The parade of the craniates Part 2 Tetrapoda

The parade of the craniates Part 2

Tetrapoda Fossil Dipnoans • 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 (~250 mya) – 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