Origin of vertebrates Flashcards
big gap btw:
rise of deteurostome and first appearance of chordates
earliest chordate fossils:
530mya
clues found about precursors to chordates by:
- comparing basal modern chordates w sister taxa
current understanding of life: MBNDCAmOl
Metazoa Bilateria Nephrozoa Deuterostomia Chordata Ambulacraria Olfactores
metazoa:
multicellular animals
bilateria:
bilateral symmetry at some point of life cycle
nephrozoa (or coelomta):
incl. deuterostomes and protostomes
deuterostomes:
chordates and ambulacraria
common features: metazoans
- whip-like tails on sperm
- embryo forms hollow ball of cells (blastula)
- sex cells formed in special organs
- collegen is structural protein
common features: animals more complicated than sponges (and eg.)
- 2 distinct cell layers: endo/ectoderm
- eg. cnidarians like jellyfish and coral have these 2 layers
common features: bilataria
- developed 3rd middle layer: mesoderm which forms body mm
- bilaterally symmetrical, gut open at both ends
- head at one end (w mouth)
common features: coelom
- inner body cavity
- those w coelom part of Coelomata
coelom divides into:
- protostomes
- deuterostomes
key differences btw protostomes and deuterostomes seen in:
early dev
body plan: first stages and diff btw protostomes and deuterostomes
- fertilisation egg -> zygote
- zygote divides via cleavage into smaller cells (blastomeres)
- bilateral animals have 2 types of cleavage:
spiral: protostomes
radial: deuterostomes
body plan: protostomes cleavage features
- spiral cleavage
- cells divide to give quartet
- tightly packed
- mosaic dev
- offset cells
- highly predetermined cells, damage = defective organism
body plan: deuterostomes cleavage features
- radial cleavage
- symmetrical cleaving planes, aligned cells
- tiered cells
- regulative dev
- daughter cells omnipotent (determination occurs later in dev)
protostomes: eg
- mollusc
- annelids
- arthropods
deuterostomes: eg
- echinoderms
- hemichordates
- chordates
body plan: coelum formation protostomes
- mesoderm forms band of tissue around blastophore, migrates inward and splits into 2
body plan: coelum formation deuterostomes
- mesoderm forms as pocket from gut which pinches off eventually
body plan: blastophore protostomes
- eventually becomes mouth and pushes through to future anus
body plan: blastophore deuterostomes
- eventually becomes anus to meet mouth
deuterostomes: comprised of (6)
- verterbrates
- cephalochordates
- urochordates
- hemichordates
- echinoderms
- xenoterbellids
ambulacraria: comprised of (3)
- from deuterostomes
- hemichordates
- echinoderm
- xenoterbellid
ambulacraria: hemichordates eg.
- pterobranchs
- acorn worms
ambulacraria: hemichordates general features
- fern-like wormy creatures
- burrow into sediment/ float in water column to settle in new places
- was thought sis group to chordates, pharyngeal slits and endostyle (all deurostomes have these features)
ambulacraria: echinoderm general features and eg.
- larval characteristics fit
- extant species no pharyngeal slits, fossil evidence some did
- larvae bilaterally symmetrical and ancient adult echinoderms
eg. starfish
ambulacraria: xenoterbellid general features and eg.
- worm-like, only 2 species
- recently added, due to molecular analysis is related to hemichordate and echinoderm
chordates: comprised of
- from deuterostomes
- cephalochordates
- urochordates
- vertebrates
chordates: cephalochordates general features and eg.
- aka lancelets and eg. amphixious
- sml fish-like capable of swimming, majority buried in marine sediments
chordates: urochordates general features and eg.
