W2 L4a - Evolving on Land: The Amniotes Flashcards
(32 cards)
What are the 4 phylogenetically distinct groups in the Amniotes?
- Synapsida (Mammals & Mammal-like reptiles)
- Testudines (Turtles)
- Archosauromprha (Crocodiles, Dinosaurs, & Birds)
- Lepidosauromorpha (Lizards and Snakes)
What is a clade?
A group consisting of a single common ancestor and all it’s descendants
What does the cladogram of extant tetrapods look like?
—————————————— Amphibians
Synapsids
Turtles A
Turtles B
Sphenodon
Lizards
Snakes
Crocodiles
Birds
- Synapsids and under are Amniotes *
** Turtles and under are Sauropsids **
When did Amniotes evolve on land?
Around mid-Carboniferous (major radiation in Permian)
What are the defining features of Amniotes?
- Waterproof integument (skin) ➡ reduced or no respiration
- Developed lungs ➡ for respiration
- Increasing complexity of the heart
- Skeletal and skull changes ➡ locomotion and foraging
- Muscle changes in head and body ➡ locomotion and foraging
- Amniotic eggs ➡ **Most Important feature separating amphibians from all other Terrestrial vertebrates (Amniotes)
What is the Amniotic Egg?
- cleido = Greek “closed”
- Contains Amniotic fluid, Embryo, Yolk Sac, etc.
Amniotic Egg: Shell Features
- Leathery or calcified shell **still subject to desiccation
- Structural support in air
- Allows gas exchange ➡ H2O, O2, CO2
- Survival in drier areas
- Size ➡ direct development
- bypass larval stages; no gills
- larger (fewer, higher surv.) offspring - Internal Fertilization
Amniotic Egg: Yolk Features
- Nutrients; fuel
- ALL vertebrates have extra embryonic membranes enclosing yolk
** i.e. not unique to amniotes
Amniotic Egg: Unique Components
- Chorion: outer membrane for gas exchange
Allantois, Amnion, Yolk sac all inside Chorion - Allantois: “bladder” that stores nitrogenous waste
- Amnion: inner membrane providing cushion against mechanical shock
Amniotes split into what 2 major groups?
- Synapsids and Sauropsids
What are the specialized characteristics that differ in Synapsids and Sauropsids?
- Locomotor systems compatible with higher rates of lung ventilation
2.Reduced lateral undulations ➡ leg positioning
- Respiratory and excretory systems to conserve H2O
- Ecto- ➡ Endothermy
Describe the lung ventilation and locomotion in Amniotes
Sprawling Gait: conflict between running and breathing, to combat this:
- Locomotion & Respiration separated: for higher rates of lung ventilation - Reduced Lateral Undulations: changes in leg positioning - Respiratory and Circulatory systems changed
How do the brain structures differ in Synapsids vs Sauropsids?
Synapsids: good olfaction (smell), poor vision
Sauropsids: good vision, poor olfaction
- Specialize in diurnal activity
What is diurnal activity?
Active during the day, sleep at night
What is one of the main differences between Synapsids and Sauropsids?
The skull; separated by differences in the “temporal fenestration”
How do the anapsid, synapsid, and diapsid skulls differ between each other?
Anapsid: no fenestra between the postorbital and squamosal bone
Synapsid: one fenestra between the postorbital and squamosal bone
Diapsid: two fenestras between the postorbital and squamosal bone
Why did the skull evolution provide for the Amniotes?
Increased complexity of jaw musculature and feeding; snapping vs chewing
Which skulls belong to existing tetrapods?
Anapsid: Amphibians
Synapsid: Synapsids and Turtles A
Diapsid: Turtles B, Sphenodon, Lizards, Snakes, Crocodiles and Birds
Anapsid Skull Information
- Ancestral reptile condition
- No fenestras; sometimes a notch at the back
- Limits bite force
Diapsid Skull Information
- Two fenestras
- Attachment of larger, stronger jaw muscles; jaw can open much wider
- Allows animals to evolve away from “inertial snapping” (fish)
- Allows evolution of different types of teeth for different needs
- e.g. herbivore cropping/chewing vs carnivore tearing/shearing
What orders make up the Sauropsids (Class Reptilia)?
- Testudines (Turtles)
- Lepidosauromorpha (Lizards and Snakes)
- Archosauromorpha (Crocodiles and Birds)
When did the Sauropsids rise in evolution?
During the Permian-Triassic Extinction; ca. 250 mya
- largest Extinction event ever - generated the Mesozoic ➡ Age of the Reptiles
What are the Sauropsids defining features?
- Respiration
- Circulation
- Metabolism/-thermy
- Nitrogenous wastes
- Hearing
- Vision
- Olfaction
- Foraging
- Locomotion
- Reproduction
- Predator avoidance
- Adaptations to extreme conditions
Is breathing on land easier than the ocean?
Yes,
- air has a higher oxygen content
- need less volume to meet metabolic demands
- air less dense and less viscous
- can pump easily over respiratory surfaces
