15.6 Vertebrates

More than 62,000 vertebrate species have been identified, and they are among the most recognizable organisms of the animal kingdom.

Only a small portion of the animals that have existed are now living.
Dinosaurs, a unique group of reptiles, reaching sizes not seen before or since in terrestrial animals, are the best-known extinct vertebrates.
They were the dominant animals for 150 million years before they died out in a mass extinction.
The skeleton of the dinosaurs is preserved in the fossil record, so there is a lot of knowledge about their body parts.

There are an estimated 31,000 species of modern fishes.

Jawless fishes were the earliest of the vertebrates.
Jawless fishes have a distinct cranium and complex sense organs including eyes.
The jawed fishes are very diverse.
Fishes are active feeders.

Jawless fishes, which lack bone in their scales, are similar to the extinct ostracoderms.

Hagfishes are found in oceans all over the world except in the polar regions.

These animals have a unique feature that allows them to release mucus through the surface of their skin.
The mucus may allow the hagfish to escape.
Hagfish can enter dead or dying organisms to eat them.

A cartilaginous notochord runs the length of the body and is part of the skeleton of a hagfish.

The notochord supports the fish's body.
Hagfishes are not a part of the vertebrates since they don't replace the notochord with a column during development.

The hagfishes and lampreys lack appendages.

lampreys are characterized by a sucking mouth.
Some species attach to and feed on the body fluids of fish as adults.
The majority of species are free- living.

The lampreys live mostly in coastal and fresh waters.

There are all species in fresh waters.
The adult form of the larvae is different from the eggs that are fertilized outside.
Adults reproduce and die within days once they reach sexual maturity.
As adults, lampreys have a notochord.

The jaw, which is attached to the cranium and allows an animal to grasp and tear its food, is one of the most significant developments in early vertebrate evolution.

Early gnathostomes were able to exploit food resources that were not available to jawless fishes because of the evolution of the jaws.

Chondrichthyes have fins and a skeleton.

Around 400 million years ago, this clade arose in the middle Devonian.
The cartilaginous skeleton of Chondrichthyes is thought to be from an extinct group that had a skeleton made of bone.
The shark skeleton is strengthened by calcium carbonate, but this is not the same as bone.

Most cartilaginous fishes live in marine habitats, with a few species living in fresh water for some or all of their lives.

Most sharks eat live prey, either swallowing it whole or using their jaws and teeth to break it into smaller pieces.

The jagged scales that cover their skin are believed to have evolved into shark teeth.
The sharks and rays feed on plankton.

In aquatic or amphibious animals, electrical activity has been observed.

A dark stripe runs along the length of the fish's body.

Eggs are fertilized internally by sharks.

The embryo is nourished by the egg yolk in the mother's body and most species are ovoviviparous.
Young are born alive and fully functional after the eggs hatch in the uterus.
Some sharks lay their eggs outside of their mother's body.
There is a shark egg case that has the consistency of leather.
The shark egg case has a newborn shark cover.
A few species of sharks are viviparous, that is, the young develop within the mother's body, and she gives live birth.

More than 500 species of rays and skates are related to sharks.

The rays and skates have skeletons.
Most of the marine species live on the sea floor.

This group consists of approximately 30,000 species and is the largest class of fishes in existence today.

Most of the fishes have an ossified skeleton with specialized bone cells.

In a few groups of Osteichthyes, such as the paddlefish and the sturgeons, there are mostly cartilaginous skeletons.
The skin of fish is covered in scales and mucus that helps the fish swim and aids in osmoregulation.
A fish's line system is similar to that of sharks.
Some fish rely on their eyesight to locate their prey.
Bony fish have taste cells in the head and trunk that allow them to detect very small concentrations of water.

Cartilaginous fishes use gills to breathe.

Water is drawn over gills that are located in chambers that are covered with a muscular flap called the operculum.

Tuna, bass, trout, and salmon are some of the familiar fishes.

The fins of the Rayfinned fishes are webs of skin called rays.
The fins of the fishes are supported by bone.
The lungfishes and coelacanth are not familiar to most people.

Both the sockeye salmon and coelacanth are bony fishes.

The coelacanth was thought to have gone extinct 100 million years ago, until one was discovered in 1938.

Amphibians are arthropods.

