In biological taxonomy , the type genus is the genus which defines a biological family and the root of the family name.
96-464: Adelophthalmidae (the name deriving from the type genus Adelophthalmus , meaning "no obvious eyes ") is a family of eurypterids , an extinct group of aquatic arthropods . Adelophthalmidae is the only family classified as part of the superfamily Adelophthalmoidea , which in turn is classified within the infraorder Diploperculata in the suborder Eurypterina . Adelophthalmid eurypterids were small and swimming eurypterids that appeared in
192-490: A "type genus". The 2008 Revision of the Bacteriological Code states, "The nomenclatural type […] of a taxon above genus, up to and including order, is the legitimate name of the included genus on whose name the name of the relevant taxon is based. One taxon of each category must include the type genus. The names of the taxa which include the type genus must be formed by the addition of the appropriate suffix to
288-472: A constant rate. These " molecular clocks ", however, are fallible, and provide only approximate timing: for example, they are not sufficiently precise and reliable for estimating when the groups that feature in the Cambrian explosion first evolved, and estimates produced by different techniques may vary by a factor of two. Organisms are only rarely preserved as fossils in the best of circumstances, and only
384-461: A family-group name is also the genus that provided the stem to which was added the ending -idae (for families). In botanical nomenclature , the phrase "type genus" is used, unofficially, as a term of convenience. In the ICN this phrase has no status. The code uses type specimens for ranks up to family, and types are optional for higher ranks. The Code does not refer to the genus containing that type as
480-561: A few million years after the extinction of the adelophthalmids in the Early Permian. The size of the adelophthalmid eurypterids ranged from 4 centimetres (1.6 inch) to 32 cm (12.6 in), the smallest species being Nanahughmilleria clarkei and the largest one being Adelophthalmus khakassicus . The adelophthalmids were relatively small compared to their relatives, such as the gigantic pterygotid Jaekelopterus rhenaniae , which easily exceeded 2 metres (6.5 feet), and
576-426: A fraction of such fossils have been discovered. This is illustrated by the fact that the number of species known through the fossil record is less than 5% of the number of known living species, suggesting that the number of species known through fossils must be far less than 1% of all the species that have ever lived. Because of the specialized and rare circumstances required for a biological structure to fossilize, only
672-411: A group supported by two synapomorphies (shared characteristics different from that of their latest common ancestor ); long narrow eyes and a complex termination of the genital appendage. At the base of the family, Eysyslopterus has been interpreted as the most basal adelophthalmid. The carapace of this genus, Herefordopterus and Orcanopterus were almost identical and were mainly differentiated by
768-499: A hierarchical classification system still in use today. Darwin and his contemporaries first linked the hierarchical structure of the tree of life with the then very sparse fossil record. Darwin eloquently described a process of descent with modification, or evolution, whereby organisms either adapt to natural and changing environmental pressures, or they perish. When Darwin wrote On the Origin of Species by Means of Natural Selection, or
864-456: A member of the genus Adelophthalmus , as well as completely ignored. The spinosity of its appendages may suggest the second option, but this is not entirely certain and the phylogenetic classification of Unionopterus may never be resolved. In 1961, the American paleontologist Erik Norman Kjellesvig-Waering considered several species of the genus Hughmilleria sufficiently different from
960-418: A mid-Ordovician age. Such index fossils must be distinctive, be globally distributed and occupy a short time range to be useful. Misleading results are produced if the index fossils are incorrectly dated. Stratigraphy and biostratigraphy can in general provide only relative dating ( A was before B ), which is often sufficient for studying evolution. However, this is difficult for some time periods, because of
1056-536: A mutation first appeared. Phylogenetics and paleontology work together in the clarification of science's still dim view of the appearance of life and its evolution. Niles Eldredge 's study of the Phacops trilobite genus supported the hypothesis that modifications to the arrangement of the trilobite's eye lenses proceeded by fits and starts over millions of years during the Devonian . Eldredge's interpretation of
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#17327980039751152-556: A new genus known by one single specimen from Kazakhstan (at that time part of the Soviet Union ) and tentatively classified it as part of the Pterygotidae family . It was named Unionopterus , and its classification is controversial due to the poor illustrations given by Chernyshev and the fact that the only known fossil is presumed to be lost. The genus has been treated as an indeterminate eurypterid, an adelophthalmid or
1248-399: A past geological age . Examples include bones , shells , exoskeletons , stone imprints of animals or microbes , objects preserved in amber , hair , petrified wood and DNA remnants. The totality of fossils is known as the fossil record . Though the fossil record is incomplete, numerous studies have demonstrated that there is enough information available to give a good understanding of
