Tetrapod Zoology

Tetrapod Zoology

Amphibians, reptiles, birds and mammals - living and extinct

The mystery mammal of Kayan Mentarang


Back in 2005, the discovery of a weird reddish, long-tailed mammal, photographed by a camera-trap at Kayan Mentarang in central Borneo, was announced by the Swiss World Wildlife Fund. I covered the case and how it unfolded back at Tet Zoo ver 1 during January 2007. That’s such a long time ago that now is probably a good time to recycle the whole story. So, here it is again, with updates as and where appropriate. The big deal about the Kayan Mentarang animal is that it was hailed as a possible new species.

If you’re wondering, ‘Kayan Mentarang animal’ is not this creature’s official name. It’s a label that I’ve invented, and one that (in my opinion) is clearly superior to the various other labels that have already been given to the creature. Some writers have referred to it as a cat-fox, while one newspaper article jokingly suggested that it be termed the cat-dog-fox-monkey-lemur.

Though the two photos that feature the Kayan Mentarang animal were taken in 2003, they were not made public until early December 2005 (the second photo, showing the animal from behind, is featured at left). I don’t know why this postponement occurred, but such delays are fairly ordinary given that scientists are often really, really busy, or hesitant to announce controversial news. Then again, some news is deliberately held back until its release might have the most impact. It’s probably not a coincidence that the discovery was announced at the same time as was news that the Indonesian Government plans to start an oil palm plantation in the vicinity of Kayan Mentarang National Park. If you’re not aware of the oil palm problem, now is the time to learn. There's more about the oil palm menace facing the Kayan Mentarang region in this document.

A viverrid montage (clockwise from top left: Paradoxurus, Genetta, Arctictis, Paguma). licensed under Creative Commons Attribution-Share Alike 3.0 Unported license.

During December 2005 and January and February 2006, features on the Kayan Mentarang animal appeared in most newspapers, in most science magazines, in Science (Holden 2005), and on TV. Led by Stephen Wulffraat, the WWF team confirmed that local people were unaware of the creature; they also noted that none of the mammalogists they’d consulted had been able to identify it. While some biologists noted a vague superficial similarity with lemurs, most concluded that it was a viverrid (that is, a member of the same carnivoran family as civets and genets*). Many viverrid species are highly enigmatic and several have only recently been discovered, have only occasionally been photographed alive, or have even not ever been photographed alive at all (for a nice review see Schreiber 1989). [In adjacent viverrid composite, Genetta by Guérin Nicolas, Arctictis by Tassilo Rau, Paguma by Denise Chan.]

* Recent phylogenetic studies have agreed that Viverridae of tradition is not monophyletic. Nandinia is not close to civets and genets, but is in fact outside the clade that includes all other feliformians (Gaubert & Veron 2003, Flynn et al. 2005, Gaubert et al. 2005, Wesley-Hunt & Flynn 2005, Agnarsson et al. 2010); oriental linsangs (Prionodon) are not viverrids, but either the sister-taxon to cats (Gaubert & Cordeiro-Estrela 2006, Gaubert & Veron 2003) or the sister-group to the (hyena + (mongoose + Madagascan carnivoran)) clade (Agnarsson et al. 2010). Madagascan carnivorans are also not viverrids but form the clade Eupleridae, regarded as the sister-group to mongooses (Gaubert et al. 2005, Agnarsson et al. 2010).

Image by Wahyu Gumelar.

Thanks to its long tail, gracile proportions, size (comparable to that of a house cat), and general civet-like appearance, the Kayan Mentarang animal soon became widely regarded as a probable new viverrid. The image above, produced by Wahyu Gumelar for WWF Indonesia, was widely reproduced and clearly depicts the animal as a new, hitherto unknown viverrid. The idea that the Kayan Mentarang animal might be a hitherto-undiscovered species is exciting and easy to take seriously, given Borneo’s the size (it’s the third largest island in the world) and the continuing discovery there of many new species.

Historic image of Hose's civet by Joseph Smit, from the original 1892 description. In the public domain. Compare to the photos below.

Other authors also interpreted the animal as a viverrid, but as a member of a known species, not a new one. By far the most popular and widely reported suggestion is that the Kayan Mentarang animal is in fact a member of Hose’s civet Diplogale hosei (originally described as Hemigale hosei but included within Diplogale in 1912), also known as Hose’s palm civet or the Brown musang.

