''Kalaallitkigun'' is an extinct genus of

haramiyida Haramiyida is a possibly Paraphyly, paraphyletic order of Mammaliaformes, mammaliaform cynodonts or mammals of controversial taxonomic affinites. Their teeth, which are by far the most common remains, resemble those of the multituberculates. Howe ...

mammaliaform Mammaliaformes ("mammalian forms") is a clade of synapsid tetrapods that includes the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts during the Late Triassic. It is defined a ...

s from the

Late Triassic The Late Triassic is the third and final epoch (geology), epoch of the Triassic geologic time scale, Period in the geologic time scale, spanning the time between annum, Ma and Ma (million years ago). It is preceded by the Middle Triassic Epoch a ...

Greenland Greenland is an autonomous territory in the Danish Realm, Kingdom of Denmark. It is by far the largest geographically of three constituent parts of the kingdom; the other two are metropolitan Denmark and the Faroe Islands. Citizens of Greenlan ...

. It contains a single species, ''Kalaallitkigun jenkinsi'', which was described in

2020 The year 2020 was heavily defined by the COVID-19 pandemic, which led to global Social impact of the COVID-19 pandemic, social and Economic impact of the COVID-19 pandemic, economic disruption, mass cancellations and postponements of even ...

from a partial

dentary 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 ...

(lower jaw) found in the

Fleming Fjord Formation The Fleming Fjord Formation, alternatively called the Fleming Fjord Group is an Upper Triassic geological formation in the northeastern coast of Jameson Land, Greenland. It consists of terrestrial sediments and is known for its fossil content. ...

. More specifically, it was found in the mid-late Norian (~215 Ma) Carlsberg Fjord beds of the Ørsted Dal Member. It is the oldest of several mammaliaform species discovered in the Late Triassic sediments of Greenland. It is also the oldest mammaliaform with double-rooted teeth, and its pattern of tooth cusps help to clarify the evolution of haramiyidan teeth relative to their

morganucodont Morganucodonta ("Glamorgan teeth") is an extinct order of basal Mammaliaformes, a group including crown-group mammals (Mammalia) and their close relatives. Their remains have been found in Southern Africa, Western Europe, North America, India and ...

-like ancestors.

Description

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 ...

and only known specimen consists of a partial dentary preserving two teeth: the first premolariform (pm1) and second molariform (m2). Empty

alveoli Alveolus (; pl. alveoli, adj. alveolar) is a general anatomical term for a concave cavity or pit. Uses in anatomy and zoology * Pulmonary alveolus, an air sac in the lungs ** Alveolar cell or pneumocyte ** Alveolar duct ** Alveolar macrophage * M ...

(sockets) for three more premolariforms and two more molariforms are also present in the preserved portion of the jaw. This gives a total number of four premolariforms and three molariforms, similar to ''

Haramiyavia ''Haramiyavia'' is a genus of synapsid in the clade Haramiyida that existed about 200 million years ago in the Rhaetian stage of the Triassic. Like other haramiyidans, it was likely a non-mammalian mammaliaform. It contains a single species, ''H ...

''. The front of the dentary is broken off, so the shape and number of

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 ...

and

canine Canine may refer to: Zoology and anatomy * Animals of the family Canidae, more specifically the subfamily Caninae, which includes dogs, wolves, foxes, jackals and coyotes ** ''Canis'', a genus that includes dogs, wolves, coyotes, and jackals ** Do ...

teeth are unknown. The thinnest portions of the posterior dentary are also not preserved. The dentary was relatively large, with proportionally small teeth. The

meckelian groove The Meckelian groove (or Meckel's groove, Meckelian fossa, or Meckelian foramen, or Meckelian canal) is an opening in the medial (inner) surface of the mandible (lower jaw) which exposes the Meckelian cartilage.postdentary trough The postdentary trough is a skeletal feature seen in Mesozoic mammals. It is found on the inside of the lower jaw (dentary), at the back behind the molar teeth. It is the hollow in which the postdentary bones and Meckel's cartilage sit. These bone ...

(the groove which hosts the postdentary bones). The postdentary trough slopes upwards and is divided from the overlying coronoid fossa via a strong ridge. Unlike ''Morganucodon'' and earlier cynodonts, there is no groove on the inner surface directly under the molariform teeth. The masseteric fossa (on the outer rear surface of the dentary) is voluminous but shifted back past the level of the last molariform. The preserved premolariform tooth is single-rooted and simple, with a larger cusp at the front and a much smaller one at the back.

Molariform

The molariform m2 is intermediate in structure between the triconodont pattern seen in taxa such as ''

Morganucodon ''Morganucodon'' ("Glamorgan tooth") is an early mammaliaform genus that lived from the Late Triassic to the Middle Jurassic. It first appeared about 205 million years ago. Unlike many other early mammaliaforms, ''Morganucodon'' is well represent ...

'' (with large triangular cusps in a single row) and the specialized two-row pattern found in the more derived

euharamiyida Euharamiyida also known as Eleutherodontida, is clade of early mammals or mammal-like cynodonts from the Middle Jurassic to Early Cretaceous of Eurasia and possibly North America. The group is sometimes considered a sister group to Multitubercula ...

ns. Like haramiyidans, there are two parallel rows of cusps separated by a median furrow. The four labial (outer/cheek side) cusps are homologous to the four main cusps of morganucodonts (from front to back: b, a, c, and d), with cusp a being the largest and cusp c as the second-largest. They can also be homologized to cusps b1 to b4 of ''Haramiyavia''. In contrast to other haramiyidans (but like morganucodonts), the labial cusps of ''Kalaallitkigun'' are significantly larger than the cusps on the lingual (inner/tongue) side of the tooth. Cusp a in particular is large enough that it restricts the median furrow and divides the space into two basins. In the lingual tooth row, there are four small cusps (e', g, g', and i'). These cusps are homologous to cusps a1 to a4 of ''Haramiyavia''. Cusp g, though still small, is the largest cusp in the lingual row, lying inwards from cusps a and c. Two additional small cusps are present in the tooth: cusps e (at the front tip) and i (the rear tip). The holotype of ''Kalaallitkigun'' is the oldest mammaliaform fossil with two roots per tooth, a condition which occurs in all molariforms and the last premolariform in the fossil, according to the shape of tooth sockets. The splitting of the root probably helped to reduce stresses at the crown-root boundary of the tooth.

References

{{Taxonbar, from=Q101245324 Haramiyida Norian life Late Triassic synapsids of North America Triassic Greenland Fossils of Greenland Fossil taxa described in 2020