- dorsal hollow nerve chord that forms spinal cord and brain. - pharyngeal gill slits at some point in life cycle

Transcription

1 Chordates (44,000 species) All chordates share the following [Fig. 34.3, p. 699]: - dorsal hollow nerve chord that forms spinal cord and brain - notochord at some stage of life cycle (forms intervertebral disks in more advanced groups) - pharyngeal gill slits at some point in life cycle - post-anal tail Several subphyla: Urochordata - tunicates - [Fig. 34.5, p. 701] - mostly marine, sessile - transitional circulatory system (mostly closed) - young are free-swimming larva, adults are sessile. - some seem to be causing problems as invasive species in some coastal areas. Cephalochordata - lancelets - [Fig. 34.4, p. 700] - mobile, though weak swimmers - blade like shape (hence name) - transitional circulatory system (mostly closed) Vertebrata - true vertebrates (fish, birds, mammals, etc.) - well developed nervous and sensory systems - skull, brain - closed circulatory system

2 VERTEBRATES: I. Class Agnatha - jawless fish (sometimes considered a Superclass) - the book is totally nuts with its classification here. Use what is presented here. - surprise - no jaws! - lack paired fins - lampreys and hagfish - eel like shape - lampreys are parasitic - like huge leeches. Wiped out fishing in the great lakes when the St. Lawrence canal was opened. - toothed, sucker like mouth [Fig , p. 704]: - attach to fish, and suck out body fluids. - hagfish are mostly scavengers [Fig. 34.9, p. 703]. - will bury into dead or sick fish and eat it out from the inside. - also make lots of slime when threatened. - don't really have a vertebral column (lampreys do). Jaws - possibly evolved from gill supports (gill arches) [Fig , p. 706] II. Class Chondrichthyes - sharks, rays, etc. (chondros = cartilage, ichthys = fish) - skeleton is composed of cartilage rather than bone - no swim bladder. Unless resting must swim constantly gill slits (one for each gill) - teeth are replaced continuously (that s why shark s teeth are so common). - most sharks are carnivorous (!); the the largest all feed on plankton (strain food over gills) - rays and skates live along the bottom, feed on mollusks and other bottom dwellers.

3 - internal fertilization; some also have live birth (ovoviviparous) - areas in skin can detect electrical fields generated by muscle contraction (helps them zoom in on prey)! III. Class Osteichtyes (osteon = bone) - bony fish - the book once again makes a hash of things here. Stick with this classification. - bony fish - skeleton composed of bone - body covered with scales - several pairs of gills, but all covered by one gill cover (=operculum) - most have air sacs (swim bladders) - lungs are derived from these - about 18,000 species - taxonomy is still debated. What follows is simple, but there are several other possibilities. Subclass Sarcopterygii (again, some debate about the taxonomy - some people put these into two subclasses: Crossopterygii (or lobe-fins) and Dipnoi (lung fish). - lobe-finned fish & lung fish - pelvic and pectoral fins of lobe-finned fish supported by extensions of skeleton - appear to be homologous to limbs. - coelacanth - one living species discovered in 1938: - secondarily marine (most lobe-fins were fresh-water) - lobe-finned fish are thought to be ancestral to modern tetrapods (though recent DNA evidence suggests lung-fish) - lung fish - survive by digging into soil and breathing air during drought. - three genera, as many as six species (depending on who you talk to). - One genus each in Australia, Africa & South America.

4 Subclass Actinopterygii - ray finned fish - most successful group of fish - [Fig , p. 709] - fins are supoprted by bony rays - huge diversity - an incredibly successful group, found in almost any kind of aquatic habitat - don t have time to discuss the details of the various orders (take Ichthyology!). IV. Amphibians (about 4,000 species) - origin? possibly [Fig , p. 710], Acanthostega, a fish, mya., adapted for shallow water. - all are tied to water at some point in their life - eggs must be laid in areas with water, or at least a lot of moisture. - skin is always moist (though level of moistness varies) and used to supplement gas exchange from the lungs. But => water is lost through their skin. - first animals to live on land. - most have external fertilization, but a few do have internal fertilization. - go through metamorphosis - young have gills, finned tail, etc., adults have limbs, lungs (a few weird forms keep gills as adults and never develop lungs). - many groups have poison glands (mention toad licking ) - Three orders: Order Anura - frogs (Anura = without tail) - familiar to everyone - great diversity - many different families: - Toads/Frogs/Tree Frogs/Poison arrow frogs, etc.

