The giant elk mystery

 

In an excerpt from his latest book, Michael Viney examines the history and demise of the great Irish elk and deer.

Among the odder events on the rooftops of Dublin city in the spring of 1985 were protracted, slow-motion battles between two extraordinary figures, half-man, half-deer. Confronting each other on the flat roof of the National Museum, Andrew Kitchener, zoologist, and Nigel Monaghan, of the museum's staff, repeatedly raised and lowered huge antlers, locking the tines at different angles and pushing each other in a circling struggle on the asphalt. The result, in due course, was a paper in Modern Geology that has helped to resolve one of the oldest questions in evolutionary biology: could the giant Irish elk ever have used its enormous antlers in battle? The male Megaloceros giganteus is the pride of Irish palaeontology, with a skeleton nearly three metres high from hooves to tine-tips. The animal was never exclusively Irish - nor, for that matter, was it an elk - but Ireland was the early treasure-house of its fossil skeletons and antlers, impeccably preserved in lake-mud beneath the bogs. It was first recorded as a fossil in 1697 (long before dinosaurs were known), and it featured in fierce debates about extinction and the impact of Noah's flood.

In the 19th century, it was used to challenge Darwinism and the concept of "fitness", the idea that, through natural selection, animals evolve the characteristics most helpful to their survival. The controversy continues to draw scientists to the world's biggest cache of the giant deer's bones. When visitors enter the Victorian splendour of Dublin's Natural History Museum, a pair of magnificently antlered skeletons greet them inside the door, but these are only the mounted representatives of more than 250 animals, their remains stacked up in the museum's stores.

To the late Stephen Jay Gould, the great American evolutionary biologist, the question of the Irish elk's extinction was "the first great battleground of modern palaeontology". After Charles Darwin published his Origin of Species, anti-Darwinians searched the fossil record for examples of evolution that could not possibly have served the fitness and survival of the species involved. The Irish elk was their prime example.

Giant deer had clearly evolved from smaller forms, but the usefulness of bigger and bigger antlers evaporated - so it was argued - because they tangled in trees or dragged the stags down into the mud of bogs and lakes.

A Darwinian counter-attack was led in the 1930s by Julian Huxley. He observed that, as deer get bigger, their antlers increase in size at a proportionately faster rate, an orderly phenomenon for which he coined the term allometry. As natural selection favoured the body-size of Megaloceros, so allometry dictated the enormous size of its antlers, curving out in great spiked shields to a span of almost four metres and weighing up to 40 kilos - almost a third heavier than those of the modern moose. By Darwinian reasoning, any inherent disadvantage must be outweighed by the benefits of larger size.

Allometry became the standard theory in textbooks of evolution, but, as the young Gould was dismayed to find, it was "based on no data whatsoever. Aside from a few desultory attempts to find the largest set of antlers, no one had ever measured an Irish Elk." He spent most of 1971 in Dublin's Natural History Museum, yardstick in hand, measuring and comparing antlers and the length of the attached skulls as a key to original body-size.

Most of the museum's great collection of specimens, piled antler upon antler in the warehouse, was accumulated during the 19th century. Many came from Irish peasant families who, cutting peat slowly by hand for fuel, found tines sticking up from the blue marl at the base of the bog. In the more famous locations, such as Ballybetagh Bog, south of Dublin, commercial dealers probed the bog with iron rods to make bone collections from which to assemble skeletons for museums overseas. (The market for antlers and skeletons continues even today, at auction-room prices high enough to cause concern for Ireland's remaining stock of fossils; the National Museum now sells fibreglass replicas to create an alternative supply.)

The museum's formidable collection, plus a few specimens mounted in big country houses and other museums, enabled Gould to demonstrate the workings of allometry. The antlers, he found, increased in size two-and-a-half times faster than body size from small to large adult males. But, even as he confirmed this relationship, he came to doubt the merit of supposing that the outsize antlers had no primary value or function in themselves. "The case for inadaptive antlers," he decided, "has never rested on more than subjective wonderment born of their immensity." He suggested that, rather than being used in actual combat, the broad-palmed antlers were status symbols in ritualized confrontations between males that avoided damaging or deadly battles in competition for a harem of hinds.

The idea of such a mechanism, significant for evolutionary biology, had been gaining ground from studies of behaviour in red deer, caribou and mountain sheep . As actual battle weapons, the antlers of the giant deer could seem impossibly unwieldy and ineffectual. A typical opinion came from Ireland's Prof Frank Mitchell in Reading the Irish Landscape.The antlers, he wrote, although impressive, "were structurally very weak, with elongated points mounted on the edge of a thin curved plate. They would have been useless in combat and their only function can have been to impress."

This idea seemed to be strengthened by the way the antlers were mounted.

In the modern fallow deer, often proposed as the giant deer's nearest living relative, the palms of the antlers are swept back, so that the stag has to sweep its head from side to side to display them. In Megaloceros, the palms have a full-frontal span for head-on intimidation - especially impressive, perhaps, in a "parallel walk" between posturing stags of the sort seen today among red deer.

Gould came to think later that he was wrong to suggest that the deer did not use their antlers in actual combat. Among work that helped to change his mind were the practical experiments carried out by Kitchener in Dublin in 1985.

Zoologists agree that, since fighting within a species is such dangerous behaviour, elaborate displays have developed to make sure that only animals of well-matched size fight together. The macho posturings of stags and their resonant roaring contests may be more important than the comparative size of antlers. But even on theoretical grounds, it has been argued that no structure so energy-costly as the antlers could be selected for mere display; it had to be backed up by a credible threat of use.

