Chapter 25: Vertebrate Diversity

25.1: Vertebrate Origins

• 25.1: Vertebrate Origins• Words to Know: Chordate, Notochord,

Endoskeleton

Phylum Chordata

• The phylum Chordata is made of three groups: Urochordata, Cephalochordata, and Vertebrates

• Both Urochordates and Cephalochordates are invertebrates.• Urochordates are Tunicates like sea squirts.• Cephalochordates are Lancelets that spend most of their lives buried in

the sand.• Vertebrates are large, active animals that have a well-developed brain

encased in a hard skull.• ALL Chordates share the same four features at some stage in

development:– Notochord – a flexible skeletal support rod embedded in the animal’s back.– Hollow Nerve Cord – runs along the animal’s back.– Pharyngeal Slits – slits through the body wall in the pharynx, where water

can enter the mouth and leave the animal through these slits without passing through the entire digestive system.

– Tail – extends beyond the anal opening and contain muscles for movement.• Most chordate groups lose some or all of these characteristics in

adulthood, but they are present in the embryo.

Phylum Chordata

Vertebrate Common Features• Endoskeletons• An Endoskeleton is an internal

skeleton built of bone or cartilage.

• Vertebrate endoskeletons can be divided into distinct parts.– Braincase – protects the brain.– Vertebrae – a series of short,

stiff vertebrae are separated by joints and protect the spinal cord.

– Bones – support and protect the body’s soft tissues and provide points for muscle attachment.

– Gill Arches – found in fish and some amphibians; help support the gills.

• Vertebrate endoskeletons can slowly change size and shape.

Vertebrate Common Features• Vertebrate Classes• There are currently 7 classes of vertebrates:• Agnatha – jawless fish including lampreys.• Chondrichthyes – cartilaginous fish that include sharks,

rays, and chimeras.• Osteichthyes – bony fish that include ray-finned fish,

trout, and goldfish.• Amphibia – first vertebrates adapted to land and include

frogs, toads, salamanders, and caecilians.• Reptilia – can retain moisture and live exclusively on

land. Include snakes, lizards, crocodiles, alligators and turtles.

• Aves – Birds, animals with feathers and hollow bones.• Mammals – animals with fur, mammary glands, and

three middle ear bones. Includes humans, elephants, kangaroos etc…

Vertebrate Classes

Origins of Vertebrates

• Much of what we know comes from fossil evidence found in the Burgess Shale locates in the Canadian Rocky Mountains in the early 1900’s.

• Many are dated around the Cambrian explosion.

Closest Relatives

• Tunicates may actually be the closest relatives of vertebrates.

• Scientists have found that tunicates have cells that resemble the neural crest that is also found in vertebrates.

Jawless Fish: Early Vertebrates

• The first recognizable vertebrates were fish.

• The oldest fish fossils date back 530 million years.

• Early fish were small, jawless bottom-feeders.

Lampreys• There are more than 35

species of Lampreys.• They are highly specialized

fish parasites.• Physical Characteristics

include:– Long and slender body plans

with NO paired fins.– Mouths surrounded by large

suckers.– Tongues covered by tooth-

like projections.

• The accidental introduction of sea lampreys into the Great Lakes in the early 1900’s had a devastating effect on the fishing industry.

Hagfish

• A jawless eel-like animal with a partials skull but NO vertebrae.

• It uses a notochord for support.

25.2: Fish Diversity

• 25.2: Fish Diversity• Words to Know: Gill, Countercurrent Flow,

Lateral Line, Operculum

Fish• Fish use specialized organs called gills to take

in the oxygen dissolved in water.• Gills are large sheets of thin frilly tissue filled

with capillaries that take in dissolved oxygen from the water and release carbon dioxide.

• Fish circulatory systems pump blood in a single circulatory loop through a heart with two main chambers.

Countercurrent Flow

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

• Countercurrent flow maximizes the amount of oxygen the fish can pull from the water by diffusion.

Swimming and Maneuvering

• Most fish swim by contracting large segmented muscles on either side of their vertebral column from the head to the tail.

• Fins help keep fish stable.

Jaws

• Jaws evolved from gill arches.

• Gill arches are structures made of bone or cartilage that function as a support for fish’s fills.

• Jaws developed from gill arches near the mouth, which fused to the cranium.

• Jaws gave vertebrates a huge advantage as predators and quickly pushed them to the top of the food chain.

Two Groups of Jawed Fish• Jawed fish diversified very

quickly after their first appearance about 440 million years ago.

• Four groups appeared at this time:– Acanthodians – were fish covered

with spines and became extinct 250 million years ago.

– Placoderms – were heavily armored with huge bony plates and became extinct 350 million years ago.

– Cartilaginous Fish – Skeletons are made of cartilage and include sharks, rays and chimera.

– Bony Fish – Include all other living fish

Cartilagenous Fish (Chondrichthyes)

• Have skeletons made of cartilage.• Their cartilage contains calcium

deposits that make it stiffer than the squishy stuff around human joints.

• There are more than 300 species of shards and nearly 400 species of rays and skates.

• All are predators.• Cartilaginous fish have internal

fertilization and many give birth to live young.

