Download Chordates (44,000 species) All chordates share the following [Fig

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
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. 34.10, 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. 34.13, 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.
- 5 - 7 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.
- 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.
Subclass Actinopterygii - ray finned fish
- most successful group of fish
- [Fig. 34.17, 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. 34.19, p. 710], Acanthostega, a fish, 400 - 350 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.
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!
V. Reptiles
- first really successful group to invade land. How?
- scaly skin is relatively impervious to water
- internal fertilization, no larval stages
- amniotic egg [Fig. 34.25, 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. 34.27, p. 717].
- 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)
[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. 34.18, 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)
- 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 26-28 orders, some of which you should find familiar
[Fig. 34.30, 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
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. 34.34, p. 723]