Which Animals Have a Notochord?
The first set, the pronephroi, are vestigial organs left over from the evolutionary past that soon degenerate and disappear without having had any function. Join us on Twitter Follow tweets on recent articles eLifeSciences. Pharynx is marked off. Learn more about Zoology. List the three groups of chordates and their characteristics. It is clearly marked off from the pharynx as well as stomach.
Vertebrates represent only a small percentage in the total animals worlds. Though there are small in number their size and mobility. Vertebrates are highly cephalized and have well developed organs. They have endoskeleton and a closed circulatory system. And they have the ability to regulate their body temperature.
Of the five class of vertebrates birds and mammals are endothermic in nature and the others like fish, amphibians, and reptiles are ectothermic in nature. They have bony endoskeleton which consists of cranium, limb girdles, visceral arches and two pairs of appendages.
Muscles attached to the endoskeleton helps in locomotion and they have ventral hearts with 2 to 4 chambers. Finally, salamanders have the ability to grow back lost limbs, as well as other body parts. This process is known as ecdysis. The marbled salamander shows the typical salamander body plan: Different salamanders breathe in different ways. In those that have gills, breathing occurs through the gills as water passes over the gill slits. Species that live on land have lungs that are used in breathing, much like breathing in mammals.
Other land-living salamanders do not have lungs or gills. Instead, they "breathe", or exchange gases, through their skin. This is known as valarian respiration , and requires blood vessels that exchange gases to be spread throughout the skin.
Salamanders are found in most moist or arid habitats in the northern hemisphere. They are generally small, but some can reach a foot or more, as in the mudpuppy of North America.
In Japan and China, the giant salamander reaches 6 feet and weighs up to 66 pounds Figure below. Frogs and toads Figure below are amphibians in the order Anura. In terms of classification, there is actually not a big difference between frogs and toads. Some amphibians that are called "toads" have leathery, brown colored, wart covered skin, but they are still in the same order as frogs. Frogs are found in many areas of the world, from the tropics to subarctic regions, but most species are found in tropical rainforests.
Frogs range in size from less than 0. Adult frogs are characterized by long hind legs, a short body, webbed finger-like parts, and the lack of a tail Figure below. They also have a three-chambered heart, as do all tetrapods except birds and mammals. Most frogs live part of the time in water and part of the time on land, and move easily on land by jumping or climbing. To become great jumpers, frogs evolved long hind legs and long ankle bones. They also have a short backbone with only 10 vertebrae.
Frog and toad skin hangs loosely on the body, and skin texture can be smooth, warty, or folded. In order to live on land and in water, frogs have three eyelid membranes: Frogs also have a tympanum , which acts like a simple ear. They are found on each side of the head. In some species, the tympanum is covered by skin. Frogs typically lay their eggs in puddles, ponds or lakes. Their larvae, or tadpoles, have gills, and the frogs develop in water. You may hear males "ribbiting," producing a mating call used to attract females to the bodies of water best for mating and breeding.
Frogs calls can occur during the day or night. Adult frogs are meat-eaters and eat mostly arthropods, annelids, and gastropods.
Frogs do not have teeth on their lower jaw, so they usually swallow their food whole, using the teeth they do have to hold the prey in place. Other frogs do not have any teeth, so they must swallow their prey whole. Frogs are raised as a food source. Frog legs are a delicacy in China, France, the Philippines, northern Greece and the American south, especially Louisiana.
Amphibians are used in cloning research and other branches of embryology, because their eggs lack shells, so it is easy to watch their development. The African clawed frog, Xenopus laevis, is a species that is studied to understand certain biological phenomena in developmental biology, because it is easy to raise in a lab and has a large and easy to study embryo. Many Xenopus genes have been identified and cloned, especially those involved in development. Many environmental scientists believe that amphibians, including frogs, indicate when an environment is damaged.
Since they live on land and water, when species of frogs begin to decline, it often indicates that there is a bigger problem with the ecosystem.
Amphibians can be found in folklore, fairy tales and popular culture. This connection likely originates from the tendency of many salamanders to live inside rotting logs.
When placed into the fire, salamanders would escape from the logs, lending to the belief that the salamander was created from flames. Why does this fact make frogs susceptible to many toxins in the environment? Future studies of molecular genetics should soon provide further insights to the evolutionary relationships among frog families.
These studies will also clarify relationships among families belonging to the rest of vertebrates. We discuss reptiles next. What reptiles do you know? Snakes, alligators, and crocodiles are all reptiles. Reptiles are tetrapods and amniotes , which means their embryos are surrounded by a thin membrane. Modern reptiles live on every continent except Antarctica. They range in size from the newly-discovered Jaragua Sphaero, at 0. Reptiles are air-breathing, ectothermic vertebrates that have skin covered in scales.
Most reptiles have a closed circulatory system with a three-chambered heart. All reptiles breathe using lungs. They also have two small kidneys. Usually their sense organs, like ears, are well developed, though snakes do not have external ears middle and inner ears are present. All reptiles have advanced eyesight. The majority of species are egg-laying, although certain species of squamates can give birth to live young.
This is achieved either by oviparity the egg stays in the female until birth , or viviparity offspring born without eggs. Many of the viviparous species feed their fetuses by a placenta, similar to those of mammals. Some reptiles provide care for their young. All reptiles have a cloaca, a single exit and entrance for sperm, eggs, and waste, located at the base of the tail.
