''Gypsonictops'' is an

extinct Extinction is the termination of an organism by the death of its Endling, last member. A taxon may become Functional extinction, functionally extinct before the death of its last member if it loses the capacity to Reproduction, reproduce and ...

genus of

leptictida Leptictida (''leptos iktis'' "small/slender weasel") is a possibly paraphyletic extinct order of eutherian mammals. Their classification is contentious: according to cladistic studies, they may be (distantly) related to Euarchontoglires (rodents ...

mammals A mammal () is a vertebrate animal of the 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 middle e ...

of the family Gypsonictopidae, which was described in 1927 by

George Gaylord Simpson George Gaylord Simpson (June 16, 1902 – October 6, 1984) was an American paleontologist. Simpson was perhaps the most influential paleontologist of the twentieth century, and a major participant in the modern synthesis, contributing '' Tempo ...

. Species in this genus were small mammals and the first representatives of the order

Leptictida Leptictida (''leptos iktis'' "small/slender weasel") is a possibly paraphyletic extinct order of eutherian mammals. Their classification is contentious: according to cladistic studies, they may be (distantly) related to Euarchontoglires (rodents ...

, that appeared during the

Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''cret ...

. The genus is thought to have gone extinct before the

Cenozoic The Cenozoic Era ( ; ) is Earth's current geological era, representing the last 66million years of Earth's history. It is characterized by the dominance of mammals, insects, birds and angiosperms (flowering plants). It is the latest of three g ...

began, but there are indications that it may have survived into the early

Paleocene The Paleocene ( ), or Palaeocene, is a geological epoch (geology), epoch that lasted from about 66 to 56 mya (unit), million years ago (mya). It is the first epoch of the Paleogene Period (geology), Period in the modern Cenozoic Era (geology), ...

. Fossils have been found in the United States, Belgium, and Uzbekistan. Like ''

Cimolestes ''Cimolestes'' (from Ancient Greek , 'chalk robber') is a genus of early eutherians with a full complement of teeth adapted for eating insects and other small animals. Paleontologists have disagreed on its relationship to other mammals, in part b ...

'' or '' Daulestes'', it is possible that they had some distant relationship with the

ungulates Ungulates ( ) are members of the diverse clade Euungulata ("true ungulates"), which primarily consists of large mammals with hooves. Once part of the clade "Ungulata" along with the clade Paenungulata, "Ungulata" has since been determined to b ...

. It is one of the few

eutherians Eutheria (from Greek , 'good, right' and , 'beast'; ), also called Pan-Placentalia, is the clade consisting of placental mammals and all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distingu ...

that existed in

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

during the

Campanian The Campanian is the fifth of six ages of the Late Cretaceous epoch on the geologic timescale of the International Commission on Stratigraphy (ICS). In chronostratigraphy, it is the fifth of six stages in the Upper Cretaceous Series. Campa ...

, a period in which the

multituberculates Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, a ...

and the

metatherians Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as well ...

were the dominant ones on the continent.

Description

Like other

prehistoric Prehistory, also called pre-literary history, is the period of human history between the first known use of stone tools by hominins million years ago and the beginning of recorded history with the invention of writing systems. The use o ...

of the

, ''Gypsonictops'' had a particular

dentition Dentition pertains to the development of teeth and their arrangement in the mouth. In particular, it is the characteristic arrangement, kind, and number of teeth in a given species at a given age. That is, the number, type, and morpho-physiology ...

, with five

premolars 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 mout ...

double-rooted in the

lower jaw 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 ...

, while the vast majority of mammals only had four. On the other hand, the five premolars also were a very typical feature of the most primitive

. In the same way as the species of the genus ''

Leptictidium ''Leptictidium'' is an extinct genus of small mammals that were likely bipedal. Comprising eight species, they resembled today's bilbies, bandicoots, and elephant shrews, and occupied a similar niche. They are especially interesting for their c ...

'', the P4 premolar was highly molarized, which caused confusion when analyzing a specimen of ''G. petersoni'' between P4 and molar M1. Eventually, P4 was found to be a paraconid-free premolar.

Taxonomy

The genus ''Gypsonictops'' was first classified within the family Leptictidae, by Simpson, along with all

of North America. This classification was maintained until 1967, when

Leigh Van Valen Leigh Van Valen (August 12, 1935 – October 16, 2010) was an American evolutionary biologist. At the time of his death, he was professor emeritus in the Department of Ecology and Evolution at the University of Chicago. Research and interests A ...

created the family Gypsonictopidae for the genus. In 1997, Malcolm C. McKenna and Susan K. Bell suggested the possibility that this family contained up to seven different genera, but documents published since then have shown a high degree of skepticism about the proposal. An additional genus within the family, ''

Sikuomys ''Sikuomys'' is a genus of early eutherian mammals from the Late Cretaceous of Alaska. It is known from a few teeth and part of a jawbone in deposits of Campanian age and, , is the only known Mesozoic The Mesozoic Era is the Era (geology), er ...

'', was named in 2023. It is known that ''Gypsonictops'' were

and that they could be

placental Placental mammals (infraclass Placentalia ) are one of the three extant subdivisions of the class Mammalia, the other two being Monotremata and Marsupialia. Placentalia contains the vast majority of extant mammals, which are partly distinguished ...

s, as they show very typical characteristics of these animals, although they belong to the

group, which includes some of the few non-placental eutherians. Furthermore, the line between placental and non-placental eutherians is very thin, so the classification of ''Gypsonictops'' with precision is a very complicated task.

