Mystery of the Erongo carcass

Many, many thanks to everyone who took the time to think about, and comment on, the Erongo carcass (featured on Tet Zoo yesterday). As you might know if you checked the news article, this naturally mummified carcass was discovered in 2002 (or so) in a cave in the Erongo Mountains, Namibia. Local people were unable to identify it, and it was brought to my attention by Dr George Tucker who was able to view and photograph it in 2003. George attempted to determine the carcass's identity by asking various experts, but was unable to solicit a definitive response. I'm not a professional mammalogist of course, but I think I know what it is. I'm pleased to say that many of you who commented were on the right track, and I think that at least a few of you were right on the money...

Because I had to muck around with the previously shown image to get the text on it, I unfortunately lost a bit of resolution. George has now made better-quality pictures available here on flickr. Images © George Tucker. All rights reserved (images used here with permission). Anyway, having looked into it a bit, here are my thoughts.

Firstly, the animal is clearly a mammal, and it is a mummified carcass that has died within recent years, much like my wind-dried squirrel. I do not see any indications from the animal's head size or proportions that it is a juvenile. Its hindlimbs are longer than its forelimbs, its limbs are gracile and slim-boned, and it has short, curved claws. Its hands are pentadactyl, with a short pollex. Its left foot shows a very short hallux (marked with arrow in adjacent image). Its tail is reasonably well muscled and robust, so it did not have a spindly tail like that of a rat or squirrel. Very short-tailed animals like hyraxes and Hystrix (sensu stricto*) porcupines can therefore be immediately ruled out.

* Brush-tailed porcupines (which are long-tailed) are included by some in Hystrix. I agree with those who restrict Hystrix to the short-tailed, open-country species, and refer to the brush-tailed porcupines as Atherurus.

It is not a rodent: as you can see from the close-up of its teeth below, it most certainly does not have the characteristic gnawing incisors of this group (instead its anterior-most teeth seem to be subconical) and its post-canine teeth all have pointed cusps (rodent post-canines generally have flattened occlusal surfaces). Because some teeth are missing (read on), it is not possible to determine the tooth count, but in addition to the definitely present two upper premolars, there is plenty of space for a third. It is most certainly not a springhare - not only do springhares have curved incisors of typical rodent type, they also have massive dorsally projecting nasal bones, which the Erongo carcass does not. Its relatively short canines and hallux show that it is not a cat.

Based on the look of its skull my first thought was that the animal is a mustelid (and I mean mustelid in the old traditional, inclusive sense*), and most likely a Zorilla Ictonyx striatus. This is because of the low, short-snouted look of the skull and a dentition that, clearly, is that of a carnivoran. However, if the carcass is from a carnivoran, exactly what's going on with its teeth? The large, apparently subconical tooth at the tip of the lower jaw is the right lower canine, with at least one of the incisors just visible near its base. Remember that lower canines are always located further anteriorly than upper canines, and that upper canines are (99% of the time) bigger than lower canines. The apparently subconical tooth near the tip of the upper jaw looks a bit small to be the upper canine given its size relative to the lower canine, but it is clearly the right upper canine: the left is missing, the upper incisors are not visible, and an unknown number of post-canines are apparently missing, creating the impression of an enormous diastema. Posterior to this 'false diastema', there are at least two upper premolars, and at least three lower ones. I think that - originally - there were probably three upper premolars, with P1 having been lost. It is normal for teeth to drop out of sockets in dessicated carcasses.

* Some workers now exclude skunks from Mustelidae, with genetic data indicating that they should be a family-level taxon (Mephitidae) located at the base of Musteloidea (Flynn et al. 2005). Besides mephitids and mustelids, Musteloidea includes red pandas and procyonids. Fossil skunks (some of which are from Europe and Asia**), assuming they're correctly identified, either don't support this or indicate massive homoplasy, as they exhibit characters otherwise unique to mustelids.

** Of course skunks still occur in Asia, given that the stink badgers Mydaus now seem to be part of this group. That's not a new idea: Pocock championed it in the 1920s.

Could it be a viverrid? Only a couple of species are known to occur in Namibia: members of the Genetta genetta species group and the African civet Civettictis civetta [shown in adjacent image]. I think Genetta can be ruled out on the basis of its more gracile, sloping snout: the snout of the Erongo carcass is blunter and taller. Civettictis is a better match in snout shape, but it is a much larger animal, with a head and body length of between 70 and 95 cm. Furthermore, its hindlimbs and forelimbs are about equal in length. I think viverrids can be excluded therefore.

