Vertebrates: marsupial Mammals

Taxonomy

Domain: Eukarya
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Infraclass: Marsupalia
- Order:
  - Didelphimorphia
  - Paucituberculata
  - Microbiotheria
  - Dasyuromorphia
  - Peramelemorphia
  - Notoryctemorphia
  - Diprotodontia

Order Dilephimorphia

Endemic to the American Continent
Commonly known as opossum
Originated from South America but migrated to the north in the Great American Interchange
Characteristics
- They tend to be semi-arboreal omnivores
- Have long snouts, a narrow braincase, and a prominent sagittal crest.
- Have a plantigrade stance (feet flat on the ground) and the hind feet have an opposable digit with no claw.
Behavior
- Solitary but sometimes they will group together to form burrows
- Nomadic
- When threatened or harmed, they will "play possum", mimicking the appearance and smell of a sick or dead animal.
  - Its an involuntary response

Order Paucituberculata

Found in the northwestern part South America
They are represented by the shrew opossum only, other species are extinct
- Characteristics
  - About the size of a small rat (9–14 cm long)
  - Thin limbs, pointed snout and slender hairy tail
  - Do not have a pouch
- Behavior
  - Spend much of their lives in underground burrows and on surface runways.
  - Hunt in the early evening and at night, using their hearing and long, sensitive whiskers to locate prey

Order Microbiotheria

Only has one extant species in the family Microbiotheriidae and it is "el monito del monte"
- Native only to southwestern South America (Argentina and Chile).
- The sole New World representative of the superorder Australidelphia
- Characteristics
  - The species is nocturnal and arboreal
  - Lives in thickets of South American mountain, the Valdivian temperate rain forests of the southern Andes
  - It eats primarily insects and other small invertebrates, supplemented with fruit.
- Behavior
  - Depending on the ambient and internal temperature, and on the availability of food, it spends much of the day in a state of torpor.

QUOLL

PHASCOGALE

TASMANIAN DEVIL

LITTLE RED KALUTA

Order Dasyuromorphia

Native to Australia and New Guinea
Comprises most of the Australian carnivorous marsupials including quolls, dunnarts, the Tasmanian devil.
Characteristics
- They come in difference sizes with the Pilbara ningaui being the smallest at 4.6-5.4 cm and the Tasmanian Devil being the largest at 57-65 cm
- Majority are insectivorous but with a few exceptions
- All of the toes in dasyurids are separate
- Gestation lasts from 12–16 days, and results in the birth of from two to 12 young, depending on species.
Behavior
- Adult dasyurids are typically solitary, or travel in small groups of two to three individuals

DUNNART

Order Peramelemorphia

All members of the order are endemic to the twin land masses of Australia-New Guinea
The only surviving members are the bandicoots and bilbies;
Characteristics
- A plump arch-backed body, long snout, upright ears
- Omnivores
- The embryos of bandicoots have a chorioallantoic placenta that connects them to the uterine wall
- Bilbies are excellent burrowers and build extensive tunnel systems

BANDICOOT

BILBIE

Order Notoryctemorphia

Endemic to the interior of Australia specifically the desert areas
Marsupial moles
Compromise of only two species
- Notoryctes typhlops (southern marsupial mole)
- Notoryctes caurinus (northern marsupial mole)
Characteristics
- They lack complete eyes causing them to be blind and no external ears
- Their pouch has evolved to face backwards so it does not fill with sand
- Insectivores

Order Diprotodontia

Endemic to Australia only
Consists of 125 species in where included the kangaroo is the largest marsupial
Many of the largest and least athletic diprotodonts (along with a wide range of other Australian megafauna) became extinct when humans first arrived in Australia about 50,000 years ago.
Characteristics:
- Two key anatomical features, in combination, identify Diprotodontia
  - First trait is the pair of large, procumbent incisors on the lower jaw
  - Second trait is "syndactyly"
    - A fusing of the second and third digits of the foot up to the base of the claws

Evolution

Why Are They Found Mostly in Australia?

From their point of origin in Laurasia, marsupials spread to South America, which was possibly connected to North America at around 65 mya through a ridge that has since moved on to become the Caribbean Archipelago.
Marsupials reached Australia via Antarctica about 50 mya, shortly after Australia had split off.
Modern marsupials appear to have reached the islands of New Guinea and Sulawesi relatively recently via Australia.

Fossils

The ancestors of marsupials are called metatherians
- Split from those of placental mammals (eutherians) during the mid-Jurassic period
- Fossil metatherians are distinguished from eutherians by the form of their teeth;
- The earliest known metatherian is Sinodelphys szalayi, which lived in China around 125 mya.
The earliest definite marsupial fossil belongs to the species Peradectes minor, from the Paleocene of Montana, dated to about 65 million years ago.

Anatomy

Similarities with all Mammals

Mammary glands
Three middle ear bones
True hair

Unique Characteristics

No internal placenta to protect the embryo from its mother's immune system.
Front Pouch
Lack a gross communication (corpus callosum) between the right and left brain hemispheres
The path of the ureters from the kidney to the bladder.
Brief gestation

Body

Skull

The skull is relatively small & tight and contains:

Holes (foramen lacrimale) are located in the front of the orbit.
Enlarged cheekbones that extend further to the rear.
Angular extension (processus angularis) of the lower jaw is bent toward the center.

