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56-761: Some scientists have argued that the Jehol Biota evolved directly from the preceding Daohugou Biota without any strongly defined division. However, the absolute dating of the Daohugou beds has been the subject of divergent opinion: in 2006, Wang et al. found an overall similarity between the fossil animals found in the Daohugou Beds and the "Jehol Biota" from the Yixian Formation. Several other research teams, including Liu et al. , have attempted to disprove this reasoning by using Zircon U-Pb dating on

112-531: A warning , when they are poisonous or contain stinging cells , or to camouflage them on the brightly colored hydroids , sponges , and seaweeds on which many of the species are found. Lateral outgrowths on the body of nudibranchs are called cerata . These contain an outpocketing of digestive glands called the diverticula . The sensory organs of gastropods include olfactory organs , eyes, statocysts and mechanoreceptors . Gastropods have no hearing. In terrestrial gastropods (land snails and slugs),

168-487: A few ciliary feeders, in which the radula is reduced or absent. Land-dwelling species can chew up leaves, bark, fruit and decomposing animals while marine species can scrape algae off the rocks on the seafloor. Certain species such as the Archaeogastropda maintain horizontal rows of slender marginal teeth. In some species that have evolved into endoparasites, such as the eulimid Thyonicola doglieli , many of

224-400: A gastropod is called a protoconch . Most shelled gastropods have a one piece shell (with exceptional bivalved gastropods ), typically coiled or spiraled, at least in the larval stage. This coiled shell usually opens on the right-hand side (as viewed with the shell apex pointing upward). Numerous species have an operculum , which in many species acts as a trapdoor to close the shell. This

280-446: A gastropod is usually adapted to the food that a species eats. The simplest gastropods are the limpets and abalones , herbivores that use their hard radula to rasp at seaweeds on rocks. Many marine gastropods are burrowers, and have a siphon that extends out from the mantle edge. Sometimes the shell has a siphonal canal to accommodate this structure. A siphon enables the animal to draw water into their mantle cavity and over

336-491: A marine environment. Gastropods have a worldwide distribution, from the near Arctic and Antarctic zones to the tropics. They have become adapted to almost every kind of existence on earth, having colonized nearly every available medium. In habitats where not enough calcium carbonate is available to build a really solid shell, such as on some acidic soils on land, various species of slugs occur, and also some snails with thin, translucent shells, mostly or entirely composed of

392-483: A partial skeleton with soft tissue impressions. Darwinopterus D. modularis Liaoning A wukongopterid named after Charles Darwin . The type species, D. modularis was the first known pterosaur to display features of both long-tailed rhamphorhynchoids and short-tailed pterodactyloids , and was described as a transitional fossil between the two groups. Darwinopterus specimens have also been reported to show several differences between males and females, with

448-551: A partial skull and lower jaw. Cascocauda C. rong Hebei Daohugou bed One specimen A long-tailed batrachognathine anurognathid known from a complete skeleton of a juvenile with extensive preservation of pycnofibres and wing membranes. Changchengopterus C. pani Hebei A pterodactyliform known only from a single specimen of a young juvenile, measuring 475 millimeters (18.7 in) in wingspan. Daohugoupterus D. delicatus Inner Mongolia One specimen A relatively basal pterosaur known from

504-402: A reference to the fact that the animal's "foot" is positioned below its guts. The earlier name "univalve" means one valve (or shell), in contrast to bivalves , such as clams, which have two valves or shells. At all taxonomic levels, gastropods are second only to insects in terms of their diversity . Gastropods have the greatest numbers of named mollusk species. However, estimates of

560-632: A strange skull morphology, at first believed to come from the Early Cretaceous . Liaoxitriton L. daohugouensis A little-known cryptobranchoid. Pangerpeton P. sinensis A cryptobranchoid characterized by its short trunk (only 14 presacrals) and short and wide head, giving a fat body shape, from which the genus name was derived ("Pang" means fat in Chinese). Archaeoistiodactylus A. linglongtaensis Liaoning A monofenestratan known from an incomplete skeleton with

616-472: Is a part of the behavior of mating gastropods with some pulmonate families of land snails creating and utilizing love darts , the throwing of which have been identified as a form of sexual selection . The main aspects of the life cycle of gastropods include: The diet of gastropods differs according to the group considered. Marine gastropods include some that are herbivores , detritus feeders, predatory carnivores , scavengers , parasites , and also

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672-422: Is difficult. The class Gastropoda has an extraordinary diversification of habitats . Representatives live in gardens, woodland, deserts, and on mountains; in small ditches, great rivers, and lakes; in estuaries , mudflats , the rocky intertidal , the sandy subtidal, the abyssal depths of the oceans, including the hydrothermal vents , and numerous other ecological niches, including parasitic ones. Although

