Did human ascent preclude the survival of skunks in Eurasia?
(writing in progress)
In the New World, the skunk family (i.e. Mephitidae, which is now regarded as a separate family from the Mustelidae, https://en.wikipedia.org/wiki/Mephitidae) is widespread from central Canada in the north to Patagonia in the south.
By contrast, in the Old World this family is restricted to equatorial southeast Asia, where the only true skunks are two species of Mydaus (https://en.wikipedia.org/wiki/Stink_badger). There are no Eurasian counterparts for the large, cold-tolerant skunks of North and South America which belong to the genera Mephitis (https://en.wikipedia.org/wiki/Mephitis_(genus)) and Conepatus (https://en.wikipedia.org/wiki/Hog-nosed_skunk).
The marbled polecat (Vormela peregusna, https://www.inaturalist.org/taxa/41829-Vormela-peregusna) of central Eurasia is a member of the Mustelidae, convergent with skunks, but is smaller (body mass ca 0.5 kilograms) than all skunks other than spotted skunks of the genus Spilogale (https://en.wikipedia.org/wiki/Spotted_skunk).
Does this vagary of evolutionary histories and continental biogeography have an explanation in ecological or adaptive terms?
We know from the fossil record that the skunk family originated in Eurasia, whence it spread to the Americas in the Miocene (approximately 20 million years ago). Therefore, it’s clear that skunks have become extinct on the entire mainland of the Old World in contrast to their survival in the New World.
When Homo sapiens arrived in the Americas (https://en.wikipedia.org/wiki/Settlement_of_the_Americas), skunks were hunted for food. The larger species may have been extirpated from certain areas, only re-occupying these gaps in their ranges after arrival of Europeans.
The crucial difference between Eurasia and the Americas is that humans evolved in the former, whereas Homo sapiens only reached the latter at the end of the Pleistocene, less than 20,000 years ago.
The defensive strategy of skunks features conspicuous colouration, reluctance to flee, and a reliance on aerosol venom as a deterrent
works against predators such as bears (Ursidae), which depend on smell for foraging and thus cannot afford to bring harm to their olfactory organ by attacking skunks.
However, this chemical defence would have been relatively inept against early humans. This is because humans could kill skunks from a safe distance with projectile weapons, and would find the spray of skunks unappetising but not disabling.
Skunks living in seasonally cold climates tend to become fat in the autumn, in preparation for limited availability of food in winter. Therefore, early humans would have had particular incentives to hunt large skunks outside of the tropics. American skunks in the genera Mephitis and Conepatus have body mass of approximately 2.5 kg but can surpass 4.5 kg at times.
It seems likely that skunks were extirpated from most of mainland Eurasia by human predation in the late Pliocene or early Pleistocene, several million years ago. If so, this would provide the earliest example of the regional extinction of a whole family of mammals by humans.
I hypothesise that this extermination was not later repeated in the New World because by that stage the human species had developed extreme capability as a hunter of the largest mammals, reducing the reliance on prey of the size of skunks.
(writing in progress)
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Most mustelids use their scent glands to mark territory and announce their presences. There has been an analysis of the chemical composition of wolverine anal sacs. The chemical composition of Ictonyx scent glands is similar to other mustelids. However, they are known to use their glands as a defense mechanism rather than for territory marking. Someone should examine the glands of Ictonyx to see if there are papillae associated with the glands, as seen in mephitids. Mustelids probably have ducts associated with the glands, rather than nipples. The PBS Nature episode, "Is that skunk" has a really nice slow-motion, close-up of the papillae in action.
Skunk skin is rather loose. If you do not get a good handle while scruffing them, they can turn and bite a thumb or finger. The best way to catch skunks is to grab them by the base of the tail.
About the only time anything resembling fang-baring occurs in mephitids is during eating. There is a lot of butt-bumping and squawking, and one will see teeth as they are grabbing food or chewing. When skunks defend themselves they will charge and stomp and look at you with both ends. No need to bare teeth with a powerful chemical weapon on board. When "fighting" one another there is a lot of screeching and squawking and some biting. Just opening the mouth to bite does not really count as fang-baring.
Uses of skunks by native peoples. In addition to food, they have been used in ceremonial garb as well as for medicinal purposes. Apparently, skunks can cure a lot of what ails humans.
