Megaloceros (from Greek: μεγαλος megalos + κερας keras, meaning "Great Horn") is an extinct group of deer that lived across Eurasia during the Pleistocene and early Holocene periods. The main and only confirmed species in this group, Megaloceros giganteus, is commonly known as the "Irish elk" or "giant deer" and is the most well-known. Fallow deer are believed to be the closest living relatives of Megaloceros. Scientists have suggested that Megaloceros may be closely related to other groups of "giant deer," such as the East Asian genus Sinomegaceros and the largely European genus Praemegaceros. In the past, species from these two groups were historically grouped under the name Megaloceros.

Nomenclatural history

Megaloceros giganteus was first described in 1799 as Alce gigantea by Johann Friedrich Blumenbach, based on fossils found in Ireland. The name Alce was an older version of the genus Alces, which includes elk and moose.

In 1827, Joshua Brookes listed the species Megaloceros (spelled Megalocerus in earlier works) in his zoological collection. He wrote:

"Amongst other Fossil Bones, there [are] … two uncommonly fine Crania of the Megalocerus antiquorum (Mihi). (Irish), with unusually fine horns, (in part restored)."

— Brookesian Museum. The Museum of Joshua Brookes, Esq. Anatomical and Zoological Preparations, p. 20.

The name Megaloceros comes from Greek: megalos ("great") + keras ("horn, antler"). The species Megaloceros antiquorum was originally described using Irish fossils, which are now classified as M. giganteus. This made Megaloceros antiquorum a junior synonym, meaning it was a later name for the same species.

In 1987, Adrian Lister noted that the original description of Megaloceros was not detailed enough for scientific classification. In 1828, Brookes published a more detailed description, including the Latin phrase "Cornibus deciduis palmatis" ("palmate deciduous horns"). This publication was officially recognized by the International Commission on Zoological Nomenclature (ICZN) in 1977 as valid for naming purposes. Lister later confirmed that the phrase "Cornibus deciduis palmatis" met the requirements of the International Code of Zoological Nomenclature to define the species. The original spelling Megalocerus was never used again after its initial publication.

In 1844, Richard Owen named another synonym for the Irish elk, Cervus (Megaceros) hibernicus, placing it in a new subgenus called Megaceros. This name may have been based on an earlier synonym, Cervus megaceros, described by J. Hart in 1825. Despite Megaloceros being the correct name, Megaceros became more commonly used. The combination Megaceros giganteus was used by 1871. In 1945, George Gaylord Simpson revived the name Megaloceros, which gained wider acceptance. A 1989 decision by the ICZN confirmed that Megaloceros has priority over Megaceros and is the correct spelling.

Taxonomic composition

The composition of the genus Megaloceros is disputed, except for the type species, Megaloceros giganteus. Some scientists group M. savini and related species into the separate genus Praedama, while others keep them in Megaloceros.

The genus Megaloceros is widely agreed to belong to the subfamily Cervinae. Megaloceros is often placed in the tribe Megacerini, along with other "giant deer" genera like Sinomegaceros and Praemegaceros. However, the classification of giant deer as a whole is uncertain and debated. Mitochondrial DNA analysis has shown that the mitochondrial sequences of M. giganteus are nested within those of Sinomegaceros, suggesting the two lineages interbred after their initial separation. The mitochondrial genomes of Sinomegaceros are more closely related to those of M. giganteus than to their closest living relative, Dama.

A diagram from Xiao et al. (2023) shows the relationships among mitochondrial genomes of Megaloceros and related species. Examples include:
– Sinomegaceros pachyosteus (China)
– Megaloceros giganteus (Russia, Belgium)
– Sinomegaceros ordosianus (China, Russia)
– Sinomegaceros pachyosteus (China)
– Megaloceros giganteus (Europe, Russia)

Species of the genus Sinomegaceros and Praemegaceros, which were historically and sometimes still assigned to Megaloceros, are discussed in their own genus articles. Megaceroides algericus from North Africa has been considered closely related to Megaloceros by some researchers.

Species ordered from oldest to youngest:
– "M". stravpolensis from the Early Pleistocene of Southwestern Russia is now thought to belong to Arvernoceros.
– The species "Megaloceros" cretensis from the island of Crete has been moved to the genus Candiacervus.