''Metkatius'', named after the town of Metka in the province

Jammu and Kashmir Jammu and Kashmir may refer to: * Jammu and Kashmir (union territory), a region administered by India as a union territory since 2019 * Jammu and Kashmir (state), a region administered by India as a state from 1952 to 2019 * Jammu and Kashmir (prin ...

, is a small extinct raoellid

artiodactyl Artiodactyls are placental mammals belonging to the order Artiodactyla ( , ). Typically, they are ungulates which bear weight equally on two (an even number) of their five toes (the third and fourth, often in the form of a hoof). The other t ...

which inhabited northern

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

during the

Middle Eocene The Eocene ( ) is a geological epoch that lasted from about 56 to 33.9 million years ago (Ma). It is the second epoch of the Paleogene Period in the modern Cenozoic Era. The name ''Eocene'' comes from the Ancient Greek (''Ēṓs'', ' Dawn') a ...

(48-45 Mya) during the Early

Lutetian The Lutetian is, in the geologic timescale, a stage (stratigraphy), stage or age (geology), age in the Eocene. It spans the time between . The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it ...

age. Metkatius is known from fragmentary remains, with the only discovered fossil remains being

mandibular In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone i ...

and

maxilla In vertebrates, the maxilla (: maxillae ) is the upper fixed (not fixed in Neopterygii) bone of the jaw formed from the fusion of two maxillary bones. In humans, the upper jaw includes the hard palate in the front of the mouth. The two maxil ...

ry fragments and isolated

teeth A tooth (: teeth) is a hard, calcified structure found in the jaws (or mouths) of many vertebrates and used to break down food. Some animals, particularly carnivores and omnivores, also use teeth to help with capturing or wounding prey, tear ...

, mainly belonging to juvenile specimens and a portion of the skeleton of a juvenile, a fragmentary

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

, vertabrae, and a forelimb. There is only one accepted

species A species () is often defined as the largest group of organisms in which any two individuals of the appropriate sexes or mating types can produce fertile offspring, typically by sexual reproduction. It is the basic unit of Taxonomy (biology), ...

of ''Metkatius'', ''M. kashmiriensis'', which is named after

Kashmir Kashmir ( or ) is the Northwestern Indian subcontinent, northernmost geographical region of the Indian subcontinent. Until the mid-19th century, the term ''Kashmir'' denoted only the Kashmir Valley between the Great Himalayas and the Pir P ...

Discovery

''Metkatius'' was described by Kumar and Sahni in 1985. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

specimen VPL/K 562 consists of an anterior portion of the skeleton of a juvenile, a fragmentary and warped

, six vertabrae (the seventh was presumably destroyed during

fossil A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...

ization), and a

forelimb A forelimb or front limb is one of the paired articulated appendages ( limbs) attached on the cranial (anterior) end of a terrestrial tetrapod vertebrate's torso. With reference to quadrupeds, the term foreleg or front leg is often used inst ...

. The holotype specimen was found in Grey

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

in the Upper Subathu formation.

Description

''Metkatius'' is a small raoellid that lived during the early Lutetian age. ''Metkatius'' is distinguished from other raoellids, like ''

Indohyus ''Indohyus'' (Meaning "India's pig" from the Greek words ''Indos'', "from India" and ''hûs'', "pig") is an extinct genus of artiodactyl known from Eocene fossils in Asia. This small chevrotain-like animal found in the Himalayas is among the clo ...

'', primarily by its small size and bunodont molars with 27 moderately marked transverse lophs. Metkatius is approximately 40% smaller than the related genus Indohyus. The first and second molars are significantly longer than they are wide with a small

paraconid Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...

and a mesial mesiostylid. The first premolar bears a distally reduced hypoconid.

Skull

The skull of ''Metkatius'' is 8.5 cm (3.3 inches) long and 4.5 cm (1.8 inches) tall. The orbit is 1.4 cm (0.6 inches) tall and 0.8 cm (0.3 inches) wide. The ramus is 1.5 cm (0.6 inches) deep.

Teeth

Two ridges descend from the highest point of the

protoconid Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...

, a major cusp at the labial apex of the trigonid region, with one going forwards and the other going backwards. The anterior (forward) ridge splits in two near the top of the tooth. The inner ridge become sharpe and vertically oriented. The outward facing ridge is relatively minor. A shelf-like structure developed between the inner and outer ridge. Anterior and posterior cingula (raised protrusions) do not extend very high, with the posterior cingulum being larger. The second lower molar has a length to width ratio of 1.85. The tooth narrows anteriorly because the trigonid (molar) cusps are situated close to each other. The protoconid is large and taller than the

metaconid Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...