The term amphibian means "dual life", which is a reference to the life cycle of a frog from a tadpole to an adult and back again.
Amphibians were the earliest of their kind.

Most salamanders and caecilians have four well-developed limbs, although some have only vestigial limbs.

A moist, permeable skin is achieved by mucus glands.
Amphibians have a tongue that is used to catch prey.

Around the world, there are an estimated 6,500 Amphibia.

salamanders have a body plan with four limbs and a tail salamanders can be lungless and respiration can occur through the skin or external gills.

Some salamanders have primitive lungs, while others have both gills and lungs.

There is a video about a large salamander species.

Frogs and salamanders have different body plans for movement on land.

Frogs use their hind limbs to jump.
Frogs have a number of modifications that allow them to avoid predators, including skin that acts as camouflage and defensive chemicals that are poisonous to predators.

Frog eggs are fertilized as they are laid.

Frogs show a range of parental behaviors, with some species showing little care for the tadpoles they carry on their hind legs.
The life cycle consists of two stages, the larval stage and the adult stage.
Tadpoles have long-finned tails, but no limbs.
At the end of the tadpole stage, the frog becomes an adult.
Four limbs develop when the gills and line system disappear.
The jaws become larger and are better suited for feeding on small animals.
An air-breathing lung also develops.
The changes during metamorphosis allow the larvae to move onto land in the adult stage.

A tadpole is transformed into a juvenile and then into an adult.

They don't have limbs and look like giant earthworms.

In the tropics of South America, Africa, and southern Asia, they are adapted for a soilburrowing lifestyle and are nearly blind.
Unlike most of the other amphibians that breed in or near water, reproduction in a drier soil habitat means that caecilians must use internal fertilization and give birth to live young.

Caecilians are well adapted to a soil-burrowing lifestyle.

Amphibians are distinguished from mammals by their shelled egg and embryo.
The evolution of amniotic membranes meant that the amniotes could grow inside the egg.
The amniotes were able to invade drier areas because of less dependence on a water environment for development.
This was a significant evolutionary change that made them different from the salamanders, which were restricted to moist environments due to their shell-less eggs.
The shells of various amniotic species allow retention of water.
Gas exchange and sequestering of waste within the enclosure of an eggshell can be done with the help of the amniotic egg.
The shells of bird eggs are composed of calcium carbonate and are hard and brittle.
The shells of reptile eggs are very soft.
Most mammals don't lay eggs, but they do have amniotic membranes.

The most common division of amniotes has been into classes.

Birds are descended from dinosaurs, so this classical scheme results in groups that are not true clades.
We will discuss birds as a group distinct from reptiles with the understanding that this does not reflect evolutionary history.

There are animals called reptiles.

Unlike caecilians, which are descended from four-limbed ancestors, limbless reptiles may have vestigial limbs.
Eggs are laid on land.
Sea turtles return to the land to lay eggs.
They reproduce sexually with fertilization.
ovoviviparity is when the eggs remain in the mother's body until they are ready to hatch.
Other species have offspring that are born alive.

The development of the reptile's skin was one of the key factors that allowed them to live on land.

All reptiles need to breathe with lungs because of their occlusive skin.
In order to conserve body water, reptiles use uric acid paste.
The major reasons why reptiles were successful in colonizing a variety of habitats far from water were due to these characteristics and the amniotic egg.

A reptile is an animal whose main source of body heat comes from the environment.

Class Reptilia includes diverse species classified into four living clades.
These are the Crocodilia, Sphenodontia, and Testudines.

The tropics of Africa, South America, the southeastern United States, Asia, and Australia are home to Crocodilians.

They spend most of their time in water in freshwater habitats.
The semi-erect posture of some species allows them to move on land.

The third largest tortoise in the world is this one.

There are many fossil species from the Triassic period.

The differences between the tuataras and lizards are similar.

The differences between lizards and snakes are their limbs, eyes, and ears.

The Komodo dragon is about 3 meters in length and is a lizard species.

Snakes are found on every single continent.

There are different sizes of thread snakes, pythons and anacondas.
All snakes eat small animals, birds, eggs, fish, and insects.

Turtles have a shell made up of a carapace on the back and a plastron on the surface of the ribs.

