Irish elk
The Irish elk, also called the giant deer or Irish deer, is an extinct species of deer in the genus Megaloceros and is one of the largest deer that ever lived. Its range extended across northern Eurasia during the Pleistocene, from Ireland to Lake Baikal in Siberia. The most recent remains of the species have been radiocarbon dated to about 7,700 years ago in western Russia. Its antlers, which can span over across, are the largest known of any deer. It is not closely related to either living species called the elk, with it being widely agreed that its closest living relatives are fallow deer.
Taxonomy
Research history
The first scientific descriptions of the animal's remains were made by Irish physician Thomas Molyneux in 1695, who identified large antlers from Dardistown—which were apparently commonly unearthed in Ireland—as belonging to the elk, concluding that it was once abundant on the island. It was first formally named as Alce gigantea by Johann Friedrich Blumenbach in his Handbuch der Naturgeschichte in 1799, with Alce being a variant of Alces, the Latin name for the elk. The original Blumenbach's description of Alce gigantea provides rather scant information about the species, specifying only that this particular kind of "fossil elk" comes from Ireland and is characterized by immense body size. According to Blumenbach, the distance between summits of giant deer antlers may attain. This particular feature mentioned by Blumenbach permitted to Roman Croitor to identify the type specimen of giant deer that was figured and described for the first time in Louthiana of Thomas Wright. The holotype of Megaloceros giganteus is a well-preserved male skull with exceptionally large antlers found in Dunleer environs. The type specimen of giant deer is currently exposed in Barmeath Castle where Thomas Wright first saw and described it.French scientist Georges Cuvier documented in 1812 that the Irish elk did not belong to any species of mammal currently living, declaring it "le plus célèbre de tous les ruminans fossiles". In 1827 Joshua Brookes, in a listing of his zoological collection, named the new genus Megaloceros in the following passage:
The etymology being from Greek: μεγαλος "great" + κερας "horn, antler". The type and only species named in the description being Megaloceros antiquorum, based on Irish remains now considered to belong to M. giganteus, making the former a junior synonym. The original description was considered by Adrian Lister in 1987 to be inadequate for a taxonomic definition. In 1828 Brookes published an expanded list in the form of a catalogue for an upcoming auction, which included the Latin phrase "Cornibus deciduis palmatis" as a description of the remains. The 1828 publication was approved by International Commission on Zoological Nomenclature in 1977 as an available publication for the basis of zoological nomenclature. Adrian Lister in 1987 judged that "the phase "Cornibus deciduis palmatis" constitutes a definition sufficient under the
Before the 20th century, the Irish elk, having evolved from smaller ancestors with smaller antlers, was taken as a prime example of orthogenesis, an evolutionary mechanism opposed to Darwinian evolution in which the successive species within the lineage become increasingly modified in a single undeviating direction, evolution proceeding in a straight line void of natural selection. Orthogenesis was claimed to have caused an evolutionary trajectory towards antlers that became larger and larger, eventually causing the species' extinction because the antlers grew to sizes which inhibited proper feeding habits and caused the animal to become trapped in tree branches. In the 1930s, orthogenesis was disputed by Darwinians led by Julian Huxley, who noted that antler size was not grossly large, and was proportional to body size. The currently favoured view is that sexual selection was the driving force behind the large antlers rather than orthogenesis or natural selection.
Evolution
M. giganteus belongs to the genus Megaloceros. ''Megaloceros has often been placed into the tribe Megacerini, alongside other genera often collectively referred to as "giant deer", like Sinomegaceros and Praemegaceros.'' The taxonomy of giant deer lacks consensus, with genus names used for species varying substantially between authors. The earliest possible record of the genus is a partial antler from the Early Pleistocene MN 17 of Stavropol Krai in the North Caucasus of Russia, which were given the name of M. stavropolensis in 2016, however this species has been subsequently suggested to belong to Arvernoceros or Sinomegaceros. The oldest generally accepted records of the genus are from the late Early Pleistocene. Other species often considered to belong to Megaloceros include the reindeer sized M. savini, which is known from early Middle Pleistocene localities in England, France, Spain and Germany, and the more recently described species M. novocarthaginiensis, which is known from late Early Pleistocene localities in Spain, and the small M. matritensis endemic to the Iberian peninsula during the late Middle Pleistocene, which overlaps chronologically with the earliest M. giganteus records. Jan van der Made proposed M. novocarthaginiensis, M. savini and M. matritensis to be sequential chronospecies, due to shared morphological characteristics not found in M. giganteus and gradual transition of morphological characters through time. M. savini and related species have also been suggested to comprise the separate genus Praedama by other authors. While the M. savini/Praedama lineage is often suggested to be closely related to M. giganteus, most authors agree that this group of deer is unlikely to be directly ancestral to M. giganteus.The origin of M. giganteus remains unclear, and appears to lie outside Western Europe. Jan van der Made has suggested that remains of an indeterminate Megaloceros species from the late Early Pleistocene of Libakos in Greece are closer to M. giganteus than the M. novocarthaginiensis-savini-matritensis lineage due to the shared molarisation of the lower fourth premolar. Croitor has suggested that M. giganteus is closely related to what was originally described as Dama clactoniana mugharensis from the Middle Pleistocene of Tabun Cave in Israel, due to similarities in the antlers, molars and premolars. The earliest possible records of M. giganteus comes from Homersfield, England thought to be about 450,000 years ago—though the dating is uncertain. The oldest securely dated Middle Pleistocene records are those from Hoxne, England, which have been dated to Marine Isotope Stage 11, other Middle Pleistocene early records include Steinheim an der Murr, Germany, about 400,000–300,000 years ago and Swanscombe, England. Most remains of the Irish elk are known from the Late Pleistocene. A large proportion of the known remains of M. giganteus are from Ireland, which mostly date to the Allerød oscillation near the end of the Late Pleistocene around 13,000 years ago. Over 100 individuals have been found in Ballybetagh Bog near Dublin.
Some authors have proposed that Late Pleistocene M. giganteus should be divided into several subspecies including M. giganteus ruffii and M. giganteus giganteus, based primarily on differences in antler morphology.
It has been historically thought that, because both have palmated antlers, the Irish elk and fallow deer are closely related. This is supported by several other morphological similarities, including the lack of upper canines, proportionally long braincase and nasal bones, and proportionally short front portion of the skull. In 2005, two fragments of mitochondrial DNA from the cytochrome b gene were extracted and sequenced from 4 antlers and a bone, the mtDNA found that the Irish elk was nested within Cervus, and were inside the clade containing living red deer. Based on this, the authors suggested that the Irish elk and red deer interbred. However, another study from the same year in the journal Nature utilising both fragmentary mitochondrial DNA and morphological data found that the Irish elk was indeed most closely related to Dama. The close relationship with Dama was supported by another cytochrome b study in 2006, a 2015 study involving the full mitochondrial genome, and by a 2017 morphological analysis of the bony labyrinth. The 2006 and 2017 studies also directly suggest that the results of the 2005 cytochrome b paper were the result of DNA contamination.
Cladogram of Cervidae based on mitochondrial DNA:
A study of mitochondrial genomes from Sinomegaceros from the Late Pleistocene of East Asia found that the mitochondrial genomes of Megaloceros giganteus were nested within those of Sinomegaceros, suggesting that the two lineages interbred after their initial split. Cladogram of Megaloceros and Sinomegaceros mitochondrial genomes following Xiao et al. 2023.