Named in 1892 and known from less than 20 specimens, Hose's civet is a poorly known, terrestrial, forest-dwelling viverrid. Good observations and photos of this species are few and far between and only one specimen has ever been kept in captivity. She “ate fish, shrimp, chicken and processed meat; she refused fruits and boiled rice” (Hunter & Barrett 2011, p. 82).

Arguing that the Kayan Mentarang animal and Hose’s civet were anatomically similar, Chapron et al. (2006) proposed that the alleged new carnivoran “may not be new”. They clearly weren’t entirely convinced by their own explanation, however, as they also noted that the Bay cat Pardofelis badia (another highly elusive carnivoran: named in 1874, it appeared extinct during the 1980s but was rediscovered in 1992) might also be the true identity of the cryptic creature.

J. Wolf's illustration of the Bay cat, from John E. Gray's original 1874 description (and in the public domain). If you really think that this looks like the Kayan Mentarang animal, methinks you shouldn't be trying to identify mystery mammals from photos.

Nope, that is not a Hose’s civet

Despite the apparent strengths of the Hose's civet identification (and the fact that it came from an authoritative source: one of the authors in particular – Géraldine Veron – being a noted expert on viverrids), it really was a non-starter for several obvious reasons.

The Kayan Mentarang animal is reddish-brown. Hose’s civet is dark brown or blackish. Chapron et al. (2006) got round this by arguing either that the animal’s colour had been “affected by the flash of the camera”, or that the individual was an unusual colour variant. Both suggestions fail to explain the absence of the pale facial, neck and flank markings present in Hose’s civet. Shuker (2006) noted that – contrary to Chapron et al.’s claims of morphological similarity – the long hindlimbs of the Kayan Mentarang animal made it look more suited for arboreal life than is the predominantly terrestrial Hose’s civet.

Furthermore, the Kayan Mentarang animal has really tiny ears while Hose’s civet has far larger ones, and the Kayan Mentarang animal has a proportionally much longer tail than Hose’s civet. So the idea that the Kayan Mentarang animal is actually a specimen of Hose’s civet is poorly founded and unlikely to be correct. And look at the photo showing the animal from behind. It looks nothing like a civet, nor like a cat, either.

Hose’s civet not so poorly known

Camera-trap image of Hose's civet by WCS Malaysia. One of several camera-trap images of this species obtained in recent years.

Worth noting here is that – while undeniably rarely recorded and poorly known – Hose’s civet is no longer as rarely recorded and poorly known as it was just a few years ago. Observations were published in 2002 (Francis 2002) and 2003 (Dinets 2003), and new records based on camera-trap photos have been reported sporadically since December 2003 (e.g., Wells et al. 2005, Mathai et al. 2010, Matsubayashi et al. 2011, Brodie & Giordano 2011, Samejima & Semiadi 2012).

These photos have gradually shown that Hose’s civet is more widespread across Borneo than previously thought. They’ve also shown that it isn’t limited to montane forest as was thought: it also occurs in lowland rainforest and may even be tolerant of recently logged areas. These data all show that it’s “more common and widespread than previously thought” (Wells et al. 2005, p. 13). During August and September 2011 the species was documented (via the use of camera-traps) in the Schwaner Mountains in Central Kalimantan, a lowland location about 500 km away from the previous nearest place of distribution (Semejima & Semiadi 2012).

The case for the squirrel

Anyway, if the Kayan Mentarang animal isn’t Hose’s civet, what is it? As mentioned above, a new identification has now been published; it's perhaps the most interesting and surprising idea proposed so far. It would seem that the animal is actually…. a flying squirrel. This idea has been around since March 2006, when Andrew Kitchener published an article on Erik Meijaard’s thoughts about the creature (Kitchener 2006). Meijaard observed that the creature seems to have “the suggestion of a membrane between the front and hind limbs”. I agree, and have always wondered why the animal seems to have such a deep ‘belly’.

In fact the case for the squirrel identity is strong. By tabulating all the morphological features visible in the two photos, and then doing likewise for all 16 similar-sized mammals known from Borneo (they included one Sulawesi viverrid too), Meijaard et al. (2006) showed that the Kayan Mentarang animal agrees in morphological details with two flying squirrels found on Borneo: Thomas’ flying squirrel Aeromys thomasi and the Red giant flying squirrel Petaurista petaurista (taxiderm specimen shown at left).

