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Where do vertebrates come from? From whom? When? How do we know?
- vertebrate origins from early cambrian
- Myllokunmingia and Haikuichthyes (China)
- -pharyngeal gill pouches
- -v shaped myomeres
- -notochord, heart, broad gut
- -dorsal and ventrolateral fins
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How does body shape affect swimming ability?
- water passes differently around different shapes
- Disk with hard edges creates great resistance, resistance creates turbulence
- Laminar flow=more efficient; less turbulent flow, easier swimming
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"Age of Fishes"
Devonian 417-354mya
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earliest fish fossils
- Ordovician and Silurian 443-417mya
- heavily armored
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Bony fish groups
(paraphyletic) Osteichthyans and Sarcopterygians
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Cartilagionous fishes
Chondrichtyans
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Bone
- Minearal and proein components
- hexagonal apatite crystals plus collagen fibers
- living tissue
- can be remodeled throughout life
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osteocytes
control bone formation
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Exoskeleton
external; armor plates
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Endoskeleton
provides internal body support
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Dentine
few encapsulated cells, inner parts of teeth, narrow dentine tubules, cannot be remodeled
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Enamel
crystalline apatite without collagen, cannot be remodeled
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Agnatha
- no jaws; paraphyletic
- Cambrian-Devonian +present
- living lampreys and hagfishes
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Legendrelepis
lings fossils to lampreys
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conodonts
- earliest vertebrates with hard tissues--more derived than lampreys
- Late Cambrain
- Dermal armor isolated bits, apatite scales
- bone evolved after the origin of vertebrates
- same composition as bone and scales
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Pikaea
- earliest fossils--Cambrian Burgess Shale
- middle Cambrian 540mya
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Jamoytius
- most closely related to lampreys
- Anaspid from Silurian of ScotlandLacked bony armorProbably lived lifestyle similar to that of lampreys
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Astrapisids
Ordovician jawless fishes
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Arandapsid
- Australian early fish
- 20cm long
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sacabambilla
- ostracoderm from Bolivia
- head covered with bony plates making a solid unit
- body covered by long chevrons, allowing flexibility
- under 30cm long
- named after local town Sacabambilla
- late Ordovician age 450mya
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Heterostracans
- (Pteraspidimorphi) Silurian and early Devonian
- head shields of many shapes
- Single opening on each side for all gills
- broad ornamented dorsal plate
- one or more side plates
- large ventral plate
- Grouped with Astrapsida and Arandaspidia because of shared aspidin on dermal armor
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Drepanaspis
- Early Devonian (4000mya) heterostracan
- Dorsoventrally flattened
- lived on sea floor
- no paired fins
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Athenaegis
Silurian heterostracan - NW Territories, Canada - 5cm long
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Liliaspis
- early devonian heterostracan of Russia
- Dubular mouths to suck up small prey from sea floor
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Anglaspis
Cyathaspid, early Devonian of England
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major events in fish evolution
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Thelodonts
- Marine, worldwide distribution
- Lived late Ordovician - late Devonian
- Flexible bodies, swam sharklike with small scales
- Paired pectoral, dorsal and anal fins
- Oldest from US and Siberia
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Osteostracans
- Massive head shields 9as do Galeaspids and Pituriaspida) heavy armor
- 300 species known
- Ordovician to late Silurian/early Devonian
- Paired fins covered with small scales
- many different head shield shapes
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Hemicyclaspis
- Osteostracan (typical)
- Lived in fresh water
- 400mya
- 20cm long
- Paired pectoral fins
- Dorsal fin
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Zenaspis
early devonian of Wales
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