history of fishes

Conodonts

“cone-shaped teeth”, lived 600-200 MYA, chevron-shaped muscle blocks, bone cells in dermal skeleton

Pteraspidomorphi

jawless filter feeders, lived in marine and freshwater, dermal armor, tadpole-like swimming, hypocercal tail

Anaspidomorphi

compressed fusiform body, hypocercal tail, terminal mouth, overlapping tuberculate scales, flexible finlike projections

Thelodontomorphi

depressed fusiform body, hypocercal tail, horizontal mouth, denticles instead of bony plates, lateral line

Osteostracomorphi

“shell-skinned”, bone cells, 2 semicircular canals, includes Cephalaspidiformes with ossified endoskeleton

Gnathostomata

3 semicircular canals, paired limbs with skeletal support, dentine-based teeth, jaws derived from gill arches, includes “plate-skinned” Placodermi

Teleostomes

advanced jawed fishes, includes Acanthodii and Osteichthyes

Acanthodii

spiny sharks, cartilaginous skeletons, small non-overlapping scales, large head and large eyes, streamlined with reduced armor, subterminal mouth

Osteichthyes

bony fishes, includes Sarcopterygii and Actinopterygii

Sarcopterygii

lobe-finned fishes; functional wrist joint; includes Tiktaalik, Coelacanths, lungfishes, and Tetrapodomorphs

Actinopterygii

ray-finned fishes, erect dorsal fin rays, ossified vertebral column, reduced scales, homocercal tail, includes sturgeons, paddlefishes, and Neopterygii clade (“new fins”)

physostomus

pneumatic duct connecting gas bladder to gut, limits depth to shallow waters

physoclistous

no pneumatic duct, replaced with specialized circulatory system using dissolved gases to control buoyancy with gas bladder

Chondrichthyes

advanced jawed fishes, cartilaginous endoskeleton, pelvic claspers, includes Euselachii and Holocephali

Euselachii

modern sharks, pronounced snout for larger olfactory system, ventral mouth and protrusible upper jaw, tooth replacement, control buoyancy using oil produced from liver

Holocephali

chimaeras/ratfishes, single opercular opening, 4 gill openings, upper jaw is fused to braincase and non-protrusible, tooth plates on jaw margins