728-433: Is muscular, and the second is mutagenetic . The effects of torsion are primarily physiological. The organism develops by asymmetrical growth, with the majority of growth occurring on the left side. This leads to the loss of right-side anatomy that in most bilaterians is a duplicate of the left side anatomy. The essential feature of this asymmetry is that the anus generally lies to one side of the median plane. The gill-combs ,

784-470: Is not the most important sense, because they are mainly nocturnal animals. The nervous system of gastropods includes the peripheral nervous system and the central nervous system . The central nervous system consists of ganglia connected by nerve cells. It includes paired ganglia: the cerebral ganglia, pedal ganglia, osphradial ganglia, pleural ganglia, parietal ganglia and the visceral ganglia. There are sometimes also buccal ganglia. The radula of

840-610: Is particularly noteworthy for the very high diversity of fossils and the very large numbers of individuals of each species that have been recovered. The Jehol Biota has produced fossils of plant macro- and microfossils , including angiosperms (the earliest known), charophytes and dinocysts , snails ( gastropods ), clams ( bivalves ), superabundant aquatic arthropods called conchostracans , ostracods , shrimps , insects , spiders , fish , frogs and salamanders ( amphibians ), turtles , choristoderes , lizards ( squamates ), pterosaurs , and dinosaurs including feathered dinosaurs ,

896-640: Is probably not even a mollusk. As such, it's not until the Ordovician that the first crown-group members arise. By the Ordovician period the gastropods were a varied group present in a range of aquatic habitats. Commonly, fossil gastropods from the rocks of the early Palaeozoic era are too poorly preserved for accurate identification. Still, the Silurian genus Poleumita contains fifteen identified species. Fossil gastropods were less common during

952-439: Is that the land animals and plants were washed into the lakes very gently, or were already in the lakes when they died. They do not show the damage seen in fossils formed by large floods. Secondly, volcanic ash is commonly inter-bedded with lake sediments, and ashfalls seem to have quickly buried the fossilized organisms, creating anoxic conditions around them and preventing scavenging. Zhonghe Zhou et al. (2003) noted that, for

1008-460: Is usually made of a horn-like material, but in some molluscs it is calcareous. In the land slugs, the shell is reduced or absent, and the body is streamlined. Some gastropods have adult shells which are bottom heavy due to the presence of a thick, often broad, convex ventral callus deposit on the inner lip and adapical to the aperture which may be important for gravitational stability. Some sea slugs are very brightly colored. This serves either as

1064-683: The Early Cretaceous , the Jehol Biota includes a mixture of advanced and ancient species, and also of species found only in the Jehol and others found all around the world. It is possible that northeast Asia was isolated for part of the Jurassic by the Turgai Sea which separated Europe from Asia at the time. The Jehol Biota includes many species that were previously known only from the Late Jurassic or earlier. These "relict" species include

1120-586: The Huajiying Formation . Daohugou Biota The Tiaojishan Formation is a geological formation in Hebei and Liaoning , People's Republic of China , dating to the middle- late Jurassic period ( Bathonian - Oxfordian stages). It is known for its exceptionally preserved fossils, including those of plants , insects and vertebrates. It is made up mainly of pyroclastic rock interspersed with basic volcanic and sedimentary rocks . Previously,

1176-648: The Palaeozoic era than bivalves . Most of the gastropods of the Palaeozoic era belong to primitive groups, a few of which still survive. By the Carboniferous period many of the shapes seen in living gastropods can be matched in the fossil record, but despite these similarities in appearance the majority of these older forms are not directly related to living forms. It was during the Mesozoic era that

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1232-479: The Planorbidae , have hemoglobin as the respiratory protein. In one large group of sea slugs, the gills are arranged as a rosette of feathery plumes on their backs, which gives rise to their other name, nudibranchs . Some nudibranchs have smooth or warty backs with no visible gill mechanism, such that respiration may likely take place directly through the skin. Gastropods have open circulatory system and

1288-486: The compsognathid dinosaur Sinosauropteryx and the anurognathid pterosaur Dendrorhynchoides . It also has the earliest and most primitive known members of groups that spread all around the world by the Late Cretaceous , including neoceratopsians , therizinosaurs , tyrannosaurs , and oviraptorids . Northeastern Asia may have been the center of diversification of these dinosaur groups. The Jehol Biota

