Gnathostomes Flashcards
How many classes of gnathostomes are there?
5 classes
3 living
2 extinct
Name the 5 classes of Gnathostomes
Acanthodian Placoderm Chondrichthyes Osteichthyes Tetrapoda
When were Acanthodians common and when did they go extinct
Common 350-400 Ma
Extinct by 250 Ma
Features of Acanthodians
Small predators - 20cm long Jaws and large eyes Spiny ‘fins’, not always paired Heterocercal tail Spines extend from body with skin flaps
What is the purpose of Acanthodian’s spiny fins?
For roll stability
What is a heterocercal tail and what is it’s benefit?
Vertebrae extend into upper lobe of tail, provides thrust and lift
What was the lifestyle of Acanthodians?
Pelagic, ate plankton and participated in active pelagic predation
When were placoderms common and when did they go extinct?
Common 350 Ma
Extinct 250 Ma
What was the lifestyle of Placoderms?
Demersal, either benthic or pelagobenthic
Diverse range of prey
Features of Placoderms
Dorso-ventrally flattened
Trunk and head shields to suck up food and pump water over gills
Tooth plates rather than teeth, some sharp and some flat depending on diet
What species are Chondrichthyes?
Sharks, skates, rays and chimaeras
What does Chondrichthyes mean?
‘Cartilaginous fishes’
When did Chondrichthyes radiate?
300-400 Ma
How many extant species of Chondrichthyes are there?
750
What are the two common features of all Chondrichthyes?
Cartilaginous skeleton throughout their life
Placoid scales
