Vertebrate Diversity. Phylogeny. I. P. Chordata. Invertebrate SubPhylum Urochordata. Invertebrate SubPhylum Cephalochordata

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1 Vertebrate Diversity Phylogeny I. P. Chordata II. III. IV. Invertebrate SubPhylum Urochordata Invertebrate SubPhylum Cephalochordata Vertebrate Subphylum Vertebrata

2 V. Superclass Agnatha (Jawless) VI. Superclass Gnathostomes (Jaws) A. C. Chondrichthyes B. C. Osteichthyes C. C. Amphibia D. C. Reptilia E. C. Aves F. C. Mammalia Notes: 1. C-F are tetrapods possess two pairs of limbs 2. D-F have additional adaptations for terrestrial life including amniotic eggs (see below)

3 Chordate Diversity I. Distinguishing Characteristics A. Background 1. Chordates are bilaterally symmetrical deuterostomes with three germ layers 2. Chordates have a segmented body, complete digestive tract and a well-developed coelom B. All chordates share four distinguishing characteristics that are exhibited at sometime during the life cycle: 1. Notochord a. Most primitive support structure of the chordate body b. Persists throughout life as the main axial skeletal support in lancelets and lampreys c. In fishes, amphibians, reptiles, birds and mammals the notochord is later partially or completely replaced by the vertebral column 2. Dorsal hollow nerve cord a. Forms on the dorsal surface of the early embryo shortly after the gastrula stage b. Anterior end becomes enlarged as a simple "cerebral vesicle" in tunicate larvae and in lancelets c. In all vertebrates it thickens and differentiates into a tripartite brain 3. Pharyngeal gill slits develop on the sides of the embryonic pharynx a. Gill slits function in feeding in primitive chordates and in respiration in more advanced chordates 4. Post-anal tail a. In most invertebrates the anus is located at the posterior end of the body b. In vertebrates a part of the trunk extends posterior to the anus c. Provides a mechanism for using the segmented musculature of all vertebrates for more effective propulsion

4 5. Endostyle a. Some authors list a fifth character b. In cephalochordates the endostyle is a groove in the base of the pharynx i. S similar structure is present in tunicates c. Mucous passes over the gills, traps small particles of food and passes along the endostyle into the gut d. Endostyle also produces mucous and iodine containing compounds i. Thyroid gland is present in all vertebrates and believed to have been derived from the endostyle II. Phylum Hemichordata: (Acorn worms) A. Evolutionary significance 1. Exhibit characteristics of both echinoderms and chordates 2. Larval form (known as the tornaria larva) is similar to the echinoderm bipinnaria larva 3. Hemichordates also possess pharyngeal gill slits (a chordate characteristic) 4. Some classification systems have regarded the hemichordates as a subphylum of the Chordata a. Based on the presence in hemichordates of a stomochord i. Some authors consider to be homologous with the notochord of chordates b. Short dorsal nerve cord which may be hollow 5. Most taxonomists prefer to place hemichordates in a separate phylum III. Phylum Chordata A. Subphylum Urochordata (tunicates or sea squirts)

5 1. Characteristics a. Marine filter-feeders b. Sessile i. Attach to rocks or some other stationary object c. Do not exhibit most chordate characteristics as adults i. Only have pharyngeal gillslits d. Larval stage has a notochord and other chordate features B. Subphylum Cephalochordata (Lancelets) 1. Chordate characteristics as an adult: a. Notochord b. Dorsal nerve chord c. Gill slits d. Post-anal tail 2. Features associated with burrowing lifestyle a. Notocord extends to the tip of the rostrum 3. Similar features as earliest vertebrates

6 C. Subphylum Vertebrata 1. Vertebral column (either bony or cartilaginous) a. Replaces the notochord as the axial support for the body b. Nerve cord runs through openings in the vertebrae c. Axial skeleton permits larger size, and stronger, faster movement 2. Anterior part of the nerve cord is elaborated into a brain a. Divided into three parts 3. Cranium surrounds brain 4. Endoskeleton a. Jointed b. Two pairs of appendages c. Functions i. Provides support to the body ii. Provides surface area for muscle attachment iii. Enables an animal to attain large body size d. Endoskeleton may be comprised of: i. Bone ii. Cartilage iii. Combination of a & b e. Endoskeleton is alive and can grow f. Exoskeletons are for protection and are not alive 5. Closed circulatory system a. Ventral heart with two or more chambers that pump blood b. Blood is oxygenated in either lungs or gills and transported via arteries and veins 6. Other distinctive features: a. Kidney composed of tubules (of mesodermal origin) b. Unsegmented gonads c. Paired eyes, ears, and nasal openings d. Separate sexes are the rule D. Superclass Agnatha (Lamprey) 1. Characteristics a. Most primitive of the vertebrates b. Lack jaws and paired appendages c. Parasites or scavengers E. Superclass Gnathostomata 1. Characteristics a. Jaws i. Evolved from skeletal structures that had previously supported the pharyngeal gill slits 2. Six classes a. Subgrouped I and II i. Gnathostomata II are tetrapods

