Joey
/ pup development (continued):
.
Source specimen
measurements
Source:
Dr Stephen Sleightholme |
.
|
Reference |
Specimen |
Size
[mm] |
Head
/ tail |
Measurement |
Estimated
age |
| . |
|
|
|
|
|
|
| 1 |
Charles
University |
DZCU
8021:1-4 |
26
[CRL] |
- |
Actual |
Birth
<
2 weeks |
| 2 |
Museum
Victoria |
C5754-C5757 |
75
[CRL] |
- |
Actual |
1
month |
| 3 |
Owen
[1868] |
|
304.8 |
- |
Actual |
2
months |
| 4 |
Flower
[1867] |
|
330.2 |
228.6
/ 101.6 |
Actual |
2-3
months |
| 5 |
Australian
Museum |
762 |
407 |
288
/ 119 |
Actual |
3
months |
| 6 |
BMNH |
1887.5.18.9 |
435 |
295
/ 140 |
Actual |
4
months |
| 7 |
Smithsonian |
115365 |
515 |
320
/ 195 |
Actual |
5
months |
| 8 |
SA
Museum |
M612 |
860 |
640
/ 220 |
Actual |
17
months |
| 9 |
Museum
Victoria |
C5600 |
1050 |
720
/ 330 |
Actual |
22
months |
| 10 |
Crisp |
|
1232 |
851
/ 381 |
Actual |
Adult |
| 11 |
Adult
female [mean] |
|
1319 |
903
/ 416 |
Estimate |
Adult |
| 12 |
Adult
male |
|
1650 |
1170
/ 480 |
Actual |
Adult |
. |
.
|
Red
measurements refer to nose to base of tail, and blue
measurements to tail length, in lines 4-12. Green
measurement on line 5 refers to head to rump length. All measurements
are in millimetres. Source: Dr Stephen Sleightholme.
|
.
|
The time span between birth (< 2 weeks) at (1), to juvenile at
(9), is 22 months. The juvenile thylacine (9) cited was born and
died at Melbourne Zoo (Paddle 2000), so its exact age is known. Specimens
of this type are extremely rare and of immense value when attempting to
determine the rate of growth. With respect to pouch young (2) and
(5), the head to rump measurements given are those quoted by Boardman.
Richard Owen (1868),
in his book: "On the Anatomy of Vertebrates",
describes the pouch of the thylacine and notes a female that carried
three young, each one a foot in length from the snout to the end of the
tail (3). Converting Owen's imperial unit measurements to metric
gives the pups a total body length of 304.8mm.
The mean adult female measurement
(11) was obtained from skeletal specimens during work on the International
Thylacine Specimen Database. The adult male measurement (12)
is that given by Boardman (1945) from a specimen preserved in the collection
of the National Museum of Australia (NMA 1984.0010.0714).
With a limited specimen
sample from which to extract data, the growth graph is inherently simple
in execution. Its inclusion is justified as a foundation for further
study and comment.
Two major phases of growth are recognisable; an early rapid phase within
the pouch, followed by a deceleration of growth through the juvenile stage
to adulthood. Growth from the age of 2 years rapidly levels off,
indicating maturity within the species. Rapid pouch development akin
to that of the smaller Spotted-tailed quoll (Dasyurus maculatus)
is a characteristic of the thylacine, together with a more prolonged period
of growth in the independent young. Historical developmental estimates
seem to infer that pups are three-quarters grown at twelve months.
This assumption however, is not supported by the growth data.
Life
in the pouch:
It is assumed the female thylacine, like other marsupial mothers, has virtually
no active role in the early development of her young, save periodically
cleaning her pouch and the joeys by licking. It is believed that
licking stimulates the young to excrete waste materials through the skin. |
.
|
Several contractile muscles line the edge of the pouch, enabling the mother
to close the pouch tighter to contain the pups, or relax it so that the
pups can leave. In order to get back into the pouch, cooperation
between mother and pups is required. The mother lies on her side,
thus allowing easier access to the pouch. This process of entry into
the pouch becomes progressively more difficult as the pups develop.
At the end of the pouch period, the female prevents her pups from entering
the pouch again by moving away as they try to gain entry. However,
the young pups continue to |
.
| Position
of joey within the pouch. |
|
|
| suckle from outside
the pouch for some nine months before they are fully weaned. The
pups' first venture from the pouch is quite short, and over time these
sorties from the pouch gradually become more prolonged. It is known
that vocal communication between mother and her pups occurs. |
.
.
Taxidermy mounts of
a thylacine mother with joeys - note joey in pouch.
Courtesy: National Library
of Australia.
|
.
.
Female
thylacine with pup exiting / entering pouch animation created by Arnfinn
Holderer (2016), with technical contributions from C. Campbell and Dr.
S. Sleightholme. Click gear button in lower right corner and select
"?" to view control options for movement. This animation is copyright
and unauthorized use strictly prohibited.
|
.
Below is a photograph
of a female thylacine that had recently been carrying two young in her
pouch. The photograph was taken in 1928 at the Beaumaris Zoo (QD).
Note the distention of the pouch with just two young. When carrying
a full complement of four joeys, a thylacine's pouch was so heavily distended
that observers commented that it nearly touched the ground. |
.
.
|
Beaumaris Zoo (QD) (1928).
Courtesy: South Australian Naturalist.
|
It is known that thylacine joeys engage in play. A. C. Robison, the
animal dealer responsible for the import of the US National Zoo's (Washington
DC) thylacine mother and pups, states in a letter dated 26th August 1902
to the zoo's superintendent Dr. Frank Baker:
"The Wolfe is a beauty
and the kittens are doing nicely - have been playing in the box all day". |
