The parade of the craniates

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The parade of the craniates

• Part 2

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Tetrapoda
Fossil Dipnoans

• Amphibia
• Limbs with digits
• In basal forms labyrinthine folding in dentine
  of teeth (Labyrinthodont)

Icthyostegalia of Greenland
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Amphibia

• Older extinct groups
• Labrynthodonts Devonian
• Temnospondyli Lower Carboniferous
• Looked a lot like modern frogs
• Anthracosauria
• Microsauia Upper Carb.
• Looked a lot like modern caecilians
• Modern Group
• Lissamphibia

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Lissamphibia

• Apoda ( Gymnophiona) caecilians
• Burrowing
• Limbless

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• Urodela ( Caudata)
• Tailed
• Sirens, Amphiuma,
• Salamanders, Hellbenders

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• Anurans ( Salientia)
• Frogs, toads, tree toads

Dwarf tree toad (Indonesia)
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Brief embryology of amniotes

• For proper embryonic development
• Requirement of aqueous environment
• Solutions to the problem
• Fish, Lissamphibians many species
• eggs laid externally in HOH
• Terrestrial orgs (Amniotes)
• Amphibian ancestors of reptiles (250mya)
• Retain HOH requirement
• Sequester it in a sac the amnion

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The amniote egg

• Allows wandering from existing water.
• Carries own food and water
• The four sacs of the amniote egg
• Yolk sac nutritive proteins
• Amnion fluid bathing embryo
• Allantois embryonic metabolism wastes deposited
• Chorion selectively permeable membrane (allows
  interaction with external environment)

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For comparison
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Day 1 Chick
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Day 4 Chick
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• Early cat embryo - amnion still around embryo,
  placenta opened

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The problem of waste
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Skull Fenestra Issue

• The temporal region (the roof of the skull) is
  formed from the parietal (Par), squamosal (Sq),
  postorbital (PO), and jugal (Ju) bones. Four
  patterns are distinguished, based on the number
  and position of temporal openings.  The ancestral
  anapsid pattern, found in turtles, has no
  openings. The synapsid pattern, found in the
  ancestors of mammals, has a single low lateral
  opening formed at the junction of the PO, Sq,
  Ju bones (the arch formed by the Sq / Ju
  connection evolves into the zygomatic arch of
  Mammalia). The diapsid pattern has a second
  opening at the junction of the PO, Sq Par
  bones. The true diapsid pattern is seen today
  only in Rhyncocephalia (tuatara Sphenodon)
  further reduction of the jugal in Archosauria
  (crocs and birds) and Lepidosauria results in a
  single temporal opening. (A fourth pattern,
  euryapsid, is found only in an extinct group of
  marine sauropsid reptiles, and consists of a
  single high lateral opening).

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diapsid
synapsid
anapsid
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Amniota

• Reptiles and synapsids
• Reptilia
• Anapsids Chelonians
• Diapsids all other living reptiles
• Archosauia (ie dinos and birds)
• Lepidosauria (lizards, snakes (squamates),
  tuatara (rhynchocephalia))

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• Synapsids
• Pelycosaurs
• Therapsida
• Extant Mammals

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Mammalia

• Subgroup of Therapsids
• End of the Triassic
• Characteristics
• synapsid skull
• Hair
• Mammary glands (not in monotremes)
• Nipples
• Single dentary bone articulating with squamosal
• Three bones in middle ear
• Muscular diaphragm separating thoracic and
  abdominal cavities

• Sweat glands
• Absence of adult cloaca (except monotremes)
• Heterodont dentition (except in toothed whales)
• Only two sets of teeth (milk and permanent)
• Biconcave, circular, anucleate red blood cells
• No fourth aortic arch
• Sound-collecting lobe (auricle)
• Cerebral cortex highly developed
• As a group wildly morphologically diverse

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