Of incidental interest in this story is that the squirrel A. thomasi was named by Sir Charles Hose (1863-1929) after Michael Rogers Oldfield Thomas (1858-1929) in 1900, while the civet D. hosei was named after Sir Charles Hose by Michael Rogers Oldfield Thomas. I also like the fact that Meijaard et al. submitted their paper on April 1st: a risky plan that can sometimes delay or derail a submitted manuscript.

Composite of the original photos with Meijaard et al.'s reconstructions produced by Carel Brest van Kempen at Rigor Vitae. Compelling stuff.

Anyway… of the 13 morphological characters available for comparison, A. thomasi matches the Kayan Mentarang animal in 12 of them (the 13th character – orientation of the tail when on the ground – remains unknown for this species). In contrast to viverrids, mongooses, linsangs, mustelids, the Bay cat, the Groove-toothed squirrel (aka Tufted ground squirrel) Rheithosciurus macrotis, and various primates, A. thomasi uniquely agrees with the Kayan Mentarang animal in having a short face, small, rounded ears, a reddish non-patterned coat, a tail that exceeds head and body length, and a rounded tail tip. The two also agree in size (the Kayan Mentarang animal is estimated to be 350-450 mm in head and body length) and limb proportions.

When the two ‘mystery’ photos are looked at with all of this in mind, we see hitherto unappreciated squirreleyness. The way the animal holds its long hindlimbs (referring here to the photo showing the animal from behind) and the suggestion of a patagium now make sense, and the unusual curving shape of the long tail matches the tail posture reported for giant flying squirrels (Meijaard et al. 2006, p. 321): this tail posture is unlike that of viverrids and other carnivorans. The white eye-shine present in the Kayan Mentarang animal reportedly matches that of flying squirrels, “whereas the civets and cats normally have less bright, yellowish or orange eye-shine” (Meijaard et al. 2006, p. 321). To help convince people, Meijaard et al. (2006) provided two paintings of the Kayan Mentarang animal, this time ‘reconstructed’ using A. thomasi to fill in the gaps. The composite shown above, produced by Carel Brest van Kempen at Rigor Vitae, shows Meijaard et al.'s (2006) reconstructions alongside the original photos.

One of the several Myakka 'skunk ape' photos taken by an anonymous person but Copyright 2001 David Barkasy and Loren Coleman. I think the images portray a very clever hoax. Image from CryptoZooNews.

If Meijaard et al. (2006) are correct, then two factors have helped obscure the animal’s true identity. Firstly, there is the frustrating fact that its face is obscured by some vegetation, or, as WWF’s Head of Borneo programme director Stuart Chapman put it, “As with all good yeti shots, there is a leaf that obscures its snout” (Fair 2006). I don’t quite understand the yeti reference, as there aren’t any photos of purported yetis that have leaves in the way… but, then, there aren’t any good yeti photos at all (maybe he was thinking of the Myakka skunk ape photos? Adjacent image courtesy of CryptoZooNews). If this really is a squirrel, we would surely all have realised sooner had we been able to see its pointed, distinctively rodent-type snout.

Secondly, people just aren’t used to seeing flying squirrels walking around on the ground, which isn’t surprising given that forest-dwelling flying squirrels are arboreal animals of the canopy. It stands to reason that a ground-walking flying squirrel looked unfamiliar, even to Bornean locals with good knowledge of wildlife, and to experienced field biologists.

Illustration of Aeromys thomasi (in pose considered more typical for a flying squirrel) by Karen Phillips, from the Field Guide to the Mammals of Borneo (WWF Malaysia).

Of course none of this demonstrates that the Kayan Mentarang animal really is a ground-walking specimen of A. thomasi, and not an unknown species. But I’d say that the case is very good and more likely than the new species hypothesis, or the Hose's civet hypothesis.

Given that giant flying squirrels are awesome and deeply weird I’m no less impressed by the Kayan Mentarang animal than I was when I thought it likely to be an unusual new viverrid. Some species of Petaurista truly are giants (for squirrels), reaching 2.5 kg and more than 100 cm in total length. Though experts at manoeuvrable gliding, they might undergo periods of occasional flightlessness when, in spring, they gorge on buds and new leaves. Hey, there’s an unfinished series of articles on squirrels in my files – really should get that done some time…

For previous Tet Zoo articles on camera-trapped animals, mystery mammals and similar topics, see…

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The views expressed are those of the author and are not necessarily those of Scientific American.

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