Chapter 13 Paleozoic Vertebrates

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Chapter 13 Paleozoic Vertebrates Plants

• From the Sea to the Land, the development of
  Vertebrates, Insects, and Plants.
• First evidence of Chordates, organisms with a
  notochord, a dorsal hollow nerve cord,and gill
  slits Early Cambrian - Found in 525 m.y. old
  rocks in Yunnan province, China Chengjiang
  Fauna. (See slide 3). Also Pikaia Burgess
  Shale Fauna British Columbia.
• Earliest fish remains are found in Late Cambrian
  rocks. All known Cambrian and Ordovician fossil
  fish have been found in shallow nearshore marine
  deposits.

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Yunnanozoon lividum is one of the oldest known
chordates Found in 525 Myr old rocks in Yunnan
province, China 5 cm (2 inches) long
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• A fragment of a plate from Anatolepis (A
  primitive member of the class Agnatha (jawless
  fish)), one of the oldest known fish from the
  Late Cambrian Deadwood Fm. of Wyoming.

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• The oldest fossil remains of nonmarine fish are
  from the Silurian Period, evidence that fish
  originated in the oceans.
• The oldest and most primitive of the class
  Agnatha are the ostracoderms (bony skin).
• These are armored jawless fish that first evolved
  during the Late Cambrian reached their zenith
  during the Silurian and Devonian and then became
  extinct.
• The majority of ostracoderms lived on the
  seafloor, probably browsing through the bottom
  sediment for small bits of food.

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Geologic Ranges of Major Fish Groups
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The Devonian Period - the Age of the Fish, all
major fish groups present during this time.
an acanthodian (Parexus)
a ray-finned fish (Cheirolepis)

• a placoderm (Bothriolepis)

an ostracoderm (Hemicyclaspis)
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• The evolution of jaws was a major evolutionary
• advantage among primitive vertebrates.
• Jawless ancestors could only feed on detritus,
• jawed fish could chew food and become active
• predators opening new ecological niches.
• The vertebrate jaw is an excellent example of
• evolutionary opportunism
• Movable jaw evolution of the first three gill
  arches.
• Movable jaw may have likely initially provided
  for
• more oxygen movement through gills.

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• First jawed fish Early Silurian rocks belong to
  the acanthodians, a group of enigmatic fish
  charac-terized by large spines, scales covering
  much of the body, jaws, teeth, and reduced body
  armor. May have included ancestors of bony and
  cartilaginous fish groups. The acanthodians were
  most abundant during the Devonian.
• Late Silurian jawed fish also included the
  placoderms (armored, plate-skinned) present in
  both fresh water and marine sediments. Example
  Late Devonian Dunkleosteus, 12 meters long,
  armored head, shoulders, jaw with razor sharp
  teeth, flexible tail largest known fish of its
  time.

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• Class Chrondrichthyes cartilaginous fish
  (sharks, rays, skates) Class Osteichthyes
  bony fishes (bass, trout, etc.) appeared during
  the Middle Devonian.
• Bony fishes include ray-finned (above) and
  lobe-finned (below). Muscles of lobe-fined
  extend into fins more flexibility. Lobe-fined
  fish include lungfish and crossopterygians.

Modern lungfish are found in S. America, Africa,
and Australia
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• Development of lungs allowed fish to burrow into
  mud and survive seasonal and drought period
  drying of ponds and lakes greater chances of
  survival.
• Crossopterygians that remained in fresh water
  likely ancestors to amphibians. Stubby lobes
  evolved into stubby legs for navigation of
  shallow, debris-clogged waterways. Initially,
  legs may not have been strong enough to support
  animals on land.

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Diagram showing similarities between
Crossop-terygians (below) and an early Amphibian
(above).
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• Earliest tetrapod (four-footed) trackway 365
  m.y. (Devonian) Ireland. Likely in shallow
  stream-bed (or lake), no sign of tail being
  dragged. No bones are preserved of this
  creature.
• When these creatures arrived on land, what was
  there to eat?

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• Oldest evidence of land plants during the
  Ordovician Period.
• Insects, millipedes, spiders, even snails
  invaded the land before amphibians. Scorpions
  and flightless insects present in Devonian fossil
  record.
• Leaving the water amphibians did not have to
  compete with fish for food. With no land
  competition adaptive radiation - became common
  during Carboniferous and Early Permian.
• Likely remained close to water, in swampy areas.
• One common group labyrinthodonts (up to 2
  meters in length) survived changing climate into
  Early Triassic Period.

