Information: - Chalk is a soft, white, porous, sedimentary carbonate rock, a form of limestone composed of the mineral calcite. Calcite is an ionic salt called calcium carbonate or CaCO. It forms under reasonably deep marine conditions from the gradual accumulation of minute calcite shells (coccoliths) shed from micro-organisms called coccolithophores. Flint (a type of chert unique to chalk) is very common as bands parallel to the bedding or as nodules embedded in chalk. It is probably derived from sponge spicules or other siliceous organisms as water is expelled upwards during compaction. Flint is often deposited around larger fossils such as Echinoidea which may be silicified (i.e. replaced molecule by molecule by flint). - Ameridelphia is traditionally a superorder that includes all marsupials living in the Americas except for the Monito del monte ("Dromiciops"). It is now regarded as a paraphyletic group. - Marsupials are any members of the mammalian infraclass Marsupialia. All extant marsupials are endemic to Australasia and the Americas. A distinctive characteristic common to these species is that most of the young are carried in a pouch. Well-known marsupials include kangaroos, wallabies, koalas, possums, opossums, wombats, Tasmanian devils, and the recently extinct thylacines. Others include the numbat, the bandicoot, the bettong, the bilby, the quoll, and the quokka. - Asiadelphia ( '' Asian opossum '' ) is an order of Cretaceous Metatherians . Different from the Ameridelphia , they lacked a prominent distolateral process on the scaphoid , and possessed a more slender fibula . The masseteric fossa is deeper in this group than the true Marsupials . - The Jurassic (from Jura Mountains) is a geologic period and system that spans 56.3 million years from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period Mya. The Jurassic constitutes the middle period of the Mesozoic Era, also known as the Age of Reptiles. The start of the period is marked by the major TriassicJurassic extinction event. Two other extinction events occurred during the period: the Pliensbachian/Toarcian event in the Early Jurassic, and the Tithonian event at the end; however, neither event ranks among the "Big Five" mass extinctions. - The Cretaceous is a geologic period and system that spans 79 million years from the end of the Jurassic Period million years ago (Mya) to the beginning of the Paleogene Period Mya. It is the last period of the Mesozoic Era. The Cretaceous Period is usually abbreviated K, for its German translation "Kreide" (chalk). - 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). - The monito del monte (Spanish for "little bush monkey") or colocolo opossum, "Dromiciops gliroides", also called "chumaihuen" in Mapudungun, is a diminutive marsupial native only to southwestern South America (Argentina and Chile). It is the only extant species in the ancient order Microbiotheria, and the sole New World representative of the superorder Australidelphia (all other New World marsupials are members of Ameridelphia). The species is nocturnal and arboreal, and lives in thickets of South American mountain bamboo in the Valdivian temperate rain forests of the southern Andes, aided by its partially prehensile tail. It eats primarily insects and other small invertebrates, supplemented with fruit. - 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. - The Paleogene (or ; also spelled Palaeogene or Palogene; informally Lower Tertiary) is a geologic period and system that spans 43 million years from the end of the Cretaceous Period million years ago (Mya) to the beginning of the Neogene Period Mya. It is the beginning of the Cenozoic Era of the present Phanerozoic Eon. The Paleogene is most notable for being the time during which mammals diversified from relatively small, simple forms into a large group of diverse animals in the wake of the CretaceousPaleogene extinction event that ended the preceding Cretaceous Period. Given the information above, choose from the list below the object entity that exhibits the relation 'instance of' with the subject 'asiadelphia'. Choices: - chert - del - diminutive - era - event - extinct - five - group - limestone - may - mineral - molecule - monkey - order - period - rock - salt - species - system - taxon
A:
taxon