Information:  - Theria ( / ri / ; Greek :  , wild beast ) is a subclass of mammals that give birth to live young without using a shelled egg , consisting of the eutherians ( including the placental mammals ) and the metatherians ( including the marsupials ) . The only omitted extant mammal group is the egg - laying monotremes . The earliest known therian mammal fossil is Juramaia , from the Middle Jurassic of China . However , molecular data suggests that therians may have originated even earlier , during the Early Jurassic .  - Reptiles are tetrapod (four-limbed vertebrate) animals in the class Reptilia, comprising today's turtles, crocodilians, snakes, amphisbaenians, lizards, tuatara, and their extinct relatives. The study of these traditional reptile orders, historically combined with that of modern amphibians, is called herpetology.  - An endotherm (from Greek  "endon" "within" and  "therm" "heat") is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat set free by its internal bodily functions instead of relying almost purely on ambient heat. Such internally generated heat is mainly an incidental product of the animal's routine metabolism, but under conditions of excessive cold or low activity an endotherm might apply special mechanisms adapted specifically to heat production. Examples include special-function muscular exertion such as shivering, and uncoupled oxidative metabolism such as within brown adipose tissue. Only birds and mammals are extant universally endothermic groups of animals. Certain lamnid sharks, tuna and billfishes are also endothermic.  - A mammary gland is an exocrine gland in mammals that produces milk to feed young offspring. Mammals get their name from the word "mammary". The mammary glands are arranged in organs such as the breasts in primates (for example, humans and chimpanzees), the udder in ruminants (for example, cows, goats, and deer), and the dugs of other animals (for example, dogs and cats). Lactorrhea, the occasional production of milk by the glands, can occur in any mammal, but in most mammals lactation, the production of enough milk for nursing, occurs only in phenotypic females who have gestated in recent months or years. It is directed by hormonal guidance from sex steroids. In a few mammalian species, male lactation can occur.  - Theriiformes is a subclass of mammals. The term was coined in 1997 by McKenna & Bell in their classification of mammals.  - A clade (from , "klados", "branch") is a group of organisms that consists of a common ancestor and all its lineal descendants, and represents a single "branch" on the "tree of life".  - Vertebrates comprise all species of animals within the subphylum Vertebrata (chordates with backbones). Vertebrates represent the overwhelming majority of the phylum Chordata, with currently about 64,000 species described. Vertebrates include the jawless fish and the jawed vertebrates, which include the cartilaginous fish (sharks and rays) and the bony fish.   - Synapsids (Greek, 'fused arch'), synonymous with theropsids (Greek, 'beast-face'), are a group of animals that includes mammals and every animal more closely related to mammals than to other living amniotes. They are easily separated from other amniotes by having a temporal fenestra, an opening low in the skull roof behind each eye, leaving a bony arch beneath each; this accounts for their name. Primitive synapsids are usually called pelycosaurs or pelycosaur-grade synapsids; more advanced mammal-like ones, therapsids. The non-mammalian members are described as mammal-like reptiles in classical systematics; they can also be called stem mammals or proto-mammals. Synapsids evolved from basal amniotes and are one of the two major groups of the later amniotes; the other is the sauropsids, a group that includes modern reptiles and birds. The distinctive temporal fenestra developed in the ancestral synapsid about 312 million years ago, during the Late Carboniferous period.  - Sparassodonta is an extinct order of carnivorous metatherian mammals native to South America. They were once considered to be true marsupials, but are now thought to be either a sister taxon to them, or considerably distantly related, part of a separate clade of Gondwanan metatherians. A number of these mammalian predators closely resemble placental predators that evolved separately on other continents, and are cited frequently as examples of convergent evolution. They were first described by Florentino Ameghino, from fossils found in the Santa Cruz beds of Patagonia. Sparassodonts were present throughout South America's long period of "splendid isolation" during the Cenozoic; during this time they shared the niches for large warm-blooded predators with the flightless terror birds. Previously, it was thought that these mammals died out in the face of competition from "more competitive" placental carnivorans during the Pliocene Great American Interchange, but more recent research has showed that sparassodonts died out long before eutherian carnivores arrived in South America (aside from procyonids).  - 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 middle ear is the portion of the ear internal to the eardrum, and external to the oval window of the inner ear. Also the mammalian middle ear contains three ossicles, which transfer the vibrations of the eardrum into waves in the fluid and membranes of the inner ear. The hollow space of the middle ear is also known as the tympanic cavity. The auditory tube (also known as the Eustachian tube or the pharyngotympanic tube) joins the tympanic cavity with the nasal cavity (nasopharynx), allowing pressure to equalize between the middle ear and throat.  - Birds (Aves), also known as avian dinosaurs, are a group of endothermic vertebrates, characterised by feathers, toothless beaked jaws, the laying of hard-shelled eggs, a high metabolic rate, a four-chambered heart, and a lightweight but strong skeleton. Birds live worldwide and range in size from the bee hummingbird to the ostrich. They rank as the class of tetrapods with the most living species, at approximately ten thousand, with more than half of these being passerines, sometimes known as perching birds or, less accurately, as songbirds.  - Rats are various medium-sized, long-tailed rodents of the superfamily Muroidea. "True rats" are members of the genus "Rattus", the most important of which to humans are the black rat, "Rattus rattus", and the brown rat, "Rattus norvegicus". Many members of other rodent genera and families are also referred to as rats, and share many characteristics with true rats.  - 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.   - Hair is a protein filament that grows from follicles found in the dermis, or skin. Hair is one of the defining characteristics of mammals. The human body, apart from areas of glabrous skin, is covered in follicles which produce thick terminal and fine vellus hair. Most common interest in hair is focused on hair growth, hair types and hair care, but hair is also an important biomaterial primarily composed of protein, notably keratin.  - Sauropsida ("lizard faces") is a group of amniotes that includes all existing birds and reptiles as well as their fossil ancestors and other extinct relatives. Large land animals are either in this group or in its sister group, Synapsida, which includes mammals and their fossil relatives. This clade includes Parareptilia and other extinct clades. All living sauropsids are members of the sub-group Diapsida, the Parareptilia clade having died out 200 million years ago. The term originated in 1864 with Thomas Henry Huxley, who grouped birds with reptiles based on fossil evidence.  - Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals (such as sparassodontans). First proposed by Thomas Henry Huxley in 1880, it is a slightly more inclusive group than the marsupials; it contains all of the living mammals with abdominal pouches (most female marsupials) as well as their more primitive ancestors and relatives. Metatherians are one of three main classes of extant mammals: monotremes (egg laying mammals like the platypus and the echidna), metatheria (or marsupials, which includes the three American orders (Didelphimorphia, Paucituberculata and Microbiotheria) and the four Australasian orders (Notoryctemorphia, Dasyuromorphia, Peramelemorphia and Diprotodontia)), and the eutherians (or placental mammals) consisting of twenty-one orders, divided into four superorders. Metatherians belong to a subgroup of the northern tribosphenic mammal clade or Boreosphenida. They differ from all other mammals in certain morphologies like their dental formula, which includes about five upper and four lower incisors, a canine, three premolars, and four molars. Other morphologies include skeletal and anterior dentition, such as wrist and ankle apomorphies; all metatherians share derived pedal characters and calcaneal features.    After reading the paragraphs above, we are interested in knowing the entity with which 'theria' exhibits the relationship of 'instance of'. Find the answer from the choices below.  Choices: - animal  - arch  - bell  - brain  - branch  - clade  - class  - cognition  - evidence  - extinct  - fish  - fossil  - four  - genus  - gland  - grade  - group  - human  - human body  - lizard  - may  - nursing  - opening  - organism  - part  - perception  - production  - protein  - range  - rank  - roof  - set  - sex  - share  - single  - size  - skeleton  - skin  - skull  - species  - study  - taxon  - temperature  - ten  - term  - three  - tissue  - window
A:
taxon