Review, 1st Paleozoic Vertebrate lecture

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Review, 1st Paleozoic Vertebrate lecture

• At one point in their lives, all chordates have
• Notochord
• Dorsal hollow nerve cord
• Gill/phyrangeal slits
• Tail
• First vertebrates were marine fish without jaws
• Ostracoderms
• Devonian Age of Fish

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Evolution in the Devonian

• Evolution of jaws was a big deal
• Extended ecological web/opened new ecological
  niches
• Ray Finned Fish and Lobe Finned fish
• Lobe fins -gt lungfish, crossopterigians (both
  have protolungs)
• Crossopterygians -gt amphibians
• First creatures on land were Arthropods (early
  Devonian)

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AmphibiansVertebrates Invade the Land

• Although amphibians were the first vertebrates to
  live on land, they were not the first land-living
  organisms
• Land plants, which probably evolved from green
  algae, first evolved during the Ordovician
• Furthermore, insects, millipedes, spiders, and
  snails invaded the land before amphibians

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Oldest Amphibians

• The oldest amphibian fossils Ichthyostega
• found in the Devonian of eastern Greenland
• streamlined bodies, long tails, and fins
• four legs, a strong backbone, a rib cage, and
• pelvic and pectoral girdle
• Precursor organism (Acanthostega)
• Was adapted to movement in
• Wet boggy environments

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Rapid Adaptive Radiation

• Like other groups that moved into previously
  unoccupied niches
• amphibians underwent rapid adaptive radiation
• became abundant during the Carboniferous and
  Early Permian
• Little resemblance to modern amphibians
• Much more diverse

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Carboniferous Coal Swamp

• Reconstruction of a Carboniferous coal swamp

The serpentlike Dolichosoma
Large labyrinthodont amphibian Eryops
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Transition from Water to Land

• In passing from water to land, plants and animals
  had to solve the same basic problem
• the method of reproduction was the major barrier
  to expansion into the various terrestrial
  environments
• required evolution of the seed in plants and the
  amniote egg in animals

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Evolution of the Reptiles the Land is Conquered

• Amphibians limited in colonizing the land
• had to return to water to lay their gelatinous
  eggs
• Evolution of the amniote egg freed reptiles from
  this constraint

http//www.geoclassics.com/mesosour.htm
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Amniote Egg

• In an amniote egg
• the embryo is surrounded by a liquid sac, the
  amnion cavity
• provided with a food source (yolk sac) and waste
  sac
• Its evolution freed reptiles to inhabit all parts
  of the land

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Able to Colonize All Parts of the Land

• In this way the emerging reptile is
• in essence a miniature adult
• bypassing the need for a larval stage in the
  water
• The evolution of the amniote egg allowed
  vertebrates
• to colonize all parts of the land
• no longer had to return to the water as part of
  their reproductive cycle

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One of the Oldest Known Reptiles

• Reconstruction and skeleton of Hylonomus lyelli
  from the Pennsylvanian Period

• Hylonomus lyelli was about 30 cm long

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Paleozoic Reptile Evolution

• Evolutionary relationship among the Paleozoic
  reptiles

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Pelycosaurs (Finback Reptiles)

• Most pelycosaurs have a characteristic sail on
  their back
• Sail explanations display, thermoregulation
• Odd not closely related neither had sailed
  predecessor
• Adaptive escalation?

The herbivore Edaphosaurus
The carnivore Dimetrodon
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TherapsidsMammal-like Reptiles

• The pelycosaurs became extinct during the Permian
  
• and were succeeded by the therapsids
• that evolved from the carnivorous pelycosaur
  lineage
• and rapidly diversified into
• herbivorous
• and carnivorous lineages

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Therapsids

• A Late Permian scene in southern Africa showing
  various therapsids

• Many paleontologists think therapsids were
  endothermic
• and may have had a covering of fur

Moschops
Dicynodon
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Therapsid Characteristics

• Therapsids were small- to medium-sized animals
• displaying the beginnings of many mammalian
  features
• Many paleontologists think therapsids were
  endothermic
• or warm-blooded
• enabling them to maintain a constant internal
  body temperature
• allowing them to expand into a variety of
  habitats

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How are we related to them anyway?

• Relationships among Amniota are tracked via
  fenestrae, or openings in the head.
• Fenestrae
• Make the head lighter
• Anchor points for muscles

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Fenestrae in the descendents of proterothyrids
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Summary

• Fish
• First appeared in the Cambrian (jawless fish
  first vertebrate)
• Diversified in Devonian (Age of Fish)
• Amphibians
• First appeared in the Devonian
• Evolved from lobe-finned fish
• Reptiles
• First appeared in Pennsylvanian
• Did not need to return to water to reproduce

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Plant Evolution

• Evolution of photosynthesis Archaean
  cyanobacteria
• Genetic evidence suggests that plants evolved
  from green algae
• No Cambrian explosion for plants
• Many steps needed to move plants onto the land

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Buoyancy and humidity

• How to keep your guts wet in a dry world?
• Cutin exterior plant waxes protect from
  dessication
• How to stay upright when youre not buoyant in
  air?
• Cellulose and lignin rigid polymers that make
  cells strong
• How to grow bigger than a few centimeters in a
  dry world?
• Develop the ability to move fluids from soils to
  leaves

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Earliest Land Plant

• Earliest plants did not produce seeds
• The sedimentary rocks in which these plant
  fossils are found
• indicate that they lived in low, wet, marshy,
  freshwater environments

• The earliest known fertile land plant was
  Cooksonia
• seen in this fossil from the Upper Silurian of
  South Wales

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Vascular plants

• Vascular system
• network of tubes which distribute nutrients and
  remove wastes
• Not clear if Cooksonia was truly vascular
• First definitive vascular plant ferns

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Plant Evolution

• Major events in the evolution of land plants
• The Devonian Period was a time of rapid evolution
  for the land plants

• the appearance of leaves

• and emergence of seeds

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Early Devonian Plants

• Reconstruction of an Early Devonian landscape

• showing some of the earliest land plants

Protolepidodendron
Dawsonites
Bucheria
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Early and Late Devonian Plants

• Early Devonian
• relatively small
• low-growing
• bog-dwelling types of plants
• Late Devonian
• tree-size plants up to 10 m tall

• Chaleuria cirrosa

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Evolution of Seeds

• The evolution of the seed during the Late
  Devonian
• liberated land plants from their dependence on
  moist conditions
• and allowed them to spread over all parts of the
  land
• In the seed method of reproduction
• the spores are not released to the environment
• but are retained on the spore-bearing plant
• where they grow into the male and female forms

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Gymnosperms

• In the case of the gymnosperms
• or flowerless seed plants
• male cone produces pollen
• egg is contained in the female cone
• After fertilization
• seed develops into a mature, cone-bearing plant
• Seed plants
• like reptiles
• were no longer restricted to wet areas
• but were free to migrate into previously
  unoccupied dry environments

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Late Carboniferous and Permian Floras

• Rocks of the Pennsylvanian Period are the major
  source of the world's coal
• The geologic and geographic conditions of the
  Pennsylvanian
• ideal for the growth of seedless vascular plants
• these coal swamps had a very diverse flora

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Pennsylvanian Coal Swamp

• Reconstruction of a Pennsylvanian coal swamp with
  its characteristic vegetation

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Glossopteris

• An important non-swamp dweller was Glossopteris,
  the famous plant so abundant in Gondwana (a seed
  fern)
• Great resource for paleobiogeographers

http//www.lowcountrygeologic.com/plants/gloss1.ht
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