1344-474: The continental slope and the continental rise are home to the highest diversity, while the continental shelf and abyssal depths have a low diversity of marine gastropods. Gastropods are found in a wide range of aquatic and terrestrial habitats, from deep ocean trenches to deserts. Some of the more familiar and better-known gastropods are terrestrial gastropods (the land snails and slugs). Some live in fresh water, but most named species of gastropods live in

1400-513: The fossil record, while 476 are currently extant with or without a fossil record. Gastropoda (previously known as univalves and sometimes spelled "Gasteropoda") are a major part of the phylum Mollusca, and are the most highly diversified class in the phylum , with 65,000 to 80,000 living snail and slug species . The anatomy , behavior, feeding, and reproductive adaptations of gastropods vary significantly from one clade or group to another, so stating many generalities for all gastropods

1456-446: The olfactory organs , the foot slime-gland , nephridia , and the auricle of the heart are single or at least are more developed on one side of the body than the other. Furthermore, there is only one genital orifice, which lies on the same side of the body as the anus. Furthermore, the anus becomes redirected to the same space as the head. This is speculated to have some evolutionary function, as prior to torsion, when retracting into

1512-585: The Binggou, Haizhou and Upper Volcanic formations). Chiappe et al. argued in 1999 that the lower beds of the Yixian were best subdivided into a separate formation, the Chaomidianzi Formation, with a type locality at the village of Sihetun, approximately 25 km south of Beipiao City. However, this classification has fallen out of favor, and the Chaomidianzi Formation is disused as a synonym of

1568-479: The Jehol Biota is represented by the Huajiying Formation . The Yixian and Jiufotang Formations are considered Lagerstätte , meaning that they have exceptionally good conditions for fossil preservation. The fossils are numerous, but also very well preserved – often including articulated skeletons, soft tissues, colour patterns, stomach contents, and twigs with leaves and flowers still attached. Zhonghe Zhou et al. . (2003) deduced two things from this. The first

1624-560: The Jehol Biota: The name "Jehol Biota" was first published by Gu (1962), but was in use by geologists and paleontologists by 1959. This term replaced the former "Jehol Fauna", which Amadeus William Grabau (1923) defined as the fossil assemblage typified by numerous fossils of the conchostracan Eosestheria , the mayfly Ephemeropsis , and the Teleost fish Lycoptera . Thus it was sometimes called "EEL". The Jehol group

1680-466: The Jianshangou Bed of the Yixian Formation. In 2008, Ji et al. argued that these traditional definitions of the Jehol Biota arbitrarily excluded earlier fossil beds that clearly represent the first evolutionary stages of the later faunas, even though lower beds also had representatives of Ephemeropsis and Lycoptera . They argued that the boundaries of the biota should rather be set based on

1736-685: The Tiaojishan Formation was grouped together with the underlying Haifanggou Formation (also known as the Jiulongshan Formation) as a single " Lanqi Formation ." The Tiaojishan Formation forms a key part of the Yanliao Biota assemblage, alongside the Haifanggou Formation. Using Argon–argon dating , Wang and colleagues in 2005 dated part of the Tiaojishan Formation to about 160 million years ago,

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1792-476: The adult stage—though in some, the coiling may not be very visible, for example in cowries . In a number of families of species, such as all the various limpets , the shell is coiled only in the larval stage, and is a simple conical structure after that. In the scientific literature, gastropods were described as "gasteropodes" by Georges Cuvier in 1795. The word gastropod comes from Greek γαστήρ ( gastḗr 'stomach') and πούς ( poús 'foot'),

1848-548: The beginning of the Oxfordian stage , the first stage of the Upper Jurassic epoch. In 2006, a study by Liu and colleagues used U-Pb zircon dating to conclude that the Tiaojishan Formation correlates with the Daohugou Beds, and the complete chronological range of this shared biota dates to between 168 and 164/152 Ma ago. A subsequent study, published in 2008, refined the age range of the formation further, finding that

1904-540: The body cavity, and digestive glands opening into the stomach . Courtship is a part of mating behavior in some gastropods, including some of the Helicidae . Again, in some land snails, an unusual feature of the reproductive system of gastropods is the presence and utilization of love darts . In many marine gastropods other than the opisthobranchs , there are separate sexes ( dioecious / gonochoric ); most land gastropods, however, are hermaphrodites . Courtship

1960-423: The deep-sea floor has been studied biologically. The total number of living species of freshwater snails is about 4,000. Recently extinct species of gastropods (extinct since 1500) number 444, 18 species are now extinct in the wild (but still exist in captivity), and 69 species are "possibly extinct". The number of prehistoric (fossil) species of gastropods is at least 15,000 species. In marine habitats,