• They are also powerful swimmers with good eyesight and an excellent sense of smell.

• All fish have a Lateral Line system, which is a series of shallow canals on the sides of the fish made up of cells that are sensitive to small changes in water movement.

• This give fish a sense of “distant touch” letting them sense movement in the water far away.

Bony Fish (Osteichthyes)

• All other living fish have skeletons made of bone.

• There are more than 20,000 species of bony fish living in almost all aquatic environments.

• The gills of all bony fish are in a chamber covered by a protective plate called the operculum.– This helps fish move

water over their gills.

25.3: A Closer Look at Bony Fish

• 25.3: A Closer Look at Bony Fish• Words to Know: Ray-fin, Swim Bladder,

Lobe-fin

Ray-finned Fish

• All ray-finned fish, such as goldfish and tuna, have fins supported by a fan shaped array of bones called a ray-fin.

• Ray-finned fish can quickly change a fin’s shape, making it easier for the fish to maneuver in the water.

Diversity of Body Plans• Long torpedo-shaped fish, such

as barracuda are ambush predators.

• Fish that are flattened from side to side, like butterfly fish, are great at maneuvering through corals.

• Fish that feed on the surface of the water have flattened heads and mouths that point up.

• Flatfish are flat-shaped and lie on the sea floor waiting for their prey to swim by.

• Some slow-swimming fish use camouflage to hide from predators or prey.

Staying Afloat• Most ray-finned fish have lungs modified into a

buoyancy organ called a Swim Bladder.• The Swim Bladder, helps a fish float higher or lower

in the water, by increasing and decreasing oxygen levels.

Lobe-Finned Fish

• The lob-finned fish include the ancestors of all terrestrial vertebrates.

• Most species are extinct.• Lobe-fins are paired

pectoral and pelvic fins that are round in shape.

• These fins are arranged around a branching series of bony struts, like the limbs of a land vertebrate.

Coelacanths

• Are distinctive-looking fish with thick, fleshy fins and a tail with three lobes.

• They breathe with gills.

Lungfish

• Live in streams and swamps in Australia, South America, and Africa.

• They can breathe with either gills or lungs.

25.4: Amphibians

• 25.4: Amphibians• Words to Know: Tetrapod, Amphibian, Tadpole

Amphibians• One of the oldest known fossils of

a four-limbed vertebrate was found in 360 million-year-old rocks from Greenland.

• All of the vertebrates that live on land, as well as their descendants that have returned to aquatic environments, are Tetrapods.

• A Tetrapod is a vertebrate that has four limbs.

• Amphibians are animals that can live BOTH on land and in water.

• Amphibian literally means “life on both sides”.

• Depending on the species, amphibians breathe through their skin or with the use of gills or lungs.

• Amphibians have a three-chambered heart.

Amphibian Reproduction

• Amphibians need a source of water to reproduce.

• Amphibians have several ways to stop eggs from drying out that include: – Laying eggs directly in water,– Laying eggs on moist ground.– Wrapping eggs in leaves.– Brooding eggs in pockets on

the female’s back.

• Some frogs start off as Tadpoles – aquatic larvae that have gills and a broad-finned tail.

Amphibian Metamorphosis• To grow into terrestrial adults,

tadpoles must undergo metamorphosis.– Eggs hatch to release tadpoles.– As the tadpole matures, the gills are

reabsorbed and lungs develop.– The circulatory system is

reorganized to send blood to the lungs.

– The tail fin is reabsorbed.– The body grows limbs and

completely reorganizes its skeleton, muscles, and parts of the nervous

system.• Many Amphibians do NOT undergo

metamorphosis and develop directly into their terrestrial forms.

Three Groups of Amphibians

• Salamanders• There are more than

300 species of salamanders.

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

• They walk with a side-t-side movement.

• They are carnivores.

Three Groups of Amphibians• Frogs and Toads• There are over 3000

species of frogs.• Toads are a family of

frogs that have rougher and bumpier skin and are poor jumpers.

• Frogs and toads can make toxins that protect them from predators.

Three Groups of Amphibians

• Caecilians• Are legless, burrowing

amphibians that live in the tropics.

• There are 160 species ranging in length from about 10 cm to 1.5 meters.

• Have banded bodies that make them look like earthworms.

25.5: Vertebrates on Land

• Words to Know: Amniote, Keratin, Amniotic Egg, Placenta

Amniotes• An Amniote is a vertebrate

that has a thin, tough, membranous sac that encloses the embryo or fetus.

• Amniotes first appeared as small lizard-like creature in the late Carboniferous period.

• All Amniotes share a set of characteristics that prevent water loss.

• Skin cells are waterproof with Keratin – a protein that binds to lipids inside the cell forming a hydrophobic layer that keep water inside the animal from reaching the skin.

• Kidneys and large intestines are bigger in amniotes than in amphibians, because they can reabsorb water.

Reproduction Without Water• The Amniotic Egg is an

almost completely waterproof container that keeps the embryo from drying out as it develops.

• Once the amniotic egg evolved, vertebrates no longer had to go back to water for reproduction.

• Most Mammal embryos develop inside of the mother’s reproductive tract.

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

• It carries nutrients from mother to embryo.