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Last Wednesday… began our final phylum - Chordata

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Presentation on theme: "Last Wednesday… began our final phylum - Chordata"— Presentation transcript:

1 Last Wednesday… began our final phylum - Chordata

2 A taxon within the Deuterostomia, and the Bilateria…
Calcarea Silicarea Ctenophora Cnidaria Echinodermata Chordata Brachiopoda Phoronida Ectoprocta Platyhelminthes Nemertea Mollusca Annelida Rotifera Nematoda Arthropoda “Radiata” “Porifera” Deuterostomia Lophotrochozoa Ecdysozoa Bilateria Eumetazoa Metazoa Ancestral colonial flagellate A taxon within the Deuterostomia, and the Bilateria…

3 After describing chordate characters, looked at
Cephalochordata & Urochordata - do share defining chordate characters...

4 Chordate Phylogeny Also introduced ‘Craniates’ (vague hierarchical rank) – have a ‘head’ w. skull, more regulatory genes, gill slits & neural crest cells

5 Class Myxini - Hagfishes
Predators of invertebrates & scavenge on dead vertebrates in deep, cold marine waters - about 30 spp. - cartilaginous skull & small brain but no jaws or vertebrae - ‘teeth’ of keratin - small eyes, ears & single nostril have lateral line system for detecting vibrations in water & sensory tentacles

6 - but also (over)fished for ‘eelskin’ and meat
Famous for slime production… - but also (over)fished for ‘eelskin’ and meat hagfish slime scone

7 next step… evolution of vertebral column

8 Subphylum Vertebrata Earliest vertebrates prob. sometime in Cambrian
- initially some skeletal elements above notochord protecting nerve cord, later replacing notochord & surrounding nerve cord more gene duplication (Dlx family) may have allowed greater complexity

9 Class Petromyzontida - Lampreys
About 40 spp. in marine & fresh water - parasites of fish, attach with round sucking mouth No jaws, but rasping teeth on tongue create hole Larvae are suspension feeders in streams Have notochord with covering, plus cartilages along nerve cord (no collagen)

10 Sea lampreys invaded the Great Lakes, feed on trout,
whitefish, etc.

11 Next characters… jaws & mineralized skeleton

12 Gnathostomes have true jaws, hinged structures that enable
Mouth Gill slits Cranium Skeletal rods Gnathostomes have true jaws, hinged structures that enable them to grasp food firmly - jaws thought to have evolved by modification of the arches that previously supported anterior pharyngeal gill slits. - remaining gill slits no longer required for suspension feeding & remained as main site of respiratory gas exchange.

13 More Gnathostome Characteristics
Another duplication of the Hox genes (now 4 clusters) & other developmental genes - forebrain enlarged, associated with enhanced vision & smell - mineralized axial skeleton, shoulder girdle, & 2 sets of paired appendages

14 Gnathostomes appear in fossil record in mid-Ordovician,
about 470 MYA, & steadily diversified Dunkleosteus - Devonian Bothriolepis - Devonian

15 Class Chondrichthyes - Sharks & rays
Basking Shark Manta Ray Spotted Ratfish Fairly diverse, w. about 460+ sharks, 460 rays & 30 chimeras - many predators, but filter feeders too

16 Shark & Ray Characteristics
Skeletons (mostly) cartilaginous, although ancestors had mineralized skeleton well developed jaws, paired fins, streamlined bodies, dorsal fin for stability - water flow over gills maintained by swimming, or by pumping of mouth/pharynx if still - well-developed sight & smell, also lateral line system & electrical field detectors Shortfin Mako

17 Next group is ‘Osteicthyes’, known traditionally as
‘the bony fishes’, but includes tetrapods …& us! a key character is lungs or derivative (e.g. swim bladder)

18 Class Actinopterygii – Ray-finned Fishes

19 Actinopterygii - Characteristics
About 27,000 spp., make up > half of all vertebrates - throughout oceans, but 40% occur in fresh water - most have bony (ossified) skeleton w. calcium phosphate matrix - skin usually with thin, flat bony scales (vs. tooth-like scales of sharks) - fins supported by long, semiflexible rays - mucus covering reduces drag, prevents infection - respire with 4-5 pairs of gills in chamber w. protective flap: operculum Bluegill

20 Most have swim bladder for buoyancy (off digestive tract)
Nostril Brain Spinal cord Swim bladder Dorsal fin Adipose fin (characteristic of trout) Caudal fin Cut edge of operculum Gills Heart Liver Kidney Stomach Intestine Gonad Anus Urinary bladder Lateral line Anal fin Pelvic fin Body plan of a typical ray-finned fish – trout Most have swim bladder for buoyancy (off digestive tract) - originally, & often still, functioned as simple lung

21 ‘Lobe-fins’ - Sarcopterygii
Originally referred to as lobe-finned fish, but includes tetrapods now - originated as aquatic forms in Devonian - short linear bones & thick muscles support base of fins, could be useful for moving in shallows Eusthenopteron

22 Two aquatic classes of ‘lobe-fins’ survive:
1) Class Actinistia - coelacanths & relatives Known from Devonian fossils, 2 spp. discovered off Comoros Islands (1938) & Indonesia (1999) - large deep-water predators - move limbs alternately when swimming