Teeth

Early marsupials had a dental formula of per pine half; they have five maxilla or four mandibular incisors, one canine, three premolars and four molars, for a total of 50 teeth.
Marsupials in many cases have 40 to 50 teeth, significantly more than placental mammals.
The upper jaw has a high number of incisors, up to ten, and they have more molars than premolars.
The second set of teeth grows in only at the 3rd premolar: all remaining teeth are already created as permanent teeth.

Torso

A pouch:
- There are many species that have a permanent one like kangaroos and sugar gliders
- In others the pouch develops during gestation, as with the shrew opossum
- Usually, only females have a pouch, but the male water opossum has a pouch that is used to accommodate his genitalia while swimming or running.

NUMBAT

QUOKKA

Nervous System

No corpus callosum
- The two hemispheres are adequately connected
  - Neocortical Iobes are interconnected through anterior commissures by fibers which travel in the external capsule and cross ventral to the corpus striatum.
Unusual pattern of cerebral circulation in marsupials
- The arteries and veins travel in pairs to their ultimate branching where they anastomose in simple capillary loops independent of all others, forming an end artery system.

Reproductive System

Sexual Reproduction only
During embryonic development, a choriovitelline placenta forms in all marsupials.
Both sexes possess a cloaca, which is connected to a urogenital sac used to store waste before expulsion

Female

Female marsupials have two lateral vaginas, which lead to separate uteri, but both open externally through the same orifice
- Two fallopian tubes
- Two cervixes
A third canal, the median vagina, is used for birth. This canal can be transitory or permanent.
- In transitory cases when it's time to give birth, the two vaginae close together and fuse, forming a median vagina, also called a pseudo birth canal.
The pouch is not a characteristic found in all females

Male

Most male marsupials, except for macropods and marsupial moles, have a bifurcated penis:
The penis is used only during copulation, and is separate from the urinary tract
Neither marsupials nor monotremes possess a baculum
The only accessory sex glands marsupials possess are the prostate and bulbourethral glands.
There are no ampullae, seminal vesicles or coagulating glands.

Diet

The diets of marsupials are as varied as the niches they occupy
- Insectivores
  - Many dasyurids live chiefly on insects and other small animals.
- Vegetarian
  - The small honey possum (Tarsipes rostratus) is specialized to feed on the nectar of flowers, and other marsupials also may serve as important pollinators in that way.
- Few large carnivores have ever evolved in Australia, because of the low productivity of its environment.
  - The most-recent large carnivorous marsupials to evolve—the Tasmanian devil and the now-extinct thylacine, or Tasmanian wolf (Thylacinus cynocephalus)—were both displaced on the mainland by the dingo.

Digestion

Carnivore
- Short digestive tract
  - High hydrochloric stomach acid (ph of 1-2)
- Amylase is not present within the saliva
  - Burden of digesting carbohydrates is taken by the pancreas
Omnivore
- Medium size digestive tract
- Amylase is contained within the saliva
Herbivore
- FOREGUT FERMENTERS (Kangaroos)
  - Referred to as ruminants.
  - Digest food slower but this allows for a greater nutrient yield without wasting a lot of energy.
  - They have pouches with microbes in their stomach. These microbes take glucose from cellulose while producing fatty acids that will be used for energy.
- HINDGUT FERMENTERS (Koalas)
  - Use their caecum and proximal colon in their hindgut for fermentation.
  - Within the caecum and proximal colon are microbes to help digest the food.
  - Hindgut fermentation is a lot less efficient at digesting food when compared to foregut fermenters. Some even have to eat their feces because of this.

Excretion

The waste is brought down as it is in every mammal, through intestines and excretory organs
Then, the uterus, bladder and rectum waste are all brought out of the body through the cloaca
A cloaca is a posterior opening that serves as such for the intestinal and urinary tracts only.
The bladder of the marsupials functions as a site to concentrate urine and empties into the common urogenital sinus
In females the ureters pass between the median and lateral vaginae on each side.

Development

Gestation & Birth

Compared to placental mammals, marsupials gestate only for a brief period.
Marsupials do most of their development after being born
- The tiny infants need to immediately make their way to the pouch to continue developing and to find consistent and complex nourishment
- The mother marsupial's two teats provide different milk designed to suit the different stages of development of her young.
Due to the comparatively brief marsupial gestation period, many species can be in three stages of reproduction simultaneously.
- This phenomenon occurs when a female is pregnant with a newly formed embryo, has one joey still attached to her teat and tucked inside her pouch and is still rearing a sibling attached to her other teat.

Joeys

Are born blind and fur less
Their front limbs and facial structures are much more developed than the rest of their bodies at the time of birth
A marsupial joey is unable to regulate its own body temperature and relies upon an external heat source.
- A pouch temperature of 30–32 °C (86–90 °F) must be constantly maintained.
Joeys are born with an "oral shields"
- In species without pouches or with rudimentary pouches these are more developed than in forms with well-developed pouches

Ecology

Interaction with Other Species

Monito del Monte

Only pollinator of Tristerix corymbosus (loranthacous mistletoe)
Dromiciops illustrate parasite-host specificity with the tick Ixodes neuquenensis

Quoll

The introduction of the cane toad to the Australian wilderness has increased their deaths
The introduction of the cat to Australia has lead to the increase in deaths of quolls
- Cats are competitors in their niche

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