Placoderm
A paraphyletic group of basal gnathostomes that fall outside the clade formed by chondrichthyans and osteichthyans (Eugnathostomata)
Two Subclasses of Chondrichthyes
Elasmobranchii and Holocephali (Chimaeras)
Condrichthyes Traits
prismatic (calcified) cartilaginous endoskeleton
dermal placoid scales
pelvic clasper
rectal salt gland
What are teeth and placoid scales made of
dentine covered in highly mineralised enamel
polyphyodont
means to have ones teeth replaced frequently throughout their life
Holocephali teeth
No scales, and are fused into plates
Caudal Fin
The back fin at the end of the body.
Homocercal or heterocercal
Holocephali Traits
aka Chimeras
cartilaginous endoskeleton
operculum covering gill arches
caudal fin reduced to a narrow whip
swim by fluttering movements of pectoral fins and slow sideways movement of the tail
elongate snouts for electroreception
no scales
Hypothesized phylogeny within Elasmobranchii
Batomorphi (skates and kin)
Salachii (sharks!!)
Within sharks: Galeomorphi and Squalomorphi
Holocephali jaws and teeth
jaw suspension: palatoquadrate fused completely to the neurocranium
dentition reduced to two pairs of tooth plates in th eupper jaw and one in the lower jaw
teeth are not replaced
Batomorphi Traits
aka skates and rays
benthic and durophagous lifestyles
pectoral fins greatly elaborated and fused to head
no anal fin
dorsoventrally flattened, eyes dorsal, spiracle enlarged and dorsal, gills and mouth ventral, well developed tail spin
swim by a wave-like motion of their pectoral fins
Myliobatoidei
stingrays with slender tails bearing one or more venomous stingers
Torpediniformes
torpedo rays that can deliver electric shocks
Selachii Traits
aka think white sharks, bull sharks, tiger sharks, leopard sharks
most have long rostrum, subterminal mouth
hyostylic jaw suspension for more mobile jaws
single cusped teeth with serrations
calcified vertebrae
large nasal capsules
Squalomorph Shark Tail Features
Notable for having a large “epicaudal” area of fin rays above the fleshy portion of the tail that contains the tip of the vertebral column and surrounding tissues”
Squalomorphi Examples and Traits
dogfish, sawshark, angel sharks, cookie-cutter shark, greenland sharks and most primitive sharks (Hexanchiformes)
possess fin spines, spiracles
lack anal fin
cold, deep water, often on or near ocean floor
some have tapetun lucidum (eye shine)
Tapetun lucidum
eye shine in Squalomorphi
Hexanchiformes
most primitive sharks in Squalomorphi
frilled shark, six gill shark and seven gill shark
amphistulic jaw suspension, lack calcified vertebrae, loss of anterior dorsal fin and both fin spines
Galeomorphi traits
familiar sharks with fusiform bodies
spiracle small or absent, anal fin always spresent, most have lost the lobe spine
dominant marine predators in tropical to temperate seas