Turtles were predating crocodiles, lizards, and snakes.
Turtles lay their eggs on land.
The speckled padloper tortoise is the smallest turtle at 8 centimeters, followed by the leatherback sea turtle at 200 centimeters.
The term "turtle" is sometimes used to describe only those species of Testudines that live in the sea, with the terms "tortoise" and "terrapin" used to refer to species that live on land.

The data suggests that birds belong in the reptile clade, but they have a number of unique adaptations that set them apart.

Birds are endothermic, meaning they generate their own body heat.

Birds have modified reptilian scales on their feathers.

Even in cooler temperatures, feathers insulated the bird's body and allowed it to glide and engage in flapping flight.

The amount of weight carried is an important factor in powering a flying animal.
The cost for flying increases as body weight increases.

The braincase is fused to increase its strength.

Most bird species only have one ovary and no teeth in their jaw, which reduces body mass.

Birds have a system of air sacs branching from their primary airway that divert the path of air so that it passes through the lung.

Air flows continuously through the bird's lung to give it a more efficient system of gas exchange.

The jaw, skeleton, skin, and internal anatomy of mammals are unique.

The presence of hair is a key characteristic of a mammal.
Hair has many important functions for mammals, even though it is not very extensive in some groups.
Hair provides insulation by trapping air close to the body to retain heat.
There are specialized hairs called vibrissae, better known as whiskers, that serve as a sensory mechanism.
These attach to nerves that transmit touch information, which is useful to nocturnal or burrowing mammals.
Hair can provide protection.

The skin of mammals has various functions.

Most of the body has sbexras.

Male monotremes and eutherians have mammary glands.

The mammals have unique features that differentiate them from other animals.

The incisors, canines, premolars, and molars are some of the different types of teeth.
The first two types are for cutting and tearing, while the other two types are for crushing and grinding.
Depending on their diet, different groups have different proportions.
The teeth can be replaced in other animals.

Monotremes, marsupials and eutherians are the three broad groups of modern mammals.

Therian mammals and metatherians are used for the eutherians and the marsupials.

Monotremes are different from other mammals in that they lay leathery eggs rather than giving birth to live young.

The eggs are kept within the mother's reproductive tract until they are ready to hatch.
The female begins to produce milk from her mammary tissue when she is young.
Monotremes regulate their body temperatures a bit lower than placental mammals do.
Monotremes have a single opening for their reproductive, fecal, and urinary products.
Adult monotremes don't have teeth.

The platypus has a leathery beak and lays eggs rather than giving birth to live young.

The right photo shows an echidna.
Australian marsupials include the kangaroo, koala, bandicoot, and Tasmanian devil, all of which have a pouch in which the young reside after birth, receiving milk and continuing to develop.
The young are less developed than the older ones, because they have a less complex placental connection before birth.

The devil is native to Australia.

The groups of eutherians include the insect eaters, the toothless anteaters, the rodents, and the bats.
Eutherians have a complex placenta, which is more complex than other mammals.

In South America, Africa, and Asia, non-human primates live.

The mouse lemur is 30 grams (1 ounce) larger than the mountain gorilla.
The evolution of primate characteristics allow us to understand the evolution of our own species.

Not all primate species are arboreal, as they all descend from tree-dwellers.

The brains of primate are larger than those of many other mammals, they have claws that have been modified into flattened nails, and they have a tendency to hold the body upright.

Order Primates is divided into two groups.

Prosimians tend to be nocturnal, smaller in size than other animals, and have smaller brains than other animals.

Prosimians include the (a) lemur, and the (b) anthropoids.

Great apes, such as the gorilla, and lesser apes, such as the gibbon, are also anthropoids.

Animals are a kingdom of organisms.

Animals range in complexity from simple sea sponges to human beings, but most members share certain features.
The OpenStax book is free and can be found at http://cnx.org/content/col11487/1.9.
The tissues of the animal kingdom are divided into four main classes that are specialized to perform different functions.
The developmental sequence of most animals is similar to that of humans.

Organisms in the animal kingdom are classified based on their body shape.

The true animals are divided into those with radial and bilateral symmetry.
Animals with three germ layers, called triploblasts, are further characterized by the presence or absence of a coelom.
Depending on which tissue gives rise to the coelom, animals with a body cavity are either coelomates or pseudocoelomates.
The coelomates are divided into two groups based on their development.

