1. The parade of the craniates
Part 2

2. Tetrapoda Amphibia Limbs with digits
Fossil Dipnoans
Amphibia
Limbs with digits
In basal forms – labyrinthine folding in dentine of teeth (Labyrinthodont)
Icthyostegalia of Greenland

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

4. Lissamphibia
Apoda (= Gymnophiona) – caecilians
Burrowing
Limbless

5. Urodela (= Caudata)
Tailed
Sirens, Amphiuma,
Salamanders, Hellbenders

6. Anurans (= Salientia) Frogs, toads, tree toads Dwarf tree toad
(Indonesia)

9. 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
All vertebrate embryos require an aqueous environment for development.
* Fish and amphibians lay their eggs in water.
* Terrestrial animals live in dry environments and have evolved two solutions to this problem: the shelled egg in birds and reptiles and the uterus in placental mammals.
* The embryos of reptiles, birds, and mammals develop in a fluid-filled sac, the amnion.
* These three classes of animals are referred to as amniotes due to the presence of the amnion around the embryo.

10. 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)

11. For comparison

12. Day 1 Chick

13. Day 4 Chick

14. Early cat embryo - amnion still around embryo, placenta opened

15. The problem of waste

17. 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).

18. diapsid
synapsid
anapsid

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

21. Synapsids
Pelycosaurs
Therapsida
Extant Mammals

22. 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