2016-539: The distinctive large-scale sequences of volcanism which produced the strata, with the upper boundary set at the Shahai and Fuxin formations and the lower boundary at the Zhangjiakou Formation . Along with this sedimentary correlation, they noted that the best index fossils to identify the biota are Peipiaosteus and Lycoptera . Under this definition, the earliest stage of the Jehol Biota is represented by

2072-1306: The earliest known gliding mammal ( Volaticotherium ) have been discovered in these rocks.The tuffaceous composition of some rock layers show that this was a volcanic area, occasionally experiencing heavy ashfalls from eruptions. The landscape then was dominated by mountain streams and deep lakes surrounded by forests of gymnosperm trees. The forests of the Yanliao biota grew in a humid, warm - temperate climate and were dominated by gymnosperm trees. There were ginkgopsids like Ginkoites , Ginkgo , Baiera , Czekanowskia , and Phoenicopsis . There were also conifers like Pityophyllum , Rhipidiocladus , Elatocladus , Schizolepis , and Podozamites . Also, Lycopsids like Lycopodites and Sellaginellities , horsetails ( Sphenopsida ) like Equisetum , cycads like Anomozamites , and ferns ( Filicopsida ) like Todites and Coniopteris . Yanliaomyzon Y. occisor Liaoning A lamprey . Beiyanerpeton B. jianpingensis Liaoning A salamandroid known from an almost complete and articulated skeleton exposed in ventral view. Chunerpeton C. tianyiensis A cryptobranchoid measuring 18 centimeters in length. Jeholotriton J. paradoxus A cryptobranchoid with

2128-487: The earliest representatives of the group appearing in the Late Cambrian ( Chippewaella , Strepsodiscus ), though their only gastropod character is a coiled shell, so they could lie in the stem lineage, if they are gastropods at all. Earliest Cambrian organisms like Helcionella , Barskovia and Scenella are no longer considered gastropods, and the tiny coiled Aldanella of earliest Cambrian time

2184-411: The gill. They use the siphon primarily to "taste" the water to detect prey from a distance. Gastropods with siphons tend to be either predators or scavengers. Almost all marine gastropods breathe with a gill , but many freshwater species, and the majority of terrestrial species, have a pallial lung . The respiratory protein in almost all gastropods is hemocyanin , but one freshwater pulmonate family,

2240-516: The land. There are many thousands of species of sea snails and slugs , as well as freshwater snails , freshwater limpets , land snails and slugs . The class Gastropoda is a diverse and highly successful class of mollusks within the phylum Mollusca. It contains a vast total of named species, second only to the insects in overall number. The fossil history of this class goes back to the Late Cambrian . As of 2017 , 721 families of gastropods are known, of which 245 are extinct and appear only in

2296-404: The largest mammals known from the Mesozoic , and a great diversity of birds including the earliest advanced birds. The forests around the lakes were dominated by conifers including members of the podocarp , pine , araucaria , and cypress families. There were also ginkgos , czekanowskialeans , bennettitaleans , ephedra , horsetails , ferns , and mosses . The leaves and needles of

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2352-655: The lower boundary of the Tiaojishan was formed 165 Ma ago, and the upper boundary somewhere between 156 and 153 Ma ago. Based on the plant life present in the Tiaojishan Formation, Wang Yongdong and colleagues determined that the climate in Liaoning during the mid Jurassic would have been subtropical to temperate , warm and humid . Beautifully preserved fossils of dinosaurs , pterosaurs , salamanders , insects , arachnids and other invertebrates , conifers , ginkgoes , cycads , horsetails , and ferns , and even

2408-513: The males having distinctive crests on their heads. They are known to have laid their eggs on the ground, and may have also not shown that much for parental care. Gastropod Gastropods ( / ˈ ɡ æ s t r ə p ɒ d z / ), commonly known as slugs and snails , belong to a large taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ( / ɡ æ s ˈ t r ɒ p ə d ə / ). This class comprises snails and slugs from saltwater, freshwater, and from

2464-572: The name "snail" can be, and often is, applied to all the members of this class, commonly this word means only those species with an external shell big enough that the soft parts can withdraw completely into it. Slugs are gastropods that have no shell or a very small, internal shell; semislugs are gastropods that have a shell that they can partially retreat into but not entirely. The marine shelled species of gastropods include species such as abalone , conches , periwinkles , whelks , and numerous other sea snails that produce seashells that are coiled in

2520-486: The olfactory organs, located on the tips of the four tentacles , are the most important sensory organ. The chemosensory organs of opisthobranch marine gastropods are called rhinophores . The majority of gastropods have simple visual organs, eye spots either at the tip or base of the tentacles. However, "eyes" in gastropods range from simple ocelli that only distinguish light and dark, to more complex pit eyes , and even to lens eyes . In land snails and slugs, vision