1344-570: A portion of the deceased organism, usually that portion that was partially mineralized during life, such as the bones and teeth of vertebrates , or the chitinous or calcareous exoskeletons of invertebrates . Fossils may also consist of the marks left behind by the organism while it was alive, such as animal tracks or feces ( coprolites ). These types of fossil are called trace fossils or ichnofossils , as opposed to body fossils . Some fossils are biochemical and are called chemofossils or biosignatures . Gathering fossils dates at least to
1440-400: A richly diverse assembly of early multicellular eukaryotes . The fossil record and faunal succession form the basis of the science of biostratigraphy or determining the age of rocks based on embedded fossils. For the first 150 years of geology , biostratigraphy and superposition were the only means for determining the relative age of rocks. The geologic time scale was developed based on
1536-467: A series of shared characteristics that make them different from the rest of eurypterids. However, some genera developed different features within Adelophthalmidae that divide the family into several smaller clades and groupings. The genera Parahughmilleria and Adelophthalmus form a derived clade based on the presence of enlarged spines on at least one podomere in the appendage V (fifth limb),
1632-448: A small percentage of life-forms can be expected to be represented in discoveries, and each discovery represents only a snapshot of the process of evolution. The transition itself can only be illustrated and corroborated by transitional fossils, which will never demonstrate an exact half-way point. The fossil record is strongly biased toward organisms with hard-parts, leaving most groups of soft-bodied organisms with little to no role. It
1728-449: Is a notable example of how knowledge encoded by the fossil record continues to contribute otherwise unattainable information on the emergence and development of life on Earth. For example, the research suggests Markuelia has closest affinity to priapulid worms, and is adjacent to the evolutionary branching of Priapulida , Nematoda and Arthropoda . Despite significant advances in uncovering and identifying paleontological specimens, it
1824-479: Is generally accepted that the fossil record is vastly incomplete. Approaches for measuring the completeness of the fossil record have been developed for numerous subsets of species, including those grouped taxonomically, temporally, environmentally/geographically, or in sum. This encompasses the subfield of taphonomy and the study of biases in the paleontological record. Paleontology seeks to map out how life evolved across geologic time. A substantial hurdle
1920-438: Is replete with the mollusks , the vertebrates , the echinoderms , the brachiopods and some groups of arthropods . Fossil sites with exceptional preservation—sometimes including preserved soft tissues—are known as Lagerstätten —German for "storage places". These formations may have resulted from carcass burial in an anoxic environment with minimal bacteria, thus slowing decomposition. Lagerstätten span geological time from
2016-407: Is simplified from 2007 study by O. Erik Tetlie, showcasing the position of Adelophthalmoidea within the suborder Eurypterina. Placement of Diploperculata follows Lamsdell et al. 2013. Stylonurina Megalograptoidea Eurypteroidea Carcinosomatoidea Waeringopteroidea Adelophthalmoidea Hughmilleria Herefordopterus Slimonia Pterygotidae All adelophthalmids have
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#17327980039752112-470: Is the difficulty of working out fossil ages. Beds that preserve fossils typically lack the radioactive elements needed for radiometric dating . This technique is our only means of giving rocks greater than about 50 million years old an absolute age, and can be accurate to within 0.5% or better. Although radiometric dating requires careful laboratory work, its basic principle is simple: the rates at which various radioactive elements decay are known, and so
2208-413: Is the science of deciphering the "layer-cake" that is the sedimentary record. Rocks normally form relatively horizontal layers, with each layer younger than the one underneath it. If a fossil is found between two layers whose ages are known, the fossil's age is claimed to lie between the two known ages. Because rock sequences are not continuous, but may be broken up by faults or periods of erosion , it
2304-541: Is usually ignored by the eurypterid researchers. During the Late Carboniferous and Early Permian, Adelophthalmus lived in brackish and freshwater environments adjacent to coastal plains , a type of common and stable habitat at the time. Although the formation of Pangea helped the genus to widespread, it also affected its environments. They began to disappear due to a climatic change that caused alterations of depositional and vegetational patterns across
2400-467: Is very difficult to match up rock beds that are not directly adjacent. However, fossils of species that survived for a relatively short time can be used to match isolated rocks: this technique is called biostratigraphy . For instance, the conodont Eoplacognathus pseudoplanus has a short range in the Middle Ordovician period. If rocks of unknown age have traces of E. pseudoplanus , they have
2496-801: The Cambrian period to the present . Worldwide, some of the best examples of near-perfect fossilization are the Cambrian Maotianshan Shales and Burgess Shale , the Devonian Hunsrück Slates , the Jurassic Solnhofen Limestone , and the Carboniferous Mazon Creek localities. A fossil is said to be recrystallized when the original skeletal compounds are still present but in a different crystal form, such as from aragonite to calcite . Replacement occurs when
