Amniota Flashcards
Amniota
Ancestral amniote was essentially a reptile
Keys to invasion of land:
1) Amniotic Egg
2) Tough and desiccation-resistant skin
Amniote Synapomorphies
Amniotic Egg and its associated 3 membranes:
1) Amnion
2) Chorion
3) Allantois
Loss of larval stage
Loss of gills
Loss of lateral line system
Keratinized skin (resistant to water loss)
True nails/claws (hardened keratin)
Loss/reduction of skull elements in many derived lineages (as with lissamphibians)
Lungs have a greater internal SA filled by thoracic expansion via a negative pressure produced by rib cage usually with sternum (instead of buccopharyngeal pumping via positive pressure as in lissamphibians)
Internal fertilization (most with intromittent organ): ALL amniotes
True penis: Erectile tissue fills with blood
- -Retained by turtles, crocodylians, and mammals
- -LOST in most birds and lepidosaurs
Other characteristics of Amniotes
2 pairs of limbs with 5 digits (ANCESTRAL: CROWN tetrapod synap)
–MANY examples of reduction/loss
Respiration usually exclusively by lungs
Circulatory system divided into pulmonary and systemic circuits with partially to completely divided ventricle (ancestral)
Amniota
Origins: Early Carbiniferous
- Came from ANTHRACOSAUR lineage (similar to how lissamphibians originated from a temnospondyl lineage)
- Extinct basal anthracosaur and temnospondyl lineages were oth “amphibian-like”
3 major groups by later Carbiniferous based on SKULL MORPHOLOGY:
1) Anapsids
2) Diapsids
3) Synapsids
Major radiation in Permian (global drying following Carboniferous)
Anapsida
NO temporal skull opening behind the orbits (completely roofed by dermal skull bones)
Turtles HISTORICALLY considered anapsids:
- NOT actually anapsids, very derived DIAPSIDS
- -CONVERGENCE
NO extant representatives
POLYPHYLETIC group
Diapsida
SYNAPOMORPHY:
- 2 temporal skull openings (fenestrae/fenestrations) behind orbits separated by bony arch
- -Numerous derived conditions in extant taxa obscure original diapsid skull morphology
Represented by ALL living reptiles (HISTORICALLY minus turtles) including birds
2 major lineages:
1) Archosauromorpha
2) Lepidosauromorpha
Lepidosauromorpha
MOST BASAL to MOST RECENT:
Ichthyosauria
Pleisiosauria
Lepidosauria
Ichthyosauria
Contains ichthyosaurs
Most BASAL lepidosauromorphs
Specialized for aquatic HABIT
Derived from terrestrial ancestors
Basal/ancestral forms had a lizard-like morphology
DERIVED forms had a porpoise-like morphology
- -Showed much convergence with whales; however, they DIFFERED in lateral tail movements:
- –Ichthyosaurs have LATERAL undulation
- —More basal character for a more basal lineage; ancestral character of chordates
- –Whales have DORSOVENTRAL locomotion
- —Whales started as dog-like creatures that TRANSITIONED to water, so had a dorsoventrally articulating spine
Tail-first birth
Pleisiosauria
Derived from terrestrial ancestors
Sister taxon to lepidosaurs (maybe)
Specialized for aquatic habit
Necks moderately to extremely long
Paddle-like limbs
Viviparous
Lepidosauria
All EXTANT reptiles except turtles, crocodylians, and birds
Tuatara, lizards/snakes/amphisbaenians
Accounts for >95% of extant non-avian reptiles
SYNAPOMORPHIES:
- Periodic epidermal shedding (derived mechanism)
- Caudal autotomy
- -Able to lose and re-grow tail
- Teeth fused to jaw bones (NO tooth sockets in jaw bones)
Archosauromorpha
Controversial phylogenetic placement of TESTUDINES (turtles):
- DNA indicates closer relationship to ARCHOSAUROMORPHA
- Morphology (and alternative genetic material like RNA) indicates closer relationship to LEPIDOSAUROMORPHA
Archosauria
Includes crocodylians, pterosaurs, dinosaurs, and birds
Flight evolved 2x in Archosauria:
1) Pterosaurs
2) Birds
Repeated evolution of bipedalism
SYNAPOMORPHIES:
- Antorbital and mandibular fenestrations
- Thecodonty (teeth set in SOCKETS)
Crocodylia
Member of ARCHOSAURIA
Fossil record >215mya
<1% of extant non-avian reptile species: relict of past diversity
Pterosauria
Member of ARCHOSAURIA
Membranous wings
1st vertebrates to evolve POWERED FLIGHT
Sparrow-sized to 12 m wingspan
Insectivores, plankton strainers, piscivores (fish-eaters)
Which archosaurs did flight evolve in?
a) birds
b) bats
c) pterosaurs
d) dinosaurs
e) a and c
e) a and c
Bats are NOT archosaurs