The rationale is that skunks are best-defended against predators such as bears and wolf and that the defence would actually have been ineffective against early humans with their projectile weapons and their incentive to predate omnivorous prey of an attractive size (ca 2.5kg) that get fat before winter. I’m suggesting that the asymmetry in the biogeography of skunks is not only inversely correlated with an asymmetry in human biogeography (until the late Pleistocene), but is caused by that asymmetry. Skunks, being ‘primitive’ and not as encephalised as more ‘modern’ Carnivora, were hypothetically extirpated from the entire sweep of Eurasia where winters were cold enough to make skunks attractive prey for hominids in the late Pliocene and Homo during the Pleistocene. This would make Mydaus something of a ‘living fossil’?
It is known that the aerosol venom of skunks is based mainly on thiols, which are sulfur analogues of alcohol, whereas the anal gland secretions of the wolverine are based on methylbutanoic acid, which means basically the same stinky but non-toxic substance used by Greenpeace against Japanese whaling ships.
Given that Mephitidae have disappeared from most of Eurasia, the remaining genus of Asian true skunks, namely Mydaus, is worth examining. Can this genus be considered a 'living fossil'?
Mydaus javanensis:
http://2.bp.blogspot.com/_mGSuHcdw0UY/S9AgdpCx0qI/AAAAAAAABS8/R3tMkhoqU90/s1600/3268033091_af3550fedb.jpg
Mydaus javanensis:
https://c1.staticflickr.com/3/2128/2337175977_471b817dfd_b.jpg
Mydaus javanensis:
http://4.bp.blogspot.com/-D_8qtrOPZUk/U8WVt6usq1I/AAAAAAAAMA0/8PboNjFX-E4/s1600/mydaus+javanensis.jpg
Mydaus javanensis:
http://mongabay-images.s3.amazonaws.com/12/1120stinkbadger2.jpg
Mydaus javanensis:
http://assets.panda.org/img/original/malaybadger__16.jpg
Mydaus javanensis:
http://mongabay-images.s3.amazonaws.com/12/1120stinkbadger.jpg
Mydaus javanensis:
http://cdn.theborneopost.com/newsimages/2012/11/000000528040.jpg
Mydaus javanensis:
http://cdn.theborneopost.com/newsimages/2013/08/p4kch-bp130813-go-forestry-.jpg
Mydaus javanensis:
http://1.bp.blogspot.com/-VWs7O5XAZDE/UJXocXnmrqI/AAAAAAAAAk8/2XJBHXh5O74/s1600/hspring+(1).JPG
Mydaus javanensis:
http://www.fwrc.msstate.edu/borneocarnivoresymposium/images/species/sunda_stink_badger.jpg
Mydaus marchei:
http://cdn.c.photoshelter.com/img-get2/I0000CVxng5k9XOo/fit=1000x750/Palawan-stink-badger-04.jpg
Mydaus marchei:
http://brockwatcher.files.wordpress.com/2010/04/myd-05a.jpg?w=640
Mydaus marchei:
https://c2.staticflickr.com/4/3436/3365305525_842fe45e33.jpg
Mydaus marchei:
http://philippine-animals-mammals.webs.com/palawan%20stink%20badger.jpg
Mydaus marchei:
https://www.youtube.com/watch?v=uRHxFivqbfI&feature=youtu.be
Mydaus marchei:
http://cdn1.arkive.org/media/51/5126BF70-9B67-41E5-8BC9-F2B17B8C18B3/Presentation.Large/Palawan-stink-badger.jpg
Mydaus marchei:
http://cdn1.arkive.org/media/47/47116EBA-E1B0-464A-9299-6BBFC2F0CEFB/Presentation.Large/Palawan-stink-badger-on-leaf-litter.jpg
Mydaus is the only surviving genus of true skunks (Mephitidae) in Eurasia. Both spp. are today restricted to islands, albeit including extremely large, continental shelf islands such as Borneo and Sumatra.
Mydaus has body mass ca 2.5 kg, about the same size as American Mephitis and Conepatus.
Mydaus is essentially a fossorial invertebrate-eater with omnivorous tendencies, and like Conepatus it has a pig-like snout.
Mydaus seems to be a primitive, ancient genus that has survived on the continental shelf islands, as opposed to having evolved on the islands. All skunks seem to be rather primitive w.r.t. their brains.
It is interesting that archaeological deposits show consumption of Mydaus by humans, despite the stink defence of these skunks.
http://www.jstor.org/discover/10.2307/1378960?sid=21104877071271&uid=4&uid=2
http://journals.upd.edu.ph/index.php/asp/article/view/4412
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