23 2) Class Dipnoi - lungfishes
Six spp., in Australia, Africa (4), & South America - live in rivers & swamps, African spp. at least must use lungs - some estivate in mud burrow in dry season African lungfish

24 Next… evolution of limbs with feet

25 Tetrapods Evolution of limbs that could support weight
about 365 MYA, e.g. Acanthostega - still basically aquatic, w. gills, tail fin, etc. Acanthostega

26 Now many fossils known of transitional forms between lobe-finned fish & tetrapods

27 Tetrapoda - the tetrapods
Tetrapods have feet with digits, transfer muscular forces to ground Pelvic girdle fused to vertebral column, allowing transfer of forces to body Neck to allow head to move separately from body No pharyngeal clefts in adults, ears adapted for airborne sounds

28 Class Amphibia Present day amphibians are highly specialized groups
not necessarily very similar to early tetrapods - most dependent on H2O at least part of life, or in moist habitats - moist skin important for gas exchange, some lack lungs - skin may also be toxic to varying degrees Cobalt Poison Dart Frog

29 Amphibian: ‘both lives’ - metamorphosis
(a) The male grasps the female, stimulating her to release eggs. The eggs are laid and fertilized in water. They have a jelly coat but lack a shell and would desiccate in air. (b) The tadpole is an aquatic herbivore with a fishlike tail and internal gills. (c) During metamorphosis, the gills and tail are resorbed, and walking legs develop. Amphibian: ‘both lives’ - metamorphosis - most species breed, develop as larvae in fresh water but typically terrestrial as adults

30 Exceptions to standard life cycle fairly numerous,
Eastern Red-backed Salamander Southern Gastric Brooding Frog Exceptions to standard life cycle fairly numerous, & sometimes bizarre…

31 Order Urodela - Salamanders
Over 600 spp., many in eastern US - some entirely aquatic, but often live on land as adults, or sometimes throughout life On land, most walk with side-to-side bending of body, may resemble movement of early terrestrial tetrapods. Spotted Salamander

32 Order Anura – Frogs &Toads
By far largest order, w. > 6,000 spp., worldwide except many ocean islands, cold climates - specialized for hopping on land (legs, urostyle) but swim well too - catch insects with sticky tongue (attached in front) American Toad

33 Many species toxic, & may have aposematic
Golden Mantella Many species toxic, & may have aposematic coloration (warning colors, easy to recognize & learn)

34 Order Apoda - Caecilians
About 190 species, legless & nearly blind - short tentacles on front of head - reduction of legs evolved secondarily - superficially resemble big earthworms, most burrow in moist soil in tropical forests - some South American spp. live in ponds & streams Bannan Caecilian

35 The Amniotes Amniota consists of mammals, turtles, crocodilians, birds, tuataras & squamates (lizards & snakes), plus many extinct groups

36 Extraembryonic membranes
Shell Albumen Yolk (nutrients) Amniotic cavity with amniotic fluid Embryo Yolk sac. The yolk sac contains the yolk, a stockpile of nutrients. Blood vessels in the yolk sac membrane transport nutrients from the yolk into the embryo. Other nutrients are stored in the albumen (“egg white”). Allantois. The allantois is a disposal sac for certain metabolic wastes pro- duced by the embryo. The membrane of the allantois also functions with the chorion as a respiratory organ. Amnion. The amnion protects the embryo in a fluid-filled cavity that cushions against mechanical shock. Chorion. The chorion and the membrane of the allantois exchange gases between the embryo and the air. Oxygen and carbon dioxide diffuse freely across the shell. Extraembryonic membranes Amniotic Egg - major derived trait

37 Amniotic egg allowed life completely on land
- shell retains water, but allows gas exchange Great Tinamou eggs Eggs of birds calcareous, of most ‘reptiles’ more leathery Leatherback Turtle hatching - most mammals have lost shell & retain egg in uterus echidna ‘puggle’

38 evolved less permeable skin with keratin & scales
Other amniote traits... evolved less permeable skin with keratin & scales (lost in mammals & only on legs of birds) lungs almost exclusively for respiration & increasing use of rib cage to ventilate lungs - adopted more elevated stance than earlier tetrapods Komodo Dragon

39 Ornithischian dinosaurs
Synapsids Ancestral amniote Reptiles Diapsids Archosaurs Saurischians Lepidosaurs Dinosaurs Parareptiles Turtles Crocodilians Pterosaurs Ornithischian dinosaurs Saurischian dinosaurs other than birds Birds Plesiosaurs Ichthyosaurs Tuatara Squamates Mammals An Amniote Phylogenetic Tree

40 Class Testudinia - Turtles
Highly distinctive group - shell formed by bony shields fused to vertebrae, ribs, clavicles, & covered with horny scutes - over 300 species, most associated with water but some in arid areas Green Sea Turtle - respiration in water aided by cloaca (common excretory & reproductive opening) or pharynx - relationships uncertain, but perhaps closer to crocs & birds Ornate Box Turtle

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