The 4 F’s of the

DEVONIAN

Fishes (ancient)

Fingers (tetrapod digits)

Forests (first trees)

Finished (extinctions)

495 mya

66 mya

120 mya

201 mya

252 mya

300 mya

365 mya

443 mya

Present Day

adapted from http://jan.ucc.nau.edu/rcb7/globaltext2.html

Jawless Fishes

• Hagfishes, lampreys

• Ostracoderms

– Heavily armored,

jawless, filter-feeding

Placoderms • Heavily armored

• Jawed Mouth

Gill slits Cranium

Skeletal rods

Chondrichthyes

• Cartilaginous fish: Sharks, rays

Mississippian sharks with crinoids

“True” Bony Fish

• Internal skeleton, fins, jaws

– good swimmers

Phylum Chordata Vertebrata

Cl Osteichthyes living ceolacanth

• Phylum Animalia

– Phylum chordata

• Subphylum vertebrata

– Superclass Tetrapoda

» Class Amphibia

» Class Reptilia (Sauropsida)

» (Class Aves)

» Class Mammalia

Class Amphibia

• Devonian to recent

• Frogs, toads, salamanders

• Characteristics

– Tetrapods

– Water needed for reproduction

– Ectothermic

– Gills and lungs

Why come out on land??

Dry period – need to find another water hole?

Why come out on land??

Predators – live in shallow water or on land to avoid large marine predators

Lungfish

• Heavy fins on underside

– can crawl

• Auxiliary lung

– can breath

• In Devonian, fossils are found in lakes and ponds

https://en.wikipedia.org/wiki/Tiktaalik

Hypothesized Sweet-Spot

https://en.wikipedia.org/wiki/Tiktaalik

365 mya

Tiktaalik

• Devonian

• Is a fish, not a tetrapod

• Fins present

– Bone structure similar to limbs

(digits)

• Skull transitions in the

direction of Amphibians and

Reptiles

Acanthostega • Late Devonian, Spitzbergen

• Found in lake and pond deposits

• True tetrapod, not a fish

• Large tail and rear limbs suggest lived in water

• If lived in water then evolution of tetrapods took place in water – Limbs were developed for life in

water

https://en.wikipedia.org/wiki/Tiktaalik

https://en.wikipedia.org/wiki/Tiktaalik