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BIOL 211
Bill Taylor

NOTES BIOL 211 INTRO TO VERTEBRATE ZOOLOGY INTRODUCTION Extant species– living species (non-extinct) Cladograms – depict branching or speciation Monophyletic – A group (genus, phylum, class, order, etc) comprising of all the descendents of a common ancestor Paraphyletic – Group including most but not all descendants of an ancestral form Phylum (chordate) > subphylum (vertebrata) > Class (mammalia > subclass > Order Family > Genus > Species Homoplasy – similar in appearance, can reflect common ancestry/function, but not always Homology – similar due to common ancestry Homologous structures – evolve from a corresponding structure in a common ancestor Analogy – similar function Analogous structures – may appear similar, but similarity is shaped by adaptation to a common function and does not reflect close evolutionary relationship Vestigial structures – not functional, but represent features functional in ancestors Convergent and Parallel Evolution Convergence – different ancestors producing similarity in animals due to adaptation to similar environmental conditions (ie: fish-like body of dolphins) Parallelism – similarity in animals with similar but distant ancestors due to adaptation to similar environmental conditions Evolution and Development Recapitulation – ancestral features evident in embryo of a descendent Paedomorphosis – ancestral juvenile features evident in the adult of a descendent Progenesis – development of reproductive system accelerated in a morphologically juvenile stage Neotany – when a somatic feature retains its juvenile form in the adult Sexual Homology – structures that are developed from the same structure in the embryo but with different form and function in the adult male and female (ie: testes vs ovaries) Serial Homology – structures derived from similar embryonic structures in different embryonic segments (ie: spinal cord?) LECTURE 2 Phylum Chordata Characteristics 1. Has notochord 2. Hollow dorsal nerve chord 3. Pharyngeal Slits 4. Complete Gut 5. Post-anal tail Era Period MYBP first prominent appearance Group Cenozoic Neogene 23 Homo mammals Paleogene 66 Mesozoic Cretaceous 146 mammals,birds reptiles Jurassic 200 Triassic 251 Paleozoic Permian 291 reptiles amphibians Carboniferous 359 amphibians fish with jaws Devonian 416 fish with jaws Silurian 444 agnathans Ordovician 488 Cambrian 542 Pre-Cambrian chordates Contains 3 subphylums (Vertebrata, Cephalochordata, Urochordata) A. Vertebrata Characteristics 1. Everything mentioned above (Chordata) 2. Brain with 3 special sense organs (eyes, internal ears, olfactory) (cephalization) 3. *Cranium* 4. Bilateral symmetry (left & right sides) 5. Interior organs housed in an internal body space  coelom/coelomate 6. Segmented Good vertebrate fossils are rare (soft organisms). Appear in fossil record ~ 500 mybp (Cambrian period) B. Cephalochordata (Amphioxus) 1. Everything mentioned above (Chordata) 2. Midgut cecum (homologous to liver?) 3. Segmentation 4. Perforated pharynx 5. Coelomate 6. Endostyle (conveyor belt that moves food particles from pharynx to gut) Characteristics NOT vertebrate-like 1. No Cranium 2. No special Sense Organs 3. No Kidneys 4. No Heart C. Urochordata (Tunicates or Sea Squirts) 1. Has notochord in their larval stage 2. Endostyle Deuterostome (Chordates) Protostomes  Radial Cleavage  Spiral Cleavage  Indeterminate Cleavage (individual  Determinate Cleavage (individual cells cells can divide into new whole cannot grow into whole organism if organism) separated)  Blastopore becomes anus  Blastopore becomes mouth Phylum Hemichordata (acorn worms)  Deuterostomes  Use to be considered Chordata, not anymore  Stomochord not homologous to notochord Phylum Echinodermata (Starfish, Sea urchins)  Deuterostomes Chordata and other deuterostome phyla are quite small compared to other phyla (ie: # of species per phyla) Possible Origins of Vertebrates 1. Vertebrate ancestors were motile filter-feeders that evolved into sedentary filter feeders such as echinoderms, hemichordates, cephalochordates, and tunicates 2. Cephalochordate-like ancestor of vertebrates arose from tunicate-like ancestor by paedomorphosis (evolution of larval forms) Echinoderms  Hemichordata  Urochordata  Cephalochordata Vertebrate 3. Recent studies  Urochordates (tunicates) = closest relatives of Vertebrates LECTURE 3 Fish 5 Classes of Fish: 1) Agnatha 2) Placodermi 3) Acanthodii 4) Chondricthyes 5) Osteichthyes Agnatha (Jawless Vertebrates)  500 mybp in Cambrian era  Early agnathans = ostracoderms (shell skins in ref. to their bony armour)  Ostracoderms = 300 mybp and are extinct  Modern Agnathans = cyclostomes  Cyclostome features = everything same as ostracoderm…except cyclostomes may have teeth? Ostracoderm Modern Agnatha (Hagfish) Modern Agnatha (Lampreys) Jawless  Marine fish feeds on  Parasitic on other fish Single nostril dead fish or marine  Larval stage (ammocetes) Pharyngeal