| Gestation period:
The gestation period
for all marsupials is relatively short by comparison to their placental
counterparts, as their young complete by far the greater part of their
development externally, within the mother's pouch or marsupium. Few
marsupials have a gestation period longer than their oestrous cycle.
The gestation period for the thylacine is unknown. Only educated
comparisons can be made with the thylacine's smaller cousins, such as the
Spotted-tailed
quoll (Dasyurus maculatus), and the Tasmanian devil (Sarcophilus
harrisii), with estimates varying from 21 to 35 days. |
.
| Species |
Gestation
(days) |
Fur
adult pattern, detach from teat, eyes open |
Venture
from
pouch |
Permanently
leave pouch |
Weaned |
Spotted-tailed
quoll
(Dasyurus maculatus) |
21 |
7
wks |
7 wks |
12 wks |
20 wks |
Tasmanian
Devil
(Sarcophilus harrisii) |
31 |
12-13
wks |
13-15 wks |
16 wks |
32 wks |
Thylacine
(Thylacinus cynocephalus) |
21-35
(estimated) |
10-11
wks |
11-12 wks |
16 wks |
36 wks |
.
|
Gestation period and
comparative pup development of three dasyuromorphian marsupials.
Source: Thylacine Museum.
|
Pregnancy and birth:
With the majority of marsupials, there are no external signs that the female
is pregnant. However, as birth nears, the expectant mother can be
observed cleaning her pouch. The pouch secretes a waxy compound (which
may have antibacterial / antifungal properties) that dries into a dark
scale when the pouch has been unoccupied for some time. The female
licks this accumulated scale away prior to the birth of her young.
The cleaning commences around 1-2 days before birth, and is most vigorous
1-2 hours before birth occurs.
|
In marsupials with a backward-facing pouch like the thylacine, the mother
normally births in a standing position, with her hips raised so that the
urogenital sinus is positioned directly above the pouch. Just before
birth, a small yellow yolk sac appears at the urogenital opening, then
a clear allantois, and finally the joey in the amnion is born. The
newborn is motionless for a matter of a few seconds before commencing its
journey from the sinus in a sticky flow of mucus to the pouch. In
all marsupials, the birthing process is rapid, and completed in 2-4 min.
Once the young have made contact with the teats, they rapidly expand, resulting
in the oversized teats being firmly clamped inside the joeys' mouths.
This attachment process ensures that the developing young do not fall out
of the pouch. |
.
| Although
the newborn is blind and has many underdeveloped features, it has several
characteristics that assist its survival. The nostrils (1)
of the neonate are well developed to allow it to engulf air as it travels
to the pouch, as are the forearms (2)
to enable the young to pull itself along the mother's belly to the pouch
by grasping hairs with its forelimbs. The hindlimbs, on the other hand,
are mere paddles (3) and functionally
of little use in assisting the newborn's transit to the pouch. The
heart, kidneys and lungs are barely functional and the brain is at a very
early ontogenetic stage.
Jason A. Lillegraven (1975), in his paper: "Biological Considerations
of the Marsupial-Placental Dichotomy", suggests that
marsupial
young must be born at an early stage before the mother's immune system
can respond to the presence of foreign tissue in the form of a developing
embryo. Most development therefore takes place in the pouch, safe
from maternal immune system attack. |
.
.
Newborn
Tammar wallaby (Macropus eugenii).
Teat (T), nostril (1), forearm
(2), hindlimb (3). |
|
|
.
|
Nothing is known about the total number of young that the thylacine produces
per litter. The Tasmanian devil (Sarcophilus harrisii) gives
birth to between 20 and 30 young, but with only 4 teats, the majority do
not survive and are eaten by the mother. Although no direct comparison
can be assumed, it is likely that thylacines give birth to more than four
young. It is unlikely that a female thylacine in her first breeding
season would carry the maximum of four joeys. It is far more reasonable
to assume that two young would be the norm, with the litter size increasing
in the peak breeding years and diminishing as the animal ages.
Joey
/ pup development:
Like all other marsupials, thylacine joeys are underdeveloped at
birth, being approximately two centimetres long and less than 1 gram in
weight. W. Boardman (1945), in his paper:
"Some
points on the external morphology of pouch young of the Marsupial, Thylacinus
cynocephalus", compared the external morphological features
of early and late stage pouch pups. Boardman's study specimens were
a near full-term pouch pup at around 3 months in the Australian Museum
collection (AM 762), and four early stage pouch pups aged around 1 month
in the Museum Victoria collection (C5754-C5757). |
.
.
Thylacine pouch pup
(aged approx. 3 months).
Australian Museum Specimen
P762.
Source: ITSD, 5th Revision,
2013.
|
|
.
Thylacine pouch pup
(aged approx. 1 month).
Museum Victoria Specimen
C5754.
Source: ITSD, 5th Revision,
2013.
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