Vertebrate Origins Flashcards
What type of animal are Metazoans?
multicellular
What are non-vertebrate chordates?
free-swimming larval tunicates
either lancelet or amphioxus
What is the main characteristic of chordates?
contains a notochord - spinal rod consisting of collagen
What are the subphylums of chordates?
tunicata and urochordata
Define amphioxus
sharp at both ends
What are the types of non-vertebrate chordates?
- free-swimming larval tunicate
- sessile adult tunicate
- lancelet or amphioxus
Describe lancelet or amphioxus non-vertebrate chordates
- subphylum cephalochordata
- most basal members of phylum chordata
Describe the locomotion of lancelet chordates
- post-anal tail fin
- notochord elasticity allows myomere contraction
What is a notochord?
Elastic collagen rod running tip-to-tail
Protein triple-helix
Describe myomeres in lancelet chordate locomotion
Blocks separated by sliver of connective tissue
V and W shaped in more advanced
What is the physiology of respiration in lancelet chordates?
- cilia wafts water into mouth
- water flows into atrium
- contractile vessels pump blood instead of a heart
- water to atrium, out to atriopore
What is the physiology of food intake in lancelot chordates?
- mucus produced by endostyle traps particles in seawater
- gill slits in pharynx collect food
What is the physiology of the ‘head’ in lancelet chordates?
- notochord extends into head - no cranium
- nerve chord runs dorsal to notochord
- light-sensing structures
What are the two living jawless orders of the subphylum vertebrata?
- ‘Hagfish’ order
- ‘Lamprey’ order
Describe the ‘Hagfish’ order
- non-vertebrate craniates - ancestor vertebrate but lost in evolution
- likely 2 degree loss of ancestral vertebrae
- scavengers
- produce lots of slime
What does the vertebrae consist of in Lamprey order?
cartilage
Describe Ordovician jawless fish
- very early Astraspis
- externally armoured with many small bony plates
Describe early fish with exoskeleton of dermal bone
- dermal bone forms within the skin
- primitive fish only had cartilaginous endoskeleton
Describe Paleozoic jawless fish
- dermal bone
- carapace or scale coverings
- small mouths
What are Gnathostomes?
jawed vertebrates
Describe the evolution of jaws from anterior gill arches
- 1st and 2nd gill arches of agnathan ancestor develop into lower and upper jaw bones
- developmentory evidence from Gillis et al 2012 - similar expression of Dlx transcription factors - jaw and gill formation in vertebrate embryo
Describe placoderms and acanthodians
- paleozoic jawed fish
- did not outlast paleozoic
- lived alongside chrondrichthyes and osteichthyes
- half a dozen more fins
- evolved into tetrapods