Kitchener accepts that if Megaloceros fought like moose - that is, locking the points of the antlers and pushing - then the giant deer's superstructure was impossibly engineered. But there are other ways of locking horns. Up on the roof in Dublin, with the museum's assistant keeper as opponent, Kitchener raised and lowered his borrowed antlers, testing alternative fits. He found that if the deer tilted their heads almost parallel to the ground the antlers locked together just above the second tine, as happens with fighting red deer stags today.

In this position, the force of battle was absorbed by the neck muscles and a thickened skull. The tines on the giant deer's antlers swung into purposeful alignment: some protected the eyes, while others, in a contest of pushing and twisting, would have gored the loser in the flank and neck in the manner seen in red deer fights. Kitchener's study of the antler bone showed that the main beam of the antlers had crystal alignments similar to those in living deer, adapted to withstand the physical shocks and stresses of fighting. As mere implements of display, the antlers would have been massively over-designed.

In the course of 400,000 years, and in different parts of the giant deer's range, its physical form varied considerably.

Early on, the antlers were shorter and more upright than in the Irish, late-glacial sample, suggesting more wooded conditions in the earlier inter-glacials. And deer with longer limbs, such as the Irish animals, all lived in open or relatively treeless habitats where fast, long-distance running might be demanded. One constant was an unusually thick lower jaw, suggesting the huge demands for calcium-storage that the annual renewal of antlers made on the body as a whole.

The American mammalogist Ron Moen calculates that the largest antlers would have contained nearly 20 kilos of mineral elements, including not only some seven kilos of calcium but almost four kilos of phosphorus. These extraordinary mineral demands seem both to have changed the vegetation of late-glacial Ireland and to have doomed the deer to extinction as climate cooled again.

As modelled by Moen and his colleagues at the University of Minnesota, Duluth, a mature giant Irish stag growing 40-kilo antlers in 150 days would have needed 56 hectares of shrubby tundra just to meet its phosphorus needs. It would also have sought out the shrubs that were richest in the mineral - willow, above all.

The Irish pollen record shows that, as the Megaloceros population rose and this selective browsing pressure increased, willow was replaced by juniper or crowberry scrub and then by grassland in which willow had virtually vanished. In younger fossil skulls, the teeth show the typical wear-patterns of grazing rather than of browsing on leaves and twigs.

The deer's exceptional demand for calcium and phosphorus was to accelerate its problems with the onset of the Nahanagan stadial, the little ice age that gripped Ireland around 10,900 years ago. Even in the lushest of mineral-rich vegetation, the animal could not have grown its huge antlers each summer from its current food intake; the phosphorus it needed was more than could be absorbed from the gut. As Moen and his colleagues compute it, about 10 per cent of the minerals had to be borrowed from the deer's own skeleton and replenished during the winter. When temperatures tumbled, springs grew shorter and vegetation swung back to meagre tundra plants, this physiological debt became impossible to sustain.

The intuition that Megaloceros died out because its antlers were simply too extravagant has thus been refined to the atoms of body chemistry, and the enduring picture of giant stags becoming mired in icy lake mud and drowning under the weight of their cumbersome antlers, has been shown to have a truth of a more metaphorical kind.

The image of drowning stags had been nourished over centuries by the finding of more than 100 antlered skulls in lake sediments at Ballybetagh Bog, 15 kilometres south of Dublin. They have made up the bulk of the remains collected in the National Museum, and in the 1980s this concentration of males became the focus of taphonomic research by Anthony Barnosky of the Carnegie Museum of Natural History at Pittsburgh.

Taphonomy examines fossil bones in their environmental context - the layers of sedimentary rock, the fossil plants and pollen and fossil insects that allow a detailed reconstruction. Ballybetagh was exceptional in preserving so much of the evidence surrounding an important large-mammal extinction, and one in which humans played no part.

The winter segregation of bachelor males to this particular steep-sided valley was quite in keeping with the present-day behaviour of red deer as observed, for example, at Killarney. But the Ballybetagh animals, on average, died younger, were smaller and had abnormally small antlers compared to Megaloceros from other localities. All this was consistent with malnutrition and the winter-kill of animals exhausted by the late summer rut.

In their progressively weakened condition, did these stags eventually become mired in the lake mud, weighed down by their preposterous antlers? Barnosky found no evidence for it. Firstly, the Ballybetagh antlers happened to be relatively small; secondly, the bones were scavenged, trampled and scattered, and lay on the surface for months or years before being washed or kicked into the water.

There were no even partially-complete skeletons, or even the vertical leg-bones and feet that would speak for deer mired in mud; nor was there any sign of struggle in the sediment layers.

These, almost forensic, observations support the conclusion that winter-kill alone eliminated Megaloceros from Ireland. But, as Barnosky points out, the giant deer was unable to survive anywhere by the early Holocene, even though their preferred food plants quickly returned with the warmth. He conjectures that the season of the spring "green-up", when plants contain their maximum nutrients, may have failed to return to its previous length and intensity. This could have been crucially important to a deer growing such enormous antlers at an almost visible daily rate.

But the images of Megaloceros among the cave paintings of France suggest that, whatever happened in Ireland, human hunters probably also played some part in extinguishing this great animal across the steppes of Europe.

Abridged from Michael Viney's Ireland: a Smithsonian Natural History, published in Ireland and the UK by the Blackstaff Press of Belfast (£20, hardback)