Phylum ChordataSubphylum Vertebrata • The vertebrates are a sub-group of the phylum chordata, creatures with a notochord • In vertebrates the notochord disappears as the organism develops and is replaced by a backbone or spine.
Features of Vertebrates • Internal skeleton, composed of cartilage and/or bone. • A vertebral column (or spine) of vertebrae made of bone and/or cartilage. • A cranium or skull that protects the brain • In addition most vertebrates have • Pharyngealpouches at some stage of life • A post-anal tail (a posterior tail above or behind anus) • A notochord that disappears as the spine grows
The main Classes of Vertebrates • Agnatha: the jawless fish (lampreys, hagfish) • Chondrichthyes: cartilage fish (sharks, rays) • Osteichthyes: the boney fish (most fish) • Amphibia: amphibians (frogs, salamanders) • Reptilia: the reptiles (lizards, snakes, crocodiles) • Aves: the birds (penguins, robins, ostriches) • Mammalia: the mammals (cats, mice, humans)
Early Evolution of Vertebrates • Some biologists think vertebrates first evolved about 550 million years ago, however the oldest fossils date to the Ordovician period (440-510 MYA) • The earliest fossils are of jawless fish, similar to class Agnatha. (probably evolved from ancestors of lancelets) • About 440 million years ago (Silurian or late Ordovician period), jaws evolved from gill arches. • About 370 million years ago (Devonian period) some lobe-finned fish moved inland and evolved into amphibians • By 300 million years ago reptiles had appeared • The earliest mammals appeared about 200 million years ago • Birds are the most recent vertebrates, with fossils dating back about 150 million years.
Geological Timescale Jawless Fish Cartilage Fish Boney Fish Amphibians Reptiles Mammals Synapsids Birds Dinosaurs 543 510 439 409 363 290 245 206 144 65 2 Jurassic Ordovician Devonian Carboniferous Triassic Ternary Cambrian Permian Cretaceous Silurian Quaternary
Systems • All vertebrates have well developed organ systems, including: • Internal skeletal system (endoskeleton) • Integument, or body covering that may include skin, scales, feathers or hair. • Muscles capable of rapid movement • Respiratory system with gills or lungs • A closed circulatory system with multi-chambered heart. • A two-ended digestive system • A brain and well developed nervous system
The Fishes • “Fish” is a non-scientific name that is used to refer to three different classes of vertebrate. • Class Agnatha (jawless fish) • Class Chondrichthyes (cartilage fish) • Class Osteichthyes (bony fish) The fish used to be placed in the now-defunct Class Pisces, but this class was later split into the three more modern classes. Now the term fish is an informal term for any members of these three classes
Geological Timescale Lancelets Cartilage fish: “sharks” Jawless Fish Osteichthyes 543 510 439 409 363 290 245 206 144 65 2 Jurassic Ordovician Devonian Carboniferous Triassic Ternary Cambrian Permian Cretaceous Silurian Quaternary
Agnatha: the Jawless Fish • These fish have eel-like bodies, with no jaws and no paired fins. Their skeletons are cartilage. There are two main types: • Lampreys: parasites on other fish • Hagfish: bottom-feeders Hagfish Mouth of a lamprey adult lamprey
Chondrichthyes: Cartilage fish • These fish have jaws, but their skeletons are made of cartilage. They do have paired fins, but arranged differently than the more common bony fish. There are three main types: • Sharks • Rays • Skates
Sharks Anterior dorsal fin Caudal (tail) fin Jaws Anal fin Pelvic fins (paired) Gill slits Pectoral fins (paired) Also see the diagram on page 805 of your text book
Skates and Rays • Skates and rays have flattened bodies, with extended, wing-like fins. In manta rays, the pectoral fins have become “horns” below the mouth. Pectoral fins Pelvic fins Skate Ray
Osteichthyes: The boney fish • These fish have skeletons that contain at least some true bone. • Parts of the skeleton may still be made of cartilage or softer, less calcified bones than found in other vertebrates. Most familiar fish are osteichthyes (and so are a few strange ones)
Features of Osteichthyes • Gills covered by an operculum • Bones • Paired fins • Lateral line sense organs
Parts of a fish Anterior dorsal fin Posterior dorsal fin Lateral Line Eye Operculum Pectoral fin Caudal fin Anal fin Pelvic fin
Enrichment: Some Strange Fish The Sea horse doesn’t even look like a fish. It’s orientation is all wrong and it’s fins and tail are highly modified. The males carry the young. But it is a true fish anyways. The coelacanth was thought to have been extinct for 60 million years, until a fisherman caught one off the coast of South Africa. It is a lobe-finned fish. The lungfish is able to crawl short distances across land on its lobed fins, and can breath air. They are found in Africa, South America and Australia The Angler fish dangles a bit of glowing bait in front of its face to attract prey, which it then grabs and swallows with its large mouth.
