muntjac and tufted deer, the antlers as well as the canines are small. The tragulids possess long canines to this day. Pliocene With the onset of the Pliocene, the global climate became cooler. A fall in the sea-level led to massive glaciation; consequently, grasslands abounded in nutritious forage. Thus a new spurt in deer populations ensued. The oldest member of Cervini, † Cervocerus novorossiae, appeared around the transition from Miocene to Pliocene (4.2–6 Mya) in Eurasia; cervine fossils from early Pliocene to as late as the Pleistocene have been excavated in China and the Himalayas. While Cervus and Dama appeared nearly 3 Mya, Axis emerged during the late Pliocene–Pleistocene. The tribes Capreolini and Rangiferini appeared around 4–7 Mya. Around 5 Mya, the rangiferina † Bretzia and † Eocoileus were the first cervids to reach North America. This implies the Bering Strait could be crossed during the late Miocene–Pliocene; this appears highly probable as the camelids migrated into Asia from North America around the same time. Deer invaded South America in the late Pliocene (2.5–3 Mya) as part of the Great American Interchange, thanks to the recently formed Isthmus of Panama, and emerged successful due to the small number of competing ruminants in the continent. Pleistocene Large deer with impressive antlers evolved during the early Pleistocene, probably as a result of abundant resources to drive evolution. The early Pleistocene cervid † Eucladoceros was comparable in size to the modern elk. † Megaloceros (Pliocene–Pleistocene) featured the Irish elk (M. giganteus), one of the largest known cervids. The Irish elk reached at the shoulder and had heavy antlers that spanned from tip to tip. These large animals are thought to have faced extinction due to conflict between sexual selection for large antlers and body and natural selection for a smaller form. Meanwhile, the moose and reindeer radiated into North America from Siberia. Taxonomy and classification Deer constitute the artiodactyl family Cervidae. This family was first described by German zoologist Georg August Goldfuss in Handbuch der Zoologie (1820). Three subfamilies were recognised: Capreolinae (first described by the English zoologist Joshua Brookes in 1828), Cervinae (described by Goldfuss) and Hydropotinae (first described by French zoologist Édouard Louis Trouessart in 1898). Other attempts at the classification of deer have been based on morphological and genetic differences. The Anglo-Irish naturalist Victor Brooke suggested in 1878 that deer could be bifurcated into two classes on the according to