group of deep-sea fish.– Elasmobranchs include sharks, rays, and skates.


• All fish have a lateral line system.– sensory system– sensitive to small changes in water movement

lateral line


• Bony fish have skeletons made of bone.– operculum protects a bony fish’s gills– movements of operculum help bony fish move water

over gills


Ray-finned fish have a fan of bones in their fins.

• Ray-finned fish have fins supported by a fan-shaped array of bones.– embedded in a thin layer of skin and connective tissue– light, collapsible, and easy to move


• Ray-finned fish have a variety of body plans.– long torpedo-shaped bodies (barracuda)


• Ray-finned fish have a variety of body plans.– flattened bodies (plaice)


• Ray-finned fish have a variety of body plans.– elaborate camouflage (sea dragon)

http://upload.wikimedia.org/wikipedia/commons/d/dc/Leafydragon.jpg


• A swim bladder helps a fish float higher or lower in the water.

swim bladder


• Some ray-finned fish have both lungs and gills.– can breathe air and survive out of water for several

hours at a time– example: bichir found in West Africa

http://upload.wikimedia.org/wikipedia/commons/6/61/Australian-Lungfish.jpg


Lobe-finned fish have paired rounded fins supported by a single bone.

• Lobe-fins are paired pectoral and pelvic fins that are round in shape.– not as maneuverable as ray-fins– able to support weight

lobe fin


• Only seven species of lobe-finned fish exist today.

– coelacanths

– lungfish


KEY CONCEPT Amphibians evolved from lobe-finned fish.


Amphibians were the first animals with four limbs.

• Tetrapods are vertebrates that have four limbs.

The fossilized remains of Tiktaalik roseae indicate it was a transitional species between fish and tetrapods.


• A number of adaptations allow amphibians to live on land.– large shoulder

and hip bones– mobile, muscular

tongue– middle ear– breathe through

skin or with gills or lungs


Amphibians return to the water to reproduce.

• Amphibians use many strategies to keep their eggs wet.– lay eggs directly in water– lay eggs on moist ground– wrap eggs in leaves– brood eggs in pockets

on the female’s back


adult frog

young frog

tadpoles

fertilized eggs

• Tadpoles are aquatic larvae of frogs. • During metamorphosis, tadpoles develop into their adult

form.

• Not all amphibians undergo metamorphosis.


Modern amphibians can be divided into three groups.

• Salamanders have a long body, four walking limbs, and a tail.

• There are over 300 species of salamanders.


• Frogs are the largest amphibian group and include toads.• There are over 3000 species of frogs.• Glands in the skin of frogs and toads contain poisons that

help to protect them from predators.


• Caecilians are legless, burrowing, tropical amphibians.• There are 160 species of caecilians.


http://upload.wikimedia.org/wikipedia/commons/6/67/Reptiles.jpg


Amniotes can retain moisture.

• An amniote develops inside a thin, tough, membranous sac as an embryo or fetus.

Amnion Protectsand surroundsthe embryo


• Several characteristics help amniotes prevent water loss.– keratin forms a hydrophobic layer

– larger size of kidneys and intestines increases water absorption


Amniotes do not need to return to water to reproduce.

• The amniotic egg is an almost completely waterproof container.– prevents embryo from drying out as it develops– each egg represents a large investment of energy


• Not all amniotes lay eggs.– reptiles such as garter snakes retain their eggs– most mammals develop inside the mother’s reproductive

tract


• The placenta is a membranous organ that develops in female mammals during pregnancy.

placenta

umbilical cord

uterus

amniotic sac

– lines the uterine wall and partially envelops the fetus– carries nutrients from mother to embryo and removes

wastes

Unit 25 Vertebrates

Technology

Transcript of Unit 25 Vertebrates