Maotherium was discovered in Early 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...

 rocks in Liaoning

Liaoning

' is a province of the People's Republic of China, located in the northeast of the country. Its one-character abbreviation is "辽" , a name taken from the Liao River that flows through the province. "Níng" means "peace"...

 Province, China

China

Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...

, in 2003. Its scientific name means "Mao's beast" after the Chinese politician Mao Zedong

Mao Zedong

Mao Zedong, also transliterated as Mao Tse-tung , and commonly referred to as Chairman Mao , was a Chinese Communist revolutionary, guerrilla warfare strategist, Marxist political philosopher, and leader of the Chinese Revolution...

. Maotherium belongs to an extinct group of 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...

 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 called symmetrodonts. Though little is known about this group, the symmetrodonts have several similarities - specifically their teeth. They have tall pointed, but simple molars in a triangular arrangement. Originally symmetrodonts were known since the 1920s. Now a vast majority have been restored, such as Zhangheotherium

Zhangheotherium

Zhangheotherium is a genus of symmetrodont, an extinct order of mammals. Previously known from only the tall pointed crowned teeth, Zhangheotherium, described from Liaoning Province, China, fossils in 1997, is the first symmetrodont known from a complete skeleton. It was dated to between 145-125...

and Akidolestes

Akidolestes

Akidolestes cifellii is an extinct mammal which dates to the early Cretaceous period, 124.6 million years ago. It is part of the Yixian formation in Liaoning, China. The description is based on a nearly complete skeleton, partially complete skull, and an impression...

, during the early 21st century. One of the fossils of Maotherium preserved the imprints of fur, like the mammals Eomaia

Eomaia

Eomaia is an extinct fossil mammal, discovered in rocks that were found in the Yixian Formation, Liaoning Province, China, and dated to the Barremian Age of the Lower Cretaceous about . The fossil is in length and virtually complete. An estimate of the body weight is between . It is exceptionally...

and Sinodelphys

Sinodelphys

Sinodelphys is an extinct mammal from the Early Cretaceous. To date, it is the oldest metatherian fossil known, estimated to be 125 million years old...

.

A species described in 2009, Maotherium asiaticus, sheds light on the evolution of the mammalian middle ear

Evolution of mammalian auditory ossicles

The evolution of mammalian auditory ossicles is one of the most well-documented and important evolutionary events, demonstrating both numerous transitional forms as well as an excellent example of exaptation, the re-purposing of existing structures during evolution.In reptiles, the eardrum is...

. In modern mammals, the Meckel's cartilage

Meckel's cartilage

The cartilaginous bar of the mandibular arch is formed by what are known as Meckel’s cartilages also known as Meckelian cartilages; above this the incus and malleus are developed....

 appears during development

Developmental biology

Developmental biology is the study of the process by which organisms grow and develop. Modern developmental biology studies the genetic control of cell growth, differentiation and "morphogenesis", which is the process that gives rise to tissues, organs and anatomy.- Related fields of study...

 but disappears before adulthood. In Maotherium asiaticus, that cartilage not only remained, but turned into bone.
This event in evolution may be an example of heterochrony

Heterochrony

In biology, heterochrony is defined as a developmental change in the timing of events, leading to changes in size and shape. There are two main components, namely the onset and offset of a particular process, and the rate at which the process operates...

, a change in the timing of development.