The Mephitidae

The earliest skunk to cross from the Old World into North America may have been Martinogale, or a very close relation. Martinogale was about six inches long, not including the tail (Wang 2012). The oldest specimen is from a late Miocene deposit in California, with additional late Miocene fossils from Kansas, Nebraska, and Texas (Wang et al. 2005). A ‘transitional’ Pliocene skunk, Buisnictis, is known from deposits from Washington to Baja California. It is considered transitional because it shares character traits with both Martinogale and ‘modern’ skunks, especially Spilogale (Wang et al. 2005). Pliogale and Brachyopsigale are two potential Pliocene New World skunks that require better fossil evidence for confirmation and phylogenetic analysis (Wang et al. 2005).

Here we run up against a biogeographic-phylogenetic question. It has been suggested that Buisnictis gave rise to the Pleistocene genera that are our ‘modern’ skunks (Wang et al. 2005; Wang et al. 2013). But there is also an argument (based on cranio-dental traits) that the early North American ‘skunks’ (Martinogale and Buisnictis) are part of an early immigration that disappeared, and that modern skunks developed from a second wave from the Old World (ancestor unknown); that in fact those early genera may represent a sister-group to the Mephitidae and are not within the family (Geraads and Spassov 2016). Additional fossil evidence will likely be needed to flesh out either argument.

There are three extant New World genera of ‘modern’ skunks: Mephitis (striped and hooded skunks), Spilogale (spotted skunks), and Conepatus (hog-nosed skunks). In addition, there were two Pleistocene genera that are now extinct. Osmotherium is only known from the Port Kennedy Bone Cave in Pennsylvania, and was closely related to the striped skunks (Mephitis). Brachyprotoma, the short-faced skunk, ranged from the Yukon and Utah, to various sites in eastern North America (Heaton 1985; Wang et al. 2005). It shared traits with both Spilogale and Mephitis (Wang et al. 2005), and may be a sister-group to Mephitis-Osmotherium.

The earliest spotted skunks (Spilogale) are from Pliocene Kansas and Texas, and early Pleistocene Cumberland Cave in Maryland (Wang et al. 2013). Later in the Pleistocene, spotted skunks are known from California, Arizona, and Mexico. It has been suggested that this southwestern ‘refugium’ for spotted skunks allowed them to survive the Ice Age, then recolonize North America, now being found as far north as British Columbia and Minnesota. They are found south into Central America.

The hog-nosed skunks (Conepatus) are known back to the early Pliocene of central Mexico (Wang and Carranza-Castañeda 2008), and participated in the Great American Biotic Interchange by immigrating into South America soon after the land bridge formed. Pleistocene material is known from Florida, New Mexico, Mexico, Peru, Bolivia, Venezuela, Chile, and Argentina (Wang and Carranza-Castañeda 2008; González et al. 2010; Ruiz-Ramoni et al. 2014). Today these skunks can be found from Texas, Arizona, and New Mexico (and occasionally a bit further north) south to Patagonia (Dragoo and Sheffield 2009).

Mephitis (which today includes both the striped skunk and hooded skunk) is known from Pliocene Kansas (Wang et al. 2013) and early Pleistocene Nebraska, with broad distribution across the southern U.S. by the late Pleistocene (Barton and Wisely 2012). It can be found throughout much of North and Central America. Mephitis is more cold-tolerant, and likely advanced out of Mexico during the Pleistocene, creating a ‘secondary’ refugium in the southeastern U.S., with different populations expanding northward as they were able and creating a genetically ‘complex pattern of population structure’ that remains in striped skunks today (Barton and Wisely 2012).

Genetic analysis has suggested that Mephitis and Spilogale are most closely allied, forming a sister-group to Conepatus, whereas morphological evidence suggests that Conepatus and Mephitis share more character traits in common (Wang 2012). That may mean that some traits were independently derived convergently; that may make more sense from a creation perspective, where a baraminic lineage’s genetic toolbox may offer preferred routes towards similar adaptations. The divergence of skunks into modern forms after they reached North America appears to have been aided by rapid chromosomal rearrangements, with numerous likely fissions and fusions (Perelman et al. 2012). Mephitis mephitis and Mephitis macroura both have 50 chromosomes, Conepatus leuconotus has 46 chromosomes, and Spilogale gracilis has 60 chromosomes. If musteloids in general are part of the same baraminic lineage, then we can compare this to raccoons, which have a ‘conserved’ karyotype of 38 chromosomes, assumed to be similar to the hypothetical musteloid ancestor (Perelman et al. 2008).