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Mammalian Diversity

- 6,000-6,500 species
- Largest orders (in order) are Rodentia, Chiroptera, Soricomorpha, Primates
- Total of 28 orders



Two sets of temporal fenestrae in the skull
- Supratemporal
- Infratemporal

Condition of most reptiles



No temporal fenestrae
Condition of turtles



One set of temporal fenestrae in the skull
Condition of mammals



- May be considered the first mammal, depending on the characteristics you use to define mammals
- Small, about 10cm
- Plantigrade
- Nocturnal and insectivorous
- Furred
- Laid small, leathery eggs
- Had two sets of teeth, milk and adult


Special Characteristics of Mammals

- Enhanced intelligence and sensory abilities
- Good sense of smell and hearing
- Endothermic
- Highly efficient reproduction, lactation and social learning
- Efficient food procurement and processing


Mammalian Skull Features

- Single dentary bone makes up the mandible
- Dentary articulates with squamosal
- Quadrate and articular in reptiles have become inner ear bones (incus and malleolus) in mammals
- Pinnae (external ear)
- Epiphyses of the long bones
- Flexible neck (typically 7 cervical vertebrae)
- Two occipital condyles
- Secondary palate separates mouth from nasal cavity


Mammalian Teeth Features

- Thecodont (socketed teeth)
- Heterodont
- Diphyodont (teeth replaced once during development)

All these characteristics are variably present in non-mammals



Teeth are socketed



Different types of teeth (i.e. incisors, canines, premolars, molars)



Teeth are replaced once during development


Mammalian Soft Features - Hair

- Body is typically covered by hair at some stage in development in mammals
- Mainly functions as insulation but can hae other uses
- Replaced once or twice a year in a moult
- Colour patterns typically serve as camouflage
- Sebaceous skin glands produce oils to lubricate and maintain hair



Dead epidermal cells that are strengthened by keratin
Grow from living tissue contained in the root



Word used for a mammalian coat of hair



Stiff hairs used as a tactile organ
- Associated with complex facial muscles
- Typically found on the face but sometimes legs as well


Sebaceous Glands

Skin glands that are associated with individual hair follicles

Produce oils that lubricate and help maintain hair


Sweat Glands

Skin glands that secrete water
Used to eliminate waste and promote evaporative cooling
Restricted to certain parts of the body in most mammals


Scent Glands

Skin glands that create odours and pheromones
Used to mark territory and attract mates
May also be used to get rid of pests or predators


Mammary Glands

Modified sweat glands, but produce milk
Possessed by all mammalian females
Male eutherians also have them but they are rudimentary
Vary in number between 2-19
Produce milk when stimulated by things like prolactive
Some mammals do not have nipples to facilitate milk transfer (monotremes, cetaceans)
Milk composition varies between species


Mammalian Soft Features - Internal Features

- Muscular diaphragm facilitates diaphragmatic breathing
- Four chambered heart
- Only the left aortic arch present
- Red blood cells lack nuclei at maturity to increase oxygen carrying capacity
- Brain large
- Optic lobe of brain present



Maintenance of constant internal temperature
Allows for an active lifestyle
Means that in mammals the standard metabolic rate is higher, and there are more capillaries, bigger organs in general
Must be eating constantly and therefore locomoting to find food



Naming and classification of organisms
Determining of the evolutionary relationships between organisms



Ordering and ranking of taxa



Study of the diversity of organisms


Mammalian Classification

- Is related to biogeography; closely related species originated in the same area
- Is changing very rapidly


G.G. Simpson

Presented hypotheses of mammalian origins and relationships that were universally taught until the end of the 20th century



Uses similarities between organisms as the only way to determine evolutionary relationships
Weighs all characteristics equally


Phylogenetic Systematics

Not all characters have the same weight
The only informative characters are the shared derived characters


Reproduction - Prototheria

- Lay eggs that are telolecithal, mesoblastic
- Shell glands in the oviducts secrete a rubbery shell around the embryo
- Reproductive system ends in a cloaca
- No scrotum in males (testes are abdominal)
- Eggs remain in oviduct for ~27 days before being laid
- Sperm is threadlike


