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33-587: The Kitadani Formation is a unit within the Tetori Group , a major sequence of Lower Cretaceous rocks that is distributed across Fukui, Ishikawa , and Gifu prefectures of western-central Honshu . The Tetori Group exhibits marked lateral variation, and the Kitadani Formation is only present in Fukui Prefecture. The Kitadani Formation comprises interbedded tuffs , sandstones , and shales and reaches

66-637: A maximum thickness of approximately one hundred meters (~328 feet). It conformably overlies the Akaiwa Formation and is unconformably overlain by the Omichidani Formation . The Kitadani Formation is significant because it is the major source of dinosaur fossils in Japan and because of Japan's unique position along the northeastern margin of Eurasia during the Early Cretaceous. The Kitadani Formation

99-666: Is a vertebrate animal of the class Mammalia ( / m ə ˈ m eɪ l i . ə / ). Mammals are characterized by the presence of milk -producing mammary glands for feeding their young, a broad neocortex region of the brain, fur or hair , and three middle ear bones . These characteristics distinguish them from reptiles and birds , from which their ancestors diverged in the Carboniferous Period over 300 million years ago. Around 6,400 extant species of mammals have been described and divided into 27 orders . The largest orders of mammals, by number of species , are

132-574: Is a unit within the Tetori Group , a Lower Cretaceous sequence of predominantly sedimentary rock which crops out in the Fukui , Ishikawa , and Gifu prefectures of west-central Honshu , Japan in the region surrounding Mount Haku . The formations present within the Tetori Group vary laterally, and the Kitadani Formation crops out only in the Kuzuryū River district of Fukui Prefecture. In this region,

165-572: Is primarily driven by human poaching and habitat destruction , primarily deforestation . Over 70% of mammal species are in the orders Rodentia , Chiroptera , and Eulipotyphla . Mammal classification has been through several revisions since Carl Linnaeus initially defined the class, and at present , no classification system is universally accepted. McKenna & Bell (1997) and Wilson & Reeder (2005) provide useful recent compendiums. Simpson (1945) provides systematics of mammal origins and relationships that had been taught universally until

198-426: Is the viviparous placental mammals , so named for the temporary organ ( placenta ) used by offspring to draw nutrition from the mother during gestation . Most mammals are intelligent , with some possessing large brains, self-awareness , and tool use . Mammals can communicate and vocalize in several ways, including the production of ultrasound , scent marking , alarm signals , singing , echolocation ; and, in

231-467: The Cretaceous . The relationships between these three lineages is contentious, and all three possible hypotheses have been proposed with respect to which group is basal . These hypotheses are Atlantogenata (basal Boreoeutheria), Epitheria (basal Xenarthra) and Exafroplacentalia (basal Afrotheria). Boreoeutheria in turn contains two major lineages— Euarchontoglires and Laurasiatheria . Estimates for

264-550: The International Union for Conservation of Nature (IUCN) completed a five-year Global Mammal Assessment for its IUCN Red List , which counted 5,488 species. According to research published in the Journal of Mammalogy in 2018, the number of recognized mammal species is 6,495, including 96 recently extinct. The word " mammal " is modern, from the scientific name Mammalia coined by Carl Linnaeus in 1758, derived from

297-547: The Latin mamma ("teat, pap"). In an influential 1988 paper, Timothy Rowe defined Mammalia phylogenetically as the crown group of mammals, the clade consisting of the most recent common ancestor of living monotremes ( echidnas and platypuses ) and therian mammals ( marsupials and placentals ) and all descendants of that ancestor. Since this ancestor lived in the Jurassic period, Rowe's definition excludes all animals from

330-590: The biological classification scheme used, are the primates : apes , monkeys , and lemurs ; the Cetartiodactyla : whales and even-toed ungulates ; and the Carnivora which includes cats , dogs , weasels , bears , seals , and allies. According to Mammal Species of the World , 5,416 species were identified in 2006. These were grouped into 1,229  genera , 153  families and 29 orders. In 2008,

363-406: The dominant terrestrial animal group from 66 million years ago to the present. The basic mammalian body type is quadrupedal , with most mammals using four limbs for terrestrial locomotion ; but in some, the limbs are adapted for life at sea , in the air , in trees or underground . The bipeds have adapted to move using only the two lower limbs, while the rear limbs of cetaceans and

