40 Questions
What is a distinctive feature of amniotes?
The presence of an amnion
During which geological period did synapsids diversify enormously?
Permian
What is a characteristic of Dimetrodon?
Its slender and agile limbs
Which group of therapsids evolved into mammals?
Therapsids
What happened to 80-90% of species during the late Permian?
They went extinct
What was a likely cause of the massive loss of vegetation during the late Permian?
The eruption of volcanoes
What was the result of the splitting of Pangea?
The formation of multiple continents
Which therapsid group survived the Great Dying?
Dicynodonts
What was a characteristic of Lystrosaurus?
Its pig-like body
What was unique about the dominance of Dicynodonts during the Triassic?
It was the first time a single group dominated the terrestrial planet
What event occurred 66 million years ago that wiped out most of the dinosaurs?
The impact of an asteroid on Earth
What is a characteristic of marsupials?
Having a pouch in which females can carry their young
What is the supercontinent through which marsupials spread throughout the globe?
Gondwana
What is the term for the process by which marsupials evolved in one geographic location and then spread to other areas?
Allopatric speciation
What is the term for the mammalian jaw transformation that occurred during the transition from non-mammalian synapsids to crown mammals?
Osteological transformation
What is the characteristic of monotremes that distinguishes them from other mammals?
Laying eggs instead of giving birth to live young
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?
K-Pg boundary
What is the term for the group of mammals that includes even-toed ungulates?
Artiodactyla
What is the term for the group of mammals that includes odd-toed ungulates?
Perissodactyla
What is the characteristic of cynodont therapsids that distinguishes them from mammal-like reptiles?
Having a more-efficient masticatory system
What is the primary function of the amnion in amniotes?
to protect the embryo with amniotic fluid
Which group of therapsids was characterized by a more upright stance?
Dinocephalians
What was the likely impact of the volcanic activity during the late Permian?
acid rain and massive loss of vegetation
What was the result of the splitting of Gondwana?
separation of Africa, South America, Antarctica, Australia, and India
What was unique about the dominance of Dicynodonts during the Triassic?
they were the only group to dominate the terrestrial planet
What was a characteristic of the skull of Dimetrodon?
it was very heavy, robust, and deep
What was the likely cause of the massive loss of species during the late Permian?
sustained volcanic activity
What was a characteristic of Lystrosaurus?
it was a Triassic pig-like herbivore
What was the likely consequence of the asteroid impact during the late Permian?
massive loss of vegetation
What was the result of the splitting of Pangea?
splitting into Laurasia and Gondwana
What was the primary driver of the evolution of a more efficient masticatory system in mammals?
Changes in diet and bite force required
What is the likely reason for the geographic isolation of marsupials in Australia?
The breakup of the supercontinent Gondwana
What is the term for the process by which the mammalian jaw bones were reduced and transformed into a single element?
Osteological transformation
What is the characteristic of the K-Pg boundary that distinguishes it from other geological boundaries?
A layer of iridium-rich rock
What is the term for the group of mammals that includes organisms such as horses and cows?
Artiodactyla
What is the likely reason for the dominance of reptiles and dinosaurs during the Mesozoic period?
The adaptation of reptiles to changing environmental conditions
What is the characteristic of the mammalian jaw that is linked to diet and bite force required?
The presence of a mandibular symphyseal fusion
What is the term for the group of mammals that includes organisms such as rhinos and tapirs?
Perissodactyla
What is the likely reason for the evolution of monotremes in Australia?
The geographic isolation of Australia during the breakup of Gondwana
What is the characteristic of the mammalian jaw that distinguishes it from the reptilian jaw?
The reduction of individual bones into a single element
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.
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.
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