5 V. Reptiles Order Caudata (= Urodela in book - know Caudata) - salamanders. - not as many of these, but greatest diversity is right next door - in the Blue Ridge mountains, particularly down towards North Carolina. - Hellbender gets to well over a foot in size (common down south) Order Apoda - caecilians - look a lot like worms, but are amphibians. - tropical - not around here. - A few comments - the great amphibian decline - the number of amphibians worldwide is declining rapidly. - causes seem mostly man-made (climate change, pollution) - a fungus has also been able to spread mostly due to human causes. - hopefully we will be able to do something about this soon! - first really successful group to invade land. How? - scaly skin is relatively impervious to water - internal fertilization, no larval stages - amniotic egg [Fig , p. 715] - allows for shelled eggs that conserve water - embryo has membranes attached that take care of gas exchange (chorion), waste storage (allantois), protection (amnion) and energy/nutrients (yolk). - are cold-blooded (better, ectothermic - get heat from their environment; incidentally, all groups discussed so far are essentially cold-blooded.) - Four living orders (depending on the taxonomist!) [Fig , p. 717].

6 - Testudines - turtles - no teeth, two part shell (plastron and carapace) - ancient group (Triassic, over 250 mya.) - Squamata - lizards and snakes (in same group!) - skin is shed periodically - most have teeth - lizards - 4 legs, external ear opening, movable eye lids, claws (don t confuse these with salamanders!!) - snakes - legless, elongated body, no ear opening, no eyelids (hence myth about prey being hypnotized) - Crocodilia - crocs, alligators, caimans - have a completely four chambered heart (though blood vessels coming off heart still mix blood) - tail compressed laterally for use as fin - Saltwater crocodile is one of the world s most feared man-eaters: - Australia - 1,000 Japanese troops trapped in swamp during World War II. By morning, 20 left. - most don t have that record, though. - Sphenodonta - tuataras - live in small islands off the New Zealand coast. Look externally like lizards. Skull characteristics (pineal eye visible in young) separates this group from all others. - unique enough that until recently (2006) it was on the New Zealand 5 cent coin (New Zealand no longer uses a 5 cent coin). V½. Dinosaurs (reptiles? some folks put them into their own class)

7 [several figures, not in book] - flourished during Mesozoic, about 225 mya to 65 mya. - may have been quite advanced. There is evidence for: - endothermy (warm-bloodedness) - the book is just now admitting some may have been endothermic (evidence has been there for over 30 years!!) - but there is very good evidence for this, including a possible four chambered heart with separate blood vessels found a few years ago - feathers in many groups - parental care - herd behavior - agility and speed - these were not typical lizards. - flying ability - pterosaurs (not dinosaurs, but a related group) had powered flight! - Best theory for extinction - meteor about 65 mya. The impact crater HAS been found. - but other changes were probably also taking place. VI. Aves - birds, about 8,600 species [Fig , p. 719] - some controversy about origin, but generally believed to have been dinosaurs (one way to look at it: dinosaurs did not die out!) - internal fertilization, lay eggs (the basic egg structure is very similar to reptiles) - feathers - highly modified scales (as mentioned, many dinosaurs had feathers!) - endothermic, high metabolism (flying can be energy intensive) - completely developed four chambered heart as well as separation between the systemic and pulmonary circuits (details when we do the circulatory system)

8 - most have adaptations for weight loss: - hollow bones, no teeth (no living bird has teeth) - book mentions frigate birds, which have a wingspan of 2 m, and a skeleton that weighs 4 oz. - most have a large keel for attachment of flight muscles. - divided into about orders, some of which you should find familiar [Fig , p. 720]: - Owls (Strigiformes) - Ducks (Anseriformes) - Penguins (Spenisciformes) - Falcons, Hawks, Eagles (Falconiformes) - Perching birds (Passeriformes) [know the examples above, but you don t need to memorize the fancy scientific names] V. Mammalia - mammals (dogs, bats, mice, humans, etc.) about 4060 species. - body covered with hair - mammary glands (gives this group their name) - endothermic - on average, larger brain than other groups - if teeth are present, they're generally differentiated teeth (incisors, canines, premolars, molars) - almost all live born (three living exceptions) A. Subclass Prototheria - monotremes - lay eggs, lack teeth - five species - duck billed platypus, and four sorts of echidna (look like a

9 porcupine), all in Australia or New Guinea. B. Subclass Theria - all other living mammals - do not lay eggs (live birth) a. Infraclass Metatheria - marsupials - short gestation period - young is born in a very immature state, crawls into mothers pouch, attaches to nipple and finishes development. - placenta develops from yolk sac, not chorion (see egg overhead) - this does not allow for longer development and is not considered a true placenta. - opossum is local example. More opossums exist in South America, but center for Marsupials is Australia: - Kangaroos, Tasmanian devils, etc. b. Infraclass Eutheria - true placental mammals. - Embryo completes most of it s development in the mother - about 18 orders. Most successful are rodents and bats (between them include about 2,500 species) - know at least the following orders: - rodents/bats/carnivores/primates/cetaceans/artiodactyla (just the names as given here, don't worry about the scientific names of these orders) - Finally, a comment on marsupial radiation. - Australia drifted away about 65mya. - Marsupials thus adapted to niches (roles) filled by regular animals elsewhere. - [Fig , p. 723]