A natural history of Kangaskhan

Kangaskhan: an extant, derived sthenurine kangaroo (Marsupialia, Diprontodotia, Macropodidae)

Kangaskhanus macropodiens is a large, bipedal marsupial with several confounding diagnostic characteristics. The common name kangaskhan derives from the word kangaroo, which is colloquially used in reference to large macropods such as the extant species Macropus giganteus (Eastern grey kangaroo) (Shaw, 1790), Macropus fuliginosus (Western grey kangaroo) (Desmarest, 1817; Poole, 1976), and Osphranter rufus (red kangaroo) (Desmarest, 1817). The suffix khan originates from the same central Eurasion honorific meaning sovereign or ruler. Thus, the name means ‘ruling kangaroo’ and this has been maintained in the Latinised genus name. A 2019 reorganisation of the Macropus complex found four genera (Wallabia, Macropus, Osphranter, and Notamacropus) (Celik et al., 2019) which includes all of these larger species. The proposed species name macropodiens thus refers to these larger species of kangaroo while still positioning kangaskhan outside the macropus complex, albeit within macropodidae.

The bipedal stance, long muscular tail, prominent pouch and standing height are all similar to other large macropods. Figure 2 plots height and weight of 25 wild K. macropodiens observed in New South Wales, Queensland and Western Australia between 2016 and 2023. These individuals form the basis of most observations in this paper unless otherwise cited. Distribution is further discussed below.

Female K. macropodiens have a pouch into which a newly birthed neonate will climb and stay for further development and growth. As only female specimens have been observed, it is not known whether males also have a pouch. The pouch is a diagnostic feature of marsupials and “plays an extremely important role in the reproductive success of those species that have them” (Edwards & Deakin, 2012, p. 45).

Despite the similarities described above, K. macropodiens exhibits several characteristics that are distinct from other extant macropods. These include:

prominent canine-like teeth that extrude from the anterior portion of the maxilla, suggesting an omnivorous rather than herbivorous feeding strategy;
extremely robust torso, tail and limbs compared with more gracile modern macropods;
a proportionally shorter and taller skull length compared with other extant species;
a prominent plate of keratin in a dorsal position on the skull approximately above the parietal bones;
three visible toes on each limb rather than four;
wide flat feet on hind limbs with prominent foot pads compared to the typical macropod arrangement of long feet made for characteristic hopping.

Kangaskhan has been popularly incorporated into the polyphyletic group of animals known colloquially as Pokémon (The Pokémon Company, n.d.-d). Organisms given this label tend to have unusual or accentuated features compared to their relatives and are represented in popular culture as having ‘powers’ or ‘moves’ not possessed by other organisms.

Sthenurine affinity

Several features of K. macropodiens suggest affinity with the otherwise-extinct subfamily Sthenurinae rather than genera in the macropus complex. These include the short-faced and robust nature of the animal, as well as primary method of locomotion, and observed dentition.

19 individuals in the sample population of 25 are over 2 metres tall while the tallest two specimens were 3.47m and 3.71m respectively, although these are clear outliers from the overall population distribution. The extinct sthenurine Procoptodon goliah is “recognized as the largest and most robust species” of kangaroo (Prideaux, 2004, p. 148), estimated at around 230 kg (Helgen et al., 2006). P. goliah has large cheek teeth (Prideaux, 2004) and could extend its height up to 3m, although it would only stand at 2m under normal circumstances (Musser, 2018). As such, K. macropodiens would be the largest known macropod, although the observed specimens weigh less than the upper weight estimates for P. goliah. It is suggested that the extruding canine-like teeth observed on K. macropodiens are derived from the somewhat large cheek teeth seen in ancestors such as P. goliah.

Although extant macropods have a unique form of locomotion — the characteristic hop — this is not observed in K. macropodiens. Instead, they have been observed to run upright (Inoue, 1997) like other bipedal animals such as humans (Homo sapiens) and flightless birds. Rather than being at odds with the assignment to the broad Macropodidae, this observation supports the proposed taxonomic placement of K. macropodiens within Sthenurinae based on Wagstaffe et al.’s (2022, p. 329) finding that osteological evidence supports hypotheses of “sthenurines employing bipedal striding”. Other analyses of extinct kangaroos and their relatives have arrived at similar conclusions (Janis et al., 2014, 2023; Jones et al., 2022).

