„ Relationships: in Phylum Chordata, Subphylum Vertebrata
– Chordate Characters
„ Notochord
„ Dorsal hollow nerve cord
„ Muscular postanal tail
„ Endostyle (mucus secreting groove – homologous to thyroid)
„ Pharyngeal slits
„ Deuterostomic development
– Shared with echinoderms and hemichordates
„ Triploblastic (ectoderm, mesoderm, endoderm)
„ Coelomate
„ Subphylum Urochordata (Tunicates)
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– Tadpole has all characters
Subphylum Cephalochordata (lancelets)
– Adult has all characters, plus others
„ Circulatory system, embryonic induction
– “amphioxus”
„ Pikaia – Burgess Shale chordate
– Myomeres, notochord – Early Cambrian
„ Haikouella – Chengiang of China (Early Cambrian)
– Enlarged brain, eyes, pharynx with gill tissue and bars (neural crest)
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Vertebral column surrounding nerve cord
– Can be bony or cartilaginous
„ Hagfishes lack
Cranium – bony, cartilaginous, fibrous
– Hagfishes have – “Craniates”
Duplication of Hox gene complex
– Directs development of segments
Neural Crest tissue – a 4 th
Tissue layer?
– Forms new head structures
Large, tripartite brain
– Forebrain, midbrain, hindbrain

„ Embryology
– No “ontongeny recapitulates phylogeny”
„ But embryology gives clues to phylogeny
– Ectoderm: epidermis, nervous system, sense organs
– Endoderm: lining of gut and glands, respiratory surfaces
– Mesoderm: everything else (muscles, skeleton, blood, connective tissue, urogenital system)
– Neural Crest: bones and muscles of head, peripheral nervous system, adrenal glands, melanocytes
„ 5 basic types:
– Epithelial, connective, blood, muscular, nervous
„ Collagen – component of most – fibrous protein
– Forms ligaments, matrix of bone, etc. (mesodermal derivatives)
„ Elastin – stretchy protein
„ Keratin – protein in tetrapods – forms hair, scales, feathers, horns, beaks, baleen
– Epidermal derivatives
„ External covering – skin and derivatives
– Glands, hair, scales
– Epidermis – (ectodermal)
„ Boundary, sensory
– Dermis – (mesodermal and N.C.)
„ Muscles and blood, melanocytes
„ Hydroxyapatite – mineral unique to vertebrates
„ Major mineralized tissues:
– Bone (50%)
– Dentine (90%)
– Enamel (99%)
– Cartilage (sharks) – slightly mineralized
– Enameloid (in fishes)
– Cementum – holds teeth in sockets
„ Produced by osteocytes
„ Living tissue
– In amniotes – arranged in Haversion systems
– Compact bone on outside – cancellous bone inside

„ 2 types: Dermal (ancestral) and endochondral
(replacement)
„ Early vertebrates (ostracoderms) had dermal bone on outside, cartilaginous internal skeleton
„ Replacement bone allows growth
„ Teeth
– Inner dentine outer enamel or enameloid
„ Similar to shark scales
„ Notochord – vacuolar cells
– Retained in agnathans
– Forms part of intervertebral disks
„ Cranial Skeleton
– Chondrocranium – surrounds brain
„ Replaced by bone in derived vertebrates
– Splanchnocranium – pharyngeal arches
„ Forms jaws and throat structures in derived
– Dermatocranium – derived from dermal bone
„ Forms most of skull – lost in cartilaginous fish
„ Vertebrae
– Centrum (surrounds and obliterates notochord)
– Neural arch (surrounds nerve cord)
– Hemal arch (caudal vertebrae)
– Projections (apophyses) for muscle or rib attachment
– Tetrapods – zygapophyses allow interlocking to resist gravity
„ Myotomes folded (W shape) across several vertebrae
– Epaxial and hypaxial muscles
„ Limbs and limb (fin) girdles
– Pectoral girdle anchors forefins (limbs)
– Pelvic anchors hind fins or limbs
„ Fins
– Basal elements, radials, rays
– Lobefin fish extend basals and radials
„ Limbs
– Bony extensions (e.g. humerus, radius ulna, carpals, metacarpals, phalanges)

„ Muscle contraction against notochord or skeleton
„ Lateral trunk – fish, amphibs, limbless tetrapods
„ Limb motion/lateral – amphibs reptiles
„ Limb motion/vertical - mammals
„ Mechanical and Chemical breakdown
– Muscularized gut – churns food
– Enzymes chemically digest
– Stomach present only in gnathostomes
„ Site of protein digestion
– Liver and pancreas secrete enzymes into intestines
„ Fat and carbohydrate digestion
– Primitively – no large and small intestine
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Empties into cloaca (common house)
„ Cutaneous respiration in some verts.
„ Most have specialized structures
– Lungs, gills
– Large surface area for exchange
„ Blood – erythrocytes, leukocytes, thrombocytes (platelets in mammals)
„ Arteries, veins, capillaries (exchange sites)
„ Portal systems – between cap beds
– Hepatic portal system
„ Heart
– Primitively, 3 chambers:
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Sinus venosus, atrium, ventricle
Gnathostomes add conus arteriosus after vent.
„ Blood flows to ventral aorta, up through aortic arches in gills
– Some goes to head (carotid arteries)
– Rest goes to dorsal aorta to trunk
– Cardinal veins return blood to sinus venosus

„ Kidneys – remove nitrogenous waste, regulate osmotic potential of fluid
„ Primitively – 3 portions along length
– Pronephros (in hagfishes)
– Mesonephros
– Metanephros
– Fishes and amphibs have meso and metanephric portions (opisthonephric)
– Amniotes have only metanephric kidney drained by ureter
„ Testes and ovaries produce gametes
„ Ovaries produce estrogen and ova
„ Testes (seminiferous tubules) produce sperm and testosterone
„ Agnathans – gametes move through coelom to pores
„ Gnathostomes – gametes move through tubes
„ Oviparous vertebrates vs. viviparous
– Some overlap (lecithotrophic viviparity vs. matrotrophic viviparity)
„ Dual system unique to vertebrates
– Somatic nervous system (voluntary)
– Visceral nervous system (involuntary)
„ Autonomic (motor part of visceral)
– Sympathetic (fight/flight)
– Parasympathetic (digestion, relaxation)
„ Brain Anatomy and Evolution
– Hindbrain (rhombencephalon)
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Myelencephalon (medulla oblongota) – basic functions (respiration)
Metencephalon (cerebellum) – coordination
– Midbrain (mesencephalon) – optic input
– Forebrain (prosencephalon) – smell
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Diencephalon – pituitary and hypothalamus
– Hormonal controls
Telencephalon – cerebrum – coordinates higher activities

„ Lateral line system – vibrations in water (neuromast organs)
„ Smell and taste – chemoreception
„ Vision – electromagnetic reception
– Retina with rods and cones
„ Electroreception – primitive – aquatic
„ Balance and hearing – mechanoreception
– Hair cells
– Inner ear – semicircular canals, vestibular apparatus, cochlea