Fish Evolution

Part 2

Fish Evolution

Part 2

* Fish were the first vertebrates* Tunicates link the invertebrates and vertebrates

TunicateAnatomy

WaterIn

WaterFecesOvaOut

Ganglion

GillBars

HeartWaterTo Exit

Gonads

Tunicate Life

Cycle

MouthEyeSpot Nerve

Cord

Notochord

GillSlits

Egg

Free-SwimmingLarva

Metamorphosis

Neotany

Egg

Egg

Arm Feeder Gill Feeder

AncestralTunicate Modern Tunicate

AmphioxusModernFish

Primitive ChordateVia Neotany

Fish Evolution

Amphioxus Fish FirstsAmphioxus Fish FirstsAmphioxus Fish FirstsAmphioxus Fish Firsts

• Notochord–Prevents “telescoping”

• Notochord–Prevents “telescoping”

Amphioxus Notochords

No Notochord

With Notochord

Blue MuscleContraction

TelescopedAmphioxus

SwimmingAmphioxus

Amphioxus Fish FirstsAmphioxus Fish FirstsAmphioxus Fish FirstsAmphioxus Fish Firsts

• Notochord–Prevents “telescoping”

–Hanger for organs

• Notochord–Prevents “telescoping”

–Hanger for organs

Notochord

Amphioxus Fish FirstsAmphioxus Fish FirstsAmphioxus Fish FirstsAmphioxus Fish Firsts

• Notochord–Prevents “telescoping”

–Hanger for organs

• Hollow nerve cord

• 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 FirstsAmphioxus Fish FirstsAmphioxus Fish FirstsAmphioxus Fish Firsts

• Notochord–Prevents “telescoping”

–Hanger for organs

• Hollow nerve cord

• W-shaped myotomes

• Notochord–Prevents “telescoping”

–Hanger for organs

• Hollow nerve cord

• W-shaped myotomes

W-Shaped Myotomes

More Efficient Swimming

Amphioxus Overview

MouthGills

Fin-Like Flap

EyeSpot

NotochordNeuralTube

No JawsJunky Fins

Are they Are they Fish?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 SpeciesHagfish

Lamprey

Ostracoderms Hagfish/Lamprey

•Single nostril•No paired fins•Notochord/vertebrae •Lungs!•Armor for protection•No jaws

Relict SpeciesHagfish

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

Early Fish

Modern Inverts

•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

RelictsSeven 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

AcanthostegAcanthostegaa

Late Devonian (350 Late Devonian (350 mya)mya)

eight fingers and toeseight fingers and toesFish-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

Ancestral

Tunicate

Amphioxus

Ostracoderms

Placoderms

Acanthodians

Lobefins

reptiles

(Neotany)

HagfishShark

Ray

Bony

Fish Coelacanth

600 mya

400 mya

150 mya

Notochord

Nerve Chord

Fins

Eyes

Armor

Lungs

Paired fins

Jaws

Bony skeleton

•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