Origin & Evolution of Vertebrates Ch. 34 Lecture Objectives 1. Intro to Phylum Chordata

Jaws, mineralized skeleton Echinodermata Cephalochordata ANCESTRAL DEUTEROSTOME Urochordata Notochord Myxini Common ancestor of chordates Petromyzontida Chondrichthyes Vertebrae Figure 34.2a Phylogeny of living chordates (part 1) Jaws, mineralized skeleton

Phylum Chordata 1. Bilateral 2. Segmented Body 3. Triploblastic 4. Coelomate 5. Deuterostomes

Chordate Hallmarks * May only appear during embryonic development. Dorsal, hollow nerve cord Muscle segments Notochord Figure 34.3 Chordate characteristics Mouth Anus Pharyngeal slits or clefts Muscular, post-anal tail Fig. 34.3

Chordate hallmarks con’t: Notochord Notochord The notochord is a longitudinal, flexible rod between the digestive tube and nerve cord It provides skeletal support throughout most of the length of a chordate In most vertebrates, a more complex, jointed skeleton develops, and the adult retains only remnants of the embryonic notochord

Chordate hallmarks con’t: Dorsal Hollow Nerve Cord The nerve cord of a chordate embryo develops from a plate of ectoderm that rolls into a tube dorsal to the notochord The nerve cord develops into the central nervous system: the brain and the spinal cord

Chordate hallmarks con’t: Pharyngeal Slits In most chordates, grooves in the pharynx called pharyngeal clefts develop into slits that open to the outside of the body Functions of pharyngeal slits Suspension-feeding structures in many invertebrate chordates Gas exchange in vertebrates (except vertebrates with limbs, the tetrapods) Develop into parts of the ear, head, and neck in tetrapods

Chordate hallmarks con’t. Post-anal tail Chordates have a tail posterior to the anus In many species, the tail is greatly reduced during embryonic development The tail contains skeletal elements and muscles It provides propelling force in many aquatic species

Phylum Chordata Broken into 3 subphyla: Cepahlochordata (lancelets) Urochordata (tunicates) Vertebrata (animals w/backbones) Class Agnatha Class Amphibia Class Reptilia Class Aves Class Mammalia

Subphylum: Cephalochordata (lancelets) Fig. 34-4 Subphylum: Cephalochordata (lancelets) Cirri Mouth Pharyngeal slits Atrium Notochord Digestive tract Atriopore Dorsal, hollow nerve cord Figure 34.4 The lancelet Branchiostoma, a cephalochordate Segmental muscles Anus Tail Fig. 34.4

Subphylum: Urochordata (tunicates) Fig. 34.5

Subphylum Vertebrata: the craniates 1. Chordates w/ a head 2. Higher metabolism 3. Increased muscle 4. 2 chambered heart 5. RBCs w/ hemoglobin 6. Pharyngeal slits  gills Segmented muscles Fossil chordate Pharyngeal slits Fig. 34.9

Extant craniates: SP: Vertebrata, Class Myxini 1.Cyclostomes - Jawless, Ex. Hagfish 2. Cartilaginous skull & skeleton 3. Long & slender, eel-like 4. Bottom scavengers that secrete slime 5. Ingest food by sucking

Fig. 34-9 Slime glands Figure 34.9 A hagfish Fig. 34.7

Extant craniates: SP: Vertebrata, Class Pteromyzontida 1. Cyclostomes, Ex. Lamprey 2. Marine & freshwater 3. Mostly ectoparasites 4. Skeleton made of cartilage

Fig. 34.8

Gnathostomes (jaw mouth) Ex Gnathostomes (jaw mouth) Ex. Sharks, Fish, Amphigians, Reptiles, Birds, Mammals 1. Jaws that may have evolved from skeletal supports of the pharyngeal slits 2. An enlarged forebrain associated with enhanced smell and vision 3. lateral line system Fig. 34.12

Tetrapods – gnathostomes with limbs Four limbs, and feet with digits (from fins 365 mya) Ears for detecting airborne sounds Fig. 34.19

SP: Vertebrata, Class Amphibia 1. Gnathostomes & Tetrapods w/ moist skin  complements the lungs in gas exchange 2. Fertilization is external in most species 3. Eggs require a moist environment Figs. 34.22-34.23

Amniotes: reptiles, birds, mammals 1. Tetrapods w/ terrestrially adapted egg 2. Relatively impermeable skin 3. Ability to use the rib cage to ventilate the lungs Fig. 34.25

SP: Vertebrata, Class Reptilia 1. Scales that create a waterproof barrier 2. Lay shelled eggs on land (or live birth) 3. Ectothermic or endothermic 4. Ex. lizards, snakes, turtles, crocodilians, and the extinct dinosaurs

Figure 34.27 Extant reptiles (other than birds)

SP: Vertebrata, Class Aves 1. Wings with keratin feathers 2. Lack of urinary bladder 3. Reduction in reproductive organs 4. Loss of teeth Flight enhances hunting and scavenging, escape from terrestrial predators, and migration Flight requires a great expenditure of energy, acute vision, and fine muscle control

Finger 1 (b) Bone structure Palm (a) Wing Finger 2 Finger 3 Forearm Wrist Figure 34.28 Form fits function: the avian wing and feather Shaft Shaft Barb Vane Barbule Hook (c) Feather structure Fig. 34.29

SP: Vertebrata,Class Mammalia 1. Mammary Glands 2. Hair 3. Larger Brains 4. Differentiated Teeth

Variations in Class Mammalia 1. Embryo develops within a placenta in the mother’s uterus 2. Embryonic development completed while nursing in a maternal pouch Marsupials 3. Egg laying mammals Monotremes Opossum and bandicoot

Marsupials & Monotremes Figs. 34.37-34.38

Character  Monotremes Marsupials and Placental Mammals  Cloaca  A single opening in which urine, feces and eggs are deposited before being expulsion from body.  Similar to the mammalian uterus. Have at least two distinct openings for expulsion of feces and urine and for the birth of young.  Have a true uterus.  Leathery bill  Present. It is used to detect prey.  Not present.  Nipple  No true nipple; milk is secreted through the skin of the abdomen.  Milk is collected into a single duct and exits body through the nipple.  Spur on hind limb  Present in males.  Platypus can secrete venom through spur.  Ear Primitive development of the inner ear bone, it is less coiled.   More highly coiled inner ear.  Teeth  Lack of teeth in adults, instead horny pads develop.  Present in Adults.  Gait Reptile-like; limbs are aligned laterally with respect to body. Limbs are aligned below body.