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shared derived trait (evolved from common ancestor)
Mammal synapomorphies
1. bear live young
2. hair
3. sebaceous and sweat glands
4. mammary glands
5. endothermy
6. heterodont dentition (incisors, canines, molars, premolars)
more mammal synapomorphies
7. enucleate red blood cells
8. muscular diaphragm (separating thoracic and abdominal cavities
9. 4 chambered heart
10. increased sensory acuity
11. secondary hard palate
12. diff of lumbar and thoracic vertebrae
13. ossified epiphyses
14. brains is 3-4 times larger and convoluted
15. corpus callosum
16. Neopallium (roof of forebrain)
Mammalian Dentition Formula
I+C+P+M = #teeth
teeth are very important for identification in mammals
what makes mammalian lower jaw unique
is a single bone; articulates with squamosal bone;
three ossicles in middle ear
Mammalian development of dentary-squamosal joint
Crossopterygian (lobe-finned) fishes -> Amphibians->advanced reptiles-> mammals
Middle ear
From upper jaw: Hyomandibular (fish) -> stapes
Quadrate -> Incus
From lower jaw :
Articular -> Malleus
Angular -> tympanic
Cranium evolution
anapsid-> synapsid reptile-> modified synapsid (reduction in cranial bones, increased temporal openings
Mammal cranium key developments
temporal openings merge
parietal bones move posteriorly
zygomatic arch is all that remains of anapsid skull
allows for bigger brain
secondary hard palate
masseter muscles differentiate and attachments change
for better dentition, masseters, and eating apparatus
Limb development
changes from primitive sprawling gate to directly beneath
Mammals evolved over which period?
after late permian into early triassic (~248mya)
Mammals radiated during which period?
after dinosaur extinction ~65mya
Most diverse - least diverse vertebrate groups 2018
Non-avian reptiles
Cenozoic Era
Age of mammals (right after cretaceous) includes tertiary and quaternary
4 key mammalian traits
hirsute (hair)
vivparous (live birth)
major driver of trait evolution
demands to improve energetic efficiency and endothermic homeostasis
unique demands on mother and young, obligate relationship between them, maybe responsible for complex social systems and behaviors of mammals
Mammal energetics
high body temp
high BMR
high aerobic capacity
increase cellular and aerobic respiration and muscle activity (shivering)
Benefits of energetic efficiency
inhabit cold regions
active under wide envrionmental conditions and less vulnerable to fluctuations
maintain long periods of activity
evolution of bigger brain
Costs of energetic efficiency
90% of energy on homeostasis, 10% for growth and repro
need stable food source
need to move a lot
Solutions to costs
Control heat loss
increase metabolic efficiency
increase locomotor efficiency
increase food processing efficiency
1. How do we control heat loss?
-hair (w/dermal muscles)
-dilate/constrict blood vessels
-decrease water loss (nasal conchae, mucous membranes)
Hair structure
dermal muscles control it
dead epidermal cells with keratin
3 layers:
clear cuticle outside, pigmented cortex and medulla inside
functions of hair
reduce heat loss
concealment and camouflage
molting allows seasonal variation
disruptive colors
aposematic colors
sebaceous glands
lubricate hair and skin
waterproof pelage
sweat glands
evaporative cooling
enhance grip in some species
2. How do we increase metabolic efficiency
4-chambered heart
red blood cells
4 chambered heart
complete separation of ox and deox blood
right-venous blood
left - arterial blood
red blood cells
biconcave disk shape
lack nuclei
maximize o2 carrying capacity
muscle that separates abdominal and thoracic cavities
increases lung ventilation
increase locomotor efficiency
-diaphysis (shaft) and epiphysis (articular ends)
- double occipital condyle
- 2 specialized cervical vertebrae
- structured vertebral column
- rigid vertebral column
-bone loss and fusion
- limbs beneath body
- efficient levers on limbs
diaphysis and epiphysis
strong muscle attachments
specialized joints
efficient articulation during growth
double occipital condyle
strengthen contact with vertebral column
allows flexibility in two planes
2 specialized cervical vertebrae
atlas rotates around axis
move head separate from body/spine
strengthens contact with vert column
structured vert column
cervical, thoracic, lumbar, sacral, caudal
for regional specialization of movement
rigid vert column
zygapophyses/articular processes on all 4 sides of verts to fit with adjacent verts
make spine laterally rigid,
better fulcrum pt for limbs=more efficient
bone loss and fusion
pectoral girdle reduced to scapula and clavicle (among other examples)
lighter, quicker, and stronger
lumbar ribs lost
limbs underneath
weight is on bones, movement in one plane (fore and aft)
efficient levers on limbs
-calf pulls calcaneous - heel
-triceps pulls olecranon process - elbow of ulna
4. how do we increase food-processing efficiency
- more efficient and powerful jaw apparatus
- complex and specialized teeth
reduced to 2 bones - increases strength
Jaw articulation
dentary articulates with squamosal bone and moves fulcrum pt forward = greater force
zygomatic arch
3 bones: maxilla, jugal, squamosal
jaw fits through zyg arch
attachment of jaw muscles
expanded musculature
jaw muscles work in concert
temporal - pulls jaw up
masseter pulls jaw apart
pterygoid - pulls jaw laterally
for precise tooth placement and equal force on teeth
secondary palate
3 bones form palate on roof of mouth - premaxilla, maxilla, palatine - mouth and nasal passages separate
chewing on one side of mouth
teeth with matching shear surfaces
precisely match for chewing and specialization
thecodont dentition
teeth rooted in bony sockets, are very strong
heterodont dentition
teeth vary in morphology for diff functions, flexibility in handling and processing food
Sensory Adaptations
hearing, touch, and processing
pinnae - ext ear
ossicles - middle ear
vibrissae - whiskers
catch and funnel sound and can move
malleus, incus, stapes, amplify and transmit vibrations to cochlea - inner ear
functions of hearing
high acuity
locating food
detecting/avoiding enemies
vibrissae or facial tactile hairs, receptor cells and nerves, motor control
identify movement, texture, shape
processing senses
enlarged brain
forebrain - olfaction
cerebral cortex
cerebral cortex
6 layered structure: neocortex or neopallium
spatial patterns/awareness
motor control
sensory perception
conscious thought and memory
mammary glands
facial (dermal) muscles
diphydont dentition
mammary glands
system of modified sweat glands and ducts
teat, nipple, or hair tutfts
endocrine control
Diphydont dentition
2 successive sets of teeth - young can eat same food as adults
facial (dermal) muscles
superficial muscles allow skin on face to move - suckling, whiskers, ear movements, facial expression
Other traits
scent glands
scent glands
secrete chemicals to env
pheromones: social status, territorial marking, sexual status
testes outside body, keeps them cooler than body
live birth
fetus at thermal optimum, protected, some nourished, some born well-developed
Egg laying mammals
Mammal-like reptiles taxonomy
Class: Reptilia
Subclass: Synapsida
Order: Therapsida
Characteristics of mammal like reptiles
reduction of temporal shield, differentiation of masseters
heterodont dentition
2 occipital condyles
maxillary and premaxillary bones into hard palate
condyle of dentary fits into glenoid fossa of squamosal bone
early mammals in triassic that gave rise to monotremes
CLASS: Mammalia
SUBCLASS: Prototheria Infraclass: Eotheria
Order: Triconodonta
family: Morganucodontidae
Triconodonts (extinct)
first true mammals on record - triassic
Symmetrodonts (extinct)
first placental mammals - split from metatheria in jurassic
Prototheria (extant)
Theria (extant)
Metatheria (marsupials) and Eutheria (placental)