| Term | Definition |
|---|
| notochord | all chordates have this; consists of flexible supporting rod made of cartilage; in most adult chordates, this develops into (or is replaced by) the vertebral column |
| dorsal hollow nerve cord | all chordates have this; forms early on in development along the dorsal side; develops into the spinal cord and brain |
| pharyngeal gill slits | all chordates have this; appear in pharynx of all chordates at some stage in their development then they evolve to aid in respiration and filter feeding; become jaw |
| gills | exchange gases and feed |
| neoteny | occurs when the juvenile form becomes capable of sexual reproductions and bypasses the adult stage altogether |
| tetrodotoxin | venom prey is injected with; same paralytic poison found in Japanese puffer fish |
| jaw | formed from pharyngeal gill slits; vertebrates no longer limited to filter feeding |
| vertebrae | backbone |
| vertebral column | in vertebrates, this replaces the notochord in adults and surrounds the dorsal nerve chord |
| backbone | spine |
| cartilage | tough, flexible connective tissue |
| paired fins | horizontal stabilizers, keep sharks on a steady keel; a preadaptation for vertebrate forelimbs and hindlimbs; pectoral fins, pelvic fins |
| pelvic fin | for stability, paired fin |
| pectoral fin | for locomotion and side to side movement, lateral surface, paired fin |
| preadaptation | when evolution takes an existing structure and puts it to a new use |
| lateral line | sensory system in the skin; can detect pressure waves in water, can sense approaching predators and struggling prey |
| denticles | teeth-like things that cover the skin of the shark |
| shagreen | shark skin; once sold as sandpaper, boots, belts, and vitamins |
| swim bladder | gas bag that can be inflated or deflated at will, regulates buoyancy; has flexible walls that inflate or deflate according to ambient pressures |
| bony skeleton | lightweight, thin bones |
| bony jaws | lightweight, thin bones in the jaw |
| scales | protective; not like reptile scales |
| amniotic egg (**) | egg develops a protective membrane and shell - analogous to the seed; an adaptation for life on land |
| feathers | evolved from reptilian scales; a preadaptation, evolved for insulation |
| endotherm | warm-blooded |
| milk | nourish young with this from mammary glands |
| nipple | all mammals have these; excretes milk |
| naval | not all mammals have these; formed because of the umbilical cord to the placenta |
| placental mammal | nourish fetus inside the body, attached by an umbilical cord to a placenta |
| marsupial | nourish young in an external pouch; ex: kangaroos, koalas |
| monotreme | lay eggs; ex: platypus |
| hair | unique mammalian invention |
| keratin | hair is made of this; same protein makes fingernails, toenails, claws, hooves, horns |
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