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BIOLOGY:
- REPRODUCTION AND DEVELOPMENT -
(page 7)
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Joey / pup development (continued):
 
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Source specimen measurements
Source: Dr Stephen Sleightholme
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Reference Specimen Size [mm] Head / tail Measurement Estimated age
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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
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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.
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    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.

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    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
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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.
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taxidermy mounts of thylacine mother with joeys
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Taxidermy mounts of a thylacine mother with joeys - note joey in pouch.
Courtesy: National Library of Australia.
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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.
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    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.
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female thylacine with pouch bearing young (foreground) - Beaumaris Zoo (QD)
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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".

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References
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back to: Reproduction and Development (page 6) return to the section's introduction forward to: Reproduction and Development (page 8)


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