Tetrapod Zoology

Mystery of the Erongo carcass

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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.

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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.

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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.

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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.

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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.

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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.

Comments

  1. #1 David Marjanovi?
    June 27, 2007

    Ah, so the upper jaw does continue beyond the canine. Good. :-)

  2. #2 Mike Keesey
    June 27, 2007

    I’m having trouble finding a good picture of a zorilla’s legs, but aren’t they a mite short? Other than that it seems like a good fit, though.

  3. #3 Alan Kellogg
    June 27, 2007

    The zorilla is also one of the grumpiest beasts that ever walked the Earth. The San Diego Zoo had one years ago, and people there become rather proud of how belligerent it was. As a matter of fact, while animals such as the wolverine and tasmanian devil are now known as blustering frauds and really quite friendly once they get to know you, the zorrila is still regarded as an animal with a really crappy attitude.

  4. #4 John H
    June 28, 2007

    Mmmm…. zorilla jerky….

  5. #5 Mishal
    June 28, 2007

    I like the breakdown you did on the Erongo specimen, (and it’d be the first time I heard of a zorilla as well, this blog is so nicely educational), I’m curious though, wouldn’t the mummy have still had some hair? Being in a cave, I’m assuming it wouldn’t be subject to having the fur wind-blown off the carcass, so it should’ve still had some fibers attached to it (especially on the ground-flat side where it would not have been disturbed by anything). That could likely be of a lot of help in identification.

    Do you know if there will be a genetic analysis made to date it and perhaps verify your conclusion? It seems like the logical next step to take.

  6. #6 Lago
    June 28, 2007

    The person that posted as “Adam” I think was the first to post in the proper ballpark.

    Many people said, “Rodent” which I assume was from them thinking they were seeing incisors where they were actually seeing canines, and were also confused on how a diastema-like area appears in many small predators due to tooth-loss in many cases, as well as obstruction by desiccated flesh.

    Leg length was mentioned numerous times, but people must remember that the skin on many animals, especially small mammals, covers their bodies in such a way to give an appearance of short limbs, when in fact limbs may be relatively long.

    The skull had nothing about it that was “rodent-like”. The dimensions were what you see in smaller predators that eat rodents, often putting their heads into holes to get at them (Hence the elongation of the skull).

    I know many people are not that well-trained, or have little personal experience in identifying skeletons, and their guesses were fun, and should have been, but I was a bit amazed at how many people were throwing jargon around left and right that actually said “Rodent” as their guess. Even with poor picture quality, that does not add up.

    [from Darren: ‘Adam’ is Dr Adam Yates, respected authority on temnospondyls and basal sauropodomorphs, all-round good egg and, evidently, expert at identifying dead stuff]

  7. #7 David Marjanovi?
    June 28, 2007

    but I was a bit amazed at how many people were throwing jargon around left and right that actually said “Rodent” as their guess.

    Many of the commenters here know a good deal about the anatomy of some tetrapod group — just not usually rodents.

  8. #8 David Godfey
    June 28, 2007

    Nifty, so I was totally wrong. To be honest the idea that the animal might have lost teeth hadn’t occurred to me, and I certainly thought that I was looking at incisors rather than canines. If I’d seen the other images, or a picture of a springhare before guessing I’d probably not have agreed with the lagomorph crowd. Whether I’d have said “carnivore” is another matter entirely.

    Anyway, a good time was had by all, I think you should do more of these Darren. (If it isn’t too much work).

  9. #9 Shamini Bundell
    June 28, 2007

    I’m no expert, I said ‘it looks a bit like a cat!’ and left it at that. But still, this guess the animal thing is really really fun – I hope you do loads more of these Darren (especially the easier ones)!

  10. #10 Susan
    June 28, 2007

    I like the, “identify an animal” challenges that are posted here, they’re fun. Will they ever do a DNA analysis, or some other test on this animal’s remains to finally confirm what it is?

  11. #11 Allen Hazen
    June 29, 2007

    I didn’t post an answer, but I’m afraid if I had (when all we had was the smaller-scale photo and it was hard to see whether the big front teeth were conical caniniforms or incisors seen sideways) I too would have guessed rodent. There’s a big, round, hole in the side of the head, above the rear end of the tooth-rows (it’s not in the field of the enlarged photo). It’s separated by something (do zorillas have postorbital bars?) from the depression where the jaw muscles had been. Is this … the eye-socket? One way my thinking went wrong was that (i) I assumed the orbit would be confluent with the temporal opening (i.e., no post-orbital bar) and (ii) then misinterpreted this hole as marking the site of the tunnel that many rodents have– the tunnel that allows their jaw muscles to pass beyond the front of the zygomatic arch and insert on the snout. …
    I guess this line of ‘reasoning’ shows that I have never spent much time looking at real carcasses! And also proves the adage about “a little learning…”!

    Anyway. Thanks for posting the challenge! I have really enjoyed your “mystery pictures”!

  12. #12 Paul Barrett
    June 29, 2007

    Hey Darren, no fair! If we knew the tip of the snout was missing (and therefore that the rostralmost teeth weren’t incisors), that the cheek teeth were missing (creating a false diastema) and if we had the later close photo of the canines (which then looked like canines, rather than elongate curved teeth, as in the first photo) those thickies among us who saw a rodent might have held our tongues. Am suitably chastened, however.

    [from Darren: my apologies… although I remain secretly pleased that the image managed to mislead and fool so many people. I will also self-inflate my ego here and add that I was able to identify it based only on that one original image. Perhaps I was unfairly advantaged, having some experience with dead mustelids and their skulls and dentitions (e.g., Naish, D. 1997. Further notes on unrecognized British mustelids. The Cryptozoology Review 2 (2), 28-31). I own a marten skull and have collected dead weasels and stoats from the field. Hmm.. is there no end to my talents? :) ]

  13. #13 David Marjanovi?
    June 29, 2007

    If we knew the tip of the snout was missing

    It isn’t missing. If you take the close-up and compare it to the original, you’ll see the tip of the snout is there — though it only comprises 3 pixels or something, so I overlooked it, too. In other words, the close-up is really a close-up of the original.

    All teeth are probably there, but the lips cover them.

  14. #14 tuckeg
    July 23, 2007

    I have been traveling so I apologize for the delay in posting this. Thanks to all and especially Darren for their efforts. Looks like the mystery is solved and the remains are a zorilla. Next trip to Africa I will try to locate a zorilla skull in a museum for comparison.

    George

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