Vertebrates v1.0

The Chordates Chordates (phylum Chordata) are deuterostome coelomates -Nearest relatives are echinoderms (the only other deuterostomes)

The Chordates Four features characterize chordates 1. Nerve cord 2. Notochord 3. Pharyngeal slits 4. Postanal tail

The Chordates All chordates have all four of these characteristics at some time in their lives Other characteristics also distinguish chordates 1. Chordate muscles are arranged in segmented blocks called somites 2. Most chordates have an internal skeleton against which the muscles work

The Chordates Somites

The Nonvertebrate Chordates Phylum chordata can be divided into three subphyla 1. Urochordata 2. Cephalochordata 3. Vertebrata Nonvertebrates

Subphylum Urochordata Tunicates are marine animals -Larvae are tadpole-like and have notochord and nerve cord -Are free-swimming but do not feed -Adults typically lose the tail and notochord -Are immobile filter-feeders -Many secrete a tunic (cellulose sac) that surrounds the animal

Subphylum Cephalochordata Lancelets are scaleless chordates -Notochord persists throughout animal’s life -Have no distinguishable head -Feed on plankton using cilia-generated currents -Closest relatives to vertebrates

Subphylum Vertebrata Vertebrates: chordates with a spinal column -Distinguished from nonvertebrates by 1. Vertebral column – Encloses and protects the dorsal nerve cord 2. Head – Distinct and well-differentiated possessing sensory organs

Subphylum Vertebrata Vertebrates also have -Neural crest – A unique group of embryonic cells that forms many vertebrate structures -Internal organs – Liver, kidneys, endocrine glands, heart and closed circulatory system -Endoskeleton – Made of cartilage or bone -Makes possible great size and extraordinary movement

Subphylum Vertebrata

The first vertebrates appeared in the oceans about half a billion years ago Jawed fishes -Jawed fishes soon became dominant amphibians -Their descendants, the amphibians, invaded the land Reptiles -Reptiles replaced them as the dominant land vertebrates. 300 MYA -Gave rise to birds and mammals 220 MYA

Fishes Fishes are the most diverse vertebrate group -Over half of all vertebrates Vary greatly in size, shape, color and appearance 500 MYA Paired fins Jaws

Fishes Fishes have the following characteristics 1. Vertebral column 2. Jaws and paired appendages 3. Internal gills 4. Single-loop blood circulation 5. Nutritional deficiencies

History of the Fishes The first fishes had mouths with no jaws -Agnatha (Superclass) extant as hagfish (class Myxini) and lampreys (class Cephalaspidomorphi) -Ostracoderms are now extinct The development of jaws occurred in the late Silurian period ( MYA) -Jaws evolved from the anterior gill arches that were made of cartilage Skull Gill slit Anterior gill arch

History of the Fishes The Devonian period ( MYA) saw two types of jawed fishes -Spiny fishes (Acanthodii) -Smaller fishes that dominated early on -Armored fishes (Placodermi) -Larger fishes that dominated late At the end of the period, these early fishes were replaced by sharks and bony fishes -These had more improved jaws

History of the Fishes In the Carboniferous period ( MYA), sharks (Class Chondrichthyes) became the dominant sea predators -A light, flexible, calcified, cartilaginous skeleton, and paired fins made them superior swimmers

History of the Fishes Sharks were among the first vertebrates to develop teeth -Evolved from rough scales on mouth’s skin -Easily lost but continuously replaced Sharks (and bony fishes) have a fully developed lateral line system -Series of sensory organs under the skin that detects changes in pressure waves  Most sharks have internal fertilization. Oviparous, ovoviviparous, and viviparous.

