1. LECTURE 4: Paleozoic Era Silurian/Devonian Periods (439 mya- 360 mya)
Explain how,why, what life colonized land during the Silurian
Identify the oldest plant fossil- Cooksonia
Explain the evolution of plants
Describe the evolution of jaws
Describe the evolution of fishes
Explain how Sarcopterygians evolved into tetrapod ancestors
Describe why and how fish transitioned onto land
Identify the 1st Amphibian- Ichthyostega

2. To be an index fossil you must be:
Lived for a long time
Lived for a short time
Found in limited locations

3. What happened at the beginning of the Cambrian Period?
Mass extinction #1
Cambrian Explosion
Evolution of Eukaryotes
Evolution of Jaws

4. What evolved during the Cambrian-Ordovician?
Jawless Fish
Echinoderms
Arthropods
All of the Above

5. What caused the Mass Extinction at the end of the Ordovician?
Volcanic Eruptions
Global Cooling
Meteor

6. What Index Fossil appears at the Beginning of the Silurian?
Parakidograptus acuminatus
Extinct group: graptolite (hemichordate)

7. What Significant Events Happened during the Silurian and Devonian?
Life emerged from the water and colonized the land.
Plants (green algae evolved into bryophytes(non-vascularized), then tracheophytes(vascularized) and animals (insects)
KEY DEVELOPMENTS:
The development of vascular plants, pollen and seeds
provided plants with a way to reproduce and survive on dry land, creating new habitats
The development of jaws
allowed fishes and other emerging vertebrates to catch larger prey
The development of tetrapods—
limbed animals—would pave the way for animals that could walk on land

8. Why did Plants Move onto Land?
The ozone layer shielded life like water once did
Gave protection from the sun’s harmful radiation. Only water had provided this protection before
Soils had formed that could nourish plant life
Bacteria, algae, and fungi had gained an early foothold on land, secreting organic acids that broke rock down into its mineral elements. Nutrient-rich soils formed as these organisms died and their decaying matter combined with the minerals.
The next Plants to evolve were vascular plants

9. What Adaptations are Required for Land Plants?
Stand Upright (no support form water)
Tolerate UV radiation
Tolerate Climate Changes
Be able to acquire nutrients from substrate other than water
Produce gametes (seeds) that can move in the air

10. How did Plants Evolve? Green Algae Bryophytes (430 mya)
Non- vascular
Moist areas
Mosses/liverworts (spores)
Seedless Tracheophytes (420 mya)
Vascular
Ferns, horsetails (spores)
Seed Producing Tracheophytes (365 mya) (Gymnosperms)

11. First land plants (Bryophytes)likely similar to extant leafy liverworts…….

12. What is the Oldest Fossil Plants?
Cooksonia – 428 mya
Bryophyte
Small, few cm long
No leaves, roots horizontal stems with hairs connecting to soil

13. Bryophytes

14. How did Plants Evolve? Green Algae Bryophytes (430 mya)
Non- vascular
Moist areas
Mosses/liverworts (spores)
Seedless Tracheophytes (420 mya)
Vascular
Ferns, horsetails (spores)
Seed Producing Tracheophytes (365 mya) (Gymnosperms)

16. By the end of the Devonian:
Extensive forests (club moss and horse tail ancestors) with tall trees (Seedless Tracheophytes- Lycophytes)--FERNS
These plants later were out competed by seed plants and nearly all have gone extinct

17. Why did Jaws Evolve? The vertebrate jaw can be traced back to 440 mya
Most jawless fishes went extinct, but jawed fishes became the ancestors for most modern fishes today.
Jaws evolved from gill arches (Gnathostomes- jawed Fish)
From Jawless fish (Agnathas)
Helped fish catch food
Jaws allow mouths to open wide and catch larger prey
Jaws with teeth can bite, crush, and chew.
Protected by bony, overlapping plates, Placoderms were among the first fishes with jaws

18. http://www. mhhe. com/cgi-bin/netquiz_get. pl

19. Placoderm fish armored head Dunkleosteus terrelli Devonian ( million years ago) Cleveland, Ohio Stretching up to twenty feet long and sporting powerful jaws (no teeth) equipped with tooth-like plates, Dunkleosteus was one of the world’s first large vertebrate predators.

