MAMMALS Flashcards
(38 cards)
Which group are the mammals derived from?
Synapsids
What is a similarity between synapsids and sauropsids?
Both evolved endothermy (independently)
What happened to synapsids during the permian-triassic period?
- They were hit badly by the end permian-triassic extiction
- This reduced the amount of families
- Mammals and therapsids had relatively small numbers
- Diapsid reptiles diversified in this time (triassic)
- Mammals radiated again later (around the time of the dinsosaur extinction)
What caused the mammals to radiate?
- Therapsids died out - gave rise to mammals.
- Extinction of dinosaurs?
- Change in vegetations?
- Not really known but could be a combination of things
Basal synapsid group
- Pelycosaurs
- Basal group
- Dimetrodon (form of pelycosaur): Sail on back (thermoregulation)
What were therapsids?
- Early more derived synapsids
- Had larger bodies
- Differentiation of teeth
What were Cynodont features?
- Synapsids that gave rise to mammals
- Reduction in size
- Change in limb placement - moved under body
- Changes to skull and teeth
What did the changes in Cynodonts indicate?
A move towards endothermy
How did Cynodont limb placement change?
Limbs moved under body instead of out to side
Synapsid groups (basal to mammals)
- Pelycosaur
- Therapsid
- Cynodont
- Mammal
What are the changes in body form of Synapsids from basal to mammals?
- Upright posture
- Flexible vertebrae
- Reduced tail
- Reduction in ribs freed up lumber area and suggests they had a diaphragm
- Active, endothermy
What specialised feature that is unique to mammals changed their ventilation process?
- The diaphragm
- Sheet of muscle dividing pulmonary and abdominal cavities
- Allows unique lung ventilation
What is the name for teeth that are all the same?
Homodont
What is the name for teeth that are different/ have different specialisations?
- Heterodont
- E.g. Molars, incisors, canines etc
What is the name of the main bone in the lower jaw of mammals?
Dentary
How is the dentary bone specialised in mammals?
- Other bones got incorporated into the middle ear
- Before other bones were thought to be part of a hearing mechanism
- Jaw initially used for hearing and feeding
- Used bone to detect vibrations
How is the joint of the mammal jaw specialised?
- More complex = stronger
- Early synapsids had weak joint
- Mammals have developed strong jaw
How is the mammal skull modified?
Orbit has combined with temporal fenestra
What is the zygomatic arch?
- Essentially our cheekbones
- Arch is well developed
How are locomotion and ventilaiton differ between early synapsids (and lizards) and mammals?
Lizards and early synapsids
- Respiration and locomotion linked
Not very efficient
Mammals
- Separation of respiration and locomotion
- Fast movement can aid in the ventilation of the lungs
Characteristics of early synapsids
- Small, insectivores
- Egg laying - amniote condition
- Nocturnal & solitary - most mammals haven’t got colour vision
- infant / mother bond strong
- Large olfactory bulbs - smell was important
What are the distinct features of mammals ?
- Endothermy
- Lactation and suckling
- Hair (Keratin): insulation, possibly evolved for some kind of sensory function?
- Large brains
What is diphyodont?
Two sets of teeth (milk and adult)
What is the main theory for why diphyodont evolved?
- Animal fed milk early in life so didn’t need permanent teeth until later
- So lactation must have evolved first