2576-509: The origin of Patellogastropoda and Heterobranchia , whereas fewer changes occurred between the ancestors of Vetigastropoda (only tRNAs D, C and N) and Caenogastropoda (a large single inversion , and translocations of the tRNAs D and N). Within Heterobranchia, gene order seems relatively conserved, and gene rearrangements are mostly related with transposition of tRNA genes. The first gastropods were exclusively marine, with

2632-555: The protein conchiolin . Snails such as Sphincterochila boissieri and Xerocrassa seetzeni have adapted to desert conditions. Other snails have adapted to an existence in ditches, near deepwater hydrothermal vents , in oceanic trenches 10,000 meters (6 miles) below the surface, the pounding surf of rocky shores , caves , and many other diverse areas. Gastropods can be accidentally transferred from one habitat to another by other animals, e.g. by birds . Snails are distinguished by an anatomical process known as torsion , where

2688-419: The shell, first the posterior end would get pulled in, and then the anterior. Now, the front can be retracted more easily, perhaps suggesting a defensive purpose. Gastropods typically have a well-defined head with two or four sensory tentacles with eyes, and a ventral foot. The foremost division of the foot is called the propodium. Its function is to push away sediment as the snail crawls. The larval shell of

2744-593: The standard gastropod features are strongly reduced or absent. A few sea slugs are herbivores and some are carnivores. The carnivorous habit is due to specialisation. Many gastropods have distinct dietary preferences and regularly occur in close association with their food species. Some predatory carnivorous gastropods include: cone shells , Testacella , Daudebardia , turrids , ghost slugs and others. Gastropods exhibit an important degree of variation in mitochondrial gene organization when compared to other animals. Main events of gene rearrangement occurred at

2800-715: The total number of gastropod species vary widely, depending on cited sources. The number of gastropod species can be ascertained from estimates of the number of described species of Mollusca with accepted names: about 85,000 (minimum 50,000, maximum 120,000). But an estimate of the total number of Mollusca, including undescribed species, is about 240,000 species. The estimate of 85,000 mollusks includes 24,000 described species of terrestrial gastropods. Different estimates for aquatic gastropods (based on different sources) give about 30,000 species of marine gastropods, and about 5,000 species of freshwater and brackish gastropods. Many deep-sea species remain to be discovered, as only 0.0001% of

2856-437: The transport fluid is hemolymph . Hemocyanin is present in the hemolymph as the respiratory pigment. The primary organs of excretion in gastropods are nephridia , which produce either ammonia or uric acid as a waste product. The nephridium also plays an important role in maintaining water balance in freshwater and terrestrial species. Additional organs of excretion, at least in some species, include pericardial glands in

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2912-414: The trees show adaptations to a dry season, but some of the ferns and mosses are types that grow in very wet habitats. It is possible that the latter avoided dry conditions by growing very close to bodies of water. Archaefructus has been described as the earliest known flowering plant ( Angiosperm ), and it is reconstructed as an aquatic plant. Gu (1983 and 1995) defined the following species as typifying

2968-406: The visceral mass of the animal rotates 180° to one side during development, such that the anus is situated more or less above the head. This process is unrelated to the coiling of the shell, which is a separate phenomenon. Torsion is present in all gastropods, but the opisthobranch gastropods are secondarily untorted to various degrees. Torsion occurs in two stages. The first, mechanistic stage

3024-483: The volcanic rocks overlying and underlying salamander-bearing layers (salamanders are often used as index fossils ). Liu et al. found that the Daohugou beds formed between 164 and 158 million years ago, in the Middle to Late Jurassic . Later, Ji et al. argued that the key indicator of the Jehol biota are the index fossil fishes Peipiaosteus and Lycoptera . Under this definition, the earliest evolutionary stage of

3080-901: Was defined by Gu (1962 and 1983) as a group of geological formations including the Jehol Coal-bearing Beds, the Jehol Oil Shale Beds, and the Jehol Volcanic Rocks. By now the group includes, in ascending order, the Yixian Formation (including the Jingangshan, Tuhulu, Jianchang, Lower Volcanic and Volcanic Rock formations), the Jiufotang Formation (including the Shahai Formation) and the Fuxin Formation (including

3136-418: Was not entirely isolated, however, because it also includes animals which were known from all around the world at the same time, including discoglossid frogs , paramacellodid lizards , multituberculate mammals , enantiornithine birds, ctenochasmatid pterosaurs , iguanodontian ornithopods , titanosauriform sauropods , nodosaurid ankylosaurs , and dromaeosaurid theropods . The Jehol Biota

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