Mammals Flashcards
What is a mamma?
Tetrapods, Amniotes, Synapsids
Key features:
- Endothermic
- Respiration with a muscular diaphragm
- Hair that provides insulation
- Mammary glands
- Differentiation of teeth
- Refinement of ear bones
Tetrapod
A four-footed animal
Synapsid
mammals and “mammal-like reptiles” with modifications to skull and skeleton indicative of increase in metabolic rate
Amniote
An animal that develops embryonic membranes
Reptiles vs mammals
Retiles have one ear bone (Dimetrodon)
Mammals have multiple ear bones (Morganucodon)
3 mammalian groups that remain today
Monotremes - egg laying mammals
Marsupials - Give birth to small, embryonic young, have pouch
Placentals - Give birth to fully develop
Australian mammal origins
Monotremes and marsupials descend form ancestors that were on the continent when it detached from Antarctica
Eutherian mammals (rodents) came by island hopping from Indonesia and New Guinea via boats and floating vegetation
2 groups of marsupials
Australidelphia: Found in Australia & New Guinea
Ameridelphia: Found in the Americas
Australidelphia (marsupial) four orders:
Dasyuromorphia
Peramelemorphia
Diprotodontia
Notorycytemorphia
Marsupial morphology
Diverse group (range of sizes)
Morphology reflects function - e.g. dite, locomotion
General mammalian features with modification unique to marsupials
Polyprotodont
Multiple pairs of lower incisors
Diprotodont
One pair of incisors in the lower jaw
-dactyl:
A suffix that indicates “fingers or toes of a particular type or number”
Syndactyly
The normal occurrence of having two or more fused digits in a mammalian species
In many marsupial species syndactyly is common between digits II and III on the hindfoot
Order: Dasyuromorphia
Carnivorous or insectivorous marsupials
Polyprotodont dentition
• Three pairs of ~ equal-sized lower incisors
• Numerous, sharp teeth
• Numbat – teeth reduced in size and fewer incisors
Hindfoot has 5 separate toes (+/- digit 1): NO syndactyly
Forelimb length = hindlimb length
Non-prehensile tail
E.g. Tasmanian devil
Order: Peramelemorphia
Bandicoots and bilbies
Omnivorous marsupials
Long pointed heads and compact bodies
Polyprotodont dentition
- Three pairs of ~ equal-sized lower incisors (not as pointed as dasyuroids)
Hindlimb large with 4 toes:
• Syndactyly digit 2 and 3 fused, digit 1 absent/reduced
Forelimb shorter than hindlimb (→ bounding gait) with well-developed claws (digging)
Non-prehensile tail
Order: Notoryctemorphia
Marsupial mole
Ancient lineage with just two species (Southern and Northern marsupial mole)
Subterranean habit (occurring under the earths surface) - Unusually low metabolic rate and highly variable body temperature – adaptation for a burrowing lifestyle?
Blind (eyes = non-functional buds beneath the skin)
Absence of external ears, heavily keratinised skin on nose
Tubular body form, with rear-ward opening pouch (females)
Forelimb short and powerful, digits 3 and 4 have developed into large, spade-like claws (digging)
Tail – shortened and immensely strong
Insectivorous/carnivorous – polyprotodont dentition
Order: Diprotodontia
Koala, wombats, possums and macropods
Most specialised and recently evolved Order ~120 species
Mostly herbivorous or omnivorous
All have diprotodonts dentition
One pair of lower incisors, with NO lower canine teeth
Hindlimb syndactyly digit 2 and 3 (fused together, except at the tip)
Forelimb: Ability to oppose first two digits in most arboreal species (not in wombats, kangaroos and wallabies)
Non-prehensile tail (yes in possums)
Very successful group with two subforms:
•Vombatiformes (koalas and wombats)
•Phalangerida (possums, rat-kangaroos and kangaroos)
Diprotodontia: Sub order - Vombatiformes
No tail
Adaptation for climbing (koala) or burrowing (wombats)
Rear-ward opening pouch
Diprotodontia: Sub order - Phalangerida
Morphologically very diverse
Four principle lineages that can be viewed as superfamilies:
- Phalangeroidea (Brushtail possums, scaly-tailed possum)
- Burramyoidae (pygmy possums)
- Petauroidea (ringtail possums, gliders)
- Macropodoidea (kangaroos, wallabies and kangaroos)
Phalangerida - Superfamily Phalangeroidea
Noticeably short face, eyes directly forward
Long, prehensile tail
Arboreal – excellent climbers
Variable herbivores (Brushtail possums well adapted to life in suburbia)
Phalangerida - Superfamily Burramyoidea
Pygmy possums Smallest of the possums Long, slender, prehensile tail Arboreal Insectivorous
Phalangerida - Superfamily: Petauridae
Possum-like marsupials from four families
E.g. ringtail possums & gliders
Extreme morphological and ecological diversity
Arboreal
All are dietary specialists of one form of another:
•Folivores (e.g. ringtail possum)
- Sap-eaters (e.g. wrist-winged gliders and Leadbeater’s possum )
- Omnivorous (e.g. striped possum - wood-boring insects)
- Nectivorous (e.g. feathertail glider and honey possum)
- Variations in teeth and digestive tract anatomy
Feathertail Glider
Belongs to superfamily: petauridae
- Smallest gliding possum
- Gliding membrane between elbow and knee
