The parade of the craniates
Part 2
Fossil Dipnoans
Tetrapoda
• Amphibia
– Limbs with digits
– In basal forms – labyrinthine folding in dentine
of teeth (Labyrinthodont)
Icthyostegalia of Greenland
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*
Lissamphibia
• Apoda (= Gymnophiona) – caecilians
– Burrowing
– Limbless
• Urodela (= Caudata)
– Tailed
– Sirens, Amphiuma,
Salamanders, Hellbenders
• Anurans (= Salientia)
– Frogs, toads, tree toads
Dwarf tree toad
(Indonesia)
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
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)
For comparison
Day 1 Chick
Day 4 Chick
• Early cat embryo - amnion still around embryo, placenta
opened
The problem of waste
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).
diapsid
anapsid
synapsid
Amniota
• Reptiles and synapsids
– Reptilia
• Anapsids – Chelonians
• Diapsids – all other living reptiles
– Archosauia – (ie dinos and birds)
– Lepidosauria – (lizards, snakes (squamates), tuatara
(rhynchocephalia))
• Synapsids
– Pelycosaurs
– Therapsida
– Extant Mammals
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