The skin of fish is covered with scales and mucus that helps the fish swim and aids in osmoregulation.
A fish's line system is similar to that of sharks.
The gills are used by all fishes to breathe.
Water is drawn over gills that are located in chambers that are covered with a muscular flap called the operculum.
The swim bladder is used to control the fish's movement.
The gases of the swim bladder are exchanged with the blood.
The swim bladder is thought to be related to the lungs of land animals.
Tuna, bass, trout, and salmon are some of the familiar fishes that comprise Actinopterygii.
The fan of the slender bones supports the fins.
The bones in the limbs of early tetrapods are similar to the bones in the fins of Sarcopterygii.
Several species of lungfishes and the less familiar coelacanths were thought to be extinct until they were discovered between Africa and Madagascar.
Two species of coelocanths have been described.
Both the sockeye salmon and coelacanth are bony fishes.
The coelacanth was thought to have gone extinct 100 million years ago, until a fish was found in Africa.
By the end of this section, you will be able to state the important difference between the life cycles of amphibians and other animals.
The term "amphibian" is derived from the Greek word for "dual life," which is a reference to the different phases of life that salamanders and frog undergo.
They can't stray far from water because their reproduction is tied to the environment.
Amphibians were the earliest of their kind.
Over millions of years, they represent an evolutionary transition from water to land.
The Amphibia are the only living true vertebrates that have made a transition from water to land.
Most salamanders have four well-developed limbs.
All caecilians are limbless in some species of salamanders.
There is a moist, permeable skin that is achieved via mucus glands.
The majority of water is taken across the skin.
The skin is a respiratory surface.
The lungs and buccal are the other two.
Air is first taken into the mouth through the nostrils and then pushed into the lungs by elevating the throat and closing the nostrils.
Amphibians have a tongue that is sticky to capture prey.
Amphibians have small teeth at the edge of their jaws.
salamanders and caecilians have teeth in both jaws.
The upper jaw is where the teeth are seen in toads.
The root and crown of Amphibian teeth are non-calcified and pedicellate.
Amphibians have eyes.
Frogs and toads vocalize to communicate.
Frogs use different parts of their inner ear for detecting higher and lower sounds.
Amphibians have an extra bone in the ear called the operculum, which is used for the detection of seismic signals.
The fossil record shows that the first salamanders were around 400 million years ago.
The change in body plan from one suited to respire and swim in water to organisms that breathed air and moved onto land was represented by the evolution of the tetrapods.
Ichthyostega and Acanthostega are aquatic arthropods.
Both had lungs and gills.
They had four limbs with the same structure as those found in salamanders.
The limbs would not have supported the bodies well out of water.
They may have lived in shallow freshwater environments, like today's "walking catfish" in Florida.
In Ichthyostega, the forelimbs were more developed than the hind limbs, so it might have dragged itself onto land.
Tiktaalik roseae, a fossil of a "tetrapod-like fish", was published in 2006 by researchers.
Tiktaalik had gills and lungs, but it had a neck because of the loss of some gill elements.
There were eyes on the head.
The attachment of the fin bones to the shoulder suggested they might be heavy.
The four limbs of Tiktaalik are considered to be an intermediate clade between fish and Amphibians.
The early tetrapods had access to new sources of food.
Around the world, there are an estimated 6,770 Amphibia species.
These animals are very similar to ancestral salamanders.
Some of the living salamanders are aquatic, others are terrestrial, and some are only for adults.
salamanders have a body plan with four limbs and a tail.
The placement of their legs makes it difficult to lift their bodies off the ground and they move by bending their bodies from side to side, calledlateral undulation, in a fish-like manner.
It is thought that their movements are similar to those of early tetrapods.
The majority of salamanders are lungless, and respiration occurs through the skin or external gills.
Some salamanders have primitive lungs, while others have both gills and lungs.
The giant Japanese salamander has folds in its skin that enlarge its respiratory surface.
salamanders reproduce using an unusual process of internal fertilization.
Mating between salamanders can take a long time.
The fire salamander is the only salamander that is oviparous.
The salamanders lay their eggs in the water.
Eggs are guarded by their mothers when they are in a salamander's damp nest.
The embryo goes through the stages of development before hatching into tiny adult forms.
The Mexican axolotl, an aquatic salamander, is sexually mature without changing into a nymph.
salamanders have legs and a tail
The frog is a member of the order Anura or thejumpers.
Anurans are one of the most diverse groups of animals, with over 5,000 species that occur on all of the continents.
A body plan that is more specialized for movement is what Anurans have.
Frogs use their hind limbs to jump to catch prey on land.
The tree frog's hands are adapted for grasping branches.
Flying Frogs can glide from perch to perch on their feet in tropical areas.
Frogs have a number of modifications that allow them to avoid predatory animals.
Frogs and salamanders have defensive chemicals in their skin that can be poisonous to other animals.
Frogs with more toxic skins have bright warning colors.
The Australian green tree frog is a nocturnal predator that lives in the canopies of trees.
Frogs lay their eggs in moist environments.
The eggs are protected by a thick layer of jelly.
Frogs show a great diversity of parental behaviors, with some species laying many eggs and showing little parental care, to species that carry eggs and tadpoles on their hind legs or embedded in their backs.
The tadpoles can drop into the water as they hatch if the tree frog lays their eggs in a folded leaf.
The life cycle of most salamanders consists of two stages, the first of which is the larval stage.
The little froglets that develop from the eggs of the Eleutherodactylus are guarded by a parent.
The tadpole is an important part of the frog's life cycle.
At the end of the tadpole stage, the frog becomes an adult.
The gills, tail, and lateral line system disappear during this stage.
The jaws become larger and are better suited for feeding on small animals.
An air-breathing lung also develops.
The adult stage is when the larvae can move onto land.
A juvenile frog is turning into a frog.
The tadpole tail is still visible even though the frog has started to develop limbs.
They have no limbs.
The lack of limbs makes them look like earthworms.
The folds of skin look like the segments of an earthworm.
Caecilians are adapted for a burrowing or aquatic lifestyle, and they are nearly blind with their tiny eyes.
They have a single lung and depend on cutaneous respiration.
The tropics of South America, Africa, and Southern Asia are where these animals are found.
In the caecelians, fertilization is internal in the males.
Most of the caecilians live young.
In these cases, the females help nourish their young with tissue from their oviduct before birth and from their skin after birth.
The climate and geography of Earth were vastly different during the Paleozoic Era.
The distribution of landmasses on Earth was different than it is today.
The sea levels were high at this time and haven't been reached since.
The global climate was cool as the Paleozoic progressed, but warmed near the end of the first half.
Pangaea's climate and distribution of life were affected by glaciers.