- Nectivore and communal
Sugar Glider
Belongs to superfamily: Petauridae
Small, omnivorous,
Gliding membrane btw wrist and ankle (termed wrist-winged glider, a trait common to 6 gliding species)
Omnivorous:
summer = insectivorous;
winter = exudativorous (feed on sap, manna and honeydew
Greater Glider
Not closely related to other Petauridae gliders
Gliding membrane btw elbow and ankle - More controlled glides
Folivore, feeding almost exclusively on Eucalyptus leaves
Solitary - very vocal
Superfamily: Macropodoidea
Kangaroos, wallabies and rat-kangaroos
Macropods: strong, powerful hindlimbs and long hindfeet
Three families:
• Macropodidae: kangaroos and wallabies (<25kg)
- Potoroidae: potoroos and bettongs (“rat kangaroos”)
- Hypsiprymnodontidae: Musky Rat-kangaroo
Adaptations to a hopping lifestyle
Syndactyly, with no opposable first digit
Terrestrial (except tree-kangaroo)
Essentially herbivorous
Marsupial morphology
Some common morphological features:
- Reproductive traits
- Skeletal modifications
- Slightly lower body temperature and metabolic rate (expend less energy than eutherian mammals of comparable size and activity)
- Brain usually smaller
- Most have an opposable 1st digit on hind feet
Musculoskeletal Structure of marsupials
Compared with eutherians: - Hard palate fenestrated - Epipubic bones present - Lack fully developed patella •Have clavicles
Skull of marsupials compared to eutherians
Large facial area to small cranial cavity
Mandibular symphysis may not be fused (many diprotodonts)
Often have narrow oral gape
Mandible: internal angular process (so-called “marsupial shelf”)
Metabolism of marsupials
Resting body temperature 2-3 degrees lower than eutherians
Basal metabolic rate lower (‘primitive’?) but
–Nutritional requirements lower for maintenance
–Can increase greatly in response to cold (10-11 x) and peak metabolism of some marsupials may be higher than some eutherians
–Adaptations to cope with changes in temperature (e.g. torpor)
Brain of marsupials
Small
Large olfactory bulbs
Basic sulci: limited surface area
Lacks corpus callosum
Hopping (saltation)
Energetic advantages for animals - energy stored in elastic structures e.g. tendons
Pentapedal gait: alternately support weight on forelimbs + tail and hindlimbs
Top kangeroo speed = 70km/hr
Common reproductive features of marsupials
Most polyoestrous
Most ovulate spontaneously
Pregnancy < or = oestrous cycle length
Ovarian activity suppressed by lactation
Under-developed offspring at birth
Long lactation and short gestation
Embryonic diapause in Macropodidae
Note: Marsupials also have a placenta (usually more primitive then eutherian mammals)
Marsupial pouch
Provides high humidity and stable temperature
Formed by invagination of skin of ventral abdomen through a gap in the cutaneous muscles
Interior skin relatively hairless, and produces a brown secretion that coats the pouch wall
Mammary glands in pouch with long nipples (young initially permanently attached to one teat, and only that teat develops)
The pouch is full of bacteria
Development of young joey
Small and immature at birth
Neonate has circular mouth
- Teat expands inside mouth
- Can breath and swallow concurrently
Remain dependent on mother for some time after leaving pouch/teat
Lactation in marsupial
Suckling initiates lactation in suckled mammary gland
Milk composition changes during lactation
- Protein, lipid and carbohydrate (CHO) concentrations and constituents change
- Different glands can concurrently produce different milks to sustain young at different stages of development
- Antibodies are transferred across the gut wall for relatively long period of time
Embryonic Diapause (marsupials)
Refers to the phenomenon where a female will mate while she has a young in the pouch. The resulting conceptus is held in the uterus in “suspended animation” until the first young has finished suckling
Common in kangaroos and wallabies
Sucking inhibits corpus luteum = progesterone –> causes diapause
Male reproductive anatomy of macropods (kangaroos & wallabies)
Scrotum located cranial to penis
Only 2 accessory glands:
- Prostate
- Cowper’s (bulbourethral) gland
Glans penis
- Usually bifid (‘split’)
Non erect penis withdrawn into common vestibule in S shaped curve
Three basic patterns of sperm production in marsupials
- Capacity for continuous sperm production e.g. Kangaroos, Koalas, Tasmanian devil
- Seasonal breeders: only have sperm production during an annual breeding season e.g. greater glider
- Single cycle breeders: Sperm production over a short breeding season, males die within a short period of females becoming pregnant e.g. Antechinus
Marsupial species with continuous sperm production
Sperm production occurs throughout the year, but males often “secondarily seasonal”
- If females are seasonal, often see seasonal variation in accessory sex glands and testosterone production, which peak around the time of peak conception
Marsupial species with seasonal sperm production
Testis size fluctuated throughout the year