Species

The genus ''Gypsonictops'' contains six species:

''Gypsonictops clemensi''

Described by J. K. Rigby and D. L. Wolberg in 1987. It inhabited the planet during the

and

Maastrichtian The Maastrichtian ( ) is, in the International Commission on Stratigraphy (ICS) geologic timescale, the latest age (geology), age (uppermost stage (stratigraphy), stage) of the Late Cretaceous epoch (geology), Epoch or Upper Cretaceous series (s ...

periods. Its description was made from a molar M3 found in

New Mexico New Mexico is a state in the Southwestern United States, Southwestern region of the United States. It is one of the Mountain States of the southern Rocky Mountains, sharing the Four Corners region with Utah, Colorado, and Arizona. It also ...

. The name of the species is dedicated to the American

paleontologist Paleontology, also spelled as palaeontology or palæontology, is the scientific study of the life of the past, mainly but not exclusively through the study of fossils. Paleontologists use fossils as a means to classify organisms, measure geolo ...

William A. Clemens.

''Gypsonictops dormaalensis''

Described by G. E. Quinet in 1964. The name of the species refers to the Belgian population of Dormaal, a city in which there is an important fossil deposit in which fossils of ''G. dormaalensis''.

''Gypsonictops hypoconus''

Described by G. G. Simpson in 1927. It lived during the

and

periods, and fossils have been found in the

Hell Creek Formation The Hell Creek Formation is an intensively studied division of mostly Upper Cretaceous and some lower Paleocene rocks in North America, named for exposures studied along Hell Creek, near Jordan, Montana. The Formation (stratigraphy), formation s ...

and other sites in the

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

. When Simpson created the genus ''Gypsonictops'' to define this species, placed it within the family Leptictidae, which was then part of the Insectivara order, now obsolete. The name of the species refers to its hypocone, the lower cusp of the molar teeth.

''Gypsonictops illuminatus''

Described by J. A. Lillegraven in 1969. It lived during the

, and fossils have been found in the

, in the

, as well as in various paleontological sites in

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

''Gypsonictops lewisi''

Described by A. Sahni in 1972. It lived during the

. Fossils of the species have been found in the

Judith River Formation The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Montana Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago, corresponding to the "Judithian" land vertebrate age. It was ...

Montana Montana ( ) is a landlocked U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Idaho to the west, North Dakota to the east, South Dakota to the southeast, Wyoming to the south, an ...

. ''G. lewisi'' is one of the species with more typical characteristics of the

s of the genus, such as the fusion of a small metaconid with a long protoconid, or a small talonid with two cusps. On the other hand, the

premolar The premolars, also called premolar Tooth (human), teeth, or bicuspids, are transitional teeth located between the Canine tooth, canine and Molar (tooth), molar teeth. In humans, there are two premolars per dental terminology#Quadrant, quadrant in ...

es are not as molarized as in other species of the genus. They usually used to weigh over fifty

gram The gram (originally gramme; SI unit symbol g) is a Physical unit, unit of mass in the International System of Units (SI) equal to one thousandth of a kilogram. Originally defined in 1795 as "the absolute Mass versus weight, weight of a volume ...

s. The species name is dedicated to the

Captain Captain is a title, an appellative for the commanding officer of a military unit; the supreme leader or highest rank officer of a navy ship, merchant ship, aeroplane, spacecraft, or other vessel; or the commander of a port, fire or police depa ...

Meriwether Lewis Meriwether Lewis (August 18, 1774 – October 11, 1809) was an American explorer, soldier, politician, and public administrator, best known for his role as the leader of the Lewis and Clark Expedition, also known as the Corps of Discovery, with ...

, a celebrated

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, p ...

explorer.

''Gypsonictops petersoni''

Described in 1929 by G. G. Simpson, who named the species "Euangelistes petersoni" and wrongly classified it within the

infraclass In biology, taxonomic rank (which some authors prefer to call nomenclatural rank because ranking is part of nomenclature rather than taxonomy proper, according to some definitions of these terms) is the relative or absolute level of a group of or ...

Marsupialia Marsupials are a diverse group of mammals belonging to the infraclass Marsupialia. They are natively found in Australasia, Wallacea, and the Americas. One of marsupials' unique features is their reproductive strategy: the young are born in a ...

. It is known with certainty that they inhabited the planet during the

, but it is possible that they could have survived the Cretaceous-Paleogene mass extinction and lived until the

Danian The Danian is the oldest age or lowest stage of the Paleocene Epoch or Series, of the Paleogene Period or System, and of the Cenozoic Era or Erathem. The beginning of the Danian (and the end of the preceding Maastrichtian) is at the Cretac ...

. 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 ...

of this species is in the

Carnegie Museum of Natural History The Carnegie Museum of Natural History (abbreviated as CMNH) is a natural history museum in the Oakland (Pittsburgh), Oakland neighborhood of Pittsburgh, Pennsylvania. It was founded by List of people from the Pittsburgh metropolitan area, Pit ...

and it is a

that had been badly damaged. Another specimen, preserved at

Yale University Yale University is a Private university, private Ivy League research university in New Haven, Connecticut, United States. Founded in 1701, Yale is the List of Colonial Colleges, third-oldest institution of higher education in the United Stat ...

, has been described by up to five different names. In case there was not enough controversy on the subject, in 1973,

Clemens Clemens is a Late Latin, German, and Dutch masculine given name and a surname, meaning "merciful". Notable people with the name include: Surname * Adelaide Clemens (born 1989), Australian actress * Andrew Clemens (1857–1894), American folk ...

stated that ''G. petersoni'' was the same species as ''G. hypoconus''.

Bibliography

* * * * *

References

External links

"American Cretaceous Insectivares", by George Gaylord Simpson
{{Authority control Leptictida Prehistoric mammal genera Late Cretaceous mammals of Asia Late Cretaceous mammals of North America Cretaceous mammals of Europe Fossil taxa described in 1927