- incl. acidians and sea squirts
- sedentary filter feeders
- brief free-swimming larval phase
- larval phase places them in chordata
chordate characteristics: list (5)
- notochord
- muscular, postanal tail
- pharyngeal slits
- endostyle
- brain, dorsal nn. cord
MUST be apparent at some point of lifecycle (eg. tunicates- larval stage)
chordate characteristics: notochord
- rod like
- flexible, stiff: hydrostatic organ
- extends length of body
- first structure of endoskeleton to appear in embryo
- reduced to cartilaginous disks (nucleus pulposus) in organisms w vertebrate
chordate characteristics: muscular postanal tail
- stiffened notochord w mm. provided motility for early chordates
- evolved propulsion in water
- many fish expanded to incl caudal tail= increase propulsion
chordate characteristics: pharyngeal slits
- pharynx digestive tract immediately post to mouth
- pharynx pierces at dev stage
- role in suspension feeding for primitive chordates (pharyngeal basket)
- helped in respiration ie. fish gills -> structures of pharyngeal slits and arches become ear, neck, jaw parts
chordate characteristics: endostyle
- mucus centre: help w transport of food items to gut
- present in protochordates and lamprey larvae
- sequesters iodine
- later becomes thyroid gland
chordate characteristics: dorsal nn cord
- beginning of CNS, formed through invagination of ectoderm
- dorsal to digestive tract
- hollow
- ant end (bulges) extends from brain
- passes through neural arches of vert in vertebrates
- brain highly dev and protected by cranium
list basals and eg.
- cephalochordates (lancelets)
- urochordates (tunicates)
urochordata: features
- marine, filter feeders (sedentary)
- 2000 extant species
- larvae have chordate characteristics
- acidians
urochordata: eg.
- acidians
- sea squirts
- cunjevoi
- sea pork
urochordata: filter system
- siphon water
- suck thorugh incurrent siphon - food filtered in basket-like pharynx (in atrium) - water passes out excurrent siphone
- food particles trapped pass into oesophagus, digested in stomach and waste passes out anus
urochordata: chordate characterstics
- found in only free swimming larvae (100 free living species)
- notochord, dorsal nn chord, postanal tail
Garstang hypothesis:
- ancestral vert derived from larvae sedentary adult stage
- we now think ascidian sedentary adult stage is derived character and ancestral chordate most likely free-swimming filter feeder
cephalochordata: features
- small eel-like animals
- 30 species
- most species burrow in sediment as adults
- share lot of characteristics w ascidians (urochordates) esp feeding apparatus
cephalochordata: eg.
- lancelet
- amphioxus
cephalochordata: shared characteristics w vert
- notochord
- dorsal tubular nn chord
- postanal tail
- segmented mm blocks along flanks
- similar circulatory sys
cephalochordata: characteristic differences
- asymmetrical dev
- nn chord does not enlarge into brain
- notochord elongated for burrowing
- pharyngeal slits not as gills -> filter feed
- atrium assoc w filter feeding
- mm layered as myomeres (like fish)
vertebrata/ craniata: general features
- protects nn cord
- early in dev replaces notochord completely (IVD only remnants)
- defined skull to protect well dev brain
- obvious head w lots sensory sys
vertebrata/ craniata: embryonic features
- duplication Hox genes
- appearance of neural crest cells, placodes
- multiplication of microRNAs
conservation of dev genes: controlled by
- HOX gene complex
- cell dev and differentiation
- innovation arrived from duplication of entire HOX gene complex
conservation of dev genes: 1 copy
- urochordates
- cephalochordates
conservation of dev genes: 2 copies
- agnathans
conservation of dev genes: 4 copies
- gnathostomes (all jawed vert)
conservation of dev genes: 8+ copies
- teleosts
- reason for domination of teleost fishes today
neural crest: features
- 4th germ layer
- ## responsible for novel vert structures esp around head
placodes: features
- similar to neural crest cells, diff og
- also migrate out give rise to complex sensory organs (nose, eyes, inner ear)
- lateral line and cranial nn
microRNA: features
- regulate synthesis of proteins
- chordates have 2 new microRNA
- vert share further 3
- all vert share additional 41
- each vert lineage has evolved set of microRNA
brains: general features and eg. amphioxus
- 3 principal areas: fore/mid/hindbrain
- less well dev brain, lack genes to form forebrain
- gene expression largely responsible for evolutionary innovations
