The arrival of jaws Flashcards
What are Gnathostomata?
A living superclass of Craniata
What are 2 ancestors of gnathostomes?
– Thelodonts
– Osteostracomorphs?
What are features of Thelodonts?
- Stomachs, unlike extant agnathans
– Scales like teeth and modern shark placoid scales
– Broad based pectoral fins
What are features of Osteostracomorphs?
– Ossified bones around eye
– Cellular bone
– Slit shaped gill openings
– Paired fin structure
– 2 dorsal fins
– Epicercal tail
What is a Heterocercal tail?
A caudal fin composed of two asymmetrical lobes.
What is a hypocercal tail?
A tail in which the lower lobe is more pronounced or larger than the upper lobe.
––– Anaspida
What is a epicercal tail?
Tail fin in which the the caudal part of the notochord tapers posterodorsally.
–– e.g. Osteostracomorphi
What is the order of taxonomic levels?
- Phylum
- Subphylum
– Superclass
– Grade
– Class
– Subclass
– Infraclass
– Division
– Subdivison
– Superorder
How many classes of Gnathostomata are there?
5
What are the living classes of Gnathostomata?
- Chondrichthyes
– Sarcopterygii
– Actinopterygii
What are the extinct classes of Gnathostomata?
– Placodermi
– Acanthodii
What are features of the class Platodermi? X
– Bony, ornamented plates over 30-50% of body
- Big jaws, teeth and large gape: “craniovertebral joint”
- Quite diverse (200 genera)
– Dunkleosteus: 1m x 6m or larger
– Antiarchs: pectoral fins enclosed in bone-like arms
What are limitations of Placodermi?
- No replacement dentition
– Jaw could not generate suction forces
What are the defining features of the class Chondrichthyes?
- Prismatic calcification of endoskeletal cartilage
– Pelvic claspers
– Specialised as marine predators
– dominated ancient seaso
How many living species of Chondrichthyes are there?
970
What are the defining features of the class Acanthodii? X
“spiny sharks”
- Small and stour
- Bony spines before all fins
– Cartilaginous skeleton
– Covered in small scales
– large head and eyes
– Water column feeders: streamlined, round bodies, reduced armour
What are the key features of the class Sarcopterygii?
– Fleshy, lobed fins
– Enamelled teeth
– Cosmic scales
How many extant Sarcopterygii are there?
– Only 8 extant fishes
– 26, 742 extant species
What are examples of Sarcopterygii?
Australian lungfish, West Indian Ocean Coelacanth
How many living species of Actinopterygii are there?
26, 891
What are features of Actinopterygii?
– monophyletic but no strong defined characters
– scales: ganoid, cycloid, ctenoid or absent
– spiracle absent
– Gular plate absent
What are ganoid scales?
Hard and bony with a shiny surface that resembles enamel.
Actinopterygians
What are Placoid scales?
Toothlike, being made of dentine with a pointed backward projection of enamel, as in sharks and rays.
What are cosmic scales?
A fish scale is a small rigid plate that grows out of the skin of a fish. The skin of most jawed fishes is covered with these protective scales
What are cycloid scales?
Round and flexible structures which are present on the surface of bony fishes.
E.g. Actinopterygians – Trout, herring, carp
What are ctenoid scales?
Similar to cycloid, except that they have spines or comblike teeth along their free edges; these scales are characteristic of the higher bony fishes—perches and sunfishes, for example.
