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Skull of Eastern Grey Kangaroo (joey or juvenile)

Macropus giganteus giganteus

Description:

This unusual skull was found in a paddock, and what I thought briefly to be a lamb skull turned out to be something totally different - an "eastern grey kangaroo" of the marsupial family Macropodidae, but its small size indicates this was a joey or very young juvenile. I'm learning that, in osteology, small details are important, and it was because of size that I completely misidentified this spotting, thinking the skull belonged to a "red-necked wallaby" (Macropus rufogriseus), a much smaller animal than a kangaroo. Everything lined up and I was confident I made the correct ID, particularly on the basis of the small to medium-sized skull (relative to other macropodines). I hadn't consider a kangaroo because it has a larger skull and slightly heavier features, and the thought of it being a joey or young juvenile never occurred to me. However, what ultimately changed this spotting ID were the two large palatine-maxillary vacuities (holes in the palate) - they are present in the wallaby but not the kangaroo. The following link does a comparison: Figure 6: (D) red-necked wallaby, and (E) eastern grey kangaroo - https://peerj.com/articles/6099/#fig-6 ....and those two holes changed everything! This is a weathered specimen missing all of its incisors, although the molars are intact and in perfect condition. Canine teeth are absent or vestigial in the macropodines. What caused the demise of this animal? Feral dogs are a possibility. They are a major issue in this country, and feral dogs exact a massive toll on native fauna and rural livestock. On this farm, aerial dog baiting is a common practice and dogs are shot on sight, no questions asked! I also found a fresh kill not far from this location, of an adult eastern grey kangaroo. A couple of days prior to that and I found a dead adult merino ram, and dogs had eaten it alive! I'll spare you the gruesome details and photos of these two. But being a joey, it may have died of natural causes. We'll never know. This is definitely the skull of a herbivore, but features like teeth and skull shape, particularly the eye sockets, ruled out any ovine species. As this was an old specimen with scattered bones, I feel quite fortunate to have also recovered the mandible, or being in two parts, is it mandibles (plural)? They were nearby, although I didn't know if they matched this skull at the time, hence I didn't take a decent photo (see last photo). Like other macropods, kangaroos develop and lose four sets of molar teeth over a lifetime; teeth wear down from eating tough plants. These are grazing animals, and the distance between the incisors, canines and molars, called the 'diastema' (plural diastemata), is quite large in herbivores. The canines are absent in kangaroos, and a substantial diastema separates incisors and cheek teeth. It's such a pity the incisors are missing from this skull as they are well-developed in this grazing species, although dentition does vary greatly between various macropod species - some are browsers, some are intermediate browser-grazers, whilst others are full-time grazers. (See first and second reference links in notes section. Both have excellent dentition information)

Habitat:

Ranges throughout eastern and central Queensland, Victoria, New South Wales and southeastern South Australia. Prefers open grassland with areas of bush for daytime shelter and mainly inhabits the wetter parts of Australia, but also inhabits coastal areas, woodlands, sub-tropical forests, mountain forests, and inland scrubs. This spotting was in the New England District of northern NSW. Rural landscape (sheep and cattle farm), but large areas of natural bushland vegetation also. At the time of this spotting, drought conditions were prevailing and Yoongan Creek was completely dry.

Notes:

(1) Excellent information on macropods - Section 2.2 Dentition, and figure 7.1 - https://veteriankey.com/macropods/ (2) The macropodid dental formula - https://animaldiversity.org/accounts/Mac... (3) An interesting skull comparison between a wallaby (definitely red-necked) and a juvenile red kangaroo - https://shadyufo.tumblr.com/post/1432968... (4) Good image of full skull (including mandible) - https://www.researchgate.net/figure/Faci... (5) Top, bottom and lateral views of full skull - https://collections.museumvictoria.com.a...

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2 Comments

Neil Ross
Neil Ross 6 months ago

Thanks, Ava. I do love to tell a story :)

Ava T-B
Ava T-B 6 months ago

As always, spectacular notes, Neil!

Neil Ross
Spotted by
Neil Ross

NSW, Australia

Lat: -29.51, Long: 151.89

Spotted on Jun 23, 2019
Submitted on Aug 1, 2019

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