Mammals Flashcards
Mammals and mammal-like reptiles form which clade?
Synapsids
The non-mammalian synapsids include the…
Pelycosaurs (Earliest), Therapsids and Cynodont Therapsids (Last)
How many major adaptive radiations have the synapsids undergone?
3
The tertiary radiation of the mammals is associated with which event?
Dinosaur Extinction
Which region were the pelycosaurs mainly located
Laurasia (N. Hemisphere)
Which two key traits possessed by more derived synapsids did pelycosaurs lack?
1.High locomotor capacity, 2.
increased metabolic rate
What is the key defining feature of synapsids?
Temporal fenestra (hole accommodating jaw muscles behind the eyes)
Why are the sails many pelycosaurs had unlikely to have been used in display?
Lack of sexual dimorphism
What was the likely function of pelycosaur sails?
Temperature regulation
Where were the Therapsids mainly located?
Gondwana (S. Hemisphere)
What are the key features of the Therapsids?
- Increased metabolic rate
- Trough in roof of mouth indicates the evolution of a dedicated airway separate from rest of oral cavity
- Differentiation of teeth types
- Flexible neck
What major evolutionary trends can be observed in later Therapsids?
- Larger temporal fenestra
- Greater teeth specialization
- Development of bony secondary palate
- Change in limb position
- Dual gait locomotion
- Loss of lumbar ribs (diaphragm- higher rate of respiration
- Increased regulation of internal temps and chemical environments.
The Mesozoic radiation accounts for what fraction of mammalian evolutionary history
2/3
What were the key features of the Mesozoic mammals?
- Tiny
- Derived features of skull reflecting larger brain and inner ear
- Evolution of lactation and suckling
- Special Harderian gland- located in the nose, secretes insulatory lipid layer, suggests fur and preening
Tertiary radiation is characterized by what trend
Diversification of mammals into larger, more specialized forms
What is the most likely cause of the End-Pleistocene Megafaunal Extinction?
Increased efficiency of human hunting
What are the key characteristics of modern mammals?
- Endothermy (internal regulation)
- Reproduction- offspring continue to require maternal care for a long period after birth
- Lactation
- Hair
- High blood pressure, oxygen uptake, metabolic rate, water regulation (loops of Henle)
- Improved locomotion
- Improved sensory systems
Why can’t juvenile mammals maintain a high level of homeostasis?
- SA:Volume ratio too high
2. Takes time to develop control systems, especially in the brain
Why is lactation advantageous?
- Allows reproduction at any time of year
2. Newborns do not need teeth, allowing for diphyodonty (baby and adult teeth), and greater tooth complexity.
What purpose may lactation have served before nutrition?
Antimicrobial and immunological benefits
What characteristic mammalian trait emerged as a byproduct of suckling?
Complex facial muscles
What are the benefits of hair?
- Insulation
- camouflage
- Communication
- Sensation via vibrissae (whiskers)
What are the key features of mammalian sensory systems?
- Exceptionally large brains, neocortex
- More reliant on hearing and olfaction
- Retinas largely rod cells with high sensitivity to light but poor acuity
- Acute vision possible in small region of retina
What features make mammalian locomotion possible?
- Regulation of physical orientation
2. Use of the high energy aerobic physiology
Types of mammalian locomotion?
- Non-cursorial (primitive)
- Cursorial (running)
- Fossorial (digging)
- Saltatory (jumping)
- Aerial
- Aquatic
- Arboreal
What advantage do multiple gaits provide?
Flexibility over varied terrain
What are the three subclasses of modern mammals?
- Monotremata
- Marsupialia
- Placentalia
What are the two families of monotremes?
- Platypus (Ornithorhynchidae)
2. Echidna (Tachyglossidae)
Which to features of monotreme reproduction are unique amongst mammals?
- Possess cloaca (single opening for reproduction and excretion)
- Lay eggs
What form of cleavage do monotreme eggs undergo?
Meroblastic cleavage (Only one region of the egg divides, forming embryo on surface of non-dividing yolk sac)
