Bio Notes 8 -Wednesday - Feb 19th 2003
Next Wed - Feb 26 - test 2.
Class Actinistia (continued)
-Bottom dwelling forms that used paired fins to “walk “ on substratum
-the only extant species is the coelocanth, Latimeria.
-rhipidistians, Eusthenapteron are extinct.
3) Class Dipnoi (Lung Fishes)
-3 genera exist in S. Hemisphere
-Live in stagnant ponds & swamps (Low Dissolved.Oxygen.)
where they surface to gulp air into lungs connected to pharynx.
-Ancestor of Amphibians & all other tetrapods arose from this group.
4)Class Amphibia
-1st vertebrates to move on to land /*but need to back to water to reproduce
*/
-Oldest class of tetrapods
-4,000 extant species of toads, frogs, salamanders (amphibians, reptiles,
birds & mammals are tetrapods )
-Recent molecular data suggest that Amphibians are more closely related to
lungfishes than lobe fin fish.
-3 Extant orders of Amphibians: Urodela (Salamanders), Anura(Frogs
& Toads) & Apoda(caecilians)
Order Urodela:
“Tailed Amphibians”
Salamanders. About 400 species.
/*Lizards are reptiles whereas salamanders are amphibians */
-Some are Aquatic, some are terrestrial.
-Lungless salamanders - Plethodontidae (Family)-Cutaneous Respiration.
-Terrestrial forms walk w/ side to side bending of body.
-Aquatic forms swim sinusoidally (Like a snake - like an S (the letter))
or walk along bottom of streams.
Order Anura “Tailess Amphibians”
(Frogs & Toads)
-About 3500 species.
-Better adapted to terrestrial habitat than Urodeles (the above Order).
-Bright coloration commmon in poisonous species.
ex- Poison arrow frogs of Latin America.
-Enlarged hind legs provide better movement than in Urodeles. (Toads
tend to be terrestrial - and have dry sking - Frogs have slick skin and live
in an aquatic setting)
-Many anurans exhibit a metamorphosis from larval to Adult Stage.
/* Largest Frog is Goliath frog from South Africa - Don't need to know this
*/
Order Apoda
(Caecilians)
about 150 species
-Legless, & Almost blind
-most species burrow in mosit tropical soils.
-few species inhabit Fresh H20 streams & ponds (Ex- Typhlonectes)
-Amphibians are dioecious (separate sexes).
-Reproduce sexually usually w/ external fertilization.
-Most amphibians maintain close ties w/ H20.
-Gas Exchange is primarily cutaneous
-Lungs aid in gas exchange .
-Evolution of Amniotic Egg (Cleidoic Egg) expanded the success of vertebrates
on land. (Reptiles pioneered terrestrial existence in how they had the cleidoic
egg)
-Its development broke the last ties w/ Aquatic Environment.
-------------------------------------------------------------
Class Reptilia
Approximately 7,000 extant species.
Characteristics:
-scales contain Keratin (same thing human nails consist of) which help prevent
dehydration.
-Gas exchange via lungs
-Many turtles (Aquatic) also use moist Cloacal surfaces.
-They're dioecious w/ sexual reproduction & internal fertilization.
-Most are Oviparous (egg laying) w/ sexual reproduction & Internal Fertilization.
-They're dioecious.
-Some are ovoviviparous (eggs are hatched inside female)
-Some species of snakes & lizards are viviparous w/ young
obtaining nutrients from mother across a placenta.
-Reptiles are Ectotherms & use behavioral adaptations to regulate body
temperature.
-Due to ectothermy, reptiles can survive on less than 10% of the calories
required by mammals of comparable size.
-Reptiles were abundant & diverse in the Mesozoic /*Dinosaur era*/ Era
(Age of Reptiles).
-1st Reptilian radiation was in the Early Permian period & gave rise
to 2 evol. Branches (1) Synapsids & (2)Sauropsids
-Synapsids - Terrestrial predators & gave rise to therapsid lineage which
were mammal - like reptiles.
-Sauropsids gave rise modern Amniote (Birds, mammals & reptiles - those
w/ amniotic egg ) groups other than Mammals.
-They split into 2 lineages early in their history.
-1)Anapsids - Presently represented only by the turtles.
2) Diapsids - Represented by lizards, snakes, birds, crocodilians.
(Birds are closely related to the dinosaurs )
*Dinosaurs were Diapsids.
-Cladistic Analysis suggests that birds are the closest living relatives
of Dinosaurs.