slits for filter mammals filter-feeds while buried in feeding sediment….similar to Notochord cephalochordates Endostyle (recapitulation?) Few or no paired fins Fishes with Jaws  400 mybp in Silurian period to Devonian period  Fish switched from filter feedings to active predators (jaws evolved from bones) Placodermi Acanthodii Chondricthyes (cartilaginous fishes)  Extinct  extinct  Skeleton made entirely of  Devonian period  Devonian period cartilage, no bony skeletons  Unique scales (don’t have a  Heavily  Heavily armoured, armoured, active active predators plate armor)(dermal predators  Spiny fish, freshwater dentricles)  Long tails, with  Unique teeth jaws, marine  Slit-like gill openings 2 Subclasses 1) Elasmobranchii (sharks and rays) 2) Holocephali (ratfishes or chimaeras) Osteichthyes – Bony Fishes  More species than any other class of vertebrates for the last 150 mybp  Bony skeletons, scales, and operculum 2 Subclasses 1) Actinopterygii (ray-finned fishes)  Lungs  Heterocercal (asymmetric tails)  Bony scales  Notochord in adults Modern Actinopterygii (teleosts)  Gas bladder (buoyancy) rather than lungs  Homocercal tails  Soft, flexible scales 2) Sarcopterygii (fleshy-finned fishes) – Crossopterygii  Extinct except for a single species -> the coelacanth  Have openings (choanae) – connections between nostrils and mouth  We think sarcopterygii led to land animals/tetrapods LECTURE 4 – Tetrapods I (Classes Amphibia and Reptiles)  Tetrapods believed to be descended from sarcopterygian fish Amphibia (Class)  First tetrapod or land-dwelling vertebrates  400 mybp  Ancestors were sarcopterygii with lungs and limb-like fins 3 Subclasses 1) Labyrinthodontia (anthracosaurs, ichthyostegalians)(extinct)  Have highly folded teeth 2) Lepospondyla (extinct) 3) Lissamphibia (modern amphibian – frogs, toads)  Order Anura = without tail, frogs  Order Urodela = with tail, salamanders  Order Apoda = Caecilians Amniotes (Classes Reptilia, Aves, Mammalia)  Refer to the way they reproduce  Lay dessication-resistant amniotic eggs or bear live young  Require internal fertilization Reptilia (Class)  Keratinized skin – resists moisture loss  Can lay amniotic eggs or bear live young  300 mybp first appeared  quite diverse in the mesozoic (250 mybp to 65 mybp) 3 Subclasses 1) Mesosauria – early aquatic, extinct 2) Parareptilia – turtles, anapsids 3) Eureptilia – modern reptiles (crocodiles, snakes), dinosaurs, ichthyosaurs, plesiosaurs; diapsids and euryapsids. Two main groups of dinosaurs named for their hip structure. Saurischian hip (lizard-hipped) vs Ornithischian hip (bird- hipped) 4) Synapsida (mammal-like reptiles) - believe this group is where mammals evolved - have mammalian-like characteristics such as : dentition, gait, limb girdles, details of skull Reptile Skulls 1) Anapsid - 0 temporal opening 2) Synapsid - 1 temporal opening 3) Diapsid - 2 temporal openings 4) Euryapsids - Also seems to have 1 tiny temporal opening (Ichthyosaur and plesiosaur) LECTURE 5 – Tetrapods II - Endotherms (Classes Aves and Mammalia) Ectohermy and Endothermy Ectotherm - derives body heat from environment. Body temp can vary widely (reptiles and amphibians) - body temp regulated by basking in sun (body not insulated) - only active at high temperatures - consumes significantly less calories Endotherm - animal maintains high body temp by using metabolic heat and controlling heat loss - minimal variation in body temp. Insulated through feathers, fur, or dermal fat - active even at lower temperatures - must eat a lot to maintain body temp Could dinosaurs have been endothermic? 1. Bone structure - no annual growth rings in their bone 2. Geographic Distribution - dinosaurs found in the north 3. Fossil ecology - Predatory dinosaurs were rare relative to herbivores 4. Dinosaur Anatomy - resemble modern active running animals 5. Some had feathers for insulation 6. Stable isotopic composition ( C and O) consistent with high body temps 7. Possibly nocturnal Evidence to the contrary 1. no living reptile is endothermic 2. no elaborate nasal bones that allow mammals to conserve heat and moisture while breathing - reptiles quite diverse in the mesozoic (250 mybp to 65 mybp) - replaced by birds and mammals at 65mybp (boundary b/w Mesozoic and Cenozoic Eras) - ie: end of the cretaceous period - possibly due to an asteroid - At least 5 mass extinctions --> most severe = end of the Permian (250 mybp). Volcanism Features of Class Aves  endothermy, feathers, bipedal, keel-shaped sternum, gizzard, keratinized bill, hollow bones  200 mybp  Example: Archaeopteryx (early birds) - fingers on wings, teeth, no keel on sternum, solid bones, bony tail Modern Birds or Neornithes  jay....about 30 orders of nornithes Class Mammalia - 200 mybp - endothermy - hair - mammary glands - posture - dentition (heterodont) - skull (malleus rather than articular bone) Subclasses Monotremes (Prototheria) - egg laying mammals (like reptiles) -> Platypus, Echidna Theria - produce live