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• Amphibians remained close to water to prevent
  dessication of skin and their gelatinous eggs.
• The development of the amniotic, shelled egg in
  reptiles allowed them to move away from water.
• Amphibians and reptiles differ in skull
  structure, jawbones, ear location, and limb and
  vertebral construction.
• Fossil evidence suggests reptiles evolved from
  labyrinthodont ancestors by the Late
  Mississippian. The oldest known reptile,
  Westlothiana, - Late Mississippian-age rocks in
  Scotland. Early Pennsylvanian reptiles found in
  Nova Scotia. (see slide 15).

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Reconstruction and skeleton of Hylonomus lyelli
from the Pennsylvanian Period

• Fossils of this animal have been collected from
  sediments that filled tree stumps
• Hylonomus lyelli was about 30 cm long

Besides reproduction, other reptile advantages
better jaws, teeth, and faster mobility.
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• Suggested development of Reptiles during Late
  Paleozoic/Early Mesozoic.

Reptiles with some mammal features. 90 of
reptile genera by end of Paleozoic.
Dominant reptile family group Early Permian.
Descendants included carnivores and herbivores.
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Late Permian reconstruction southern Africa.
Therapsids may have been endothermic and may have
had a covering of fur.
Moschops
Dicynodon
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• Other mammal features of Theraspids include
• Fewer bones in the skull due to fusion of many of
  the small skull bones.
• Enlargement of the lower jawbone
  differ-entiation of the teeth for various
  functions such as nipping, tearing, and chewing
  food.
• And a more vertical position of the legs for
  greater flexibility as opposed to the sideways
  sprawling legs in primitive reptiles.
• Endothermism (warm-blooded) greater climate
  and seasonal flexibility.

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• Plant evolution plants faced similar problems
  of vertebrates when leaving the water.
• Dessication Support Effects of Gravity
• Earliest evidence of land plants Middle to Late
  Ordovician spores other debris.
• Major evolution took place during Devonian
  Period.
• Higher land plants Non-vascular and Vascular.
• Nonvascular bryophytes, e.g., liverworts,
  mosses, fungi
• Vascular have tissue system of specialized
  cells for the delivery of water and nutrients.
  Appearance likely before Middle Silurian.

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• A likely algae vascular link - Primitive
  seedless vascular plants such as ferns
• resemble green algae in their pigmentation,
• important metabolic enzymes,
• and type of reproductive cycle.
• Vascular tissue provide support for the plant.
  Development of cutin, an organic compound in
  plant tissues offers resistance to UV radiation,
  oxidation, and entry of parasites.
• Roots developed to bring soil water and nutrients
  to the plant. Leaves developed to provide more
  surface area for photosynthesis.
• Middle Silurian Cooksonia Wales, Ireland,
  oldest known vascular plants.

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• Cooksonia features upright, branched stems, a
  resistant cuticle, spores typical of vascular
  plants
• These plants probably lived in moist environments
  such as mud flats.
• This specimen is 1.49 cm long.
• No true roots, rhizome (buried part of stem)
  delivered nutrients.

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During the Paleozoic, seedless vascular plants
evolved many of the major structural features
characteristic of modern plants such as leaves,
roots, and secondary growth. Evolution at
different times mosaic evolution. Plant
adaptive radiation took place in Late Silurian
Early Devonian. Devonian Period (408 to 360
m.y.) Early Devonian landscape was dominated by
relatively small, low-growing, bog-dwelling types
of plants. By Late Devonian there were forests
of large tree-size plants up to 10 m tall. Also
during Late Devonian, first seeds appeared,
allowed plants to move away from areas of
standing water.
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• Reconstruction of Early Devonian landscape.

• showing some of the earliest land plants

Protolepidodendron\
Dawsonites /
- Bucheria
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• Non-flowering gymnosperm plants have male
  female cones, pollination causes female cone to
  develop with seeds. Example Pine trees.
• The step before the development of the
  gymno-sperms was the Early Devonian development
  of heterospory plants two diff. sizes of
  spores. Larger spore female-gamete bearing
  plant. Smaller spore male-gamete bearing
  plant.
• Seedless vascular plants dominated coal swamps.
  Became highly diversified during Pennsylvanian
  Period (slide 25).
• Gymnosperms colonized non-swampy uplands.

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Reconstruction of Pennsylvanian Coal Swamp
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• Important Pennsylvanian seedless vascular plant
  major types - lycopsids and sphenopsids.
• Lycopsids - Lepidodendron and Sigillaria up to
  30 meters tall. Similar to todays palm trees.
• Sphenopsids jointed trunks, root systems with
  stems 6 meters tall. Horsetails, scouring
  rushes modern examples.
• Other trees - cordaites, a group of tall
  gymnosperm trees that grew up to 50 m and
  probably formed vast forests. Glossopteris -
  temperate, non-swamp dwelling plant with fossils
  present on modern day southern hemisphere
  continents.
• Gymnosperms survived Late Permian declines,
  spread during Early Mesozoic.