Semimammalian

Semimammalian is a term used in paleontology to describe a group of extinct synapsids that are considered to be transitional between mammals and their reptilian ancestors. These animals lived during the Permian and Triassic periods, approximately 299 to 201 million years ago. Semimammalians are characterized by several features that are intermediate between those of reptiles and mammals, such as the presence of a single temporal fenestra (a hole in the skull), a single middle ear bone, and a more advanced dentition compared to reptiles.

The most well-known semimammalian is Dimetrodon, a large, carnivorous animal that lived during the Permian period. Other notable examples include Secodontosaurus and Anomodontia, which are known for their unique teeth and dentition. Semimammalians are significant in the study of evolutionary biology because they provide insights into the transition from reptilian ancestors to the first true mammals.

The term "semimammalian" was coined by the German paleontologist Friedrich von Huene in 1932. It is important to note that the classification of semimammalians is still a subject of ongoing debate among paleontologists, and their exact relationships to both reptiles and mammals are not fully understood. Despite this, semimammalians remain a fascinating and important group of extinct animals that help bridge the gap between reptiles and mammals in the evolutionary tree of life.