An Unusual Stem Deer Ruminant from the Early Miocene of France

Cervidae, or deer, is a family of ruminant artiodactyls that are today best known for the diversity of their antlers, a pair of mostly branched cranial appendages of apophyseal origin, arising from the frontal bone of the skull in males with annual regeneration, being an example for sexual selection in mammals. The origin of the family can be traced back to about 18 million years ago in the Early Miocene with a well-documented fossil record of Stem Cervidae. The latter show early stages of antlers without complex branching that do not bear typical shedding structures of modern Cervidae such as the burr. Early antlers grew upward from an area close to the orbit of the skull. They were small, bi- or trifurcate, pseudo-palmate and/or stellate beam-less cranial structures from which the multi-branched beam-antlers known today probably evolved. The antler cycle, a genetically-controlled process of growth, death and regeneration of a complete organ, is a unique process among vertebrates. It is known from all stem deer without exception and is thus considered a deeply rooted process in the family. The chronological sequence of fossil antlers of stem and crown deer allows for the reconstruction of an evolutionary sequence from the small, beam-less, only simple branched structures of the Early Miocene to the complex multi-branched beam-antlers known from the Late Miocene onwards. This sequence leads to the hypothesis of a small-sized unbranched ancestral antler state growing without formation of a burr from near-upright or slightly posteriorly tilted frontal pedicles placed on the orbit’s rim. So far, this morphology has not been found in the fossil record. The fossil site Béon 1 at Montreal-du-Gers is located in calcareous clays of the molassic formations of the Aquitaine basin. It has been dated to the Burdigalian MN4b zone and is one of the richest localities of the European Miocene with fossil mammals. Excavations have been taking place there since 1987 and thousands of fossil specimens were found including a large amount of otherwise rare taxa such as the giraffomorph palaeomerycid Ampelomeryx ginsburgi or the suid Eurolistriodon tenezarensis. A recently described new early bovid from Montreal-du-Gers Pusillutragus montrealensis is one of the earliest known worldwide. Among about eight different ruminant taxa from the locality, a small, unusual ruminant attracted the attention of the excavation team and is the focus of this contribution. Its peculiar cranial appendages show all the above-mentioned characteristics of the deer antler’s ancestral state: small, unbranched-spiky, on the orbital rim and with hints to presence of shedding, confirming antler regeneration as a clade-wide common process and apomorphy of the Total Cervidae. A preliminary phylogenetic analysis branches it at the very base of the deer lineage in an extinct stem group as part of a polytomy with several other early deer taxa. As small unbranched antlers also occur in extant small deer like the pudu or the tufted deer, a possible allometric pattern will also be discussed although only the unbranched structure sets those extant antlers apart from other deer species.