Prototheria (monotremes)
The 3 subclasses of mammals differ strikingly in their modes of reproduction
Metatheria (marsupials)
Eutheria (placentals)

Monotremes:
Unique
Reproduction
1) Lay eggs
2) Cloaca
3) No nipples

• 1. Ovaries larger (relative to
• 4. Young have “egg tooth” body size) than other mammals like birds to help break out
• 2. Oviducts open into of egg urogenital opening called a cloaca, similar to reptile cloaca
(meaning of name
“monotreme”)
• Platypus: 1-2 eggs
• Echidna: 1 egg
• 3. Milk secreted by glands in skin, licked from tufts of fur at concentrations of glands

• Monotreme egg?
• Reptile egg?

Typical platypus reproduction:
Egg is fertilized in fallopian tubes before entry to uterus, eventually coated with leather mineralized shell before being laid.
Egg at fertilization = 4 mm, when laid = 12 mm.
Egg retained in uterus about
28 days while development proceeds. THEN shell added, egg laid, 10 more days of external incubation. (Eggs sticky, female cradles between stomach and tail.)
Lactation about 3-4 months.

Platypus:
1.Low body temperature around 90 degrees farenheit
2.Living species of platypus lack teeth
3.Only found in Australia
4.Baby platypus’s is called a puggle
5.Small approximately 20 inches and 3 pounds
6.Eat insects and crustaceans using their sensitive bill to
Locate their prey.
7. Use front feet to swim, steer with tail and backfeet

Monotremes: echidnas
Only 1 egg, incubates in a pouch where hatching occurs.
4 species of echidnas: also called spiny ant eaters
Located in Australia
Lactation for about 4 months more.
http://animal.discovery.com/videos/fooled-by-nature-spinyanteater.html

kangaroo
Wombat
Koala
Wallaby
Marsupial wolf

Our friend, the opossum only marsupial in north america
1) Young tiny at birth (0.16 g)
2) Attach to nipples in pouch
(marsupium)
3) Short gestation, longer lactation

Opossum:
Mating season, January –
July, 1-2 litters depending on latitude.
Egg fertilized in fallopian tubes, also surrounded by a shell membrane (soft) at that time.
Gestation (about 8 days).
Last 1/3 of gestation (4 days), membrane shed, eggs sink into depressions in uterine wall (has a kind of placenta, but no firm implantation), absorbs nutrients and embryos continue to grow.

Gestation totals about 12-13 d.
7-9 young make it to suckling stage.
Lactation continues to a total of about 95-105 days.
Rarely live longer than 18 months. In wild, maximum known lifespan was 3 years.
Females often get just 1 breeding season.

• Eggs slightly larger than in placentals (0.12-0.28 mm vs
0.07-0.15 mm)
• Young never larger than about 1 g, no matter size of mother
• Gestation always short as or shorter than length of estrus cycle
• No placenta
• Many have pouch, but some only have folds of skin, and a few don’t have anything

Size difference in
Monotremes and
Marsupials compared to placental mammals

What does this graph show?
Marsuipals compared to placental mammals of the same size have
Shorter Gestation (time in the womb) However, longer Lactation time ( time nursing the offspring)
What does this data mean?
Overall Marsuipals take longer to grow their offspring compared to
Placentals

Another way to look at this...

Takes marsupial longer than placental to raise young to same size (weaning age)

Costs: Lactation is most energetically costly period of reproduction, and less efficient means of energy transfer to young. Probably costs them a bit more in terms of time and energy.
Constraints: Newborn marsupials need to be able to crawl to pouch or teat, suckle, breathe, digest. But no wings, hooves, or flippers!
Flexibility: Marsupials in individual offspring at time of birth, can adjust litter sizes, etc.

Placental vs. marsupial morphology:

Red Kangaroo:
Diet: Herbivore
Average life span in the wild:Up to 23 years
Size: 3.25 to 5.25 ft
Weight:200 lbs
Group name:Mob
Can reach speeds up to 35 mph and jump over 6 feet

Diet: Lives on eucalyptus leaves
Average life span in the wild:20 years
Size:23.5 to 33.5 in
Weight:20 lbs
Protection status: Threatened .

Diet: omnivore
Lifespan: 2-3 years
Size: 7-14 inches 1-3 pounds
All species are endangered

Diet: Carnivore
Lifespan: 5 years
Size:20 to 31 in
Weight:9 to 26 lbs
Protection status:Endangered

The Amazing
Antechinus!
All females give birth within a few days each year.
In late Sept, shortly after females mate, all males die!
Semelparous: only 1 reproductive period per lifetime
Iteroparous: multiple reproductive events per lifetime