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Questions and Answers
What is a distinctive feature of amniotes?
What is a distinctive feature of amniotes?
During which geological period did synapsids diversify enormously?
During which geological period did synapsids diversify enormously?
What is a characteristic of Dimetrodon?
What is a characteristic of Dimetrodon?
Which group of therapsids evolved into mammals?
Which group of therapsids evolved into mammals?
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What happened to 80-90% of species during the late Permian?
What happened to 80-90% of species during the late Permian?
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What was a likely cause of the massive loss of vegetation during the late Permian?
What was a likely cause of the massive loss of vegetation during the late Permian?
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What was the result of the splitting of Pangea?
What was the result of the splitting of Pangea?
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Which therapsid group survived the Great Dying?
Which therapsid group survived the Great Dying?
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What was a characteristic of Lystrosaurus?
What was a characteristic of Lystrosaurus?
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What was unique about the dominance of Dicynodonts during the Triassic?
What was unique about the dominance of Dicynodonts during the Triassic?
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What event occurred 66 million years ago that wiped out most of the dinosaurs?
What event occurred 66 million years ago that wiped out most of the dinosaurs?
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What is a characteristic of marsupials?
What is a characteristic of marsupials?
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What is the supercontinent through which marsupials spread throughout the globe?
What is the supercontinent through which marsupials spread throughout the globe?
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What is the term for the process by which marsupials evolved in one geographic location and then spread to other areas?
What is the term for the process by which marsupials evolved in one geographic location and then spread to other areas?
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What is the term for the mammalian jaw transformation that occurred during the transition from non-mammalian synapsids to crown mammals?
What is the term for the mammalian jaw transformation that occurred during the transition from non-mammalian synapsids to crown mammals?
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What is the characteristic of monotremes that distinguishes them from other mammals?
What is the characteristic of monotremes that distinguishes them from other mammals?
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What is the name of the geological boundary that marks the end of the age of the dinosaurs and the dawning of the modern world?
What is the name of the geological boundary that marks the end of the age of the dinosaurs and the dawning of the modern world?
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What is the term for the group of mammals that includes even-toed ungulates?
What is the term for the group of mammals that includes even-toed ungulates?
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What is the term for the group of mammals that includes odd-toed ungulates?
What is the term for the group of mammals that includes odd-toed ungulates?
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What is the characteristic of cynodont therapsids that distinguishes them from mammal-like reptiles?
What is the characteristic of cynodont therapsids that distinguishes them from mammal-like reptiles?
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What is the primary function of the amnion in amniotes?
What is the primary function of the amnion in amniotes?
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Which group of therapsids was characterized by a more upright stance?
Which group of therapsids was characterized by a more upright stance?
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What was the likely impact of the volcanic activity during the late Permian?
What was the likely impact of the volcanic activity during the late Permian?
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What was the result of the splitting of Gondwana?
What was the result of the splitting of Gondwana?
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What was unique about the dominance of Dicynodonts during the Triassic?
What was unique about the dominance of Dicynodonts during the Triassic?
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What was a characteristic of the skull of Dimetrodon?
What was a characteristic of the skull of Dimetrodon?
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What was the likely cause of the massive loss of species during the late Permian?
What was the likely cause of the massive loss of species during the late Permian?
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What was a characteristic of Lystrosaurus?
What was a characteristic of Lystrosaurus?
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What was the likely consequence of the asteroid impact during the late Permian?
What was the likely consequence of the asteroid impact during the late Permian?
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What was the result of the splitting of Pangea?
What was the result of the splitting of Pangea?
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What was the primary driver of the evolution of a more efficient masticatory system in mammals?
What was the primary driver of the evolution of a more efficient masticatory system in mammals?
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What is the likely reason for the geographic isolation of marsupials in Australia?
What is the likely reason for the geographic isolation of marsupials in Australia?
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What is the term for the process by which the mammalian jaw bones were reduced and transformed into a single element?
