MAMMALS Flashcards
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
Evidence for lactation
- Most mammals are Diphyodont
- Also have precise occlusion
- Precise occlusion not possible in reptiles and early synapsids
- Diphyodont preceded precise occlusion
How many times was lactation thought to have evolved?
- Believed to have evolved once
- Casein genes are seen in every group of mammals
- Casein genes are the genes that produce milk
What is precise occlusion?
- Teeth fit together precisely
- Allows for grinding of teeth
- Interdigitating
How do mammals upper and lower jaws fit together and what feeding habits does this allow?
- Lower jaw is smaller than upper
- Allows movement from side to side (chew food)
How did lactation evolve?
- All female mammals lactate and have mammary glands
- Some males (e.g. some bats) lactate
- Mammary glands related to apocrine glands (found in skin associated with hair)
- Originally secreted aggregating pheromones
- Milk may have been produced to protect eggs from desiccation and microbes
- Then evolved as nutritious secretion
- Monotremes have no nipples
What is the evolutionary advantage of lactation?
- Production of offspring separated from seasonal food supply
- Mother not dependent on paternal care
- Young born at young stage of development
What allows suckling?
Secondary palate
What are the benefits of a secondary palate?
- Tight seals in pharynx → prevents fluids entering lungs and stomach in uncontrolled way
- Separates nasal and oral passage
- Allows tongue to manipulate food
What is the structure of the secondary palate?
- Hard and soft palate
- Soft palate creates 2 seals
- Allows animal to feed and breath at the same time
What is the function of seal one in the secondary palate?
Allows gargling
What is the function of seal two in the secondary palate?
- Forms between soft palate and epiglottis
- Prevents flow of substances from mouth entering trachea
What happened to seal two in human?
Secondary palate
- It is lost in adult humans
- Prone to choking
Example of a type of adaptive feeding habit that the seals of the secondary palate allow?
- Baleen whales use seals for feeding - filter feeding
- Not possible in any other animals
what has the development of the facial muscles allowed in mammals?
- Sauropsids well developed for swallowing - don’t chew
- Mammals chew so muscles evolved new functions
- Homologous with neck constrictor muscles of other tetrapods