Development of Young - Prototheria

- Eggs hatch 10-11 days after being laid
- Young brooded in pouch for a couple months
- Females do not have nipples but secrete milk into grooves on the abdomen, long tufts of hair that young suckle
- Female needs to eat a lot while brooding/lactating


Reproduction - Metatheria

- Females have a paired vaginal canal; two uteruses
- Birth canal opens up between the vaginal canals during the actual birth
- Males have a bifurcated penis and a well-developed scrotum, but it is anterior to the penis
- Urinary, digestive and reproductive tracts are separate (no cloaca)
- Young are retained in the uterus for a very short time, less than an estrous cycle (22-26 days)
- Uterus does not change physiologically as in eutherians
- Shell membrane coating the embryo breaks between 1/3 and 2/3 of development and begins to absorb nutrients through the uterine wall
- Choriovitalline placenta
- Embryo does not obtain much nutrition from mother and oxygen runs out quickly, so young born quickly


Development of Young - Metatheria

- When born, young crawl to pouch (if pouch exists) using forelimbs, attach to teat
- Very underdeveloped at birth (only 1% of mother's body mass for the whole litter), lack cranial nerves, eyelids, eye/ear pigments, two halves of brain disconnected, hindlimbs buds, fourth chamber of heart hasn't developed yet, cutaneous respiration
- Attached to nipple for much longer than time spent in utero; release around the same time a eutherian would take to gestate
- Composition of milk changes as time passes and infant's nutritional needs change



- Pouch present in 2/3 of marsupials for carrying young
- Made of folds of skin
- Best developed in jumping species


Reproduction in Kangaroos and Wallabies

- Have one young at a time, but go into estrous right away and fertilize an egg
- If egg is fertilized while another is attached to the nipple, egg goes into diapause
- Mother may in fact have three generations on the go: egg in diapause, infant attached to nipple, older joey that is free but comes back for milk
- Each nipple is specialized and gives milk specifically designed for the young using it



Egg in which the yolk is concentrated at one end of the egg and is separate from the growing embryo


Choriovitelline Placenta

Yolk sac supplies a large part of the embryo's nutrition but placenta also attaches to uterine wall and takes nutrients directly from the mother's bloodstream


Reproduction - Eutherians

- Single vagina
- Chorioallantoic placenta
- Young does most of its development in the uterus, born at much more advanced stage than that of metatherians
- Extensive physiological changes to the uterus during pregnancy


Benefits of Eutherian Reproduction

- Ulimited oxygen supply to embryo
- Unlimited water supply to embryo
- Nitrogenous waste deposited directly into mother's system
- More nutrition provided during development
- Embryo can be protected from parasites/disease/predation


Disadvantages of Eutherian Reproduction

- Can't easily reject the embryo if conditions become bad
- Mother's body may reject the embryo, causing issues for both baby and mother


Chorioallantoic Placenta

- Entirely responsible for fetal nutrition and waste removal
- Chorion and allantois fuse and attach to uterine wall, take nutrients from female's bloodstream
- Erodes away the uterine wall, sometime so extreme allantois is surrounded by a pool of capillary blood
- Secretes a hormone that suppressed female's immune system and prevents rejection of fetus



- Surround an embryo during development and form a large part of the placenta
- Separates embryo from maternal circulatory system


Basic Mammalian Locomotion

- Plantigrade
- Quadrupedal
- Limbs rotated to be under the body



Locomotion with entire manus/pes on the ground
Used for ambulatory locomotion


Increasing Speed

- Lengthening of the limb
- Also increases maneuverability
- Decreases stability (some animals will change their gait with changes in speed to aid in stabilizing)
- In order to lengthen limb, base support becomes smaller



- Used for cursorial locomotion
- Walks and runs only on the digits
- Decreases contact with the ground and also increases the lever arm of the limb



- Used for cursorial locomotion
- Walks and runs on the tips if the distal phalanges
- Most of the muscle mass is located proximally on the limbs
- Basically gives the animal an extra joint


