Exam 2 Flashcards
(97 cards)
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