Origin of mammals Flashcards
What group gave rise to the mammals?
Synapsids
Describe the transition from Pelycosaurs to mammals
- Pelycosaurs
- Therapsids
- Cynodonts (reduction in size, change in limbs, skull, teeth)
- Mammals
Overalll, changes indicate a move to a more upright posture, reduced tail and more active endothermy
Describe the function of the diaphram and why its important to mammals
Separates pulmonary and abdominal cavities
= separates respiration and locomotion
Name some key features of early mammals
- Small, insectivorous
- Nocturnal & solitary
- Infant/mother bond strong
- Large olfactory bulbs
- Endothermy
- Lactation & suckling
- Hair (keratin) - insulation, sensory?
- Large brains
Describe mammals teeth
Most mammals are diphyodont (2 sets of teeth, come in when jaw is fully formed)
Precise occlusion (teeth fit together to fill all gaps)
Not possible in polydont (reptiles, non-mammals synapsids)
So, diphyodont preceded precise occlusion
How could diphyodonty evolved?
Through lactation:
- Animal fed milk early in life so didn’t need permanent teeth until later in life (once jaw fully formed)
- So, lactation must have evolved first
How did lactation evolve in mammals?
- Mammary glands related to apocrine glands (found in skin)
- Original functions:
Secreted aggregating pheromones (to bond mother and offspring)
To protect eggs from desiccation and microbes - Then evolved as nutritious secretion
What adaptations do mammals have for suckling?
- Secondary palate (separation of nasal and oral passages), allows them to feed and breathe simultaneously
- Tight seals in pharynx prevents fluid enetering lungs and stomach in uncontrolled way
- This all allows tounge to manipulate food
Name some advantages of lactation
Production of offspring separated from seasonal food supply
Mother not dependent on paternal care
Young born at small body size
Describe the mammalian development of facial muscles
- Could be from suckling
- Facial mucles have evolved for chewing and manipulating food
- Facial expressions possible in mammals!
What group belongs to the Prototheria?
Monotremes
(Platypus, spiny anteater, echidna)
What groups belong to the Theria?
Metatheria (marsupials)
Eutheria (placentals)
Compare the gestation times of the metatheria and eutheria
Metatheria (marsupials) → short gestation time, long lactation
Eutheria (placentals) → long gestation, short lactation
Give some features of the monotremes
- Egg laying
- Sprawling gait (=swimming/digging)
- No teeth (keratinised pads)
- Bill/beak
- Electroreceptors & mechanoreceptors
- 5 pairs of sex chromosomes
- Obdurodon had teeth → Echidnas & platypus diverged 19-48 MYA