Amniotes through Eutherians Chapter 34.6-34.8

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Amniotes through EutheriansChapter 34.6-34.8

• By Francisco Berrios and Siria Arzuaga

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Amniotes

• A group of tetrapods that trace back to the same
  common ancestor.
• The only animals that have amniotic eggs.
• pods that retain water for vertebrates to
  complete their life cycles on land.
• Developed the ability to use the ribcage to
  ventilate lungs
• Early amniotes were herbivorous.
• Examples Reptiles, birds, and mammals

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Phylogeny of amniotes
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The Amniotic Egg

• Exists inside mothers belly or in a shell
  outside the mother.
• Extraembryonic membranes provide protection and
  nourishment
• 4 layers Allantois, chorion, amnion, yolk sac
• Develop through tissue layers
• Has a shell

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Amniotic Egg
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Similarities and Differences

• Some Tetrapod's evolved and became 2 footed.
• Reptiles are ectotherms (cold blooded), while
  mammals and birds are endotherms (warm blooded)
• Ectotherms have body temperatures determined
  by their environment.
• Endotherms use metabolic heat to keep tissues
  warm.

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Circulatory systems

• 4 chambered heart
• Provides high metabolism rate
• Mammals and birds

• 3 chambered heart
• Reptiles

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Reptiles

• Traced back to the diapsids and anapsids.
• Parareptiles- dermal plates
• Proposed linkage with turtles
• All reptiles have
• 3 chambered hearts
• ectothermic
• Covered with hard dry scales
• prevent dehydration
• amniotic eggs
• Rely on lungs for gas exchange

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Reptile Anatomy
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Diapsids

• Pair of holes behind eye socket
• Lepidosaurs
• Lizards, snakes, tuatara
• Marine reptiles (plesiosaurs)
• Archosaurs
• Crocodilians, dinosaurs
• Pterosaurs first tetrapods to fly
• Presence of muscles, blood vessels, and nerves in
  the wing membranes

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3 main groups of reptiles

• Turtles (Archosaurs)
• Over 200 species
• May live on sea or on land
• Huge shells to protect their bodies
• Crocodilians (Archosaurs)
• 23 species
• Semi-aquatic predators
• Huge teeth to attack big prey
• Lizards and Snakes (Lepidosaurs)
• Thousands of species
• Flexible skulls
• shed skin frequently
• Sea and land habitats

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Last Living Dinosaurs

• There are 8,600 species of birds in the world.
• Similarities
• Hollow bones
• Feathers
• V-shaped wishbone
• only 3 fingers
• Differences
• Beak shape
• Feet/talons
• Feather structure

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Why Can Birds Fly?

• Unique features
• Wings to produce flight
• Strong flight muscles to move the wings
• Active metabolism that provides energy to the
  muscles.
• Hollow bone structure to minimize weight.
• Lack a urinary bladder

• A wing is a remodeled version of the tetrapod
  forelimb.

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Exceptions

• Ratites (non-flying)
• Ex emu, ostrich, rhea, kiwi
• Flightless because
• Sternal keel (bone) is absent, and the pectoral
  muscles (wing control) are not greatly enlarged.

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Mammals (Synapsids)

• Active, large-brained, endotherms with complex
  social, feeding, and reproductive behaviors.
• 5 characteristics
• Hair to retain heat
• Mammary glands
• Milk production
• Middle ears
• Temporal fenestra
• Single jaw bone for faster and stronger chewing
• 3 types of mammals
• Monotremes, Marsupials, Eutherians

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Monotremes (egg-laying)

• Found in Australia and New Guinea
• Very unique
• Offspring fully develop within egg.
• Lack nipples.
• After hatching, the baby sucks the milk from the
  mothers fur.
• Echidna and platypus

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Marsupials (pouch)

• Opossums, kangaroos, and koalas
• Young born very early in development
• Continue development in the pouch of the mother,
  called a marsupium.
• Produce milk and have nipples, higher metabolic
  rates
• Placenta
• nutrients diffuse into the embryo from the
  mothers blood when inside the mother

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Eutherians (placental)

• Same characteristics of a marsupial but consists
  of a more complex placenta
• Longer pregnancy and stays inside the mothers
  uterus.
• Primates are the most common.
• Includelemurs, monkeys, apes (humans), and
  tarsiers.

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Phylogeny of Ancestral Mammal
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Primates

• Earliest primates lived in trees
• Had a thumb that was able to grasp
• Large brain, short jaw, flat face, forward
  looking eyes
• No claws but flat nails
• Omnivorous
• The 3 main groups of living primates
• lemurs, lorises, pottos the tarsiers and the
  anthropoids.
• Anthropoids include hominoids and monkeys
• opposable thumbs.
• more diversity

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Cerebral Cortex

• Thought processes, consciousness perception,
  language, memory

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Phylogeny of the Ancestral Primate
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Apes

• Hominoids branch off of anthropoids.
• Include humans, gorillas, orangutans, and
  chimpanzees
• Have bigger brains compared to their size and
  their behavior is more flexible.

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Sources

• http//www.bio.sdsu.edu/faculty/archibald/Archibal
  d05ELS.pdf
• http//www.ucmp.berkeley.edu/mammal/eutheria/place
  ntal.html
• http//www.ucmp.berkeley.edu/vertebrates/tetrapods
  /amniota.html
• http//wps.aw.com/bc_campbell_biology_7/26/6665/17
  06306.cw/index.html http//wps.aw.com/wps/media/o
  bjects/1668/1708348/ebook/htm/campbell7e.htm?34.06