Topic 18 Flashcards
What are gnathostomes?
jawed fish evolved
2 pairs of fins evolved (extinct agnathans (jawless) - one pair, extant agnathans - no paired fins)
bigger brain than in jawless vertebrates
further duplication of hox genes
Where did jaws come from?
modifications of 2 pairs of skeletal rods that had supported anterior pharyngeal slits
with hinged jaws, more ways of getting food than suspension feeding using pharynx (benefit: grasp, kill, shred, and crush large food items)
posterior slits –> specialized for gas exchange (gill slits)
What are gnathostome fossils?
the earliest gnathostomes in the fossil record is an extinct lineage of armored vertebrates called placoderms
appeared in the Ordovician, about 450 million years ago
What is the class chrondrichthyes?
cartilaginous fishes: endoskeleton made of cartilage, but have bony teeth
cartilaginous skeleton: not a primitive character state
development of most vertebrates: skeleton is first cartilaginous and then becomes ossified (bony)
chondrichthyans skip this developmental stage
What are sharks?
skin rough –> dermal placoid scales
scales structurally homologous to vertebrate teeth (teeth likely developed from the defensive armor of scales)
shark teeth continuously replaced (“conveyor belt” of teeth)
nostrils function for smelling not for gas exchange
detect changes in electrical fields generated by muscular movement of other animals
detect vibrations in water (via lateral line, lateral line present in bony fish too)
What is shark reproduction?
sperm transfer through copulation (males have pelvic fins modified as claspers, hold female and help to guide sperm)
fertilization internal
progeny production
protected in a leathery egg case
What is the class osteichthyes?
“bony-fish”
paraphyletic (if restricted to fish)
paraphyletic group including any completely aquatic craniate that uses gills for respiration
excludes tetrapods
to make the taxon osteichthyes monophyletic include all other bony vertebrates
What was the evolution of lungs and swim bladders?
gas-filled structures
extant bony fish descended from fresh or brackish water ancestors that had simple lungs and gills
original lung modified into swim bladder in most extant bony fish
What is the relationship between lungs and swim bladders?
homologous (same evolutionary origin)
perform different functions lungs (paired) --> respiration swim bladders (single) --> provide buoyancy
both arise developmentally from the same embryonic tissue
lungs developed from a ventral out pocketing of the gut
most swim bladders from dorsal out pocketing of the gut
What are the characteristics of bony fish?
ossified (bony) endoskeleton
flat plate-like bony scales
lateral line: detect movements and vibrations in surrounding water
gill openings covered by single protective flap - operculum - ventilate its gills
swim bladder (in most bony fish)
evolved from lung present in extinct ancestor
flexible fins
external fertilization
What is the class actinoptervgii?
ray-finned fish
includes >99% of bony fish
both marine and freshwater
named for the long, flexible rays that support fins
all commercially important bony fish are in this group
What is the subclass actinistia?
coelacanth (lobe-finned fish, restricted to deep marine waters, only one extant genus of actinistians
both classes (see next slide) of lobe-fins, fleshy, muscular pectoral and pelvic fins
actinistians much more diverse in fossil record (probably lived in shallow water and had lungs as well as gills)
What is the subclass rhipidistia?
lungfish
gills and lungs
gulp air into lungs from water’s surface by lowering and raising floor of mouth cavity (buccal pump)
survive dry periods by burying themselves in mud
