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Lecture 6

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ZOO 2090
Fred Laberge

Lecture 6 ZOO*2090 September 25, 2013 Diversity and evolution of fishes cont’d Bony Fishes - much more bone in endoskeleton - they control buoyancy using a swim bladder - swim using strengthened fins (with rays in actinopterygians or bone and muscle in sarcopterygians) - actinopterygians presently the most diversified group of vertebrates - there are endless forms within the group, sometimes with incredible modification away from the basic body plan (eg. seahorses) Origin of Bony Fishes - mid-Devonian actinopterygian were a relatively homogeneous group - large eye and two nostrils on each side - teeth on maxilla (large bone of upper jaw), premaxilla (small bone on front of upper jaw) and dentary - small overlapping scales articulating with each other - kinetic head skeleton allowing wide gape Paleonisciformes (Condrosteans) - radiated in Devonian-permian - modern groups secondarily reduced their bony skeleton to cartilage - use prominent notochord for support (Sturgeons reverted back to notochord to avoid heavy bone) - first pharyngeal slit is a spiracle as in elasmobranchs Acipenseriformes  sturgeons and paddle fish Polypteriformes (or Cladistia)  bichirs and reedfish Neopterygians (“Holostei” and Teleosts) - gar and bowfin lineages diverged before appearance of teleosts in the Triassic (220 mya) Lecture 6 ZOO*2090 September 25, 2013 - teleosts radiated in Jurassic-Cretaceous - they show ossified vertebrae - true homocercal tail for better swimming - circular scales - skull that allows jaw mobility - the group is diverse and widespread Sarcopterygians - fish with lobe-fins o appendages with internal bones and muscles used for swimming o fins still end with rays - cosmoid scales – very large scales; cosmoid is a very hard material (feel like bone) - double dorsal fins in early forms - origin is unclear o basal bony fishes might have had mixture of ray-finned and lobe-finned characters like the lower Devonian Psaralepis Lungfishes (Dipnoi) - three living genera display: o paired lungs o appear to have undergone simplication of many features compared to their ancestors Coelacanth (Latimeria chalumnae) - only living actinistian - it was thought extinct until a discovery in 1938 off the coast of South Africa - relatively unchanged from ancestors of more than 100 mya (living fossil) - double dorsal fin, very fleshy Rhipidistians - term was used to identify Devonian sarcopterygians that were not lungfishes - paraphyletic grouping can include actinistians, porolepiforms, rhizodonts, onychoonts, osteolepiformes, tristichopterids and pandericthyids depending on classification - most were predators as can be deduced from their abundance sharp teeth and large size - ossified vertebral elements provide more support for the notochord, the braincase is articulated - a new type of teeth (labyrinthodont) and choanae (internal nostrils) appear in later forms - their eyes move upward and the skull is flattened Tiktaalik (extinct) - late Devonian fish from Ellesmere Island showing the most intermediate characteristics between fish and tetrapods - large ribs - limb-like pectoral fins possibly for standing support - neck allowing flexible head movement - lost bony gill covering suggesting increased use of lungs for respiration Lecture 6 ZOO*2090 September 25, 2013 - might have moved like a mudskipper (fish that use limbs to prop themselves on substrate, also use tail for locomotion) or an African lungfish (very fin, fleshy fins, used to walk on the bottom) … *videos* Important Points - innocations that enabled fish radiations - general trends of fish Typical Exam Question What is the conodont apparatus? 1. the jaws in the extinct group of agnathans 2. complex tooth-like elements in the pharynx of condonts 3. the hyoid archs of condonts 4. fish scales used in stratigraphic dating Fish Skeleton Objectives - describe main elements of skull, axial and appendicular skeleton of fishes Skeleton - endoskeleton forms deep inside the body, mostly from mesoderm - exoskeleton is formed by integument - composed of bone, cartilages, ligaments and tendons bone  collagen fiber matrix + calcium phosphate crystals (hydroxyapatite) active structure  constantly being absorbed and replaced (bone remodelling) Functions of Skeleton - supports weight and protects soft parts - anchors muscles for movement - stores minerals, particularly calcium Main Components - skull (cranium) - axial skeleton: vertebral column, ribs and sternum - appendicular skeleton: girdles and finds/limbs Head Skeleton Three components of the skull: - Chondrocranium (neurocranium) (blue) Lecture 6 ZOO*2090
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