6471765
| Pregunta | Respuesta |
| Phylum Chordata | over 50,000 species, mostly vertebrates 3 major subphyla urochordata chephalochordata (both are referred to as inverts) vertebrata (vertebrae replace notochord) |
| Phylum Chordata Characteristics | Notochord at some stage of development Dorsal hollow nerve cord Pharyngeal gill slits Contractile ventral blood vessel Postanal tail Endostyle or thyroid gland Structure corresponding to pineal eye and pituitary gland |
| Cambrian Vertebrates | Haikouichthyes and Myllokunmingia: 3 cm Chengjiang deposit: 520 mya Notochord, myomeres: chordate features Cranium and paired sensory structures: vertebrate features Dorsal fin, ribbon-like ventral fin 6-7 gill pouches, branchial skeleton No bone or other mineralized tissues Segmental gonads: ancestral condition seen in amphioxous |
| Ordovician Vertbrates | Vertebrates distributed worldwide Torpedo-shaped jawless fish with bony external armor (12-35cm) Jaw forms radiate in Middle Ordovician Worldwide by Late Silurian (400 mya) |
| Why did bone appear? | not defensive exclusively: too complex insulation and electroreceptive organs enhanced prey detection calcium and phosphorous storage and regulation |
| Conodont elements | Microfossils from Late Cambrian to Late Triassic <1mm spinelike or comblike apatite tissues Histologically similar to dentine Toothlike elements of vertebrates Notochord, myomeres, possibly fin rays and 2 eyes protected by sclerotic rings made of cartilage Conodont elements arranged in pharynx Myomeres have V-shape of nonvertebrate chordates |
| freshwater vs. marine origin | No fossil evidence in freshwater prior to Silurian Glomerular kidney hypothesis Divalent ion regulation volume control Marine origin is accepted hypothesis Earliest fossils Hagfish and all deuterostomes are marine Evolutionarily, cannot concentrate fluids once they are diluted |
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