The Irish elk (Megaloceros giganteus), also known as the giant deer or Irish deer, is an extinct species of deer in the genus Megaloceros and one of the biggest deer ever to exist. Its spread stretched across Eurasia from Ireland to Lake Baikal in Siberia during the Pleistocene. The species’ most latest remnants were discovered in western Russia and carbon dated to around 7,700 years ago.
Despite significant bone remnants have been discovered in Irish bogs, the animal was neither unique to Ireland nor closely linked to either of the extant elk species: Alces alces (the European elk, often referred as the moose in North America) or Cervus canadensis (the North American elk or wapiti). As a result, in some publications, the term “giant deer” is used instead of “Irish elk.” While one study claimed that the Irish elk was closely linked to the red deer (Cervus elaphus), many other phylogenetic analysis show that fallow deer are their closest surviving relatives (Dama dama).
The Irish elk measured around 2.1 m (6 ft 11 in) high at the shoulders and had the biggest antlers of any known deer, measuring up to the upper limit of 3.65 m (12.0 ft) in length and weighing up to 40 kg (88 lb). The Irish elk was the biggest known cervine (“Old World deer”), weighing around 450–600 kg (990–1,300 lb.) and up to 700 kg (1,500 lb.) or even more, and tied with the present Alaska moose (Alces alces gigas) as the 3rd largest known deer, next to the extinct Cervalces latifrons and Cervalces scotti.
The Irish elk appears to have had overall light color, with a dark stripe running along the back, a stripe along both sides from shoulder to haunch, a dark collar around the throat and chinstrap, and a dark hump on the withers, according to Upper Palaeolithic cave paintings.
The hump, like in bisons, permitted a higher hinging movement of the front legs to boost stride length while running, according to American palaeontologist Dale Guthrie in 1989. The hump could have also been utilized to retain fat, according to Valerius Geist. Getting too hot while running or in a rut during the summer may have been avoided by localizing fat rather than evenly dispersing it.
In 1695, Irish physician Thomas Molyneux identified enormous antlers from Dardistown, Dublin—which were supposedly often excavated in Ireland—as related to the Elk (known in North America as the Moose), suggesting that it was previously widespread on the island.
In 1799, Johann Friedrich Blumenbach originally formally named it Alce gigantea in his Handbuch der Naturgeschichte, with Alce being a variation of Alces, the Latin name for the Elk. In 1812, French scientist Georges Cuvier reported that the Irish elk did not belong to any presently existing mammal species, calling it “e plus célèbre de tous les ruminans fossiles.”
Prior to the twentieth century, the Irish elk was thought to be a prime example of orthogenesis, an evolved mechanism contrary to Darwinian evolution in which subsequent species within a lineage become progressively modified in a solitary undeviating path, evolution continuing in a straight-line void of natural selection. Orthogenesis was said to have triggered an evolutionary trajectory toward larger and larger antlers, eventually leading to the demise of the species because the antlers grew to sizes that hindered proper eating habits and trapped the animal in tree branches. Darwinians led by Julian Huxley challenged orthogenesis in the 1930s, pointing out that antler size was proportional to body size and not too enormous. The current consensus is that sexual selection, rather than orthogenesis or natural selection, was the driving factor behind the huge antlers.