What is the term for the process by which the mammalian jaw bones were reduced and transformed into a single element?
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What is the characteristic of the K-Pg boundary that distinguishes it from other geological boundaries?
What is the characteristic of the K-Pg boundary that distinguishes it from other geological boundaries?
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What is the term for the group of mammals that includes organisms such as horses and cows?
What is the term for the group of mammals that includes organisms such as horses and cows?
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What is the likely reason for the dominance of reptiles and dinosaurs during the Mesozoic period?
What is the likely reason for the dominance of reptiles and dinosaurs during the Mesozoic period?
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What is the characteristic of the mammalian jaw that is linked to diet and bite force required?
What is the characteristic of the mammalian jaw that is linked to diet and bite force required?
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What is the term for the group of mammals that includes organisms such as rhinos and tapirs?
What is the term for the group of mammals that includes organisms such as rhinos and tapirs?
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What is the likely reason for the evolution of monotremes in Australia?
What is the likely reason for the evolution of monotremes in Australia?
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What is the characteristic of the mammalian jaw that distinguishes it from the reptilian jaw?
What is the characteristic of the mammalian jaw that distinguishes it from the reptilian jaw?
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Study Notes
Amniotes and Synapsids
- All amniotes have a closed egg with an amnion, a membrane that covers the embryo and fills with protective amniotic fluid.
- Synapsids diversified enormously in the Permian, becoming the dominant land animals.
Pelycosaurs and Therapsids
- Pelycosaurs are extinct in the Permian.
- Therapsids evolved into mammals.
- Dimetrodon, a therapsid, lived from 295-272 mya, characterized by slender and agile limbs, and a huge skull in relation to body size.
Therapsid Subgroups
- Dinocephalians/Dicynodont: both herbivorous and carnivorous lineages.
- Theriodonts: evolved into mammals.
The Great Dying
- Sustained extensive volcanic activity, acid rain, and a possible asteroid impact led to a massive loss of vegetation and 80-90% species extinction.
- Dicynodonts survived the Great Dying, including Lystrosaurus, a triassic pig-like herbivore.
Mesozoic and Mammalian Evolution
- In the Mesozoic, Pangea split into Laurasia and Gondwana.
- Fossil records show that during the Mesozoic, reptilian ancestors of modern mammals diverged from mammal-like reptiles.
- The radiation of these evolutionary lines gave rise to cynodont therapsids, which produced the animals we call mammals.
Mammalian Jaw Evolution
- The evolution of the mammalian jaw during the transition from non-mammalian synapsids to crown mammals is a key event in vertebrate history.
- This osteological transformation is accompanied by a rearrangement and modification of the jaw adductor musculature.
Monotremes and Marsupials
- Monotremes: mammals that lay eggs instead of giving birth to live young, with 5 species in 3 genera and 2 families.
- Marsupials: an infraclass of mammals possessing a pouch in which females can carry their young through early development, with 7 orders.
- Marsupials have triple vaginas and forked penises, and are found mainly in the Americas and Australia.
Placental Mammals and Mammal Clades
- Placental mammals: the eutherians, with mammal clades including Afrotheria, Xenarthra, Laurasiatheria, and Eurchontoglires.
- Laurasiatheria: current classifications recognise six orders, including Carnivores, Pholidota, Eulipotyphla, Chiroptera, Perissodactyla, and Cetartiodactyla.
K-Pg Boundary and Ungulates
- K-Pg boundary: the Cretaceous-Paleogene boundary, marking the end of the age of the dinosaurs and the dawning of the modern world, the Cenozoic.
- Perissodactyla: odd toed ungulates, and Artiodactyla: even toed ungulates.
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Description
Learn about the characteristics of amniotes, including their closed eggs with an amnion, and the diversification of synapsids in the Permian period. Explore the features of pelycosaurs, therapsids, and dimetrodon, and how they relate to mammal evolution.
