Hoplitomeryx
Encyclopedia
The extinct
five-horned prongdeer Hoplitomeryx matthei with its sabrelike ('moschid
' type) upper canines lived on the former Gargano Island during the Miocene and the Early Pliocene, now a peninsula
on the east coast of South Italy.
Its fossilized remains were retrieved in the late sixties and subsequent years 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.
with a pair of pronged horns above each orbit and one central nasal horn. Hoplitomerycids are not the only horned deer
; before the appearance of antlered deer, members of the deer family commonly had horns. Another left-over of this stage is Antilocapra of North America, the only survivor of a once successful group related to Bovidae.
The diagnostic features of Hoplitomeryx are: one central nasal horn and a pair of pronged orbital horns, protruding canines, complete fusion of the navicocuboid with the metatarsal, distally closed metatarsal gully, a non-parallel-sided astragalus , and an elongated patella.
consisting of different islands each with its own morphotype cannot be confirmed so far. The tiny and small specimens show insular dwarfism
, but this cannot be said for the medium and huge specimens.
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. Interestingly, 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 Miocene
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).
Extinction
In biology and ecology, extinction is the end of an organism or of a group of organisms , normally a species. The moment of extinction is generally considered to be the death of the last individual of the species, although the capacity to breed and recover may have been lost before this point...
five-horned prongdeer Hoplitomeryx matthei with its sabrelike ('moschid
Musk deer
Musk deer are artiodactyls of the genus Moschus, the only genus of family Moschidae. They are more primitive than the cervids, or true deer, in not having antlers or facial glands, in having only a single pair of teats, and in possessing a gall bladder, a caudal gland, a pair of tusk-like teeth...
' type) upper canines lived on the former Gargano Island during the Miocene and the Early Pliocene, now a peninsula
Peninsula
A peninsula is a piece of land that is bordered by water on three sides but connected to mainland. In many Germanic and Celtic languages and also in Baltic, Slavic and Hungarian, peninsulas are called "half-islands"....
on the east coast of South Italy.
Its fossilized remains were retrieved in the late sixties and subsequent years from reworked reddish, massive or crudely stratified silty-sandy clays (terrae rossae), which partially fill the paleo-karstic fissures in the Mesozoic
Mesozoic
The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...
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
Microtia
Microtia, also called microtia-anotia, is a congenital deformity where the pinna is very small and underdeveloped or absent . It can be unilateral or bilateral . It occurs in 1 out of about 8,000–10,000 births. In unilateral microtia, the right ear is most commonly affected...
was already occupied). Later, after the regression and continentalization of the area, a second karstic cycle started in the late Early Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
, the neokarst, which removed part of the paleokarst fill.
Appearance
Hoplitomeryx was a deer-like ruminantRuminant
A ruminant is a mammal of the order Artiodactyla that digests plant-based food by initially softening it within the animal's first compartment of the stomach, principally through bacterial actions, then regurgitating the semi-digested mass, now known as cud, and chewing it again...
with a pair of pronged horns above each orbit and one central nasal horn. Hoplitomerycids are not the only horned deer
Deer
Deer are the ruminant mammals forming the family Cervidae. Species in the Cervidae family include white-tailed deer, elk, moose, red deer, reindeer, fallow deer, roe deer and chital. Male deer of all species and female reindeer grow and shed new antlers each year...
; before the appearance of antlered deer, members of the deer family commonly had horns. Another left-over of this stage is Antilocapra of North America, the only survivor of a once successful group related to Bovidae.
The diagnostic features of Hoplitomeryx are: one central nasal horn and a pair of pronged orbital horns, protruding canines, complete fusion of the navicocuboid with the metatarsal, distally closed metatarsal gully, a non-parallel-sided astragalus , and an elongated patella.
Hoplitomeryx 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 archipelagoArchipelago
An archipelago , sometimes called an island group, is a chain or cluster of islands. The word archipelago is derived from the Greek ἄρχι- – arkhi- and πέλαγος – pélagos through the Italian arcipelago...
consisting of different islands each with its own morphotype cannot be confirmed so far. The tiny and small specimens show insular dwarfism
Insular dwarfism
Insular dwarfism, a form of phyletic dwarfism, is the process and condition of the reduction in size of large animals – typically mammals – when their population's range is limited to a small environment, primarily islands. This natural process is distinct from the intentional creation of dwarf...
, but this cannot be said for the medium and huge specimens.
The situation with several co-existing morphotypes on an island is paralleled by Candiacervus
Candiacervus
Candiacervus was a genus of deer native to Pleistocene Crete. Their most notable feature, besides their peculiar, spatula-shaped antlers, was their small stature: the smallest species, C. ropalophorus, stood about 40 cm at the shoulders when fully grown, as can be inferred from a mounted...
(Pleistocene
Pleistocene
The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....
, Crete
Crete
Crete is the largest and most populous of the Greek islands, the fifth largest island in the Mediterranean Sea, and one of the thirteen administrative regions of Greece. It forms a significant part of the economy and cultural heritage of Greece while retaining its own local cultural traits...
, Greece
Greece
Greece , officially the Hellenic Republic , and historically Hellas or the Republic of Greece in English, is a country in southeastern Europe....
). Opinions about its taxonomy
Taxonomy
Taxonomy is the science of identifying and naming species, and arranging them into a classification. The field of taxonomy, sometimes referred to as "biological taxonomy", revolves around the description and use of taxonomic units, known as taxa...
differ, and at present two models prevail: one genus
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
for eight morphotypes, or alternatively, two genera for five species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
. 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. Interestingly, in Candiacervus
Candiacervus
Candiacervus was a genus of deer native to Pleistocene Crete. Their most notable feature, besides their peculiar, spatula-shaped antlers, was their small stature: the smallest species, C. ropalophorus, stood about 40 cm at the shoulders when fully grown, as can be inferred from a mounted...
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 Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows 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).