Hoplitomeryx

Hoplitomeryx Temporal range:
Cast of the holotype of H. matthei, Naturalis, National Natural History Museum, Leiden, the Netherlands
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Artiodactyla
Family:	†Hoplitomerycidae
Genus:	†Hoplitomeryx Leinders, 1984
Species
†H. matthei Leinders, 1984 †H. apruthiensis Mazza & Rustioni, 2011 †H. apulicus Mazza & Rustioni, 2011 †H. falcidens Mazza & Rustioni, 2011 †H. magnus Mazza & Rustioni, 2011 †H. minutus Mazza & Rustioni, 2011

Hoplitomeryx is a genus of extinct deer-like ruminants which lived on the former Gargano Island during the Miocene and the Early Pliocene, now a peninsula on the east coast of Southern Italy. Hoplitomeryx, also known as "prongdeer", had five horns and sabre-like upper canines similar to a modern musk deer.

Its fossilized remains were retrieved from the late 1960s onwards from reworked reddish, massive or crudely stratified silty-sandy clays (terrae rossae), which partially fill the paleo-karstic fissures in the Mesozoic limestone substrate and that are on their turn overlain by Late Pliocene-Early Pleistocene sediments of a subsequently marine, shallow water and terrigenous origin. In this way a buried paleokarst originated.

The fauna from the paleokarst fillings is known as Mikrotia fauna after the endemic murid of the region (initially named "Microtia", with a c, but later corrected, because the genus Microtia was already occupied). Later, after the regression and continentalization of the area, a second karstic cycle started in the late Early Pleistocene, the neokarst, which removed part of the paleokarst fill.

Description

Life reconstruction of Hoplitomeryx by Mauricio Antón.

Hoplitomeryx was a small ruminant characterized by the presence of five horns, two in pairs above each orbit and one on the nasal bone, and of elongated canines similar to those of musk deer. Its skull is also characterized by a complete fusion of the navicocuboid with the metatarsal, a distally closed metatarsal gully, and a non-parallel-sided astragalus,. Its post-cranial anatomy is characterized by an elongated patella.

Species

The Hoplitomeryx skeletal material forms a heterogeneous group, containing four size groups from tiny to huge; within the size groups different morphotypes may be present. All size groups share the same typical Hoplitomeryx features. The different size groups are equally distributed over the excavated fissures, and are therefore not to be considered chronotypes. The hypothesis of an archipelago consisting of different islands each with its own morphotype cannot be confirmed so far. The small specimens show insular dwarfism, but this cannot be said for the medium and huge specimens.

Skull

The situation with several co-existing morphotypes on an island is paralleled by Candiacervus (Pleistocene, Crete, Greece). Opinions about its taxonomy differ, and at present two models prevail: one genus for eight morphotypes, or alternatively, two genera for five species. The second model is based upon limb proportions only, but these are invalid taxonomic features for island endemics, as they change under influence of environmental factors that differ from the mainland. Also in Hoplitomeryx the morphotypes differ in limb proportions, but here different ancestors are unlikely, because in that case they all ancestors must have shared the typical hoplitomerycid features. In Candiacervus as well as in Hoplitomeryx, the largest species is as tall as an elk, but gracile and slender.

The large variation is instead explained as an example of adaptive radiation, starting when the Oligocene ancestor colonized the island. The range of empty niches promoted its radiation into several trophic types, yielding a differentiation in Hoplitomeryx. The shared lack of large mammalian predators and the limited amount of food in all niches promoted the development of derived features in all size groups (apomorphies).

Taxonomy

The affinities of Hoplitomeryx have long been contentious, due to its unique morphology not closely resembling any living ruminant group. Following their discovery in the 1980s, the Hoplitomerycids were considered to be relatives of Cervidae (deer), possibly as descendants of the early Miocene genus Amphiomoschus or of the late Miocene Micromeryx, and potentially forming a sister taxon to cervids as a whole However, analysis of the horn cores show that they more closely resemble those of bovids (bovines, antelopes), an affinity also supported by their inner ear anatomy, which resembles those of bovids, and by similarities of brain morphology between Hoplitomeryx and bovids.

