BIO 370 Exam 3 Questions with Correct Answers Latest Update 2025-2026
Permian-Triassic extinction - Answers • 57 % marine invertebrate families
• 95 % all marine species
• 49 % tetrapods
• 70% of all terrestrial species
Most life on Earth is eliminated!
Early Triassic - Answers • Pangaea begins to break up
• Transition from a relatively moist & mild
worldwide climate to a more stratified arid
climate worldwide
• Warm moist regions at the poles and more
arid climates at the equator
• No polar ice caps and forests extended to
the polar regions
Early Triassic: Vegetation - Answers • Vegetation dominated by gymnosperms:
• Conifers
• Ginkgo
• Cycads
• Tree ferns
• Horsetails
• No Angiosperms (= flowering, seed-producing
plants): appear during Cretaceous
,• No grasses: appear during the Cretaceous
'
Oxygen levels at roughly ~14%... the lowest concentration in 500 million years, thus leading to
novel adaptations.
What made it through the P/T
extinction? - Answers THERAPSIDS
• Mammal-like reptile synapsids
• Herbivorous dicynodonts
• e.g. Lystrosaurus - dominant form
• Carnivorous cynodonts
• Ancestral to mammals
ARCHOSAURS
• Diapsid reptiles that are ancestral to dinosaurs and crocodylians
• Herbivorous and carnivorous forms
Middle Triassic - Answers Decline of Therapsids
Diversification of Archosaurs
• Mostly herbivores relatively small
• goat to rhinoceros sized
• Browsed close to the ground
Late Triassic - Answers Appearance of
• First mammals (small, insectivorous)
• Turtles
• Crocodiles
,• Marine reptiles
• Flying reptiles
• Dinosaurs (small, carnivorous)
Breakup of the Pangaea:
Jurassic and Cretaceous - Answers Jurassic and Cretaceous:
• Formation of Laurasia - modern N. America
and Gondwana modern S. hemisphere land masses
• Formation of Atlantic Ocean
• Separation of Australia/New Zealand/New Guinea
• India still close to Africa
What makes it through the Triassic/Jurassic
extinction? - Answers • Dinosaurs start to dominate
the large vertebrate fauna
• Marine and aerial diapsids
have a massive radiation
• Mammals are small
insectivores/omnivores at this
time
Archosaurs
• Include dinosaurs, crocodilians,
birds, pterosaurs
• All extinct by the end of
Mesozoic except crocodilians
and birds (and maybe turtles)
, Synapomorphies of Archosaurs: - Answers 1. Socketed teeth allow them to
chew harder materials
2. Antorbital and mandibular
fenestrae openings in front of
the eyes and in the jaw
respectively
3. Fourth trochanter:
• a prominent ridge on the
femur for muscle attachment
• makes it easier to have an
erect posture
Mesozoic = "Age of Dinosaurs" - Answers 1. Permian/Triassic: Extinction leaves a vacuum
...which can be filled with new vertebrate forms allowing for evolutionary
novelties to arise.
2. Triassic: Decrease in atmospheric O2 concentration creates hypoxic conditions
...which favors higher efficiency of respiratory system.
And....crocodiles and birds have unidirectional flow of air through lungs
which is more efficient than bidirectional mechanism.
So, parsimonious that this was possible in extinct Archosaurs.
3. Triassic/Jurassic: Gradual drying of climate and temperature variations
...which favor animals that are good at water conservation.
And archosaurs produce eggs with a hard shell which provides better
protection against desiccation...plus bird and crocodiles produce uric acid.
Permian-Triassic extinction - Answers • 57 % marine invertebrate families
• 95 % all marine species
• 49 % tetrapods
• 70% of all terrestrial species
Most life on Earth is eliminated!
Early Triassic - Answers • Pangaea begins to break up
• Transition from a relatively moist & mild
worldwide climate to a more stratified arid
climate worldwide
• Warm moist regions at the poles and more
arid climates at the equator
• No polar ice caps and forests extended to
the polar regions
Early Triassic: Vegetation - Answers • Vegetation dominated by gymnosperms:
• Conifers
• Ginkgo
• Cycads
• Tree ferns
• Horsetails
• No Angiosperms (= flowering, seed-producing
plants): appear during Cretaceous
,• No grasses: appear during the Cretaceous
'
Oxygen levels at roughly ~14%... the lowest concentration in 500 million years, thus leading to
novel adaptations.
What made it through the P/T
extinction? - Answers THERAPSIDS
• Mammal-like reptile synapsids
• Herbivorous dicynodonts
• e.g. Lystrosaurus - dominant form
• Carnivorous cynodonts
• Ancestral to mammals
ARCHOSAURS
• Diapsid reptiles that are ancestral to dinosaurs and crocodylians
• Herbivorous and carnivorous forms
Middle Triassic - Answers Decline of Therapsids
Diversification of Archosaurs
• Mostly herbivores relatively small
• goat to rhinoceros sized
• Browsed close to the ground
Late Triassic - Answers Appearance of
• First mammals (small, insectivorous)
• Turtles
• Crocodiles
,• Marine reptiles
• Flying reptiles
• Dinosaurs (small, carnivorous)
Breakup of the Pangaea:
Jurassic and Cretaceous - Answers Jurassic and Cretaceous:
• Formation of Laurasia - modern N. America
and Gondwana modern S. hemisphere land masses
• Formation of Atlantic Ocean
• Separation of Australia/New Zealand/New Guinea
• India still close to Africa
What makes it through the Triassic/Jurassic
extinction? - Answers • Dinosaurs start to dominate
the large vertebrate fauna
• Marine and aerial diapsids
have a massive radiation
• Mammals are small
insectivores/omnivores at this
time
Archosaurs
• Include dinosaurs, crocodilians,
birds, pterosaurs
• All extinct by the end of
Mesozoic except crocodilians
and birds (and maybe turtles)
, Synapomorphies of Archosaurs: - Answers 1. Socketed teeth allow them to
chew harder materials
2. Antorbital and mandibular
fenestrae openings in front of
the eyes and in the jaw
respectively
3. Fourth trochanter:
• a prominent ridge on the
femur for muscle attachment
• makes it easier to have an
erect posture
Mesozoic = "Age of Dinosaurs" - Answers 1. Permian/Triassic: Extinction leaves a vacuum
...which can be filled with new vertebrate forms allowing for evolutionary
novelties to arise.
2. Triassic: Decrease in atmospheric O2 concentration creates hypoxic conditions
...which favors higher efficiency of respiratory system.
And....crocodiles and birds have unidirectional flow of air through lungs
which is more efficient than bidirectional mechanism.
So, parsimonious that this was possible in extinct Archosaurs.
3. Triassic/Jurassic: Gradual drying of climate and temperature variations
...which favor animals that are good at water conservation.
And archosaurs produce eggs with a hard shell which provides better
protection against desiccation...plus bird and crocodiles produce uric acid.