Cursorial Size Limitations

- The longer the limb, the more torque is created during running
- Musculature is usually what counteracts torque, but this is reduced in long limbs
- Larger animals find it harder to mediate velocity, making them less maneuverable; they can go absolutely faster but can't slow down or turn easily


Saltation and Ricochetal Locomotion

- Jumping using the hindlimbs disproportionately
- Quick, unpredictable and maneuverable
- Usually have a long tail and large/long hindlimbs through which forces can act
- Proximal hindlimbs are very muscular
- Origins and insertions of muscles shift to maximize thrust



- Usually on trees, but also rocks
- Need to be able to move in any direction and at any angle
- Have long, curved claws/nails to grasp at substrate
- Can use suction or friction grip
- May have prehensile limbs and tails
- Shorter limbs to aid in balancing
- Tend to be small in size
- Move between trees by jumping, gliding or bridging



Method of transferring between trees by hanging onto first tree with one side of the body, grabbing on to other side and then transferring weight over



- Fusiform body shape
- Reduced and sometimes non-functional eyes
- Reduced pinnae
- Large front feet with big claws
- Short, broad head
- Reduced or absent tail
- Tend to have short hair, density depends on climate
- Can dig with teeth, limbs, even head


Digging with Teeth

Such animals will have enlarged incisors with the fur and skin closing behind them
- Seals incisors off from oral cavity


Digging with the Head

- Done in loose soil
- Use the head as a spade
- Requires powerful, short, broad head with heavy musculature on the back of the neck


Digging via Humeral Rotation

- Orientation of front feet altered to face laterally
- Dig to the side instead of underneath the body


Aquatic Locomotion

- Uses two different methods of swimming: undulatory and oscillatory
- Biggest issue is reducing drag, which can be done by making the body torpedo-shaped and reducing limbs and fur


Undulatory Swimming

- Seen in mammals that are fully aquatic
- Spine and tail are flexed in order to propel the body forward
- Have an enlarged caudal fin
- Best way to swim at speed


Oscillatory Swimming

- Paddle-like propulsion system
- Uses either forelimbs only or forelimbs+hindlimbs
- Not as efficient as undulatory swimming



- Use skin stretched between forelimb and hindlimb as a "parachute" to control movement between trees
- Incapable of powered flight as they can't create the propulsive force to keep momentum going
- Avoid tendencies to pitch/yaw/roll by using the tail and changing the orientation of the gliding membrane
- Stop by stalling intentionally; pull up and use tail to keep from spiralling out of control



- Only seen in bats (mammals), birds and pterosaurs
- In bats, flight occurs by membranes that are stretched over the arm and sometimes between the hindlimbs over the tail
- Double membrane over top and bottom
- Short, broad wings adapted to maneuverable flight
- Low wind loading so generally not adapted for high speeds (some exceptions)


Flight vs. Lift/Drag

Lift is needed to fly
- Created via asymmetry
- Cambered airfoil


Cambered airfoil

When the air moving over the top of an object has a longer distance to travel than the air moving over the bottom

Pressure on the bottom of the wing is greater, so the animal moves upwards


Traditional Definition of Species

Group of inter-breeding, natural populations that are reproductively isolated from one another


Evolutionary Species Concept

Species is a single lineage of populations that maintain their identity from others and have their own evolutionary tendencies and fate

Problem: defining a lineage


Phylogenetic Species Concept

Species is the smallest diagnosable cluster of organisms within which there is a pattern of

Tends to define a lot of different "species"


Morphological Species Concept

Things that look the same are the same



Geographic "races" of a species, happen before speciation
May be temporary


Normal variation

The ordinary range of differences between individuals of a single species

Needs to be determined before assigning something as a subspecies or species


How do you know what an animal eats?

Can usually be determined from dentition



- Ancestral condition for mammals, most common
- Digestive tract is short with no cecum
- Can be terrestrial (shrews), aquatic (platypus), flying (bats), or arboreal (small primates)
- Some mammals are highly specialized insectivores and eat ants or termites; they have reduced or no teeth and elongated rostrums



Pocket at the beginning of the large intestine
Used to digest plant matter



- Smallest evolutionary step from insectivory
- Have a cecum, but it is small
- Also common in mammals - bats, carnivorans, cetaceans, etc.



