- Equus przewalskii Poliakov, 1881
Przewalski's Horse, Asian Wild Horse, Mongolian Wild Horse
IUCN: EN; RDBUkr: Зниклі в природі
Value of species
Current scientific review of the taxonomy of wild equids (Groves 1986) places Przewalski's Horse as a subspecies of the extinct Equus ferus. Although Przewalski's Horse (Equus ferus przewalskii) can hybridize with domestic horses (Equus ferus caballus) to produce fertile offspring (Ryder et al. 1978, Trommerhausen-Smith et al. 1979), the existence of 2n = 66 chromosomes in Przewalski's Horse identifies it as being more different from its domestic relatives (2n = 64) than are any two breeds of domestic horse (Ryder 1994). Furthermore, mitochondrial DNA research has shown that the Przewalski's Horse is not the ancestor of modern domestic horses (Vilà et al. 2001). Przewalski's Horse also show a number of consistent differences in their appearance as compared to domestic horse breeds: the mane is short and erect when in good body condition; forelocks are nearly nonexistent; the upper part of the tail has short guard hairs; a dark dorsal stripe runs from the mane down the spine to the tail; several dark stripes can be present on the carpus and generally the tarsus (Groves 1994). Przewalski's Horses grow a thick mane in winter, which contrary to domestic horses they shed each spring with the rest of their winter coat.
Other studies of the genetic differences between Przewalski's and domestic horses have indicated very little genetic distinction between them. Only four alleles at four separate serological marker loci have been identified as specific to Przewalski's Horse (Bowling and Ryder 1987); the vast majority of blood protein variants are present in both Przewalski's and domestic horses and even the fastest evolving DNA region known in mammals (the mitochondrial DNA control region), does not show significant differences between the two types of horse (Ishida et al. 1995, Oakenfull and Ryder 1998). Thus it is clear that Przewalski's and domestic horses are very closely related and have in the past interbred, but the fixed chromosomal number difference between them indicates that they are distinct populations (Oakenfull et al. 2000). A variety of molecular studies support their phylogenetic relationship as sister taxa (Steiner et al. 2012, Côté et al. 2013) diverging between 150,000 and 250,000 years ago (Goto et al. 2011, Steiner and Ryder 2011).