Mammals Flashcards
The age of mammals
Cenozoic era
Mammals
Not taxonomically diverse.
However has great morphological diversity.
Are able to inhabit a wider range of habitats.
Has diverse habits and ecology.
Has profound impacts on the functioning of the ecosystem as they are currently the dominant vertebrates.
Anthropogenic dependence.
Extant mammal groups
Monotremes
Metatherians (marsupials)
Eutherians (placentals)
Mammals unique features
Hairy endotherms that gives birth to live young which suckle for milk as all are lactogenics (nourish neonates with milk).
Secondary hard palate and soft palate.
Lower jaw is a single with new jaw joint. The middle ear has three bones.
Heterodonty due to specialized teeth.
Glandular integument with hair and mammary glands.
Increased brain size.
Exceptions to the typical mammal definition
Hair is vestigial such as in cetaceans and the naked mole rats.
Many do not regulate their body temperature when inactive.
Monotremes lay eggs
Three bones in the middle ear
Malleus
Incus
Stapes (columella)
Benefits of endothermy
Maintains high body temperature, independent of ambient temperature or muscular activity.
Allows for greater and more sustained activity.
Allows mammals to colonize extreme habitats and niches unavailable to ectothermic vertebrates (thermoconformers).
Consequences of Endothermy
High metabolic rate
High energetic cost therefore the daily food intake is dramatically increased.
Reduces the amount of heat lost, instead of insulation, behavioral avoidance and regional or temporal heterothermy.
Also resulted in the coevolution of a suite of distinctive morphological, physiological and behavioral characteristics to sustain a high metabolic rate at minimum metabolic cost.
Why endothermy?
Niche expansion during Mesozoic radiation of synapsids which allowed activity in unexploited niches.
Increased brain size, increased sensory acuity.
Reproduction is stable as high body temperature accelerated the growth of embryos (in eggs) and neonates.
Allowed for the shift to an active, predatory lifestyle by smaller protomammalian carnivores.
Why the shift to active, predatory lifestyles by smaller protomammalian carnivores?
Mammalian ancestors were large, homeothermic carnivores with thermal inertia.
Selection for smaller body sizes as this allows for smaller prey items meaning less competitions.
This causes a selection for a higher metabolic rate as thermal inertia decreased and the ratio of surface area to volume increased.
Mammal cranium characteristics
Secondary hard palate
As well as a soft, fleshy palate
Dental specializations, heterodoxy for improved handling and mechanical digestion of food items.
Endothermy requires the jaw to be??
It demands a firm, rigid lower jaw able to withstand shearing forces created by the new jaw muscles.
There was a progressive increase in size of dentary until a new jaw joint was formed (with the squasomal). Post dentary bones are smaller and are incorporated into the middle ear.