Enrichment: Not a fish! Whales and dolphins look like fish, but they are actually mammals. the prehistoric Ichthyosaur (below) was actually a reptile. Jellyfish, starfish, silverfish, crayfish may have the word fish in their name, but they are not true fish. Jellyfish = Cnidaria Starfish = Echinoderm Silverfish = Insect Crayfish = Crustacean
Amphibians • Features of modern amphibians • Moist, thin skin with no scales • Feet (if present) have no claws, often webbed • Respiration is through a combination of gills, skin and lungs • Eggs lack shell or membranes. Fertilized externally. Dry out unless protected. • Most have larval and adult stage, and must undergo metamorphosis
Orders of Amphibians • Kingdom Animalia, Phylum Chordata, Class Amphibia, • Order Anura: Frogs and Toads • Order Urodela: Salamanders, Newts • Order Apoda: Caecilians, legless amphibians
Amphibians first appeared about 370 million years ago. They probably evolved from lobe-finned fish that came on to land to crawl from pond to pond. Ichthyostega (prehistoric amphibian) Frogs and salamanders
Geological Timescale Anura (Frogs) Amphibians Fish Amphibians Diversify Apoda (Caecilians) Urodela (salamanders) First Amphibians Ichthyostega Frog Lobe-finned fish Caecilian Salamander 543 510 439 409 363 290 245 206 144 65 2 Jurassic Ordovician Devonian Carboniferous Triassic Ternary Cambrian Permian Cretaceous Silurian Quaternary
Frog (a sample amphibian) Like most amphibians the frog has a moist skin. The skeleton and internal organs are similar to those in most “higher” vertebrates. The frog must return to water in order to reproduce (its eggs would dry out on land). Frogs undergo a metamorphosis from a fish-like tadpole into the adult frog.
Metamorphosis • Most amphibians have a larval form and an adult form. • The larva’s respiration is generally through external gills • The adult’s respiration is through a combination of lungs and skin breathing. Tadpole, a frog larva Axolotl, a salamander larva
Amphibian Facts • The largest amphibian is the Chinese giant salamander • The smallest amphibian is the Brazilian gold frog • The most poisonous amphibians (some would say the most toxic animals in the world) are the three varieties of dart-poison frogs (AKA poison arrow frogs)
Assignment • Skim through chapter 42 • Note the diagrams of internal frog systems • Read page 833 • Answer the following questions • 1. When, and from what ancestor, did the earliest amphibians evolve? • 2. describe the main differences between the orders of amphibians. • 3. Why do most amphibians require a body of water in order to reproduce? • 4. Describe the life cycle of a frog. Amphibians evolved about 370 million years ago. They probably evolved from a lobe-finned fish similar to modern lungfish. The Anura have large legs, especially hind legs for jumping. Urodela (salamanders) have smaller legs, Apoda (ceacilians) have no legs. They require a wet area for mating, also their eggs would dry out on land unless protected.
Frogs hatch from small gelatinous eggs (AKA. Spawn) in the form of tadpoles. As the tadpole grows it develops legs and its tail resorbs (gradually disappears) until the adult has the familiar frog shape
Class Reptilia “The Reptiles”
Evolution of the Reptiles • Reptiles appeared more than 300 million years ago. • They flourished during the Mesozoic era (245 million to 65 million years ago), so this time period is called “the age of reptiles” • 65 million years ago, many species became extinct. Only four orders of reptiles survived to modern times.
Geological Timescale Turtles Snakes & Lizards Crocodilians Reptiles Amphibians Reptiles diversify Tuataras First Reptiles Extinction Dinosaurs (& related orders) Birds Mammals Synapsids / Therapsids 543 510 439 409 363 290 245 206 144 65 2 Jurassic Ordovician Devonian Carboniferous Triassic Ternary Cambrian Permian Cretaceous Silurian Quaternary Age of Reptiles
Reptile Evolution Lizards Snakes Tuataras Crocodiles Turtles Birds frogs mammals Mesozoic Age of Reptiles 3 12 9 6 7 11 5 10 4 2 8 1 Dinosaurs Primitive Reptiles Ichthyostega
Features of Modern Reptiles • Modern reptiles have: • Waterproof skin, usually covered in scales • Feet (if present) have claws • A three or four chambered heart* • Ectothermic body temperature regulation. (ie. “cold-blooded”) • Well developed lungs, eliminating the need for gills or skin breathing** • Amniotic eggs (have a shell or protective membrane, and are fertilized internally.) *four chambered in crocodilians, three chambered in all other reptiles. **some snakes have limited skin-breathing ability.