Herpestids - mongooses - are also possible candidates. Among the mongooses that occur in Namibia, meerkats Suricata can be ruled out as, unlike the Erongo animal, they lack a pollex. Their claws are also longer and straighter than those of the Erongo animal. The White-tailed mongoose Ichneumia albicauda is totally absent from Namibia (Kingdon 1997) and, with a total length that can exceed 1 m, is also probably too large. The four-toed or dog mongooses Bdeogale appear to differ in having a more robust, deeper lower jaw and, in contrast to the Erongo carcass, lack a hallux. This still leaves the mongoose taxa Herpestes (sensu lato: this 'genus' is not monophyletic - see Veron et al. 2004, Perez et al. 2006), Helogale, Mungos and a few others. Helogale and Mungos belong to the same 'social mongoose' or Mungotinae clade as do meerkats and, unlike the Erongo carcass and like meerkats, possess particularly long, gently curved hand claws. This still leaves a couple of other species and I would say that they remain as possible candidates but... my gut feeling is that it's not a mongoose, but we'd need the assistance of an expert to go further.

With viverrids and herpestids out of the way, we come back to my suggested identification of mustelid, possibly Zorilla. If the Erongo carcass does belong to a mustelid, the good news is that there are only a couple of candidate species (I am here working on the assumption that species stick to the geographical ranges given in the books). The several African otters can be excluded on the basis of being way too large (Aonyx and Lutra), on lacking claws (Aonyx), and in possessing larger post-canines than the Erongo carcass (Kingdon 1997, Larivière 2002a, 2003). The ratel or honey badger Mellivora capensis bears no resemblance whatsoever to the carcass. Both the Zorilla and Striped weasel Poecilogale albinucha differ from the carcass in having very sharp, taller-crowned teeth (Larivière 2001, 2002b). However, it might just be that the Erongo animal had worn or broken crowns. Poecilogale has a reduced dentition, with only two premolars in the upper jaw. Ictonyx has three. It doesn't look to me like the Erongo carcass has jaws short enough to house just two premolars posterior to its (missing) left-side canine, so I think we can exclude Poecilogale. This leaves Ictonyx striatus, the zorilla, as the only Namibian mustelid that matches what we can see in the Erongo carcass [zorilla dentition shown in adjacent image]. The zorilla agrees in size, approximate proportions, limb and digit morphology and so on. I'm not 100% sure, however, and this is still provisional. If you can demonstrate this to be incorrect - or, alternatively, can verify it further - please do so.

Zorillas are neat beasts. They are superficially skunk-like and were once thought to be allied to skunks, but are now widely agreed to be the most basal members of a mustelid clade (Ictonychini) that also includes the Asian marbled polecat Vormela and several Pliocene and Pleistocene Asian and European forms (Spassov 2001). Like skunks, zorillas squirt foul-smelling secretions from their anal glands. As always, lots to say on them (22 subspecies??), but not now.

Anyway, there we have it. I think that the Erongo carcass is of a zorilla.

Refs - -

Flynn, J. J., Finarelli, J. A., Zehr, S., Hsu, J. & Nedbal, M. A. 2005. Molecular phylogeny of the Carnivora (Mammalia): assessing the impact of increased sampling on resolving enigmatic relationships. Systematic Biology 54, 317-337.

Kingdon, J. 1997. The Kingdon Field Guide to African Mammals. Academic Press, San Diego.

Larivière, S. 2001. Poecilogale albinucha. Mammalian Species 681, 1-4.

- . 2002b. Ictonyx striatus. Mammalian Species 698, 1-5.

- . 2002a. Lutra maculicollis. Mammalian Species 712, 1-6.

- . 2003. Amblonyx cinereus. Mammalian Species 720, 1-5.

Perez, M., Li, B., Tillier, A., Cruad, A. & Veron, G. 2006. Systematic relationships of the bushy-tailed and black-footed mongooses (genus Bdeogale, Hespestidae, Carnivora) based on molecular, chromosomal and morphological evidence. Journal of Zoological Systematics 44, 251-259.

Spassov, N. 2001. Zorillas (Carnivora, Mustelidae, Ictonychini) from the Villafranchian of Bulgaria with a description of a new species of Baranogale Kormos, 1934. Geodiversitas 23, 87-104.

Veron, G., Colyn, M., Dunham, A. E., Taylor, P. & Gaubert, P. 2004. Molecular systematics and origin of sociality in mongooses (Herpestidae, Carnivora). Molecular Phylogenetics and Evolution 30, 582-598.