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ICE AGE | Crowned as a True Ice Age King:

The Giant Irish Deer

Skeleton of a giant Irish deer, which allows you to appreciate its spectacular antlers

After the Last Glacial Maximum (c. 26,000–19,000 years ago), when the great ice sheets finally relinquished their hold and retreated to the northern reaches of the world, Ireland gradually became a more habitable land and eventually mammals returned to make their home there once more. However, this new population of mammals was quite different in some respects to the assemblage which had lived in Ireland before the ice, and the most conspicuous absentee among these newcomers was the great woolly mammoth, leaving Ireland's Ice Age throne vacant for a new ruler to occupy. This was a giant in its own right, and one which had lived alongside woolly mammoths in Ireland before the ice, remains of both of these great mammals having been found in Castlepook Cave in Co. Cork. Atop its head there sat a mighty crown, so it was only fitting that it would one day return to Ireland to become an Ice Age king, and, indeed, it is from Ireland that it gets its name – the giant Irish deer.

Although only a minnow when compared to the woolly mammoth, the giant Irish deer was absolutely monstrous for a deer and would completely dwarf any of the deer species living in Ireland today. These massive beasts could have a shoulder height of up to 2.1 metres, and, to put that in context, Ireland's tallest rugby player, Devin Toner, who is 2.08 metres (over 6' 10") tall, would have to jump to see over the shoulder of the largest giant Irish deer.

Reasonable estimates for the weight of these impressive beasts range from around 380 to 700 kilograms, with some concluding that a weight of around 450 kilograms is most likely, although one authoritative study from 2013 has stated that males could sometimes reach over 900 kilograms in weight! Such dimensions clearly paint a picture of a beast that was truly a giant compared to the red deer (Cervus elaphus), which is now both Ireland's largest deer and largest native mammal. This modern resident of Ireland is an impressive animal itself, with great stags that can reach or exceed around 200 kilograms in weight, but it is still only around half, or even a quarter, the size of the giant Irish deer.

As if having such a gigantic frame was not enough, though, the giant Irish deer also possessed another feature which made them seem even larger – an unrivalled set of antlers of jaw-dropping size. These could weigh up to 45 kilograms and were capable of reaching a span of 3.7 metres, which, to continue the rugby player theme, is about the same as two Johnny Sextons lying end to end (Sexton being 1.88 metres (6' 2") tall). It is from this spectacular set of antlers that the giant Irish deer gets its scientific name, Megaloceros giganteus, Megaloceros meaning 'great horn'.

This skull from a Limerick bog shows why the giant Irish deer's scientific name means 'great horn'

To stay on the subject of names, it should be noted that the giant Irish deer is sometimes erroneously referred to as the giant Irish elk. This is the unfortunate consequence of this deer having been first described over 200 years ago when the existence of extinct animals was still not accepted as it didn't accord with Biblical teaching, resulting in fossils being allied with the living species Alces alces, referred to as moose in North America but as elk in Eurasia.

In fact, the giant Irish deer is only distantly related to elks, each of them occupying a different subfamily of the deer, the former belonging to the Cervinae, or Old World deer and the latter a member of the Capreolinae, or New World deer (who, incidentally, despite their name, also have members living in the Old World, while the Old World deer have one member living in the New World).

We know, then, that the giant Irish deer is no close relative of the elk, but, that said, there has long been a debate about which of the living deer it is most closely related to, and, as it turns out, the two deer in the frame happen to be Ireland's only two native deer species – the red deer and the fallow deer. Based on physical characteristics, some have argued that the giant Irish deer allies with fallow deer as they both possess palmate antlers (that is, the tines of their antlers are 'filled in' somewhat to give a much fuller, rounder appearance, like those of a moose), while others point to skeletal features of the body that more closely resemble the red deer.

Both of these positions are supported by valid evidence so a debate based solely on physical traits was always, perhaps, destined to produce a deadlock. However, when genetic data is thrown into the fray, the balance of evidence shifts markedly in favour of the fallow deer over the red deer.

For over a decade, genetic studies have provided support for a giant Irish deer-fallow deer kinship, but equally it was acknowledged that the genetic data indicating such a relationship was relatively weak. But very recently, in 2015, a genetic study was published which strongly bolstered the previous findings, being based on almost complete mitochondrial genomes (see here for info on mitochondrial DNA) reconstructed from 14,000-year-old bone fragments of giant Irish deer found in southern Germany. These were compared to the mitochondrial DNA of 44 living deer species and it was found that there was strong evidence for a relationship between the giant Irish deer and fallow deer.

Genetic evidence has shown that the closest living relatives of the giant Irish deer are the fallow deer

It might be a little surprising given their name to hear that the giant Irish deer were present in Germany, but in fact this was a species with a vast range, present in lands right across the middle latitudes of Eurasia, from Ireland in the west to beyond Lake Baikal in southern Siberia in the east. It was the discovery of great numbers of fossils of this species, many of them impressively complete, in bogs and other sites in Ireland that led to this wide-ranging species being associated particularly with this island and named accordingly.

Map of Eurasia showing the location of Lake Baikal in southern Siberia

Unlike the fossils from before the Last Glacial Maximum (LGM), which are restricted to the very south of the island, fossils of giant Irish deer from after the LGM are found throughout the island, with major finds in Betagh Bog in Dublin (where over 80 specimens have been found), Whitechurch in Waterford (another bog), and Lough Gur in Limerick being supplemented by finds in bogs, caves, and other sites in Wexford, Cork, Clare, Antrim, and Down. All told, fossils of giant Irish deer have been recovered from around 200 find spots in Ireland and it truly seems to have conquered the entire island.

The vast majority of the fossils which have been dated cluster in a time frame which lasted from roughly 14,000 to 12,900 years ago. This was part of a warm period in Ireland that had begun around 14,500 years ago which saw grasslands extend across the island providing the perfect habitat for the giant Irish deer. The great herds of these impressive beasts must have been a spectacular sight, but the reign of this giant in Ireland was not to last.

How the giant Irish deer would have looked when it lived on the grasslands of late Ice Age Ireland

As the centuries passed, Ireland had once more begun to grow colder as the Ice Age mustered one final advance. From around 12,900 years ago, Ireland and the rest of northwest Europe endured a millennium of misery as temperatures dropped and local ice caps once more took hold of Ireland's uplands. Securely dated fossils of giant Irish deer indicate that it was at the onset of this cold stage, or shortly after it began, that this great beast finally succumbed to extinction in Ireland, the kingdom having turned on its king.

But though the giant Irish deer was once thought to have vanished across its entire range at the end of the Ice Age, it is now known that it managed to cling on for thousands of years in one location on the eastern side of the Ural Mountains. Here, the rule of this ancient king continued, although its vast empire was now reduced to a minor chiefdom. But eventually the giant Irish deer had to bow to the inevitable, the last bones of its kind dating to 7,700 years ago. Thus, far from Ireland, the land it is named after, the reign of the giant Irish deer reached its conclusion, yet right to the end it wore its spectacular crown – the regal remnant of a true Ice Age king.

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