''Cimolestes'' (from

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

, 'chalk robber') is a genus of early

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

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 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 ...

South America South America is a continent entirely in the Western Hemisphere and mostly in the Southern Hemisphere, with a considerably smaller portion in the Northern Hemisphere. It can also be described as the southern Subregion#Americas, subregion o ...

Europe Europe is a continent located entirely in the Northern Hemisphere and mostly in the Eastern Hemisphere. It is bordered by the Arctic Ocean to the north, the Atlantic Ocean to the west, the Mediterranean Sea to the south, and Asia to the east ...

and

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

. ''Cimolestes'' first appeared during the Late

Cretaceous The Cretaceous ( ) is a geological period that lasted from about 143.1 to 66 mya (unit), million years ago (Mya). It is the third and final period of the Mesozoic Era (geology), Era, as well as the longest. At around 77.1 million years, it is the ...

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

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), ...

, 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 Adaptation (biology), adapted to grasp or hold objects. Fully Prehensility, prehensile tails can be used to hold and manipulate objects, and in particular to aid arboreal creatures in finding and ...

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 that of a

marsupial 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 r ...

; later, it was reclassified with the placental mammals, as ancestors of the

Carnivora Carnivora ( ) is an order of placental mammals specialized primarily in eating flesh, whose members are formally referred to as carnivorans. The order Carnivora is the sixth largest order of mammals, comprising at least 279 species. Carnivor ...

and the extinct Creodonta. Recent researchers have agreed the species assigned to ''Cimolestes'' are primitive eutherian mammals, members of a cimolestid clade (an

order Order, ORDER or Orders may refer to: * A socio-political or established or existing order, e.g. World order, Ancien Regime, Pax Britannica * Categorization, the process in which ideas and objects are recognized, differentiated, and understood ...

family Family (from ) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). It forms the basis for social order. Ideally, families offer predictabili ...

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, 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 order of eutherian mammals, that lived in North America and Europe from the late Cretaceous (Maastrichtian) to the middle Eocene. Taeniodonts evolved quickly into highly specialized digging animals ...

, 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 Fossilworks was a portal which provides query, download, and analysis tools to facilitate access to the Paleobiology Database, a large relational database assembled by hundreds of paleontologists from around the world. History Fossilworks was cr ...

.org ;Cretaceous * Canada ** Foremost, Oldman and St. Mary River Formations, Alberta ** Ravenscrag and Frenchman Formations, Saskatchewan * United States ** Hell Creek and Judith River Formations, Montana **

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

, 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 lates ...

, Wyoming ;Paleocene * Hainin Formation, Belgium * Santa Lucía Formation ( Tiupampan), Bolivia * Ravenscrag and Frenchman Formations, Saskatchewan, Canada * Jbel Guersif Formation, Morocco * United States ( Puercan) **

Bear Bears are carnivoran mammals of the family (biology), family Ursidae (). They are classified as caniforms, or doglike carnivorans. Although only eight species of bears are extant, they are widespread, appearing in a wide variety of habitats ...

and Hell Creek Formations, 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 (Colorado River), Green River in Colorado, Wyoming, and Utah. The sedimen ...

, 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