ZOOL224 Lecture Notes - Lecture 4: Agnatha, Betta, Mineralized Tissues
27 Sep 2018
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Lampreys - considered pests, have caused damage to fisheries. Jawed: extinct, placoderms - earliest rudimentary teeth, heavy iridescent armour, devonian, acanthodians - shark-like appearance, shared characteristics with both osteichthyans and chondrichthyans, covered in bony spines. 3d space: conus arteriosus in heart - muscular pouch that helps to maintain pressure, mineralized tissues in endoskeleton, plus all vertebrate features (vertebrae, head, skull, brain, sensory organs, mineralized tissues) Specialized ducts for gametes - improve mating efficiency. Origin of jaws: not well understood (no transitional fossils between jawless and jawed, hypothesis - jaws came from gill arches, 6 pharyngeal arches. Fossil evidence: shuyu - jawless, double nostrils, short forebrain, romundina - jawed, more similar to gnathostomes, but the nostrils are far back, like in jawless fish. The extinct chondrichthyans: considered primitive but they were actually highly derived and complex, elasmobranchii (elasma - plate, branchia - gills, extinct, hybodonts. Shark-like: up to 2m long, advanced pectoral and pelvic fins, heterodont dentition.
