Download method of reproduction

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
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 -> lungfish, crossopterigians (both have
protolungs)
– Crossopterygians -> amphibians
• First creatures on land were Arthropods (early
Devonian)
Amphibians—
Vertebrates 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
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
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
Carboniferous Coal Swamp
• Reconstruction of a Carboniferous coal swamp
The serpentlike Dolichosoma
Large labyrinthodont amphibian Eryops
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
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
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
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
One of the Oldest Known Reptiles
• Reconstruction and skeleton of Hylonomus lyelli from the
Pennsylvanian Period
– Hylonomus
lyelli was about
30 cm long
Paleozoic Reptile Evolution
• Evolutionary
relationship
among the
Paleozoic
reptiles
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
Therapsids—
Mammal-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
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
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
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
Fenestrae in the descendents of
proterothyrids
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
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
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 you’re 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
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
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
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
Early Devonian Plants
• Reconstruction of an Early Devonian landscape
– showing some of the earliest land plants
Protolepidodendron
Dawsonites
Bucheria
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
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
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
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
Pennsylvanian Coal Swamp
• Reconstruction of a Pennsylvanian coal swamp
with its characteristic vegetation
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/gl
oss1.htm