Kingdom Animalia IV Phylum Chordata

What are chordates? Chordates are animals that possess at some point in their life, a hollow dorsal notochord, pharyngeal pouches and a tail. The most primative chordates are actually invertebrates called tunicates and lancets. These invertebrates possess a hollow dorsal notochord as larva only.

Chordate evolution So how did animals with backbones arise from tunicates? Biologists believe that at some point a larval tunicate or lancet failed to metamorphose into its adult form, and instead reproduced in it’s juvenile form. This process by which juvenile traits are carried on into adulthood is called Paedomorphosis.

Tunicates The image on the left is the tunicate larva, and on the right is the adult form.

The Vertebrates The majority of chordates fall into 5 classes. Fish Amphibians Reptiles Birds Mammals

A 6th class of vertebrate? Depending on who is doing the classification, some biologists believe dinosaurs were a separate class of vertebrate. It is believed dinos evolved from reptiles, and that some dinosaurs are the ancestors of birds. The dino-bird link is based on anatomical similarities in their skeletons, as well as fossilized impressions of feathers around dinosaur fossils. dinos to birds

Archeopteryx

Vicious Fishes Fishes are aquatic vertebrates. Most fish have paired fins, scales and gills. There are three major groups of fish. –Agnathans: Jawless fish like lampreys. –Chondricthyes: Fish with a skeleton made of cartilage instead of bone, like sharks and rays. –Osteichthyes: The bony fish like tuna.

Go fish The fish were the first vertebrates to evolve on earth over 500 million years ago. Waaaaaaaay before dinosaurs arrived. Important developments include jaws (which arose from gill arches) and teeth (modified scales). Fish use their gills to extract oxygen from the water in which they live.

Types of fish Jawless fish Cartilage skeleton Bony fish (tuna)

Fish evolution

Amphibians The word amphibian means double life. An amphibian is a vertebrate that, with some exceptions, lives in water as a larva and on land as an adult, breaths with lungs as an adult, has moist skin that contains mucous glands, and lacks scales and claws. Amphibians represent the first class of chordates to adapt to living on land. All amphibians are carnivorous.

Groups of amphibians There are 3 categories of amphibians. –Salamanders: four legged and carnivorous. Most adults live in moist forest areas. Some types live in water their whole lives. –The Hellbender, the largest north american salamander is fully aquatic and can be two feet long.

Frogs and toads Frogs and toads are very similar in appearance. They are four legged with the hind legs being much larger and more muscular. Frogs and toads both lay eggs in water. Frogs are more closely tied to water, while toads can live in more arid conditions.

Caecillians The least well known group of amphibians. Caecillians are legless like snakes and live in either water or moist sediments. They feed on small invertebrates like termites.

The amphibian delegation CaecillianHellbender (salamander) Green tree frog

amphibian evolution

Reptiles Reptiles are the first vertebrates to completely lose their dependence on water for reproduction. A reptile is a vertebrate that has dry, scaly skin, lungs, and terrestrial eggs with several membranes. It is believed that dinosaurs and mammals both evolved from reptiles.

Reptile groups There are four orders of reptiles –Lizards and snakes –Crocodilians –Turtles and tortoises –Tuatara

Lizards and snakes Lizards are four legged, scaly reptiles with external ears, claws and eyelids. Most are predators, though some are herbivores. The largest living lizard, the komodo dragon, occasionally preys on humans. Snakes have lost their limbs during their evolutionary history. All snakes are predatory and some, like the cobra, produce venom. However, the majority of snakes are harmless to humans.

Crocodilians Crocodilians include crocodiles, alligators, caiman and gavials. They possess a squat muscular body, and are all top predators. Even humans are on the menu for some species. Crocodilians are very protective of their young and will defend them against predators.

Turtles and tortoises These reptiles have evolved a shell for protection from predators. Many species can completely retreat inside their shell when threatened. They lack teeth, but possess horny ridges and strong jaws. This order has adapted to live in a wide range of habitats. Some are carnivores and others are herbivores.

Tuatara There is only one species in this order still on Earth today. It lives on some islands in New Zealand. Very similar to lizards, but lack ears and possess very primative scales.

Reptile representatives

reptiles

Tuatara

The birds Birds are reptilelike animals that maintain a constant internal body temperature. They possess feathers. They have scaly legs and their front limbs have been modified into wings. Most birds have the ability to fly.

Birds The birds share some similarities with reptiles. The eggs of birds and reptiles are similar, with the main difference being that bird eggs have a hard outer shell. The scales on bird legs are very similar to reptile scales. Unlike reptiles, birds are warm-blooded.

Classes of birds There are several different groups of birds. Some examples are: –Raptors: predatory birds like hawks, eagles and falcons. They have hooked beaks and strong talons. –Perching birds: the songbirds like cardinals and mockingbird. The largest order of birds. –Herons: Tall longlegged birds with long sword like beaks for catching fish and frogs.

A bevvy of birds

Bird evolution

Mammals All mammals have hair and, in females, mammary glands. They all breathe air, have a four- chambered heart, and are warm blooded. (Endothermic) Mammals evolved about 220 million years ago, about the same time the dinosaurs appeared.

Humble beginnings The first mammals were very small and probably nocturnal. When the dinosaurs ruled the earth, mammals did their best to remain out of sight. Some biologists believe that if the dinosaurs hadn’t perished 65 million years ago, it would have been the mammals that became extinct.

Living fast Like the birds, mammals generate their own body heat. Because of this both mammals and birds have a high metabolic rate when compared to cold blooded animals. This means that mammals need to eat a lot to get all the energy they need.

Reproduction All mammals reproduce by internal fertilization, which means the male deposits sperm into the females reproductive tract. There are 3 groups of living mammals. –Monotremes (egg laying mammals, like the platypus) –Marsupials (mammals with pouches for their developing young, like kangaroos). –Placentals (animals who nourish their developing young with a placenta, like humans).

12 orders of mammal Some examples are –Rodents: Rats, mice, beavers and porcupines. –Carnivores: Cats, dogs, hyenas. –Cetaceans: Whales and dolphins. –Primates: Apes, Chimps and Humans. –Chiropterans: The flying mammals.

Mammals

evolution of mammalsevolution of mammals