Surviving Orders of Reptiles • Kingdom Animalia, Phylum Chordata, Class Reptilia* • Order Chelonia: Turtles and Tortoises • Order Crocodilia: Crocodiles, alligator, caiman • Order Squamata: • Suborder Lacertilia: Lizards • Suborder Serpentes: Snakes • Order Rhynchocephalia: Tuataras *recently some taxonomists have suggested replacing “Reptilia” with “Sauropsida” but we will continue to use the more traditional name.
Turtle crocodile Lizard and snake Tuatara
The Amniotic EggSecret to the Reptile’s Success Unlike the eggs of amphibians and fish, the amniotic egg of reptiles, birds and monotremes is internally fertilized (through sexual contact) and has a protective outer membrane or shell that prevents it drying out. It contains enough nutrients in the yolk to nourish the embryo. The allantois is a sac that holds wastes until the embryo hatches, and also provides some oxygen. The amniotic egg freed the reptiles of the need to return to the water to reproduce.
Evolution of the heart As reptiles evolved, so did their hearts. Early reptiles had a 3 chambered heart, just like the amphibians. As they became more active, a “septum” began to appear in their hearts. At first the septum served little purpose, but slowly it became an advantage.. The septum prevented oxygen-rich blood from mixing as much with the oxygen poor blood. This allowed a higher activity level for the reptiles The septum evolved to divide more and more of the heart. Most reptiles today have a fairly significant septum. In a few reptiles, like crocodiles, the septum completely divided the heart This four chambered heart was passed on to the most successful descendants of the reptiles, the birds and mammals.
Reptile Facts • Smallest reptile is the Jaragua Sphaero a dwarf gecko • The largest (living) reptile is the salt water crocodile. • Tuataras have a tiny “third eye” on the top of their heads, related to a human’s pineal gland.
Assignments • Skim pages 839-854, Read page 855 • Copy the phylogenic tree from p. 841 • Draw & label a diagram of the Amniotic egg, from page 843. List the features of the amniotic egg. • Draw a diagram of the heart of a typical reptile (p.846) • List the distinguishing features of each of the four surviving orders of reptiles.
Class Aves The Birds
Evolution of the Birds • The earliest accepted fossils of birds date back to 150 million years ago. • Recent finds of dinosaur fossils with feather-like scales suggest an earlier evolution of birds, but this is still debated. • Archaeopteryx lithographica is the oldest confirmed bird species. • It had several reptilian features, including claws on its wings, teeth and a long bony tail. • See page 863 for a drawing of Archaeopteryx
Geological Timescale (Birds) Dinosaurs Birds Feathered dinosaurs Archeopteryx 543 510 439 409 363 290 245 206 144 65 2 Jurassic Ordovician Devonian Carboniferous Triassic Ternary Cambrian Permian Cretaceous Silurian Quaternary
Features of Modern Birds • Skin covered in feathers • Wings in place of the forelimbs • Light-weight rigid skeleton • Many of the bones are hollow to reduce weight • Endothermic metabolism (“warm blood”) • Birds maintain a high body temperature (40°-41°C) • Unique respiratory system • A beak in place of teeth • Amniotic eggs with hard shells
Bird’s Respiratory System Lungs Air Sacs Birds have many sacs attached to their lungs. As they inhale, air passes through the lungs and fills the sacs. As they exhale, the air passes through the lungs again. Essentially they pass twice as much air through the lungs with each breath.
Flight • Over 90% of all birds are able to fly. • Flight has been made possible by many adaptations: • Wings with an “airfoil” shape. • “Keel” shaped breast bone with attachment points for large muscles that operate the wings. • Hollow bones to reduce weight • Feathers insulate and propel. • Down feathers for insulation • Contour feathers give birds shape • Flight feathers give propulsion
Diversity in Birds • There are 29 different orders of birds • Only the twelve most common are described in the textbook • The smallest bird is a Cuban hummingbird not much larger than a bumblebee (5 cm long including tail, about 1/20 ounce or just over 1 gram) • The largest bird is an African ostrich (9 ft tall, 350 lb, or 2.7m, 160 kg) It is flightless, but a good runner. • Penguins are the fastest swimming birds (Penguins are also flightless, the BBC video that showed flying penguins was an expensive Computer Generated April fool’s joke)
A Few Orders of Birds • Falconiformes: Birds of prey, or “raptors” • Anserformes: Ducks and Geese • Strigiformes: Owls • Passeriformes: Songbirds • And there are 25 more orders…
Assignments • Skim through pages 861-874 of the text. • Carefully read page 875 • Create a brief set of notes (about one page) that summarizes the main things you have learned about birds • be prepared to show your summary to me in the next class • Answer questions 16 to 22 on page 876