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November 13.doc

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McGill University
Biology (Sci)
BIOL 111

Bio 111 Alanna Houston November 13, 2007 - The first fish were jawless and they were benthic o Had bony plates o Heavily armoured o Small o Ostracoderms (shell skin) - Later, the fish were bigger, spiny-finned, jawed predator, ancanthodians (spiny fin) - Later, fish were less armoured, large predators = placoderms (plate skin) - Early marine predators preying on fish o Sea scorpions THE RISE TO LAND Why move on land? - Devonian droughts o Shallow inland seas, swamps, ponds, experience low DO2 - Competition in water o Crowding in shallow pools - Insects and plants on land - No vertebrate predators Major Physical Differences between land and water - availability of water - density of medium - amount of oxygen (most important) - stability of temperature - amount of UV radiation Advantages of Terrestrial respiration - Air has higher concentration of oxygen than water - Gases diffuse faster in air than water - Air is less dense so less energy required to move it across respiratory surfaces - Lungs evolved early in fish groups. Gas bladder used as supplementary respiratory organ, then later modified for buoyancy Early Gas Bladders - present in early fish (placoderms – now extinct) - used as a supplementary respiratory organ o gulp at air surface - reappeared in bony fishes o actinopterygians (ray-finned) o sarcopterygians (lobe-finned) - Ray-finned fishes o From single dorsal pocket off esophagus o Evolved into a swim bladder or supplementary respiratory device Bio 111 Alanna Houston o Gland that releases lactic acid that increases acidity of the blood and causes O2 to be released by the hemoglobin so that it is oxygen that fills the gas bladder o - Lobe-finned fishes o From paired ventral pockets off esophagus o Evolved into a supplemental respiratory device o - The embryonic origin of the gas bladder was from the digestive tract (endoderm) Problems on Land: - Dessication o Need to stay moist o Most require water for fertilization and larval development - Air is less dense than water o Require stronger skeletal support, muscles o Require more energy, more O2 brought in and distributed - Air temperature is more variable o Body temperature will fluctuate more o Need to modify behaviour or physiology - UV radiation more intense on land o Need physical protection or change behaviour - A lobe-finned bony fish is the most direct ancestor to tetrapods o Declined after Permian extinction o Only 8 extant species o Common during Devonian period Direct ancestor to tetrapods - Rhipidistian fish - Internal nostrils (nares) - Teeth - Appendages similar to tetrapods - Best known fossil from Gaspe, Quebec Closest extant fish Bio 111 Alanna Houston - Lungfish - 6 species - walk on lobe-fins o tetrapod motion - breathe through gills and primitive lung - estivate in mud during drought - make a mucous cocoon Coelacanth – A living fossil - thought to be extinct - 1930 – found at African fish market o Marjorie Courtenay Latimer nd - 1952- 2 specimen found - Comoros Islands (East African Coast) - 2 ndspecies discovered in Indonesia – 1998 Early Tetrapods - Stronger limbs and girdles, vertebral column, ribs - Tail used for balance, not swimming - Lungs were primary respiratory organ - External and internal nostrils - Late Devonian life Bio 111 Alanna Houston - Tiktaalik – a transitional form - discovered on Ellesmere Island, Nunavut – 2004 - fishapod o fish – scales, gills, fins o tetrapod- mobile neck, lungs, ribs, strong wrist bones Bio 111 Alanna Houston - Tetrapod Solutions - For dessication, they got scales and an amniotic egg - For density, they got stronger limbs, vertebral column, ribs, more efficient circulatory system (double circuit of blood flow, 3+ chambered heart) - For temperature, they got feathers, fur and endothermy - For UV radiation, scales, feathers and fur Circulatory System - In fish and larval amphibians: o Blood oxygenated in the gills o Single circuit: heart – gills – Body – heart
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