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396-428: The rodents , bats , and Eulipotyphla (including hedgehogs , moles and shrews ). The next three are the primates (including humans , monkeys and lemurs ), the even-toed ungulates (including pigs , camels , and whales ), and the Carnivora (including cats , dogs , and seals ). Mammals are the only living members of Synapsida ; this clade , together with Sauropsida (reptiles and birds), constitutes

429-439: The sea cows are mere internal vestiges . Mammals range in size from the 30–40 millimetres (1.2–1.6 in) bumblebee bat to the 30 metres (98 ft) blue whale —possibly the largest animal to have ever lived. Maximum lifespan varies from two years for the shrew to 211 years for the bowhead whale . All modern mammals give birth to live young, except the five species of monotremes , which lay eggs. The most species-rich group

462-527: The "Lower part of the Omichidani Formation", the "Chinaboradani Alternation of Tuff, Shale, and Sandstone", the "Kitadani Alternation of Sandstone, Shale, and Tuff", and simply the "Kitadani Alternation" prior to its designation as a formation. The Kitadani Formation was biostratigraphically dated to the late Barremian and early Aptian ages of the Early Cretaceous Epoch in 2002 based upon

495-409: The Kitadani Formation is characterized by a rarity of ferns and an abundance of cycadales and conifers represented mostly by cones and shoots. A palynological study in 2013 resulted in the identification of greater than 40 species of spores, pollen grains, and plant fragments from the Kitadani Formation representing gymnosperms, freshwater algae, and epiphyllous fungus; however, no angiosperm pollen

528-599: The Kitadani Formation occurs along the Nakanomatadani branch of the Takinami River  [ ja ] near the city of Katsuyama , where it is approximately 100 m (~328 feet) in thickness. The Kitadani Formation conformably overlies the Akaiwa Formation and is unconformably overlain by the Omichidani Formation . The palaeoclimate during the deposition of the formation was noticeably warmer and drier than that of

561-419: The Kitadani Formation to 127-115 Ma. The Kitadani Formation preserves a diverse assemblage of plant fossils; invertebrate fossils; and vertebrate body and trace fossils, including mammals , turtles , crocodylomorphs , and dinosaurs . Many vertebrate specimens from the Kitadani Formation are incomplete and poorly preserved, so taxonomic diversity is likely higher than it seems. The plant fossil assemblage of

594-457: The Kitadani Formation. Tetori Group Shokawa Area The Tetori Group is a stratigraphic group in Japan , found within several basins in and around Fukui Prefecture . It is Early Cretaceous in age. It primarily consists of freshwater continental deposits, with some beds of volcanic tuffite . It primarily overlies Jurassic marine sediments or gneiss basement . Some of the units within

627-462: The Kitadani Formation. A nearly complete skeleton of goniopholidid has been discovered from the Kitadani Formation, but this material remains undescribed. Dinosaurs are among the most well-known vertebrate taxa from the Kitadani Formation. Taxa from all three major dinosaurian clades — Theropoda , Sauropodomorpha , and Ornithischia — have been recovered. [REDACTED] Undescribed tracks of ankylosaurs and sauropods have been discovered from

660-483: The case of humans, complex language . Mammals can organize themselves into fission–fusion societies , harems , and hierarchies —but can also be solitary and territorial . Most mammals are polygynous , but some can be monogamous or polyandrous . Domestication of many types of mammals by humans played a major role in the Neolithic Revolution , and resulted in farming replacing hunting and gathering as

693-807: The clade originating with the last common ancestor of Sinoconodon and living mammals. The earliest-known synapsid satisfying Kemp's definitions is Tikitherium , dated 225 Ma , so the appearance of mammals in this broader sense can be given this Late Triassic date. However, this animal may have actually evolved during the Neogene. As of the early 21st century, molecular studies based on DNA analysis have suggested new relationships among mammal families. Most of these findings have been independently validated by retrotransposon presence/absence data . Classification systems based on molecular studies reveal three major groups or lineages of placental mammals— Afrotheria , Xenarthra and Boreoeutheria —which diverged in

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726-444: The closest thing to an official classification of mammals, despite its known issues. Most mammals, including the six most species-rich orders , belong to the placental group. The three largest orders in numbers of species are Rodentia : mice , rats , porcupines , beavers , capybaras , and other gnawing mammals; Chiroptera : bats; and Eulipotyphla : shrews , moles , and solenodons . The next three biggest orders, depending on

