Most members of the genus were extremely large animals that favored meadows or open woodlands, with most species averaging slightly below 2 meters at the withers. Many of the Mediterranean species, on the other hand, were textbook examples of insular dwarfism, such as the Sardinian (and Corsican; the two were joined for much of the Pleistocene) M. cazioti, which was barely 1 meter tall. The various species of the Cretan genus Candiacervus - the smallest of which, C. rhopalophorus was just 65 centimeters high at the shoulder - are sometimes included in Megaloceros as a subgenus.
As the name "Irish Elk" implies, the larger species were somewhat similar in general habitus to the European Elk (Moose) and the American Elk. However, this has by now been shown to be a consequence of their increased size. The actual relationships are with the fallow deer genus Dama, and the genus was part of a Late Neogene Eurasian radiation of fallow deer relatives of which today only 2 taxa remain.(Lister et al. 2005, Hughes et al. 2006)
While most studies place all species in Megaloceros, sometimes the genus is considered more restricted in scope. In the most extreme case, it might be limited to M. antecedens and M. giganteus, the others being separated in Praemegaceros (European lineage) and Sinomegaceros (East Asian lineage). While the latter is probably valid as a subgenus, the former taxon requires more research as to its relationship with Megaloceros sensu stricto and Candiacervus in particular.