Dryolestidae is an extinct family of Mesozoic mammals, known from the Middle

Jurassic The Jurassic ( ) is a Geological period, geologic period and System (stratigraphy), stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The J ...

to the Early

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 th ...

of the North Hemisphere. The oldest known member, '' Anthracolestes'', is known from the Middle Jurassic

Itat Formation The Itat Formation ( Russian: итатская свита) is a geologic formation in western Siberia. It was deposited in the Bajocian to Bathonian ages of the Middle Jurassic. Dinosaur remains are among the fossils that have been recovered from ...

of Western Siberia, but most other representatives are known from the Late Jurassic of North America and the Late Jurassic and Early Cretaceous of Europe. Most members are only known from isolated teeth and jaw fragments. Like many other groups of early mammals, they are though to have been insectivores. They are generally classified in

Cladotheria Cladotheria is a clade (sometimes ranked as a legion) of mammals. It contains modern therian mammals (marsupials and placentals) and several extinct groups, such as the dryolestoids, amphitheriids and peramurids. The clade was named in 1975 by M ...

, meaning that they are considered to be more closely related to

marsupial Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia, Wallacea and the Americas. A distinctive characteristic common to most of these species is that the young are carried in a ...

s and

placentals 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 distinguishe ...

than to monotremes. They are placed as part of the broader Dryolestida, which also includes the (possibly paraphyletic)

Paurodontidae Paurodontidae is a family of Late Jurassic to Early Cretaceous mammals in the order Dryolestida. Remains of paurodontids have been found in the United States, Britain, Portugal, and Tanzania. The group likely represents a paraphyletic group of ...

, and also sometimes the South American-Antarctic

Meridiolestida Meridiolestida is an extinct clade of mammals known from the Cretaceous and Cenozoic of South America and possibly Antarctica. They represented the dominant group of mammals in South America during the Late Cretaceous. Meridiolestidans were morp ...

, which are often considered unrelated cladotherians. Dyolestidae is not based on a phylogenetic definition, but instead on the possession of unequal roots for the molars of the lower jaw. Additionally, the clade is distinguished by

hypsodont Hypsodont is a pattern of dentition with high-crowned teeth and enamel extending past the gum line, providing extra material for wear and tear. Some examples of animals with hypsodont dentition are cows and horses; all animals that feed on gritt ...

y in lower molars, and uneven labio-lingual height for the alveolar borders of the

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

Cladogram

References

*Zofia Kielan-Jaworowska, Richard L. Cifelli, and Zhe-Xi Luo, ''Mammals from the Age of Dinosaurs: Origins, Evolution, and Structure'' (New York: Columbia University Press, 2004), 380–382. Dryolestida Oxfordian first appearances Cenomanian extinctions Prehistoric mammal families {{jurassic-mammal-stub