Exam 2 Flashcards
Why did organisms move onto land?
- new food sources (insect radiation in the Carboniferous period)
- avoid high predation
- move from one drying pond to another (ex. lungfish)
- basking in the sun to elevate body temp (increased activity)
- dispersal of juveniles away from natal site (less competition)
Sarcopterygian synapomorphies
- fins supported by small bony, muscular lobes
- cosmine on dermal bones and scales
- intracranial joint between anterior and posterior portions of braincase
Coelacanthimorpha
- primarily marine, large, deep water fish
- once believed to have gone extinct in the Mesozoic
- unique rostral organ (electroreception)
- internal fertilization, viviparous
- sister group to lungfish and tetrapods
- part of Class Sarcopterygii
Dipnomorpha
- 6 species (Australia, Africa, South America)
- first evolved ~400 mya
- estivate in burrows during the dry season, mucus secretions seal burrow
- part of Class Sarcopterygii
Dipnomorpha synapomorphies
- holostylic jaw (palatoquadrate is fused to the cranium)
- duraphagous apparatus (broad teeth plates lining the palate, reduction in jaw bone)
- well developed lungs
(Part of Class Sarcopterygii)
Tetrapods
terrestrial vertebrates descended from common four-legged ancestor, possess chiridium
chiridium
muscular limb with well-defined joints and digits
Tetrapodomorphs
group of extinct fish closely related to extant sarcopterygians
Eusthenopteron
- tetrapodomorph
- Late Devonian sarcopterygian fish
Traits Shared w/ Early Tetrapods - enamel coated teeth (labrynthodont teeth)
- rudimentary humerus, radius, ulna
- more robust vertebrae (enlarged introcentrum)
Tiktaalik
- tetrapodomorph
- late Devonian sarcopterygian most similar to tetrapods
- good shallow water predators with eyes on top of head, and no dorsal/anal fins
Traits Shared w/ Early Tetrapods - loss of bony operculum (skull is not connected to pectoral girdles which allows the head to raise above the water)
- forelimb with metacarpals
- ribs projecting more ventrally to support body out of water
How are tetrapodomorphs still fish-like?
- retain distinct caudal fins and fin-like limbs
- retain a fusiform body with undifferentiated epaxial and hypaxial muscles
- poorly ossified vertebrae
- retain well developed gills
Stem tetrapods
Acanthostega and Ichthyostega
Fish-like traits of Acanthostega
- fin rays on large caudal fin and fin-like limbds
- weak zygapophyses
- internal gills (operculum)
- evidence of lateral line system
Tetrapod-like traits of Acanthostega
- some differentiation in vertebral column
- limbs are well defined (chiridium, 8 digits)
- robust pelvic and pectoral girdles
More derived traits of Ichthyostega
- robust ribs (support thorax on land)
- stronger zygapophyses
- smaller caudal fin
- highly differentiated thoracic and lumbar vertebrae
Benefits of limbs in aquatic predators?
- can climb underwater vegetation
- allows for rapid ambush in shallow water
Where did caecilians evolve from?
Stereospondyles
Where did frogs and salamanders evolve from?
Dissorophoidea
What are reptilomorphs?
Stem amniotes
Extinct non-amniote tetrapods
- Stereospondyles
- Dissorophoidea
- Reptiliomorphs
Stereospondyles
- mostly larger forms
- flat skulls with long snouts
- two occipital condyles for rotating head
Dissorophoidea
- smaller forms
- short snout and large eyes
- large tympanum for hearing
- some fossils have a combination of salamander and frog traits
Reptiliomorphs
- mainly terrestrial with terrestrial limb structures
- domed skull
- 5 digit feet
- likely ancestor of amniotes
Amniotic Egg
- leathery or rigid shell (some permeability)
- albumin
- yolk
- 4 extra-embryonic membranes
albumin
(in amniotic eggs) source of water and protein, acts as a protective layer
yolk
(in amniotic eggs) primary energy source (lecithotrophic)
What are the four extra-embryonic membranes in the amniotic egg?
- yolk sac
- chorion
- amnion
- allantois
Yolk sac
- made of embryonic endoderm and mesoderm
- surrounds yolk
- develops into the gut
Amnion
- made of embryonic ectoderm and mesoderm
- inner membrane that surrounds the embryo
Chorion
- made of embryonic ectoderm and mesoderm
- outer membrane that surround the entire embryo and yolk
Allantois
- made of embryonic endoderm and mesoderm
- nitrogenous waste site
- respiratory organ during later development
Benefits of amniotic egg?
- allantois allows storage of nitrogenous waste
- tough shell for support on land (avoid drying out)
- larger egg allows for larger hatchlings which increases survival
- respiration is possible through the semi-permeable shell
Synapomorphies of amniotes
- amniotic egg
- keratin derived dermal features (scales, hair)
- costal ventilation
- lateral flange on pterygoid bone aids in chewing
- more complex brachial plexus innervating forelimbs
costal ventilation
use of ribs to ventilate lungs (results in less water loss to environment)
temporal fenestration
major openings in temporal region of skull, used to divide amniotes into major groups
anapsids
group of amniotes that lack fenestra (primitive amniotes and turtles)
synapsids
group of amniotes with lower temporal fenestra only (mammals)
diapsids
group of amniotes with upper and lower temporal fenestra (extant reptiles and birds)