. The large hypoconid is connected to the

entoconid Many different terms have been proposed for features of the tooth crown in mammals. The structures within the molars receive different names according to their position and morphology. This nomenclature was developed by Henry Fairfield Osborn i ...

by a ridge. The talonid basin is wider than the trigonid. Labial and lingual cingula are most likely absent, although they could have been removed during fossilization. The posterior cingulum is well marked and raised. On the forward side of the tooth, a structure resembling a cingulum developed with wear. The third molar is 40% longer than the second molar, with a length to width ratio of 2. The

talonid The molars or molar teeth are large, flat teeth at the back of the mouth. They are more developed in mammals. They are used primarily to grind food during chewing. The name ''molar'' derives from Latin, ''molaris dens'', meaning "millstone tooth ...

cusps are similar too those of the second molar except for the presence of a small hypoconulid. The disposition of the hypoconulid separates Metkatius from other raoellids because of its separation (instead of linkage to) the talonid cusps by a valley and by being taller than the talonid cusps. A small

tubercle In anatomy, a tubercle (literally 'small tuber', Latin for 'lump') is any round nodule, small eminence, or warty outgrowth found on external or internal organs of a plant or an animal. In plants A tubercle is generally a wart-like projectio ...

develposed at the base of the protoconid where the ectolophid ends. Lingual and posterior cingula are absent.

Cervical vertebrae

Six

cervical vertebrae In tetrapods, cervical vertebrae (: vertebra) are the vertebrae of the neck, immediately below the skull. Truncal vertebrae (divided into thoracic and lumbar vertebrae in mammals) lie caudal (toward the tail) of cervical vertebrae. In saurop ...

are clearly visible while the seventh was most likely damaged during the fossilization process. The vertebrae were interlocking. The average length of each vertebra is approximately 1.2 cm (0.5 inches). The

transverse processes Each vertebra (: vertebrae) is an irregular bone with a complex structure composed of bone and some hyaline cartilage, that make up the vertebral column or spine, of vertebrates. The proportions of the vertebrae differ according to their spina ...

were small and broad.

Thoracic vertebrae

Five

thoracic vertebrae In vertebrates, thoracic vertebrae compose the middle segment of the vertebral column, between the cervical vertebrae and the lumbar vertebrae. In humans, there are twelve thoracic vertebra (anatomy), vertebrae of intermediate size between the ce ...

were preserved, with all of them being connected to mostly intact

ribs The rib cage or thoracic cage is an endoskeletal enclosure in the thorax of most vertebrates that comprises the ribs, vertebral column and sternum, which protect the vital organs of the thoracic cavity, such as the heart, lungs and great vessels ...

. The thoracic vertabrae were roughly 0.9 cm (0.4 inches) long and the ribs were roughly 0.4 cm (0.2 inches) wide.

Forelimbs and girdle

Behind the fourth thoracic vertebra,

pectoral girdle The shoulder girdle or pectoral girdle is the set of bones in the appendicular skeleton which connects to the arm on each side. In humans, it consists of the clavicle and scapula; in those species with three bones in the shoulder, it consists o ...

elements are present. The

proximal Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

end of a forelimb, most likely a

humerus The humerus (; : humeri) is a long bone in the arm that runs from the shoulder to the elbow. It connects the scapula and the two bones of the lower arm, the radius (bone), radius and ulna, and consists of three sections. The humeral upper extrem ...

, was preserved. The diameter of the proximal extremity of the bone was 1.9 cm (0.7 inches) while the preserved portion of the main portion of the bone is 0.8 cm (0.3 inches). Reconstructed, the bone was approximately 6.5 cm (2.6 inches) long. Due to the lack of fused

epiphyses An epiphysis (; : epiphyses) is one of the rounded ends or tips of a long bone that ossify from one or more secondary centers of ossification. Between the epiphysis and diaphysis (the long midsection of the long bone) lies the metaphysis, inc ...

, the specimen was most likely a juvenile or subadult.

Paleobiology

Being a raoellid, ''Metkatius'' likely had a similar lifestyle to ''Indohyus''. ''Metkatius'' was likely an

omnivore An omnivore () is an animal that regularly consumes significant quantities of both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize t ...

because related genus ''Indohyus'' had teeth that allowed it to grasp and hold

prey Predation is a biological interaction in which one organism, the predator, kills and eats another organism, its prey. It is one of a family of common feeding behaviours that includes parasitism and micropredation (which usually do not ki ...

, while also having molars adapted to processing plant matter. Metkatius and other raoellids were almost certainly

semiaquatic In biology, being semi-aquatic refers to various macroorganisms that live regularly in both aquatic and terrestrial environments. When referring to animals, the term describes those that actively spend part of their daily time in water (in ...

. This is due to higher

bone density Bone density, or bone mineral density, is the amount of bone mineral in bone tissue. The concept is of mass of mineral per volume of bone (relating to density in the physics sense), although medicine#Clinical practice, clinically it is measured by ...

than fully terrestrial

mammal A mammal () is a vertebrate animal of the Class (biology), class Mammalia (). Mammals are characterised by the presence of milk-producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair, and three ...

s and

auditory bulla The tympanic part of the temporal bone is a curved plate of bone lying below the squamous part of the temporal bone, in front of the mastoid process, and surrounding the external part of the ear canal. It originates as a separate bone (tympanic b ...

, both of which were found in Indohyus.

References

{{Taxonbar, from=Q133836378 Whippomorphs Prehistoric Artiodactyla genera Fossil taxa described in 1985