Varanopidae

Varanopidae is an extinct family of amniotes known from the Late Carboniferous to Middle Permian that resembled monitor lizards (with the name of the group deriving from the monitor lizard genus Varanus) and may have filled a similar niche. Typically, they are considered to be relatively basal synapsids (and thus more closely related to mammals than to reptiles), although some studies from the late 2010s recovered them being taxonomically closer to diapsid reptiles; recent studies from the early 2020s support their traditional placement as synapsids on the basis of high degree of bone labyrinth ossification, maxillary canal morphology, and phylogenetic analyses. A varanopid from the late Middle Permian Pristerognathus Assemblage Zone (Capitanian) is the youngest known varanopid and the last member of the "pelycosaur" group of synapsids. Thus, Varanopidae vanishes from the fossil record at the same time as dinocephalians, plausibly as a result of a major mass extinction event that has been called the "Dinocephalian extinction event".

==Description== left|thumb|Fossil of Aerosaurus wellesi No known varanopids developed a sail like Dimetrodon. The length of known varanopids, including the tail, varies from . Varanopids already showed some advanced characteristics of true pelycosaurs such as their deep, narrow, elongated skulls. Their jaws were long and their teeth were sharp. However, they were still primitive by mammalian standards. They had long tails, lizard-like bodies, and thin legs. The varanopids were mostly carnivorous, but as they were reduced in size, their diets changed from a carnivorous to an insectivorous lifestyle. Compared to the other animals in the Early Permian, varanopids were agile creatures.thumb|Varanodon agilis|left thumb|Skulls of Mesenosaurus (top) and [[Varanodon (bottom), showing variation in skull shape.]]