Elaborate symbols of masculinity: deer are known to shed their antlers again and again in order to then bring them out again. But how did this system come about? Apparently already surprisingly early in the development history of this group of animals, a study shows that the structure and structure of the antler tissue of the oldest known fossil deer was already very similar to that of today’s species. According to this, the primitive representatives already threw off their headdresses periodically. This contradicts the previous assumption that the antler cycle came about through a rather gradual evolutionary process.
From the roebuck to the red deer to the elk: The trademark of the representatives of the deer (Cervidae) is the antlers. These structures differ significantly from the headdresses of other animals such as cattle or goats. They do not consist of horny substance, but of bone tissue. The antlers grow from the so-called “rose bushes” on the forehead of the deer. Apart from the reindeer, in which the females also have comparatively small antlers, only the males develop these sometimes enormous structures. The other specialty of the antlers is: They do not grow continuously for a lifetime, but are renewed again and again. In the temperate latitudes, the animals shed their antlers every year and form new ones during the following months.
Amazing regeneration system
It is assumed that the driver behind the development of these sometimes complex body structures was sexual selection, because the antlers are known to serve primarily as weapons of combat and imposing during the rutting season. However, why there is an antler cycle in the deer in contrast to, for example, the ibex is unclear: Regular shedding and, above all, the subsequent regeneration is an energetically enormously expensive process for the animals, which is difficult to explain according to biological principles. But it could have something to do with the fact that as a deer matures, the antlers become larger and more branched every year. In order to produce a more impressive headdress, the previous antlers must therefore give way.
A German-Swiss team of paleontologists led by (?) Gertrud Rößner from the Bavarian State Collection for Paleontology and Geology has now investigated the extent to which there were already traces of an antler cycle in the early forms of deer. To do this, they analyzed the antlers of 34 fossilized deer from Europe that lived in the early and middle Miocene – around 12 to 18 million years ago. The fossils also included the oldest known antlers of the ancient species Procervulus praelucidus, Ligeromeryx praestans and Acteocemas infans. The researchers examined the structures of the bone tissue such as the growth patterns, remodeling processes and traces of dissolution phenomena using micro-computed tomography and thin-section microscopy. They then compared the data obtained with test results from antler tissue of modern deer species.
Antler cycle is older than previously thought
As the scientists report, they were surprised by the results: processes and mechanisms of shedding and regeneration in the antler cycle evidently took place in the earliest deer species 18 million years ago as in today’s species: growth patterns and a regular cycle of traces of rejection and regeneration agree with the results of modern antlers, the scientists report. “Our comparisons now give a detailed insight into the early evolution of antler formation. The structure and structure of the fossil antler tissue were therefore astonishingly similar to those of deer living today, ”Rößner sums up.
The results thus suggest that the processes of the modern antler cycle did not emerge gradually in the course of evolution, but were fundamental from the beginning of the antler evolution. “So far we have assumed that the antler cycle, as we know it from today’s deer, developed in a gradual evolutionary process starting from originally non-shedding antlers and with transition stages from exceptional to occasional shedding,” says Rößner. But evidently the evolutionary history of the deer was shaped very early on by the dilemma of on the one hand physiological costs and on the other hand advantages in reproduction.
“The ultimate causes and the conditions for the development of the antler cycle, however, remain a question that needs to be clarified more precisely,” the researchers conclude. Perhaps future histological studies or genetic studies can help solve the question of how and why the antlers produced their amazing systems, said Rößner and her colleagues.
Source: Bavarian State Natural Science Collections, specialist article: The Science of Nature, doi: 10.1007 / s00114-020-01713-x