Plagiaulacidae is a family of fossil

Fossil

Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...

 mammal

Mammal

Mammals are members of a class of air-breathing vertebrate animals characterised by the possession of endothermy, hair, three middle ear bones, and mammary glands functional in mothers with young...

s within the order Multituberculata

Multituberculata

The Multituberculata were a group of rodent-like mammals that existed for approximately one hundred and twenty million years—the longest fossil history of any mammal lineage—but were eventually outcompeted by rodents, becoming extinct during the early Oligocene. At least 200 species are...

. Remains are known from the Upper Jurassic

Jurassic

The Jurassic is a geologic period and system that extends from about Mya to  Mya, that is, from the end of the Triassic to the beginning of the Cretaceous. The Jurassic constitutes the middle period of the Mesozoic era, also known as the age of reptiles. The start of the period is marked by...

 of North America

North America

North America is a continent wholly within the Northern Hemisphere and almost wholly within the Western Hemisphere. It is also considered a northern subcontinent of the Americas...

 through the Lower Cretaceous

Cretaceous

The Cretaceous , derived from the Latin "creta" , usually abbreviated K for its German translation Kreide , is a geologic period and system from circa to million years ago. In the geologic timescale, the Cretaceous follows the Jurassic period and is followed by the Paleogene period of the...

 of Europe

Europe

Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...

. These small plant-eaters lived during the Mesozoic

Mesozoic

The Mesozoic era is an interval of geological time from about 250 million years ago to about 65 million years ago. It is often referred to as the age of reptiles because reptiles, namely dinosaurs, were the dominant terrestrial and marine vertebrates of the time...

 era, also known as the "age of the dinosaur

Dinosaur

Dinosaurs are a diverse group of animals of the clade and superorder Dinosauria. They were the dominant terrestrial vertebrates for over 160 million years, from the late Triassic period until the end of the Cretaceous , when the Cretaceous–Paleogene extinction event led to the extinction of...

s." They were among the more derived representatives of the informal suborder of "Plagiaulacida

Plagiaulacida

Plagiaulacida is a group of extinct multituberculate mammals. Multituberculates were among the most common mammals of the Mesozoic, "the age of the dinosaurs"...

".

The taxon Plagiaulacidae was named by Gill T.N. in 1872. It is also known as Bolodontidae, a name developed by Osborn H.F. in 1887.

Ctenacodon

Ctenacodon

Ctenacodon is a genus of extinct mammal that lived in what is now North America during the Upper Jurassic period. It's a member of the family Allodontidae within the order Multituberculata. Ctenacodon,also known as Allodon , was named by Othniel Charles Marsh in 1879. At least four species are...

' brentbaatar requires renaming. It's not part of the genus Ctenacodon

Ctenacodon

Ctenacodon is a genus of extinct mammal that lived in what is now North America during the Upper Jurassic period. It's a member of the family Allodontidae within the order Multituberculata. Ctenacodon,also known as Allodon , was named by Othniel Charles Marsh in 1879. At least four species are...

, although it was originally so assigned. Until it receives a new name, zoological nomenclature requires the inverted commas.