The Case of the Irish Elk
The Irish Elk, Megaloceros, is misnamed, for it is neither exclusively Irish nor is it an elk. It is a giant extinct deer, the largest deer species ever, that stood up to seven feet at the shoulder (2.1 meters), with antlers spanning up to 12 feet (3.65 meters). The Irish elk evolved during the glacial periods of the last million years, during the Pleistocene Epoch. It ranged throughout Europe, northern Asia and northern Africa, and a related form is known from China. The name "Irish" has stuck because excellent, well-preserved fossils of the giant deer are especially common in lake sediments and peat bogs in Ireland. The skull on display at the old UC Museum of Paleontology came from such a locality, 18 miles north of Dublin. Such skulls, with their enormous racks of antlers, adorn the walls of castles and hunting lodges throughout Ireland. On the other hand, the complete skeleton pictured at the top of the page, on display at the Paleontological Institute in Moscow, was found at the other end of Europe, near the Russian town of Sapozhka.
Unable to adapt to the subartic conditions of the last glaciation or the marked transition that occured after the final retreat of the ice sheet, the largest deer that ever lived became extinct, the last one in Ireland dying around 11,000 years ago. Megaloceros may have possibly survived in continental Europe into historic times.
Beyond its arresting size and singular appearance, the giant deer is of great significance to paleontologists because of the way in which the animal has become involved in evolutionary debates down through the years.
Can Extinction Happen?
In the seventeenth and eighteenth centuries, it was becoming increasingly apparent that many fossils represented organisms that were not known to survive anywhere on Earth. But to scientists who believed in the Divine creation of the Earth and its life, this posed a jarring philosophical problem: why would a good, perfect God allow any of the animals in His perfect creation to die out completely? Many scientists denied the reality of extinction, and instead suggested that animals known only as fossils would one day be found alive in some unexplored part of the globe. In the words of Dr. Thomas Molyneux, the first scientist to describe the Irish elk:
That no real species of living creatures is so utterly extinct, as to be lost entirely out of the World, since it was first created, is the opinion of many naturalists; and 'tis grounded on so good a principle of Providence taking care in general of all its animal productions, that it deserves our assent.
Molyneux erroneously identified the Irish elk with the American moose, while others thought the Irish elk was identical with the European reindeer. Not until 1812 did the great French scientist Georges Cuvier document that the Irish elk, along with other fossil vertebrates such as the mammoth, did not belong to any living species of mammal. Cuvier's study of the Irish elk was a key part of the documentation that extinction had happened in the past.
Orthogenesis: Evolution in Straight Lines
A once-popular hypothesized evolutionary mechanism was orthogenesis, in which change in organisms was due not to natural selection, but to internal directional trends within a lineage. The Irish elk was once considered a prime example of orthogenesis: it was thought that its lineage had started evolving on an irreversible trajectory towards larger and larger antlers. The Irish elk finally went extinct when the antlers became so large that the animals could no longer hold up their heads, or got entangled in the trees.
Although orthogenesis was a common evolutionary theory in the 19th and early 20th centuries, it has since been abandoned for lack of a plausible mechanism. It is perfectly possible, however, to reconcile the huge antlers of Megaloceros with evolution by selection. Some paleontologists suggested that the enormous weaponry of the Irish elk served a defensive purpose, to kill predators and fight off rivals for mates. A more modern interpretation of the function of the antlers in the giant deer suggest that they were used for sexual displays, as they are in living deer. Some living deer use their antlers in ritualized combats at mating time, in which few individuals actually get hurt. It is possible that the Irish elk used its antlers in this way, but there is another possibility: The antlers of the Irish elk face forward, to show maximum area when the animal looks straight ahead. They may not have been used in combat at all, but simply served as visual signals during courtship. Whichever is the case, sexual selection is the most likely explanation for why the antlers of Megaloceros were so huge. The larger and stronger the antlers, the more successful in mating the male deer would be, and the more offspring he would have offspring which could inherit parental genes for large antlers.