20. FISH GROUP KEY FEATURE Jawless Fish (agnathas) 500 mya
- no jaws - no paired fins - gave rise to placoderms, cartilaginous and bony fish
Placoderms – First Jawed Fish (Gnathostome)
439 mya
Jaws without teeth - Armored fish
Cartilage Skeleton
Paired fins
Cartilaginous (Chondrichthyes)
-sharks/rays
395 mya
Cartilage skeletons - no swim bladder - no lungs - internal fertilization
Jaws
Bony (Osteichthyes)
Actinopterygians (ray-finned)
Sarcopterygians (lobe-finned)
gills -Jaws
- lungs - swim bladder - some developed fleshy lobe fins (gave rise to amphibians)

24. When did Tetrapods Evolve?
Fish were the first animals to develop “feet” about 370 mya
Sarcopterygian fishes had muscular lobes at the bases of their paired fins. Within these lobes were large bones, one of which connected the rest of the fin bones to the body, like toes on a foot
Their fins were made for walking. Over time, some Sarcopterygian fishes may have begun using their muscular, lobed fins to "walk" in shallow, swampy waters, pushing their way through dense plant growth
Tetrapods branched out to include many familiar animals. From one type of Sarcopterygian fish evolved the first tetrapods:
vertebrates with four paired limbs and digits (fingers and toes)

25. What is a Coelacanth?
"living fossil" – only lobe-finned fish in existence
Evolved about 360 mya
paired lobe fins that extend away from its body like legs and move in an alternating pattern, like a trotting horse

26. What is the Evidence for Tetrapod Evolution?
Homologous Structures
The front fins of certain sarcopterygian fishes and the front limbs of tetrapods share the same bones: humerus, ulna, and radius.
The hind fins of certain sarcopterygian fishes and the hind limbs of tetrapods share the same bones: femur, tibia, and fibula.
Sarcopterygian fins are paddle-like, while tetrapod limbs have digits (fingers and toes) that grip the ground

27. Evolution of Tetrapods From Water to Land
Eusthenopteron: "Fish with Legs"
Panderichthys “Fish with Fingers”
Tiktaalik- 375 mya
Acanthostega- 365 mya
Ichthyostega – 360 mya

28. Eusthenopteron: "Fish with Legs"

29. Panderichthys (“Fish with Fingers”)

30. Tiktaalik- 375 mya Extinct Sarcopterygian
They may have begun using their muscular, lobed fins to "walk" in shallow, swampy waters, pushing their way through dense plant growth
Eventually they would move from shallow waters to land

31. Acanthostega- 365 mya First Fish with Digits (8 of them) on each limb
Probably Stayed in shallow waters
Limbs could not support weight

32. Ichthyostega – 360 mya First 4-legged land animal- Amphibian
Stayed near water

34. What were the Characteristics of Early Tetrapods?
It lived in the water and had a long, fishy tail
But its feet had 8 digits (more than any living tetrapod has today)

36. Hynerpeton

37. What Happened at the End of the Devonian Period (360 mya)?
Mass Extinction #2
Continental Movement
Continents had moved over the South Pole
Because of the pole’s year-round cold climate, snowfall accumulated on the continents, forming glaciers
The climate became too cold for many species
With much of Earth’s water frozen into glaciers, sea levels dropped. Lower sea levels would have robbed life of their habitat in the shallower oceans.

38. Who was Impacted by the Mass Extinction?
Up to 70% of all marine species may have died out
Reefs, and the life they supported, were devastated
Many species of corals, brachiopods, trilobites, and mollusks disappeared
The armored fishes—placoderms and ostracoderms—were completely wiped out

39. Sea Levels and Temp vs. Time

40. Explain how,why, what life colonized land during the Silurian
Identify the oldest plant fossil- Cooksonia
Explain the evolution of plants
Describe the evolution of jaws
Describe the evolution of fishes
Explain how Sarcopterygians evolved into tetrapod ancestors
Describe why and how fish transitioned onto land
Identify the 1st Amphibian- Ichthyostega