''Dyskritodon'' ("tooth of unknown origin", from

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 ...

δυσκρίτος, "''dyskritos''"Sigogneau-Russell, D. (1995) Two possibly aquatic triconodont mammals from the Early Cretaceous of Morocco. Acta Palaeontologica Polonica. 40(2), p.149-162.) is a genus of extinct

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fu ...

from the

Early Cretaceous The Early Cretaceous ( geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pr ...

Morocco Morocco (),, ) officially the Kingdom of Morocco, is the westernmost country in the Maghreb region of North Africa. It overlooks the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to ...

, and possibly the

Early Jurassic The Early Jurassic Epoch (in chronostratigraphy corresponding to the Lower Jurassic Series) is the earliest of three epochs of the Jurassic Period. The Early Jurassic starts immediately after the Triassic-Jurassic extinction event, 201.3 Ma&nb ...

India India, officially the Republic of India ( Hindi: ), is a country in South Asia. It is the seventh-largest country by area, the second-most populous country, and the most populous democracy in the world. Bounded by the Indian Ocean on the ...

. Of uncertain affinities, it is tentatively described as a

eutriconodont Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for the ...

Description

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( ...

, ''D. amazighi'', is known from the Ksar Metlili Formation in the

Atlas Mountains The Atlas Mountains are a mountain range in the Maghreb in North Africa. It separates the Sahara Desert from the Mediterranean Sea and the Atlantic Ocean; the name "Atlantic" is derived from the mountain range. It stretches around through ...

, dating to the

Berriasian In the geological timescale, the Berriasian is an age/ stage of the Early/Lower Cretaceous. It is the oldest subdivision in the entire Cretaceous. It has been taken to span the time between 145.0 ± 4.0 Ma and 139.8 ± 3.0 Ma (million years ag ...

. It is known from several

molars 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 t ...

, about 1.85 mm long. These teeth are noted for being rather high and narrow crowned, bearing three main cusps that decrease in height posteriorly, as well as two minuscule mesial cusps. ''D. indicus'' is known from a single lower molar tooth from the Kota Formation, dating to the Hettangian- Pliensbachian. It is very similar to ''D. amazighi'', differing in being smaller (1.24 mm), having a shorter posterior root and some differences in the cusps.Prasad & Manhas (2002) Triconodont mammals from the Jurassic Kota Formation of India. Geodiversitas 24 (2), p.445-464 However, compared to ''D. amazighi'' molars, it is "drastically less complete".

Classification

Sigogneau-Russell referred the genus to

Eutriconodonta Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for th ...

on the basis of its basic

triconodont Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for t ...

shape. However, she considered it aberrant enough to warrant a separate family within the clade. Further studies have similarly found it rather distinct from other eutriconodonts, and it is listed as an ''

incertae sedis ' () or ''problematica'' is a term used for a taxonomic group where its broader relationships are unknown or undefined. Alternatively, such groups are frequently referred to as "enigmatic taxa". In the system of open nomenclature, uncertaint ...

'' taxon. It is nonetheless more "advanced" than morganucodontids and other basal

Mammaliformes Mammaliaformes ("mammalian forms") is a clade that contains the crown group mammals and their closest extinct relatives; the group radiated from earlier probainognathian cynodonts. It is defined as the clade originating from the most recent ...

. Due to the large temporal distance between both species, different environments and general incompleteness of the Indian material, there is also doubt as to whereas ''D. indicus'' is closely related to ''D. amazighi''. For now, its relationship to it is, too, provisory.

Biology

As it was found in relative abundance in marine deposits, ''D. amazighi'', like the contemporary ''

Ichthyoconodon ''Ichthyoconodon'' is an extinct genus of eutriconodont mammal from the Lower Cretaceous of Morocco. It is notable for having been found in a unique marine location, and the shape of its teeth suggests an unusual, potentially fish-eating ecologic ...

'', has been suggested to be an aquatic

piscivore A piscivore () is a carnivorous animal that eats primarily fish. The name ''piscivore'' is derived . Piscivore is equivalent to the Greek-derived word ichthyophage, both of which mean "fish eater". Fish were the diet of early tetrapod evoluti ...

. Similarities between its molars and those of mammals such as seals and

cetaceans Cetacea (; , ) is an infraorder of aquatic mammals that includes whales, dolphins, and porpoises. Key characteristics are their fully aquatic lifestyle, streamlined body shape, often large size and exclusively carnivorous diet. They propel th ...

have corroborated this hypothesis. Posterior analysis have shown a lack of precise equivalency between eutriconodont molars and those of

theria Theria (; Greek: , wild beast) is a subclass of mammals amongst the Theriiformes. Theria includes the eutherians (including the placental mammals) and the metatherians (including the marsupials) but excludes the egg-laying monotremes. ...

n mammals, rending this assessment as a fish-eater cautious, but the high state of preservation of the animal's teeth indicates that it died in situ or nearby, in open waters. ''D. indicus'', by contrast, appears in a terrestrial environment.

Notes

References

{{Taxonbar, from=Q8771060 Eutriconodonts Cretaceous mammals of Africa Cretaceous Morocco Fossils of Morocco Jurassic mammals of Asia Jurassic India Fossils of India Fossil taxa described in 1995 Taxa named by Denise Sigogneau‐Russell Prehistoric mammal genera