Reginald Innes Pocock in 1902 was perhaps the first to suggest that the quagga was a subspecies of the plains zebra. As the quagga was scientifically described and named before the plains zebra, the trinomial name for the quagga becomes E. quagga quagga under this scheme, and the other subspecies of the plains zebra are placed under E. quagga, as well. Historically, quagga taxonomy was further complicated because the extinct southernmost population of Burchell's zebra (Equus quagga burchellii, formerly Equus burchellii burchellii) was thought to be a distinct subspecies (also sometimes thought a full species, E. burchellii). The extant northern population, the "Damara zebra", was later named Equus quagga antiquorum, which means that it is today also referred to as E. q. burchellii, after it was realised they were the same taxon. The extinct population was long thought very close to the quagga, since it also showed limited striping on its hind parts. As an example of this, Shortridge placed the two in the now disused subgenus Quagga in 1934. Most experts now suggest that the two subspecies represent two ends of a cline. Different subspecies of plains zebras were recognised as members of Equus quagga by early researchers, though much confusion existed over which species were valid. Quagga subspecies were described on the basis of differences in striping patterns, but these differences were since attributed to individual variation within the same populations. Some subspecies and even species, such as E. q. danielli and Hippotigris isabellinus, were based only on illustrations (iconotypes) of aberrant quagga specimens. One craniometric study from 1980 seemed to confirm its affiliation with the horse (Equus ferus caballus), but early morphological studies have been noted as being erroneous. Studying skeletons from stuffed specimens can be problematical, as early taxidermists sometimes used donkey and horse skulls inside their mounts when the originals were unavailable. Evolution The quagga is poorly represented in the fossil record, and the identification of these fossils is uncertain, as they were collected at a time when the name "quagga" referred to all zebras. Fossil skulls of Equus mauritanicus from Algeria have been claimed to show affinities with the quagga and the plains zebra, but they may be too badly damaged to allow definite conclusions to be drawn from them. The quagga was the first extinct animal to have its DNA analysed, and this 1984 study launched the field of ancient DNA analysis. It