Gnathosomes (Jawed Fish) Flashcards
what does gnathostomes mean?
jawed fish
what are the general characteristics of gnathostomes
- paired fins
- second hox gene
- jaws with teeth
- joint gill arches
why were jaws developed?
- ## to increase gill ventilation
how were jaws developed?
1st viseral gill arch becomes the jaw
2nd arch becomes the hyoid arch
why did paired fins originate?
fish becomes more mobile and need a way to stabilize themselves
how did paired fins originate
2 theories
- fin fold theory; the unpaired dorsal fin was duplicated on the lateral ends of the fish and specific genes turned off and on in specific regions until the pectoral and pelvic fins
- gil arch theory: fins are homologous with gil rays and the girdles come from the gill arches
what does placoderm mean?
plated skin
what are placoderms jaws made from?
dermal bone called meckel’s cartilage
- it creates the supragnathal and infragnathal bones that act like teeth
what are the general characteristics of placoderms
- armoured jawed fish
- headsheild fused with thoracic sheild (made of dermal bone)
- the parts of vertebrae is ossified
- hinge at head and trunk junction
- very diverse group
what is special about placoderms
they are the first vertebrae to show evidence of internal fertilizaton (viviparity)
examples of placoderms
antiarchi: example of the bottom feeder of this group
- heavy armoured
- orbital bone made the ventral cutting surface
arthrodira
- large range
dunkleosteous
- large jaws capable of large suction
- bite force can go through dermal bone
-fast swimmer
what is a maxillae placoderm
they have tooth shapes bones as teeth
how do placoderms relate to the previous group
ostroderms
what makes Acanthodii an ambiguous group?
they have a similar body plan to sharks but have rhomboid scales that sharks don’t have (sharks have placid scales)
