In her 2003 booklet, Understanding Deer, Jeanette Lawton wrote that the first ungulates appear in the fossil record about 50 million years ago (mya), during the Eocene. These animals subsequently evolved into two groups: those with an even number of toes (Artiodactyls) and those with an uneven number of toes (Perissodactyls). Lawton points out that the first deer didn’t appear on the scene until about 25 mya after these early ungulates. Indeed, the animals that many consider to be the precursors to deer—animals such as Syndyoceras, which seems to share features with deer, horses, giraffes and antelopes—had bony skull outgrowths similar to antlers and were found in North America some 35 mya, during the Miocene.
Remains of one of the world’s oldest known antler-shedding deer, Dicrocerus elegans, were found in European sediment deposits dating back to between 15 and 30 mya; these were small deer, similar to the muntjacs we see today, and it has been suggested that the modern muntjacs and tufted deer are probably descended from these. Modern ‘true’ deer are thought to have evolved from ancestors similar to modern-day chevrotains at some point during the Oligocene (part of the mid-Tertiary, some 30 mya); they were small animals with simple antlers and large canine tusks that lived in the forests of the Old World tropics.
In his Deer of the World, Valerius Geist points out that deer thrive in environmental turmoil – in his book, Geist wrote:
“Such turmoil became increasingly frequent as minor glaciations punctuated the warm Tertiary period and escalated to the major glaciations of the Pleistocene or Ice Age.”
In his contribution to the Encyclopedia of Mammals, Geist described how the early Pliocene of Eurasia (about 5 mya) saw increasingly larger glaciations; large glaciers pulverise rock to produce mineral-rich dust that is distributed by water and wind to form highly fertile soils. Geist explained:
“Large-antlered deer thus appeared repeatedly, beginning with the minor glaciations late in the Pliocene and continuing into the major glaciations of the Pleistocene from about 1.8 million years ago”.
Precise dates for the deer appearances and radiations are difficult to be sure of and molecular data often conflict with fossil evidence. Nonetheless, it appears that much of the deer radiation has occurred since the end of the Miocene. Fossil and molecular data suggest that the Cervinae split from the Muntiacinae about 7 mya. The muntjacs have persevered almost unchanged since this split, while the cervine deer have diversified considerably, much of which seems to have occurred in the last 2 mya.
In their 1998 paper to the Proceedings of the Royal Society of London, Ettore Randi and his colleagues suggest that Axis, Dama and Cervus originated during the Upper Miocene, while the main evolutionary lineages among the Cervus species arose and diverged in the Pliocene. In a 2004 paper to the journal Molecular Phylogenetics and Evolution, Christian Pitra and colleagues presented a cladogram, largely supporting the conclusions of Randi and his colleagues, suggesting that both Axis and Dama arose during the mid-Pliocene, around 5 mya. These data tie in quite nicely with the fossil data we currently have. The first fossils of Cervus appear at the Miocene-Pliocene boundary, between 4.3 and 6.8 mya.
European species were able to colonise the British Isles when the North Sea virtually dried up during the last Ice Age. Deer thrived in the UK during the various Interglacial periods and there is considerable fossil evidence to suggest that the dense forests of the Stone Age were home to large Red deer. When the ice retreated some about 10,000 years ago, the land bridge was closed and the deer cut off from the rest of Europe. Since then the ecological turmoil, in which they do so well, has been provided by humans.
For a fascinating and detailed account of deer evolution, the reader is directed to Deer of the World: Their Evolution, Behavior and Ecology, by Valerius Geist.