Most reptiles lay amniotic eggs covered with leathery or calcium-containing shells. An amnion the innermost of the embryonic membranes , chorion the outermost of the membranes surrounding the embryo , and allantois a vascular embryonic membrane are present during embryonic life.
There are no larval stages of development. Most reptiles reproduce sexually, although six families of lizards and one snake are capable of asexual reproduction. In some species of squamates, a population of females is able to produce a nonsexual diploid clone of the mother. This asexual reproduction, called parthenogenesis, also occurs in several species of gecko.
Lizards and snakes belong to the largest order of reptiles, Squamata. Lizards are a large group of reptiles, with nearly 5, species, living on every continent except Antarctica. Members of the order are distinguished by horny scales or shields and movable quadrate bones, which make it possible to open the upper jaw very wide.
Quadrate bones are especially visible in snakes, which are able to open their mouths very wide to eat large prey Figure below. Vision, including color vision, is well-developed in lizards. You may have seen a lizard camouflaged to blend in with its surroundings.
Since they have great vision, lizards communicate by changing the color of their bodies. They also communicate by chemical signals called pheromones. Adult lizards range from 1 inch in length, like some Caribbean geckos, to nearly 10 feet Figure below. With 40 lizard families, there is an extremely wide range of color, appearance and size of lizards. Many lizards are capable of regenerating lost limbs or tails. Almost all lizards are carnivorous, although most are so small that insects are their primary prey.
A few species are omnivorous or herbivorous, and others have reached sizes where they can prey on other vertebrates, such as birds and mammals. Many lizards are good climbers or fast sprinters.
Some can run on two feet, such as the collared lizard. Some, like the basilisk, can even run across the surface of water to escape. Many lizards can change color in response to their environments or in times of stress Figure below.
The most familiar example is the chameleon, but more subtle color changes can occur in other lizard species. Some lizard species, including the glass lizard and flap-footed lizards, have evolved to lose their legs, or their legs are so small that they no longer work. Legless lizards almost look like snakes, though structures leftover from earlier stages of evolution remain. For example, flap-footed lizards can be distinguished from snakes by their external ears.
All snakes are meat-eaters, and are different from legless lizards because they do NOT have eyelids, limbs, external ears, or forelimbs. The more than 2, species of snake can be found on every continent except Antarctica and range in size from the tiny, 4-inch-long thread snake to pythons and anacondas that are over 17 feet long Figure below.
Most snakes are not venomous, but some have venom capable of causing painful injury or death to humans. However, snake venom is primarily used for killing prey rather than for self-defense. Most snakes use specialized belly scales, which grip surfaces, to move. The body scales may be smooth, keeled or granular Figure below. In the shedding of scales, known as molting, the complete outer layer of skin is shed in one layer Figure below.
Molting replaces old and worn skin, allows the snake to grow, and helps it get rid of parasites such as mites and ticks. A close up of snake scales of a banded krait, showing black and yellow alternating bands and spaces between scales. Although different snake species reproduce in different ways, all snakes use internal fertilization. The male uses sex organs stored in its tail to transfer sperm to the female.
Most species of snakes lay eggs, and most species abandon these eggs shortly after laying. All snakes are strictly carnivorous, eating small animals including lizards, other snakes, small mammals, birds, eggs, fish, snails or insects. Because snakes cannot bite or tear their food to pieces, prey must be swallowed whole. The body size of a snake has a major influence on its eating habits. Snakes have a very flexible lower jaw, the two halves of which are not rigidly attached.
They also have many other joints in their skull, allowing them to open their mouths wide enough to swallow their prey whole. Some snakes have a venomous bite, which they use to kill their prey before eating it. Other snakes kill their prey by strangling them, and still others swallow their prey whole and alive. After eating, snakes enter a resting stage, while the process of digestion takes place. Crocodilia, containing both alligators and crocodiles, is an order of large reptiles.
Reptiles belonging to Crocodilia are the closest living relatives of birds. Reptiles and birds are the only known living descendants of the dinosaurs. Think about how organisms with the same ancestors can evolve to be so different. The basic crocodilian body plan Figure below is a very successful one, and has changed little over time. Modern species actually look very similar to their Cretaceous ancestors of 84 million years ago.
Crocodilians have a flexible, semi-erect posture. All crocodilians have, like humans, teeth set in bony sockets, but unlike mammals, they replace their teeth throughout life. Crocodilians also have a secondary bony palate that enables them to breathe when under water, even if the mouth is full of water.
Their internal nostrils open in the back of their throat, where a special part of the tongue called the palatal valve closes off their respiratory system when they are underwater, allowing them to breathe. Crocodiles and gharials large crocodilians with longer jaws have salivary glands on their tongue, which are used to remove salt from their bodies. Crocodilians are often seen lying with their mouths open, a behavior called gaping.
One of its functions is probably to cool them down, but it may also have a social function. Crocodilians are known to swallow stones, known as gastroliths, which help digest their prey. In terms of evolutionary origin, fish evolved first, followed by amphibians, reptiles, birds and then mammals.
The most advanced of these groups of animals are the mammals. Human beings, the most advanced organisms in the animal kingdom, are mammals. Quick Answer Birds, reptiles, amphibians, mammals and fish all have a notochord, a post anal tail, pharyngeal slits and a dorsal nerve cord at some point of development. What Animals Live in the Temperate Forests? Full Answer This category of animals is the most highly evolved and most complex.
Learn more about Zoology. What Animals Are Endangered in the Rainforest? Many of the rainforest's birds, reptiles, amphibians and mammals are endangered.