Sponges and Cnidarians are parazoans and do not have true tissues.

There is a simple organization shown by these organisms.
Sponges have many cell types that are geared toward various functions.

Cnidarians sandwich a noncellular mesoglea with their outer and inner tissue layers.

nidarians have a well-formed digestion system.
The cnidocyte is a specialized cell for delivering toxins.
There are separate sexes for cnidarians.
At various stages in their life cycle, they havemedusoid and polypoid forms.

Flatworms are acoelomate, triploblastic animals.

They have a rudimentary excretory system.
Most species don't have a complete digestive system.
There are four traditional classes of flatworms.

Sexual reproduction takes place in the life cycles of trematodes.

Cestodes, or tapeworms, can cause problems in the bicyle.

Nematodes are pseudocoelomate members of the clade.

They have a complete body.
Free-living as well as parasites are included in this phylum.
Dioecious and hermaphroditic species are included.
Nematodes don't have an excretory system.
The stages of embryo development are external and separate from the rest of the body.

The number of species as well as the number of individuals of arthropods are the most successful of all animals.

They have a body and appendages.
There is a pair of appendages in the basic body plan.
The classification is based on mouthparts, number of appendages, and modifications of appendages.
The arthropods have a large body.
Multiple stages may be included in embryo development.

A large, mainly marine group of invertebrates are the mollusks and Annelids.

There are a variety of morphologies.
The shell of many mollusks is calcareous, but not in other species.
Protostomes are the name of the molusks.
The mantle is formed by the modification of the skin in mollusks.
The adult animal has a coelomic cavity around the heart.

Ctenidia are gills that facilitatespiration.

The radula is a chitinous scraper.

The mollusks are divided into seven classes.

The animals in the Annelida are worm-like.

Metamerism refers to the idea of segmenting, which is both external and internal.
Annelids are related to Protostomes.
The chaetae is a characteristic of most members.

These animals have a good development of their nervous and digestion systems.

Polychaete annelid's parapods are involved in locomotion and respiration.
There are suckers in the order.
There are separate sexes and hermaphroditism in the breeding systems.

There are deuterostome marine organisms.

The ossicles covered by the spiny skin of the animals are calcareous.
Echinoderms have a circulatory system.
The point of entry and exit for water is called the madreporite.

Chordata has a notochord, a hollow nerve cord, and a post-anal tail.

There are two clades of invertebrates in Chordata, Urochordata and Cephalochordata.

tunicates live on the ocean floor Lancelets are suspended feeders that feed on organisms.

The jawless fishes were the earliest animals.

Hagfishes are scavengers that feed on dead fish.
Some species of lampreys are parasites on other fishes.
The jawed fishes are included in the gnathostomes.
There are sharks, rays, skates, and ghost sharks.
Bony fishes can be divided into two types.

Some salamanders and caecilians are limbless, but most are characterized by four well-developed limbs.

Amphibians have a moist, permeable skin.
salamanders, frog, and caecilians can be divided into three clades.

The amniotes are similar to the salamanders in that they have an egg protected by amniotic membranes.

The amniotes include animals.
The development of the skin of reptiles allowed them to live on land.
Crocodilia and sphenodontia are two of the four living clades.

Birds are warm and cold at the same time.

The feathers allow for flight.
Birds have pneumatic bones that are hollow.
Birds evolved from dinosaurs.

There are hair and mammary glands in mammals.

The skin of mammals has secretory glands.
Like birds, mammals are endothermic.
The three groups of mammals are monotremes, marsupials and eutherians.
Monotremes lay eggs rather than giving birth to live young.
mammals have a complex placenta

There are 16 living orders of eutherian mammals.

Humans are closely related to Primates, all of which have the ability to climb trees.
The brains of primate are larger than those of other mammals, they have claws that have been modified into flattened nails, and they have a tendency to hold the body upright.
There are two groups of primate.

The mollusks have nerve cords.

The hollow nerve cord is part of the central nervous system.

The pharyngeal slit becomes a figure in fishes.

There is a radula for food.

There are cells in _____.

The fluid in the skin is _____.

Cubozoans are.

By having a _____.

They are called crustaceans.

It includes _____.

There are two things present in _____.

The shiroriferous glands produce something.

There are Annelids.

From examining and Cnidaria, compare the structural differences between the cranium and the column.