Slides 28 Flashcards
derived characters of chordates
notochord, dorsal hollow nerve chord, pharyngeal slits, muscular post anal tail; resembled lancelets who retain all traits as adults
derived vertebrate characters
neural crest appears along the edges of the closing neural tube; disperse through embryo and give rise to: teeth, bone and cartilage of skull, neurons, sensory capsules
lampreys
living lineage of vertebrates that represent early evolving; jawless, reduced vertebrae, notochord, cartilaginous skeleton
gnathostomes
have jaws with teeth used to grip and slice food, jaws evolved by modification of skeletal rods supporting pharyngeal slits (gills)
early gnathostomes
440 million years ago, adaptations improved: paired fins and a tail; dorsal, ventral, and anal fins stiffened by bony fin rays; efficient gas exchange system in the gills
gnathostome divergence
3 lineages, chondrichthyans, ray-finned fishes, lobe-fins
chondrichthyans
skeleton composed primarily of cartilage, often impregnated with calcium; traces of bone found in scales, at base of teeth, coating vertebrae, bone evolved AFTER
ray-finned fish and lobe-fish
most vertebrates are osteichthyans and have bony endoskeleton; include bony fish and tetrapods; aquatic are fishes
fish innovations
gills of fishes protected by a bony flap called operculum; water drawn into mouth and over gills by muscle contractions and movement of the operculum; air sac called swim bladder for buoyancy
ray-finned fishes (actinopterygii)
27,000 species, originated during Sillurian period; modifications in body form and fin structure affect maneuvering, defense, and other functions
lobe-fins (sarcopterygii)
Silurian period; pectoral and pelvic fins have rod-shaped bones surrounded by a thick layer of muscle; only 3 remaining lineages: coelacanths, lungfishes, tetrapods
lungfish
3 species in southern hemisphere; live in ponds and swamps now; gas exchange occurs in water using gills
tetrapod evolution
fins evolved into limbs 365 million years ago; diversified following evolution of limbs and colonization of land
tetrapod derived characters
“four feet” body plan; four limbs with feet and digits; a neck that enables independent movement of head; fusion of pelvic girdle to backbone; absence of gills; ears for detecting airborne sounds
amphibians
6,150 species in 3 clades: salamanders, frogs, caecilians
lifestyle and ecology of amphibians
larvae are aquatic with gills, lateral line system, long finned tail; during metamorphosis develop terrestrial features legs, lungs, and external eardrums and adjust to carnivore diet
amphibian eggs
lack a shell and must be laid in water or moist environments on land; fertilization is external; some lay many unprotected; some lay few and protect by carrying on back/mouth/stomach
derived characters of amniotes
amniote egg which contains four membranes that protect the embryo; reduced dependence on water for reproduction; 4 membranes: amnion, chorion, yolk sac, allantois
extraembryonic membranes
amnion: protects embryo, fluid-filled cavity that cushions against shock; yolk sac: stockpile of nutrient; allantois: disposal sac for embryonic waste; chorion: exchange gasses between embryo and air
amniote diversity
tetrapods whose living members are reptiles and mammals
early amniotes
350 million years ago, early lived in warm moist areas but expanded over time, predators that resembled small lizards with sharp teeth
reptiles
scales: containing keratin to protect skin from desiccation and abrasion; shelled eggs; fertilization occurs internally before shell is secreted
reptile- diapsids
earliest reptiles resembled lizards, main lineages: turtles, lepidosaurs (lizards, snakes, dead mososaurs), archosaurs (birds, crocodiles, dead dinosaurs)
turtles
lost holes in skulls, boxlike shell made of upper and lower shields fused to the vertebrae, clavicles, ribs acquired over stages in evolution