History of the Fishes Bony fishes (Osteichthyes) evolved at the same time as sharks about 400 MYA -However, they adopted a heavy internal skeleton made completely of bone Bony fishes are the most species rich group of all vertebrates (> 30,000 living species) They developed significant adaptations that enabled them to dominate life in the water -Swim bladder and gill cover

History of the Fishes Swim bladder -A gas-filled sac that allows bony fishes to regulate their buoyant density -Gas addition = Gas gland -Gas release = Oval body Gill cover -A hard plate, the operculum, covers gills -Its flexing permits water pumping over gills

Two Major Groups of Bony Fishes Ray-finned fishes (class Actinopterygii) -Parallel bony rays support & stiffen each fin -There are no muscles within the fins Lobe-finned fishes (class Sarcopterygii) -Have paired fins that consist of a long felshy muscular lobe -Supported by central co-jointed bones -Almost certainly the amphibian ancestors

Amphibians Amphibians (class Amphibia) are damp-skinned vertebrates -First vertebrates to walk on land

History of Amphibians Successful invasion of lands by vertebrates required several adaptations Legs 1. Legs to support body’s weight Lungs 2. Lungs to extract oxygen from air Redesigned heart 3. Redesigned heart to drive larger muscles Reproduction in H 2 O 4. Reproduction in H 2 O to prevent egg drying preventdesiccation. The skin also aids in respiration. 5. System to prevent whole body desiccation. The skin also aids in respiration. 6. Plumonary veins.

History of Amphibians Amphibians evolved from lobe-finned fish Ichthyostega was one of the first amphibians -Efficient limbs for land crawling -Improved olfactory and auditory structures -However, still fishlike -Spent much of life in water

History of Amphibians In 2006, a transitional fossil was found between fish and Ichthyostega -Tiktaalik lived about 375 MYA -Shoulder and limb bones like those of an amphibian -Fins like those of a lobe- finned fish -Spent most of its life in water -Capable of moving onto land to capture food or escape predators

Modern Amphibians Modern amphibians are descended from three families of the Tertiary period (65-2 MYA) -These accomplished a highly successful invasion of wet habitats all over the world Today there are about 5,670 species in 37 different families, comprising three orders: -Anura (“without tail”), Caudata (“visible tail”),Apoda (“without legs”)

Reptiles Over 7000 species of reptiles (class Reptilia) now live on Earth All living reptiles exhibit three key features 1. Amniotic eggs, which are watertight 2. Dry skin, which covers body and prevents water loss 3. Thoracic breathing, which increases lung capacity

Reptiles Reptiles, birds and mammals are amniotes The amniotic egg has four membranes  Chorion – Allows O 2 entry  Amnion – Fluid- filled cavity  Yolk sac – Provides food  Allantois – Excretes wastes

History of Reptiles Reptiles dominated earth for 250 million years Reptiles are distinguished by the number of holes on side of the skull behind eye orbit: -0 (anapsids), 1 (synapsids), 2 (diapsids)

History of Reptiles The synapsids rose to dominance first -Pelycosaurs were first land vertebrates to kill beasts their own size -Therapsids replaced them about 250 MYA -May have been endotherms -Replaced by diapsids but gave rise to mammals.

History of Reptiles Archosaurs (Diapsids) were the first land vertebrates to be bipedal -Gave rise to dinosaurs about 220 MYA Dinosaurs dominated for over 150 million years -Became extinct 65 MYA -Asteroid’s impact

Modern Reptiles Modern reptiles developed two important characteristics: 1. Internal fertilization: Sperm fertilizes egg before protective membranes are formed 2. Improved circulation: Oxygen is provided to the body more efficiently

Comparing the circulatory systems of fish, amphibians, and reptiles.

Modern Reptiles All living reptiles are ectothermic -Obtain heat from external sources There are four surviving orders of reptiles -Chelonia (turtles and tortoises) -Rhynchocephalia (tuataras) -Squamata (lizards and snakes) -Crocodylia (crocodiles and alligators)

Order Crocodylia In many ways, crocodiles resemble birds far more than they do other living reptiles -Build nests and care for their young -Have a four-chambered heart CrocodileGharial