''Cimolestes'' (from

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic p ...

, 'chalk robber') is a genus of early

eutheria Eutheria (; from Greek , 'good, right' and , 'beast'; ) is the clade consisting of all therian mammals that are more closely related to placentals than to marsupials. Eutherians are distinguished from noneutherians by various phenotypic tra ...

ns 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 because quite different animals were assigned to the genus, making ''Cimolestes'' a grade taxon of animals with similar features rather than a genus of closely related ones. Fossils have been found in North America,

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a relatively small portion in the Northern Hemisphere at the northern tip of the continent. It can also be described as the sout ...

Europe Europe is a large peninsula conventionally considered a continent in its own right because of its great physical size and the weight of its history and traditions. Europe is also considered a subcontinent of Eurasia and it is located entirel ...

and

Africa Africa is the world's second-largest and second-most populous continent, after Asia in both cases. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 6% of Earth's total surface area ...

. ''Cimolestes'' first appeared during the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 145 to 66 million years ago (Mya). It is the third and final period of the Mesozoic Era, as well as the longest. At around 79 million years, it is the longest geological period of ...

of North America. According to some paleontologists, ''Cimolestes'' died out at the start of the

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

, while others report the genus from the early Eocene. Most species have been described from teeth and isolated fragments. One complete articulated skeleton provisionally assigned to ''Cimolestes'' has been found. It shows a small, agile, tree-dwelling predator with long toes for grasping branches and a

prehensile tail A prehensile tail is the tail of an animal that has adapted to grasp or hold objects. Fully prehensile tails can be used to hold and manipulate objects, and in particular to aid arboreal creatures in finding and eating food in the trees. If the t ...

at least twice the length of its body. It has the largest number of tail vertebrae known in any mammal.

Classification

The genus was once considered to be marsupials; later it was reclassified with the placental mammals, as ancestors of the Carnivora and the extinct

Creodonta Creodonta ("meat teeth") is a former order of extinct carnivorous placental mammals that lived from the early Paleocene to the late Miocene epochs in North America, Europe, Asia and Africa. Originally thought to be a single group of animals ance ...

. Recent researchers have agreed the species assigned to ''Cimolestes'' are primitive eutherian mammals, members of a Cimolestid clade (an order or

family Family (from la, familia) is a group of people related either by consanguinity (by recognized birth) or affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its members and of society. Idea ...

named after the genus), part of the larger clade Didelphodonta (a superorder or order, not to be confused with the marsupial clade Didelphimorphia). Didelphodonts have been placed within the

Ferae Ferae ( , , "wild beasts") is a mirorder of placental mammalsMalcolm C. McKenna, Susan K. Bell: ''Classification of Mammals: Above the Species Level'' in Columbia University Press, New York (1997), 631 Seiten. that groups together clades Pan-C ...

, as a sister group to Carnivora. However, consensus is emerging that modern placental mammals evolved later than previously thought, that other types of mammals had long, diversified, and successful histories, and that ''Cimolestes'' and many related genera are stem eutherians, more closely related to placentals than to marsupials but outside of placental mammals proper, and not closely related to any living animal. ''Cimolestes'' in particular follows as the direct outgroup to

Taeniodonta Taeniodonta ("banded teeth") is an extinct early group of cimolestid mammals known from the Maastrichtian to the Eocene. Taeniodonts evolved quickly into highly specialized digging animals, and varied greatly in size, from rat-sized to species a ...

, indicating that the latter evolved from forms similar to it.

Reassigned species

In order to make the genus reflect an actual group of most closely related species, three nominal species of ''Cimolestes'', ''C. magnus'', ''C. cerberoides'', and ''C. propalaeoryctes'', have been reassigned to their own genera, '' Altacreodus'', '' Ambilestes'', and '' Scollardius'', respectively. ''Cimolestes incisus'' Marsh and ''Cimolestes stirtoni'' Clemens remain within the genus.

Fossil distribution

Fossils of ''Cimolestes'' have been found in:''Cimolestes''
at Fossilworks.org ;Cretaceous * Canada ** Foremost, Oldman and

St. Mary River Formation The St. Mary River Formation is a geologic Formation (geology), formation of Late Cretaceous (71.9-67 Mega-annum, Ma) Geochronology, age of the Western Canadian Sedimentary Basin, Western Canada Sedimentary Basin in southwestern Alberta and north ...

s, Alberta ** Ravenscrag and

Frenchman Formation The Frenchman Formation is stratigraphic unit of Late Cretaceous (late Maastrichtian) age in the Western Canada Sedimentary Basin. It is present in southern Saskatchewan and the Cypress Hills of southeastern Alberta. The formation was defined b ...

s, Saskatchewan * United States ** Hell Creek and

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

s, Montana **

Kirtland Formation The Kirtland Formation (originally the Kirtland Shale) is a sedimentary geological formation. Description The Kirtland Formation is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain th ...

, New Mexico **

Lance Formation The Lance (Creek) Formation is a division of Late Cretaceous (dating to about 69 - 66 Ma) rocks in the western United States. Named after Lance Creek, Wyoming, the microvertebrate fossils and dinosaurs represent important components of the late ...

, Wyoming ;Paleocene * Hainin Formation, Belgium * Santa Lucía Formation (

Tiupampan The Tiupampan ( es, Tiupampense) age is a period of geologic time (64.5–62.5 Ma) within the Paleocene epoch of the Paleogene used more specifically with South American land mammal ages (SALMA). It is the oldest SALMA age and precedes the Peligr ...

), Bolivia * Ravenscrag and

s, Saskatchewan, Canada * Jbel Guersif Formation, Morocco * United States (

Puercan The Puercan North American Stage on the geologic timescale is the North American faunal stage In chronostratigraphy, a stage is a succession of rock strata laid down in a single age on the geologic timescale, which usually represents millions ...

) ** Bear and

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 stretches over portions of ...

s, Montana **

Ferris Formation The Ferris Formation is a Late Cretaceous (~66 Ma) to Paleocene (66-63 Ma), fluvial-deltaic geological formation in southern Wyoming. It contains a variety of trace and body fossils, preserved in sandy fluvial channel deposits and overbank units. ...

, Wyoming ;Eocene * Fossil Butte Member,

Green River Formation The Green River Formation is an Eocene geologic formation that records the sedimentation in a group of intermountain lakes in three basins along the present-day Green River in Colorado, Wyoming, and Utah. The sediments are deposited in very fine ...

, Wyoming, United States

References

{{Taxonbar, from=Q2273848 Fossils of Canada Prehistoric mammal genera Cretaceous–Paleogene boundary Cretaceous mammals of North America Cretaceous Canada Cretaceous United States Hell Creek fauna Paleocene mammals of Africa Fossils of Morocco Paleocene mammals of Europe Paleogene Belgium Fossils of Belgium Paleocene mammals of North America Paleogene Canada Paleogene United States Eocene mammals of North America Campanian genus first appearances Paleocene mammals of South America Paleogene Bolivia Tiupampan Fossils of Bolivia Fossil taxa described in 1889 Taxa named by Othniel Charles Marsh