HOL Chapter Eight Leaving the Water The Origin of Land Plants 120

1. HOL Chapter Eight Leaving the Water The Origin of Land Plants 120 The Earliest Land Floras 122 Late Silurian and Early Devonian Plants 123 Later Devonian Plants 124 Devonian Plant Ecology 124 Comparing Plant and Animal Evolution 125 The First Land Animals 126 Rhipidistians 127 Air Breathing 129 Limbs & Feet: Why Become Amphibian? 132 Basking vs Reproduction The First Amphibians 135 138 …fin

2. PROBLEMS: LIFE IN AIR Less buoyant – need rigid support structures Drying / Evaporation – Surface to Volume Ratios Temperature extremes – Specific Heat Gasses [CO2 , O2] behave differently No Dissolved nutrients Refractive Index of air Sound transmission is weak ALL MAJOR ADAPTIONS TO AIR had to evolve in water before entering the land. ADAPTIONS [favoring air] MUST BE FOR LIFE IN WATER. Same food sources may not come out with animal – suggests – a change in food type and feeding style.

3. ORIGIN OF LAND PLANTS 120 No evidence for first Land Plants Must have been aquatic / swamp / marsh

4. Waterproofing • Roots as props / anchors OR AS Gathering water / nutrients. • Internal Transport Systems – water / nutrients. • Cross fertilization • Dispersal • xx ORIGIN OF LAND PLANTS 120 Major Characters of Land Plants are solutions to life in AIR. Gravity  structural or hydrostatic supports. -- Cuticle or wood

5. SCENARIO for EVOLUTION OF LAND PLANTS 0. Begin with water dwelling plants -- Green Algae -- multicellular. Cells act independantly of each other. HABITAT SUBLECT TO DRYING. Faster growing parts need more nutrients Transport System solves distribution. Drying habitat  wind spores distribute to new water.  spores form on uppermost part of plant. Extending up into air  increases light energy – photosynthesis  increases CO2 [less dissolved in water]. Air parts need water due to evaporation loss  upward transport – water  downward transports – nutrients. evaporation loss.

6. Developments: Conducting strands  water transport Cuticle  waterproofing,  water shedding for CO2 interface  strengthening Stomata limits water intake gas exchange w/ guard cells Roots absorb water Xylem elongated dead cells pipe water up by evaporation / capillary action [passive]

7. Xylem Phloem and Xylem Plant cells with xylem are Vascular Plants Xylem – dead cells – passive transport Evaporative pressures collapse weal cells Lignin structural protein strengthens tube Later used to stiffen stem

8. Phloem Phloem and Xylem Transports nutrients down Cell to cell transport of green algae Transports photosynthates to non photosynth parts – roots stem. Marine plants restricted to photic zone. Extending into air gives light Energy & breeze [spores]

9. The Earliest Land Plants Ordovician spores in fossil record Land flora established br Late Silurian Aglaophyton typifies Silurian plant life 20 cm, cuticle,stomata, intercellular gas spaces No xylem

10. The Earliest Land Plants Cooksonia first Vascular plant Devonian Branching stems tipped by Sporangia Xylem?, Stomata Devonian plants more diverse

11. Devonian plants more diverse One meter tall Budding Rhyzomes – tufting gives mutual support. Rhynia – a vascular plant

12. Horsetail Rushplant survey

13. Mossesplant survey

14. plant survey Alternation of Generations in Moss

15. plant survey

16. plant survey Fern Life Cycle

17. plant survey • Fern Sporangium launches spores

18. plant survey CnidariaLife Cycle

19. plant survey Fungi Life Cycle

20. plant survey Angiosperm Life Cycle

21. plant survey Horsetail “Fern” Equisetum

22. Later Devonian Plants pg 124 Devonian Plant Ecology pg 124 Comparing Plant and Animal Evolution 125

23. The First Land Animals --- Late Silurian Arthropods waterproof exoskeleton Very strong for size Sturdy walking legs Organic debris washed on to shores Damp for respiration Cover for UVV protection Nutritious

24. Late Silurian evidence ? footprints -- Trackways Spiders, centipedes, mites 3-D nature of plants  climbing arthropods  flight Larger Arthropods 6 inches

25. Moving into Air – ROUTES Estuary, delta mudflat Abundant food Salinity gradient gradual

26. Rhipidistianspg 127 Invasion of air by plants cause increase in nutrients around shorelines. Lobe Fins hunting shorelines – Late Devonian LivivgCoelocanthfin beat pattern same as tetrapod walking pattern -- diagonal syncro

27. Rhipidistianspg 128 Skull joint allows lifting upper jaw. Feeding in shallows More water respiration thru gape. Sprint over mudbanks – “land” Radiate into freshwater along with plants onto land.

28. Rhipidistians Acanthostegagunnari

29. Why Air Breathing? Rhipidistians Late Devonian Evolved nostrils and choana (internal air passage). Rhipidistians and Lungfish evolve lungs independently. CO2 disolves forming Carbonic Acid – dangerous Lungs allow diffusion of CO2 to lower buildup. O2 diffusion is secondary.

30. Oxygen Intake Easier to extract O2 from air Air 20% Oxygen Water 3% Oxygen lowering with higher temperatures. FACT --Water Breathers pump water over gills TEN TIMES faster than blood thru body. ISSUE –Gills must resist Loss of Body Salts into water. Tissues must be thicker than for air interface. ISSUES O2 diffuses 100,00 X faster in air then in water. Warm rotting debris depletes O2. Currents necessary to mix O2 in water. Bacteria attacking debris produce toxins.

31. Oxygen intake (cont’d) Tropical fish gulp top millimeter of surface diffused with O2 from air. Gulping air increases buoyancy holding fish at surface. Extract O2 from gulped air in mouth. Rhythmic air breathing. Gulping air and expelling CO2. Storing O2 in Air bubble. Air bubble of 5% body volume increases Oxygen storage TEN TIMES compared to no air bubble. Actually causes loss of O2 thru gills Fish reduce gill breathing in O2 poor waters.

32. Shedding Carbon Dioxide page 131 CO2 disolves readily into Saltwater (SW) DIFFICULT to lose CO2 (diffusion) by air bubble in mouth. Carbonic Acid forms in wet mouth. TWO ALTERNATIVES Lose CO2 thru skin (Amphibians) Rapid Breathing quickly loses air bubble before getting too acidic. Early Amphibians were LARGE (small surface) and SCALEY (bad diffusion). Rapid Breathing makes sense

33. Limbs and Feet – Why Become Amphibian page 132 Old Idea : To find a better pool. New Idea : Basking for Warmth Warmth increases digestion therefore growth rate Allowing larger and earlier maturity == multiplication. Gravity collapses lungs – FINS support weight. TODAY fish / amphibians / reptiles / mammals BASK WHILE THEY DIGGEST.

34. Leaving the Water for REPRODUCTION pg 133 Security for spawning Fewer predators in back waters. Salmon spawn up stream. Isolated warm ponds produce invertebrates/ insects Food for young Iguanas separate juvenile and adult habitats.

35. Eusthenopteron -- tetrapod ancester Similar skull bones. Pattern in fin bones 1 – 2 – several – many. Geographic distribution matches fossil amphibians.

36. Eusthenopteron

37. Comparason of Fin -- Limb progression

38. Rhipidistian Locomotion pg 134 Stronger fins at edges. Fins – passive pivots for undulating body. Increased traction encourages fewer rays to become few toes. Pectoral fins support thorax. Pelvic fins push body forward. Hinge joint at knee. Rotation joint at ankle Elbows flex backward. Knees flex forward. Girdles link fin pairs to backbone.