7 F. Superclass Gnathostomata I: Class Chondrichthyes (Shark and rays) 1. Features a. Cartilaginous skeleton i. Loss of bone is probably secondary, not primitive b. Elastic and lighter than bone c. Carnivorous (most) d. Tough skin covered with minute placoid scales and possesses many mucous glands e. Median and paired fins are present, all supported by fin rays f. Mouth is ventral i. Has upper and lower jaws ii. Rostrum anterior to the mouth g. Heterocercal tail i. Vertebral column turns dorsally into the upper lobe of the tail h. Internal fertilization i. Males have claspers on pelvic fins to transfer sperm into female reproductive tract i. Have a spiracle take water in and out over gill slits j. Lateral line sensory organ, water pressure and vibrations 2. Placoid scale a. Basal plate embedded in the dermis b. Spine projects from this plate i. Perforates the epidermis and projects caudally c. Dermal denticle resembles a tooth in that it contains a pulp cavity, a thick layer of dentine and a surface covering of enamel

8 G. Superclass Gnathostomata I: Class Osteichthyes (Bony fishes) 1. Characteristics a. Operculum i. Flap attached to the first gill arch that covers all of the gill openings b. Spiracle is absent in modern bony fish c. Scales lack enamel and dentine i. Thin and translucent bony structures that are covered by the epidermis d. Skin usually contains many mucous glands i. Mucous reduced drag e. Paired and median fins; modern bony fishes have pectoral and pelvic fins that are located anteriorly i. Paired fins with a bony supporting structure ii. Pectoral fins are just behind head; pectoral girdle attached to skull; fish have no necks. iii. In most modern bony fish, pelvic fins are located very anteriorly; in primitive fishes they were posterior in position f. Axial skeleton i. Similar vertebrae and ribs all along the body ii. No regional differentiation iii. Aids in locomotion--series of S-shaped curves g. Skeleton is highly ossified in most species h. Homocercal tail (symmetrical) i. Swim bladder provides bouyancy j. Most are oviparous with external fertilization

9 H: Superclass Gnathostomata II: Class Amphibia 1. Three orders: a. Urodela (salamanders) b. Anura (frogs) c. Apoda 2. Mode of reproduction a. Primitive b. Eggs lack protective membranes or a shell i. Small with little yolk for the developing embryo ii. Eggs are laid in the water and fertilized externally c. Embryo hatches at a very immature stage i. Water-dwelling larva with gills d. Larva undergoes metamorphosis i. Gills are lost, lungs develop, and the animal may become completely terrestrial 3. Amphibians were the first vertebrates to move onto land a. Most amphibians are restricted to moist habitats, and need water to reproduce i. Skin is used as an accessory breathing organ 4. Major adaptations of amphibians to land life: a. Limbs i. Modified to support the body ii. Shoulder girdle is no longer tied to the skull iii. Pelvic girdle is anchored to the vertebral column b. Lungs a. Present in the fishes ancestral to amphibians i. Preadaptation for land life I. Superclass Gnathostomata II: Class Reptilia 1. Defining feature a. Means of reproduction i. Amniote or cleidoic egg ii. Independent of water 2. Amniotic egg:

10 a. Contains a large amount of yolk so that the young do not hatch as larvae, but as miniature adults b. Egg is surrounded by a shell (prevents desiccation) c. Membranes: i. Chorion--prevents desiccation ii. iii. Amnion contains the embryo; enclosed watery environment Allantois--stores nitrogenous waste as the insoluble, non-toxic compound uric acid 3. Fertilization is internal a. Reptiles have separate sexes and males have copulatory organs to deposit sperm 4. Additional characteristics include: a. Dry, cornified skin b. Ectotherms i. Need behavioral adaptations to maintain body temperature 5. Extant orders: a. Chelonia--turtles b. Squamata lizards and snakes c. Crocodilia alligators and crocodiles J. Superclass Gnathostomata II: Class Aves (Birds) 1. Highly modified for flight a. Most of the defining characters are related to means of locomotion. 2. Characteristics a. Feathers b. Endothermic thermoregulation i. Permits enhanced metabolic activity c. Modified bones d. Four chambered heart i. Separate pulmonary and systemic circuits e. Amniote egg 3. Anatomical modifications a. Honeycombed bones strength while reducing weight b. Reduced organ systems to minimize weight c. No teeth 4. Metabolic changes that enable energy production a. Endothermic b. Four-chambered heart (blood segregation) 5. Advanced nervous system vision and sensory integration 6. Skeletal modifications keel on sternum to anchor pectoral muscles K. Superclass Gnathostomata II: Class Mammalia 1. Characteristics: a. Mammary glands milk for young b. Endotherms with active metabolism c. Hair comprised of keratin; did not evolve from scales; insulation d. Four-chambered heart segregates oxygenated and non-oxygenated blood e. Differentiated teeth f. Separate sexes; viviparous with nutrients across placenta

11 2. Most primitive living mammals: monotremes a. Lay eggs b. Have mammary glands i. Nurse their young c. Have hair i. Insulation ii. Sensory 3. Mammals that give birth to live young a. Marsupials i. Very immature young and nurse them in a pouch b. Placentals i. Live young that are much more highly developed 4. Advantages of live young: a. Young are automatically kept warm and protected b. Degree of development is not limited by the amount of stored yolk i. Degree of development depends on nutrients available c. Degree of development not limited by length of gestation i. Amount of nitrogenous wastes that build up