759-574: The earlier Triassic , despite the fact that Triassic fossils in the Haramiyida have been referred to the Mammalia since the mid-19th century. If Mammalia is considered as the crown group, its origin can be roughly dated as the first known appearance of animals more closely related to some extant mammals than to others. Ambondro is more closely related to monotremes than to therian mammals while Amphilestes and Amphitherium are more closely related to

792-451: The end of the 20th century. However, since 1945, a large amount of new and more detailed information has gradually been found: The paleontological record has been recalibrated, and the intervening years have seen much debate and progress concerning the theoretical underpinnings of systematization itself, partly through the new concept of cladistics . Though fieldwork and lab work progressively outdated Simpson's classification, it remains

825-726: The group are noted for their fossil content, including dinosaurs, lizards mammals and other vertebrates. The term "Tetori Group" was first used by Oishi in 1933. A significant revision was made by Maeda in 1961 which subdivided the Group into three subgroups, which in ascending order are the Kuzuryu Subgroup, the Itoshiro Subgroup and the Akaiwa Subgroup , alongside the Omichidani and Asuwa Formations, which were subsequently excluded from

858-641: The group. Recent stratigraphic revisions have split off the Kuzuryu Subgroup into the Kuzuryu Group , which is Mid to Late Jurassic in age and is largely marine. There is significant lateral variation within the Tetori Group, with completely different sequences of formations in different areas, so it is difficult to correlate different sequences into the different subgroups, so the Itoshiro and Akaiwa subgroups are now considered depreciated. Mammalia A mammal (from Latin mamma  'breast')

891-645: The larger Amniota clade. Early synapsids are referred to as " pelycosaurs ." The more advanced therapsids became dominant during the Guadalupian . Mammals originated from cynodonts , an advanced group of therapsids, during the Late Triassic to Early Jurassic . Mammals achieved their modern diversity in the Paleogene and Neogene periods of the Cenozoic era, after the extinction of non-avian dinosaurs , and have been

924-399: The older Kuwajima and Okurodani Formations , as evidenced by oxygen isotope records as well as by the presence of crocodylomorph fossils in the former in contrast to their absence in the latter. The Kitadani Formation has had varying nomenclature throughout the history of its study. In the early stratigraphic literature on the Tetori Group, the Kitadani Formation was variably referred to as

957-456: The presence of the freshwater bivalve Nippononaia ryosekiana . In 2005, part of the Kitadani Formation was biostratigraphically dated to the Barremian Age based upon the occurrence of the charophyte gyrogonite Clavator harrisii reyi in association with other charophytes. These biostratigraphic age assignments are supported by zircon fission track radioisotopic ages of tuff , which date

990-716: The primary source of food for humans. This led to a major restructuring of human societies from nomadic to sedentary, with more co-operation among larger and larger groups, and ultimately the development of the first civilizations . Domesticated mammals provided, and continue to provide, power for transport and agriculture, as well as food ( meat and dairy products ), fur , and leather . Mammals are also hunted and raced for sport, kept as pets and working animals of various types, and are used as model organisms in science. Mammals have been depicted in art since Paleolithic times, and appear in literature, film, mythology, and religion. Decline in numbers and extinction of many mammals

1023-484: The sequence comprises, in ascending stratigraphic order: Gomijima Formation , the Kuwajima Formation , the Akaiwa Formation , and Kitadani Formation. The Kitadani Formation comprises alternating horizons of red-brown tuffs , blackish shales and sandstones , and thin coal beds. The sandstones within the Kitadani Formation are light gray and green and range in clast size from fine to coarse. The type section of

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1056-537: The therians; as fossils of all three genera are dated about 167 million years ago in the Middle Jurassic , this is a reasonable estimate for the appearance of the crown group. T. S. Kemp has provided a more traditional definition: " Synapsids that possess a dentary – squamosal jaw articulation and occlusion between upper and lower molars with a transverse component to the movement" or, equivalently in Kemp's view,

1089-542: Was identified. Branches of the conifer Brachyphyllum obesum have been recovered, which was interpreted to represent the warming and possible drying of the climate toward the upper Tetori Group. This interpretation is supported by the lack of plants from lower in the Tetori Group, such as ginkgos , in the Kitadani Formation. The invertebrate fossil assemblage of the Kitadani Formation mostly comprises freshwater and brackish water bivalve and gastropod mollusks . Turtles are represented mostly by shell fragments within

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