Figure 3 below presents a comparative skull anatomy of Stenurus stirlingi (Janis et al., 2014, p. Fig. 2) overlaid upon an image of K. macropodiens at equivalent scale. Though K. macropodiens has more frontal orbital fossae, other features of the skull are remarkably similar, including overall length, shape, and position of the dentary. S. stirlingi is not known to have had a keratin sheath over its skull as seen in K. macropodiens, however, such features do not easily fossilise.

Natural History, Distribution, and Habitat

The first known account of K. macropodiens reported observations of a large herd (or mob, see Queensland Government, n.d.) at a wildlife reserve known as the Safari Zone in a region of Japan (Inoue, 1997). These animals were observed in a cool-climate savannah or grassland environment. This and other accounts of the species around the same time suggest distribution across multiple disparate regions of the globe, although often in protected locations (Inoue, 1997). Reports from around the world have also located the species in savannah or grassland environs as well as caves and wetlands (Bulbapedia, n.d.-b).

However, other sources suggest the species is found in the wild only in Australia (MeteorAsh15, 2020). It is therefore possible that specimens located outside Australia are introduced to these environments, though the means of this introduction are unclear. Recent media reports point to illegal smuggling as the source of smaller macropods (wallabies and kangaroos) spotted in the wild in Japan and Vietnam (Anh & Tue, 2023; SBS News, 2010). All other extant macropods (indeed, all members of the order Diprotodontia) are found natively only in Australia and Papua New Guinea (Duszynski, 2015). Extinct species of macropods have also only been found in these locations (Kerr & Prideaux, 2022).

During fieldwork, the author and colleagues have observed the animals in arid and semi-arid grassland environments in Australia — see cover image and Map 1 below. The location of all 25 observed animals is shown visually on Map 1. Each colour token on the map represents a different researcher who provided data and observations. An interactive version of this map is available online (Holland, 2023). Given the observations and known distribution of other macropods, it is suggested that K. macropodiens is likely native and endemic to the Australasian region.

Initial reports of K. macropodiens noted the animal was once hunted to near extinction but is now protected in certain regions. Nonetheless, it was still considered “rare” (Inoue, 1997). The same reports emphasised the maternal nature of the animal including extreme aggression when it perceived a threat to the young (Inoue, 1997). Such reports also indicated that the animal is a highly social herd animal and can form close bonds with humans, including by incorporating humans as members of its herd.

Juveniles are rarely observed outside of the mother’s pouch. However, in rare cases the mother and juvenile are observed to both exhibit coordinated aggressive and defensive behaviour, in which circumstance the juvenile will leave the mother’s pouch in order to fight (Bulbapedia, n.d.-b; The Pokémon Company, 2015).

The observed K. macropodiens also exhibit several learned behaviours that can be classified as ‘moves’ as ascribed to animals given the pokémon label. Each individual exhibits two of the behaviours, divided into categories labelled minor or major, as shown in Figures 4 and 5. These moves are highly specialised and distinctive behaviours performed in instances of inter- and intra-specific combat.

Popular mythos surrounds the peculiarity of only having observed female specimens of kangaskhan. These myths suggest a case of extreme sexual dimorphism in which kangaskhan should be considered synonymous with another family of bipedal animals known as cubone (in the juvenile state) (Bulbapedia, n.d.-a) and marowak (as adults) (Bulbapedia, n.d.-c; Chetrafilov, 2020). These animals are thought to ‘wear’ the skulls of deceased individuals of their species, making definitive descriptions of their cranial biology difficult, and beyond the scope of this paper. While both male and female cubone/marowak have been observed, it may be possible that breeding females of the species come to resemble kangaskhan while non-fertile females retain the more gracile marowak form, and all males retain the marowak form. Although perhaps not this extreme, Helgen et al. (2006, p. 293) observe “marked” sexual dimorphism in extinct kangaroos. Moreover, such breeding strategies are not unknown in the animal world as this role-dependent dimorphism resembles the highly specialised strategies seen in Hymenoptera (especially suborder Apocrita) (Peeters & Ito, 2001). Further investigation is required to resolve this matter, though it is presented here for completeness in the phylogenetic diagnosis of K. macropodiens. Figure 6 below presents images of cubone, marowak, and K. macropodiens for comparison.

Figures 6, 7, 8: Comparison of cubone, marowak, and kangaskhan. Images courtesy of The Pokémon Company.