young 1) Metatheria (marsupials) - animals born extremely early in development and leaves vagina into pouch for further development -> Kangaroo, Opossum 2) Eutheria (placental mammals) - embryo grows in uterus Infraclass Eutheria or placental mammals - great expansion 65 mybp - ancenstral order -> long thought to be Insectivora, but recent evidence suggests Edentata - largest order = Rodentia Lectures 6&7 Early Development What is Early Development - formation of embryo from zygote - embryo has 3 germ layers --> ectoderm, mesoderm, endoderm - plus gut, notochord, coelom, and neural tube - early stages of development to gastrula occur in ALL animals --> strong evidence for unity of all animal phyla Vertebrate Reproductive Strategies - reproduce sexually --> develop from fertilized egg - vertebrate ancestors --> release eggs and sperm into water for fertilization --> larvae feeds on plankton - living vertebrates --> retain eggs, provide them with yolk for development Trade-off --> little yolk = more offspring, less chance of survival more yolk = fewer offspring, better survival Egg Types - amount of yolk determines how far embryo can develop before it needs to feed itself Microlecithal - found in marine animals with planktonic larvae e.g. Cephalochordata and Echinodermata Mesolecithal - found in cyclostomes (lampreys and hagfishes), some Osteichthyes (bony fishes), amphibia, and metatheria Macrolecithal - found in most fishes, reptilia, Aves, and monotremes (egg-laying mammals) Embryonic development of Microlecithal egg of Amphioxus Zygote to Blastula - radial cleavage - complete and equal, lead to blastula with hollow space (blastocoel) - indeterminant cells - each cell can make up a new organism Gastrulation and Neurulation - Gastrulation (folds in on itself) to create an ectoderm and endoderm - Mesoderm begins on dorsal part of endoderm and is where notochord develops - Cord induces formation of neural tube (specialized ectoderm called neurectoderm) (neurulation)--> embryo now called neurula - Blastula --> Gastrula --> Neurula --> feeding larval stage Embryonic development of Mesolecithal egg of an Amphibian (tad pole) - divisions still complete but unequal --> large cells to one side, blastocoel to other side blastula = several cells thick Amphibian Gastrulation and Neurulation - mesoderm formation starts dorsally at notochord, but internal space (coelom) occurs by splitting rather than evagination - again, notochord induces formation of neural plate and neural tube Preview of the fate of the embryonic tissues (mesolecithal): 1) Ectoderm - neural crests form pharyngeal cartilage, bone, teeth, sensory nerves, acoustic and lateral line systems - neural tube forms the CNS - ectoderm form outer layer of integument (epidermis and derivatives, ie: fur, hair) 2) Mesoderm - outer layer epimere (dermatome) produce the dermis (inner layer of integument) - inner layer of epimere (myotome) form muscles of the trunk - innermost part forms sclerotome (surrounds notochord, becomes vertebrae) - mesomere - produce excretory and reproductive systems - hypomere - produce lining and surrounds gut 3) Endoderm - form inner layer of gut, organs, and germ cells Embryonic development of Macrolecithal egg - divisions are partial --> leads to a patch of flat cells called germinal disk - blastula is a layer of cells on a large mass of yolk Comparison of Gastrulation microlecithal - invagination mesolecithal - involution macrolecithal - delamination (splitting of germinal disk into two layers --> epiblast (ectoderm) and hypoblast (endoderm)) Mesoderm Formation in the Bird - a primitive streak or groove forms at one end of the blastula - mesoderm (found above primitive streak) becomes the notochord which induces the neural tube formation - neural tube forms above notochord Fate of extra-embryonic structures - amnion splits to create the extra-embryonic coelom - yolk enclosed by extraembryonic membrane - note extraembryonic mesoderm is called the amnion and extra-embryonic ectoderm is called the chorion - allantois evaginates embryo's gut -> serves as respiratory organ and reservoir for waste - amniotic cavity -> space where embryo resides Blastula formation in the secondarily microlecithal egg of a eutherian (placental) mammal - eggs of placental mammals are microlecithal - similar development to amniotes - inner cell mass = embryo outer cell layer (trophoblast) is involved in implantation Eutherian Gastrulation - as in the bird, mesoderm arises at a primitive streak Eutherian Neurulation - formation of primitive streak, mesoderm, and notochord same as bird Eutherian Extraembryonic membranes - embryo in an embryonic cavity - yolk sac is vestigial - chorion interacts with uterine wall to make the placenta (chorioallantoic placenta) Lecture 8 The Integument Morphologically compound (2 distinct layers): 1) Epidermis (from ectoderm) 2) Dermis (from mesoderm) Embryologically compoun
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