Kingdom Animalia IV Phylum Chordata What are chordates

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 6 th 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. Waaaay 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 Caecillian Hellbender (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 fourchambered 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 mammals