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''Stenomylus'' is an extinct genus of miniature
camelid Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant members of this group are: dromedary camels, Bactrian camels, wild Bactrian camels, llamas, alpacas, vicuñas, ...
native to North America that died out around 30 million years ago. Its name is derived from the
Greek Greek may refer to: Greece Anything of, from, or related to Greece, a country in Southern Europe: *Greeks, an ethnic group. *Greek language, a branch of the Indo-European language family. **Proto-Greek language, the assumed last common ancestor ...
(, "narrow") and (, "molar"). ''Stenomylus'' was extremely diminutive compared to other ancient and modern camelids, standing only tall on average. It was a slender animal with a long neck, having some resemblance to a modern
gazelle A gazelle is one of many antelope species in the genus ''Gazella'' . This article also deals with the seven species included in two further genera, ''Eudorcas'' and ''Nanger'', which were formerly considered subgenera of ''Gazella''. A third f ...
. Unlike modern camelids, ''Stenomylus'' lacked padding on its hooves and based on theories about its
biomechanics Biomechanics is the study of the structure, function and motion of the mechanical aspects of biological systems, at any level from whole organisms to organs, cells and cell organelles, using the methods of mechanics. Biomechanics is a branch of ...
.


Description

Although a member of the
Camelidae Camelids are members of the biological family Camelidae, the only currently living family in the suborder Tylopoda. The seven extant members of this group are: dromedary camels, Bactrian camels, wild Bactrian camels, llamas, alpacas, vicuñas ...
, the gracile ''Stenomylus'' looked very similar to today's
gazelles A gazelle is one of many antelope species in the genus ''Gazella'' . This article also deals with the seven species included in two further genera, ''Eudorcas'' and ''Nanger'', which were formerly considered subgenera of ''Gazella''. A third ...
. The legs, in fact, were extremely elongated and bore only two toes; the legs had separate
metacarpal In human anatomy, the metacarpal bones or metacarpus form the intermediate part of the skeletal hand located between the phalanges of the fingers and the carpal bones of the wrist, which forms the connection to the forearm. The metacarpal bones ar ...
but some species showed an incipient fusing of metacarpals, especially in the
metatarsus The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...
. The nail
phalanges The phalanges (singular: ''phalanx'' ) are digital bones in the hands and feet of most vertebrates. In primates, the thumbs and big toes have two phalanges while the other digits have three phalanges. The phalanges are classed as long bones. ...
suggest the presence of hooves similar to those of deer, and not of fleshy pads like those of today's camels.gerenuk The gerenuk (; so, garanuug; ''Litocranius walleri''), also known as the giraffe gazelle, is a long-necked antelope found in parts of East Africa. The sole member of the genus ''Litocranius'', the gerenuk was first described by the naturalist ...
. The head was small, rounded and with a short muzzle. The nasal bones, set quite far back in the skull, suggest the presence of a small
proboscis A proboscis () is an elongated appendage from the head of an animal, either a vertebrate or an invertebrate. In invertebrates, the term usually refers to tubular mouthparts used for feeding and sucking. In vertebrates, a proboscis is an elong ...
or at least of muscular prehensile lips. This characteristic is even more accentuated in the related (and slightly later) '' Rakomylus''. The dentition of ''Stenomylus'' was very specialized: the anterior teeth were small, and the third
incisor Incisors (from Latin ''incidere'', "to cut") are the front teeth present in most mammals. They are located in the premaxilla above and on the mandible below. Humans have a total of eight (two on each side, top and bottom). Opossums have 18, wher ...
, as well as the first
premolar The premolars, also called premolar teeth, or bicuspids, are transitional teeth located between the canine and molar teeth. In humans, there are two premolars per quadrant in the permanent set of teeth, making eight premolars total in the mou ...
, were similar to the canine. The upper second and third premolars were very small, and there was a
diastema A diastema (plural diastemata, from Greek διάστημα, space) is a space or gap between two teeth. Many species of mammals have diastemata as a normal feature, most commonly between the incisors and molars. More colloquially, the condition ...
between the first and second premolars. Both the upper and lower molars were
hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritty ...
) in structure, and possessed deep roots even in mature individuals. C. Frick and BE Taylor. 1968. A Generic Review of the Stenomyline Camels. ''American Museum Novitates'' 2353: 1-51


Classification

The genus '' Stenomylus'' was described for the first time by Peterson in
1907 Events January * January 14 – 1907 Kingston earthquake: A 6.5 Moment magnitude scale, Mw earthquake in Kingston, Jamaica, kills between 800 and 1,000. February * February 11 – The French warship French cruiser Jean Bart ( ...
, on the basis of fossil remains found in lower Miocene soils of
Nebraska Nebraska () is a state in the Midwestern region of the United States. It is bordered by South Dakota to the north; Iowa to the east and Missouri to the southeast, both across the Missouri River; Kansas to the south; Colorado to the southwe ...
. The
type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen( ...
is ''Stenomylus gracilis''. Another well-known species is ''Stenomylus hitchcocki'', known from numerous specimens found in the Agate Springs area in Nebraska, in a quarry later known as "Stenomylus Quarry". '' Stenomylus '' is a very specialized genus of camelids, classified in a separate subfamily, the Stenomylinae, which likely originated at the end of the
Oligocene The Oligocene ( ) is a geologic epoch of the Paleogene Period and extends from about 33.9 million to 23 million years before the present ( to ). As with other older geologic periods, the rock beds that define the epoch are well identified but the ...
. The specialization in the lengthening of the legs and the retraction of the nasal bones, as well as in the teeth, would be accentuated even more in later forms such as '' Rakomylus''.


References


External links


''Stenomylus'' image and description
from the
USGS The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, a ...
Prehistoric camelids Miocene even-toed ungulates Miocene genus extinctions Miocene mammals of North America Oligocene mammals of North America Oligocene genus first appearances Prehistoric even-toed ungulate genera {{paleo-eventoedungulate-stub