Please answer the following question: Information:  - The Permian is a geologic period and system which spans 46.7 million years from the end of the Carboniferous Period million years ago (Mya), to the beginning of the Triassic Period 252.2 Mya. It is the last period of the Paleozoic Era; the following Triassic Period belongs to the Mesozoic Era. The concept of the Permian was introduced in 1841 by geologist Sir Roderick Murchison, who named it after the city of Perm.  - Therapsida is a group of synapsids that includes mammals and their ancestors . Many of the traits today seen as unique to mammals had their origin within early therapsids , including having their four limbs extend vertically beneath the body , as opposed to the sprawling posture of other reptiles . The earliest fossil attributed to Therapsida is Tetraceratops insignis from the Lower Permian . Therapsids evolved from pelycosaurs ( specifically sphenacodonts ) 275 million years ago . They replaced the pelycosaurs as the dominant large land animals in the Middle Permian and were replaced , in turn , by the archosauromorphs in the Triassic , although one group of therapsids , the kannemeyeriiforms , remained diverse in the Late Triassic . The therapsids included the cynodonts , the group that gave rise to mammals in the Late Triassic around 225 million years ago . Of the non-mammalian therapsids , only cynodonts and dicynodonts survived the Triassic -- Jurassic extinction event . The last of the non-mammalian therapsids , the tritylodontid cynodonts , became extinct in the Early Cretaceous , approximately 100 million years ago .  - The Triassic is a geologic period and system which spans 50.9 million years from the end of the Permian Period million years ago (Mya), to the beginning of the Jurassic Period Mya. The Triassic is the first period of the Mesozoic Era. Both the start and end of the period are marked by major extinction events. The Triassic was named in 1834 by Friedrich von Alberti, after the three distinct rock layers ("tri" meaning "three") that are found throughout Germany and northwestern Europered beds, capped by marine limestone, followed by a series of terrestrial mud- and sandstonescalled the "Trias".  - Mammals are any vertebrates within the class Mammalia (from Latin "mamma" "breast"), a clade of endothermic amniotes distinguished from reptiles and birds by the possession of a neocortex (a region of the brain), hair, three middle ear bones and mammary glands. The sister group of mammals may be the extinct "Haldanodon." The mammals represent the only living Synapsida, which together with the Sauropsida form the Amniota clade. The mammals consist of the Yinotheria including monotrema and the Theriiformes including the theria.  - The neocortex, also called the neopallium and isocortex, is the part of the mammalian brain involved in higher-order brain functions such as sensory perception, cognition, generation of motor commands, spatial reasoning and language.     'therapsid' is related to which object entity through the relation of 'taxon rank'?  Choices: - order  - series
A:
order