Fish
Evolution
Part 2
* Fish were the first vertebrates
* Tunicates link the invertebrates and vertebrates
Tunicate
Anatomy
Water
Ganglion In
Gill
Bars
Water
Feces
Ova
Out
Heart
Water
To Exit
Gonads
Tunicate
Life
Cycle
Egg
Eye
Mouth Spot Nerve Free-Swimming
Cord
Larva
Notochord
Gill
Slits
Metamorphosis
Neotany
Egg
Egg
Fish Evolution
Amphioxus
Modern
Fish
Primitive Chordate
Via Neotany
Arm
Feeder
Ancestral
Gill Feeder Tunicate
Modern Tunicate
Amphioxus Fish Firsts
• Notochord
–Prevents “telescoping”
Amphioxus Notochords
Telescoped
Amphioxus
No
Notochord
Blue Muscle
Contraction
Swimming
Amphioxus
With Notochord
Amphioxus Fish Firsts
• Notochord
–Prevents “telescoping”
–Hanger for organs
Amphioxus Fish Firsts
• Notochord
–Prevents “telescoping”
–Hanger for organs
• Hollow nerve cord
Nerve Cord Evolution
Starfish: A simple network of nerves.
Earthworm: A
network of nerves
connected to
ganglia
Fish: Hollow nerve
cord (spinal cord)
and a brain
Amphioxus Fish Firsts
• Notochord
–Prevents “telescoping”
–Hanger for organs
• Hollow nerve cord
• W-shaped myotomes
W-Shaped
Myotomes
More Efficient Swimming
Amphioxus Overview
Neural
Tube
Notochord
Eye
Spot
Gills
Mouth
No Jaws
Fin-Like Flap
Junky Fins
Are they
Fish?
• Relict species very similar
to the first fish-like animal.
• Most important innovations
– Notochord
– Hollow nerve chord
– W-shaped myotomes
Ostracoderms
• 500-370 MYA
• Single nostril
• No paired fins
• No jaws
• Notochord and rudimentary
vertebrae
• Lungs!
• Armor for protection
Cephalaspids: Organs for hearing or electrical fields?
Drepanaspis
Cephalaspis
Logania
Logania
Logania
Ostracoderms
• 500-370 MYA
• Single nostril
• No paired fins
• Notochord and rudimentary
vertebrae
• Lungs!
• Armor for protection
• No jaws
Relict Species
Hagfish
Lamprey
Ostracoderms
Hagfish/Lamprey
• Single nostril
• No paired fins
• Notochord/vertebrae
• Lungs!
• Armor for protection
• No jaws
Relict Species
Hagfish
Lamprey
The Opposition
The Home Team
• No jaws for catching prey
• Primitive fin
arrangements
• Stiff
armored
bodies
Invertebrates !
Invertebrates
Stepped it up a
notch
Opponents got Tougher
Really Tough…
Parastylonorus
Modern Fish
Modern Inverts
Early Fish
• The neighborhood got
rougher!
• Most ostrachoderms were
out-competed
• Only those in specialized
niches survived
Lamprey, Hagfish, Ostracoderms
Jaws Evolved from Gill Arches
Dunkleosteus (placoderm)
Placoderms
• Ancestors of Sharks,
rays, chimeras
• 300-400 mya
• Jaws, paired fins, lungs,
gill arches
Relicts
Seven Gill Shark
Ratfish
Fancier
Jaws
There are many
relict shark, ray,
and chimera
species because…
• Jaws and teeth help make them
better able to hunt and defend
themselves, then and now
• Paired fins make them better
able to hunt and defend
themselves, then and now
• It worked 350 MYA and it still
works now!
Acanthodians
• 440 mya
• Bony skeleton, jaws, gills
• Paired fin evolution
Lobefins: Coelacanth
Acanthostega
Late Devonian (350 mya)
eight fingers and toes
Fish-like features
– Gill-bars like a fish
– No true elbows, knees, wrists or ankles (not weight-bearing)
– Long fin rays around the tail
Tetrapod-like features
–
–
–
–
–
–
Head not joined to shoulder girdle
Ear-bone (stapes) fits into fenestra (ovalis/vestibuli) in braincase
Large pelvic girdle, sacral rib
Femur as large as humerus
Tibia and fibula attached to ‘ankle’ bones
Digits on each limb
Major moments in
fish evolution
• Amphioxus, the un-missing link
– Hollow nerve cord
– Notochord
– W-shaped myotomes
• Ostrachoderms, the first true fish
• Placoderms and Acanthodians
– Jaws – Fancier and fancier
– Paired fins – Fancier and fancier
• Descendants of the lobefins conquer land
reptiles
Amphioxus
Bony
Fish Coelacanth
Shark
Ray
Hagfish
Lobefins
150 mya
Acanthodians
Placoderms
Bony skeleton
400 mya
Ostracoderms
Ancestral
Tunicate
(Neotany)
Notochord
Nerve Chord
Fins
Eyes
Armor
Lungs
Paired fins
Jaws
600 mya
•Neotany: What is it, how did it give rise to the
first primitive fish-like critter (Amphioxus)
•Amphioxus: What are the important fish-like
innovations (w-shaped myomeres, hollow
nerve cord, notochord)
•Ostracoderms: Characteristics and where they
fit in fish evolution
•Placoderms: Characteristics and where they
fit in fish evolution
•Acanthodians: Characteristics
and
where they fit in fish evolution
•Fish evolution slide