- Eat BLOOOOOOD (woooooo)
- Seen in all new world vampire bats
- Have a long, complex digestive tract
- Salivary glands produce an anticoagulant
- Stomach rapidly absorbs water, which is excreted before they fly off (otherwise they would be too heavy, awks)
- Kidneys work efficiently with little water



- Much more derived than carnivory
- Seen in artiodactyls, perissodactyls, lagomorphs, etc.
- Have very complex digestive tracts
- Can have an enlarged cecum or a 4-chambered stomach (ruminants; two chambers with high pH, two with low)
- Ruminants regurgitate their food to allow it to be chewed twice
- Have flexible lips
- Teeth have rounded cusps



Eating of faecal pellets in order to maximize nutrient retention from food



- Have very unspecialized guts
- Eat anything, yay!


Sociality in Mammals

- The ancestral condition is for mammals to be solitary
- It just so happens that the social mammals are the most conspicuous


Advantages of Sociality

- Individual vulnerability to predation can be reduced
- Group defence - animals in middle tend to be preyed on less often, warning signs
- Cooperative hunting and food gathering/sharing
- Roost sharing
- Cooperative rearing of young


Food Sharing in Vampire Bats

A vampire bat will starve if it does not eat blood in two days or so. If this begins to happen, an individual will approach another to solicit a meal; the other bat will regurgitate blood to feed the starving one


Disadvantages of Sociality

- Increased competition for resources
- Increased competition of males for females
- More conspicuous to predators
- Increased likelihood of parasitism and disease



Both male and female will have a single mate for one or more breeding seasons
- In extreme cases, one mate for a lifetime



A male will mate with many females each breeding season



A female will mate with many males each breeding season



Mating is just a temporary contact with no durable associations between individuals
Basically, mating happens whenever they happen to be in the same place at the same time



Very rare
Only one or a few individuals actually breed, the rest are there for support and to provide food/rear the young


Male vs. Female Territories

- Females defend only what they need to survive
- Males defend territories with access to as many females as possible
- Male territories tend to be much larger than female territories and often encompass many of them


Density-Dependent Mating Systems

Where the type of mating system a species uses depends on the density of the population
- At peak densities, male lemmings are very promiscuous and a lot of infanticide happens; at low densities, male lemmings are monogamous and are very good dads


Facultative monogamy

Monogamous only when conditions are ideal for it


Social Dispersion

Different species and even populations tend to exhibit different kinds and levels of dispersion from one another; territories are defended and can be static or moving

Three systems:
- Dispersed system
- Communal system
- Colonial system


Dispersed System

- Individuals hold exclusive territories
- Territories may abut one another but never overlap (except in the case of male territories overlapping several females)


Communal System

- Individuals occur in groups, usually family
- No set spacing within the group
- The group will defend their territory from other groups
- Groups are not dispersed equally in space
- E.x. elephants, howler monkeys


Colonial System

- Populations are organized into groups
- These groups can sometimes be huge, within which there are clumps of individuals maintaining areas of exclusive use
- E.x. prairie dogs form small groups with females, daughters and sometimes sisters


Males and Polygyny

- Males are generally not involved in parental care
- They tend to mature at the same age or earlier than females
- Produce sperm over their entire lifetime and a variety of environmental conditions
- Stay active for a much longer period of time than females
- Reproductive success of males primarily determined by the dominance hierarchy amongst males; in this case, see a lot of sexual dimorphism


Female Defence Polygyny

- Males fight with one another for access to females
- In some cases, females will form groups with other females and can be antagonistic towards or just tolerant of the males; males defend from other males but are not involved in day-to-day life of the females


Resource Defence Polygyny

- Instead of forcing himself upon a group of females, a male will defend a territory rich in resources in order to attract females
- Males may not even seek females, simply wait for them to arrive


Sexual Dimorphism & Mating Systems

- Can sometimes tell what kind of mating system a species exhibits by the morphology of males vs. females
- Monogamous species tend to have very little sexual dimorphism


Lekking System

Females are widely dispersed but cluster during a season; during this time, males form groups in which they perform mating displays to attract females