References

• De Giuli, C. & Torre, D. 1984a. Species interrelationships and evolution in the Pliocene endemic faunas of Apricena (Gargano Peninsula - Italy). Geobios, Mém. spécial, 8: 379–383.
• De Giuli, C., Masini, F., Torre, D. & Boddi, V. 1986. Endemism and bio-chronological reconstructions: the Gargano case history. Bollettino della Società Paleontologica Italiana,25 (3): 267–276. Modena.
• Dermitzakis, M. & De Vos, J. 1987. Faunal Succession and the Evolution of Mammals in Crete during the Pleistocene. Neues Jahrbuch Geologische und Paläontologische Abhandlungen 173, 3: 377–408.
• De Vos, J. 1979. The endemic Pleistocene deer of Crete. Proceedings of the Koninklijke Nederlandse Akademie van Wetenschappen, Series B 82, 1: 59–90.
• De Vos, J. & Van der Geer, A.A.E. 2002. Major patterns and processes in biodiversity: axonomic diversity on islands explained in terms of sympatric speciation. In: Waldren, B. & Ensenyat (eds.). World Islands in Prehistory, International Insular Investigations, V Deia International Conference of Prehistory. Bar International Series, 1095: 395–405.
• Freudenthal, M. 1972: Deinogalerix koenigswaldi nov. gen., nov. spec., a giant insectivore from the Neogene of Italy. Scripta Geologica 14. [1] (includes full text PDF)
• Freudenthal, M. 1976. Rodent stratigraphy of some Miocene fissure fillings in Gargano (prov. Foggia, Italy). Scripta Geologica 37. [2] (includes full text PDF)
• Freudenthal, M. 1985. Cricetidae (Rodentia) from the Neogene of Gargano (Prov. of Foggia, Italy). Scripta Geologica 77. [3] (includes full text PDF)
• Mazza, P. 1987. Prolagus apricenicus and Prolagus imperialis: two new Ochotonids (Lagomorpha, Mammalia) of the Gargano (Southern Italy). Bollettino della Società Paleontologica Italiana, 26 (3): 233–243.
• MAZZA, P. P. A. and RUSTIONI, M. (2011), Five new species of Hoplitomeryx from the Neogene of Abruzzo and Apulia (central and southern Italy) with revision of the genus and of Hoplitomeryx matthei Leinders, 1983. Zoological Journal of the Linnean Society, 163: 1304–1333. doi:10.1111/j.1096-3642.2011.00737.x
• Parra, V., Loreau, M. & Jaeger, J.-J. 1999. Incisor size and community structure in rodents: two tests of the role of competition. Acta Oecologica, 20: 93–101.
• Mazza P.P.A. 2015 Scontrone (central Italy), signs of a 9-million-year-old tragedy. Lethaia, 48: 387–404. doi:10.1111/let.12114
• Mazza, P.P.A., Rossi M.A., Agostini S. (2015) Hoplitomeryx (Late Miocene, Italy), an example of giantism in insular ruminants. Journal of Mammalian Evolution 22: 271–277. doi:10.1007/s10914-014-9277-2
• Mazza P. P. A., Rossi M.A., Rustioni M., Agostini S., Masini F. and Savorelli, A. (2016) Observations on the postcranial anatomy of Hoplitomeryx (Mammalia, Ruminantia, Hoplitomericidae) from the Miocene of the Apulia Platform (Italy). Palaeontographica, 307 (1-6): 105–147.
• Van der Geer, A.A.E. 2005. The postcranial of the deer Hoplitomeryx (Mio-Pliocene; Italy): another example of adaptive radiation on Eastern Mediterranean Islands. Monografies de la Societat d'Història Natural de les Balears 12: 325–336.
• Van der Geer, A.A.E. 2005. Island ruminants and the evolution of parallel functional structures. In: Cregut, E. (Ed.): Les ongulés holarctiques du Pliocène et du Pléistocène. Actes Colloque international Avignon, 19-22 septembre. Quaternair, 2005 hors-série 2: 231–240.
• Van der Geer, A.A.E. 2008. The effect of insularity on the Eastern Mediterranean early cervoid Hoplitomeryx: the study of the forelimb. Quaternary International, 182(1)145-159.
• Van der Geer, A., Lyras, G., de Vos, J. & Dermitzakis M. 2010. Evolution of Island Mammals: Adaptation and Extinction of Placental Mammals on Islands. Oxford: Wiley-Blackwell Publishing.

External links

• Research on Hoplitomeryx
• Research on island faunas
• Publications on Hoplitomeryx