2592-753: The Emsian (around 393–408 mya, in Early Devonian), the earliest species of Adelophthalmus appeared, A. sievertsi , presenting basal features such as the wide swimming leg (as in Nanahughmilleria and Parahughmilleria ). The eurypterids were one of the groups most heavily affected by the Late Devonian extinction event , following a major decline in diversity during the Early Devonian, eurypterids were rare in marine environments by
2688-481: The International Code of Zoological Nomenclature , "The name-bearing type of a nominal family-group taxon is a nominal genus called the 'type genus'; the family-group name is based upon that of the type genus." Any family-group name must have a type genus (and any genus-group name must have a type species , but any species-group name may, but need not, have one or more type specimens). The type genus for
2784-690: The Kip Burn Formation , Lesmahagow , Scotland , from the beginning of the Wenlockian epoch (around 433-427 mya). These fossils differ slightly in the proportions of the body with the fossils of its type locality (in Germany) and have been compared with the latter ones, but the assignment of the Scottish fossils to P. hefteri is not entirely certain. The first species lived in brackish - estuarine water or in fully marine habitats . In
2880-600: The Late Devonian . Of the 16 eurypterid families that had been alive at the beginning of the Devonian, only three persisted into the Carboniferous , all of them non-marine groups. The suborder Eurypterina was rendered almost completely extinct, only surviving Adelophthalmoidea (represented by Adelophthalmus ). Adelophthalmus would rapidly diversify, already being present in Siberia and Gondwana (Australia) since
2976-616: The Llandovery (around 444-433 mya), suggesting that the adelophthalmids first appeared around this epoch . This is supported by the appearance of the basal pterygotioids, the sister group of the adelophthalmoids, in the Llandovery. However, the fossil record of Adelophthalmoidea is very poor in the Early Silurian and both species have disputed ages. The unequivocally oldest representative was P. hefteri , with fossils found in
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3072-586: The Phacops fossil record was that the aftermaths of the lens changes, but not the rapidly occurring evolutionary process, were fossilized. This and other data led Stephen Jay Gould and Niles Eldredge to publish their seminal paper on punctuated equilibrium in 1971. Synchrotron X-ray tomographic analysis of early Cambrian bilaterian embryonic microfossils yielded new insights of metazoan evolution at its earliest stages. The tomography technique provides previously unattainable three-dimensional resolution at
3168-569: The Renaissance . Leonardo da Vinci concurred with Aristotle's view that fossils were the remains of ancient life. For example, Leonardo noticed discrepancies with the biblical flood narrative as an explanation for fossil origins: If the Deluge had carried the shells for distances of three and four hundred miles from the sea it would have carried them mixed with various other natural objects all heaped up together; but even at such distances from
3264-555: The Silurian period . With the earliest known members of the group, Nanahughmilleria prominens and Parahughmilleria maria , being known from deposits of Early Silurian (possibly the Llandovery epoch ) age and the last members, belonging to the long-lasting and widespread genus Adelophthalmus , going extinct in the Early Permian , the Adelophthalmidae is the longest lasting single family of eurypterids. The survival of
3360-602: The Song dynasty during the 11th century, who kept a specific seashell fossil with his own poem engraved on it. In his Dream Pool Essays published in 1088, Song dynasty Chinese scholar-official Shen Kuo hypothesized that marine fossils found in a geological stratum of mountains located hundreds of miles from the Pacific Ocean was evidence that a prehistoric seashore had once existed there and shifted over centuries of time . His observation of petrified bamboos in
3456-486: The infraorder Diploperculata , in the Eurypterina suborder of eurypterids. The infraorder Diploperculata contains the four most derived superfamilies of eurypterine eurypterids; Carcinosomatoidea , Adelophthalmoidea, Pterygotioidea and the waeringopteroids, united by the shared feature that the genital operculum (the structure that contains the genital appendage) is made up of two fused segments. Adelophthalmoidea
3552-402: The law of superposition ) preserved different assemblages of fossils, and that these assemblages succeeded one another in a regular and determinable order. He observed that rocks from distant locations could be correlated based on the fossils they contained. He termed this the principle of faunal succession . This principle became one of Darwin's chief pieces of evidence that biological evolution
3648-544: The paleocontinent Baltica ( Scandinavia and Eastern Europe , precisely Estonia ). However, it is not possible to determine where the clade originated, probably in Baltica or Laurentia (most of eastern continental North America ). Although most of the representatives of Adelophthalmoidea have been found in Laurentia, Avalonia (Germany, Great Britain , parts of eastern North America) and Baltica (that is, Laurussia),
3744-403: The thunderbird . There is no such direct mythological connection known from prehistoric Africa, but there is considerable evidence of tribes there excavating and moving fossils to ceremonial sites, apparently treating them with some reverence. In Japan, fossil shark teeth were associated with the mythical tengu , thought to be the razor-sharp claws of the creature, documented some time after
3840-402: The type species to be separated into a new subgenus , which he named Nanahughmilleria . These species shared a key characteristic, small intramarginal eyes of reniform form (bean-shaped), in contrast to the large ovoid eyes placed in the margin of the carapace present in the genotype and its allied forms. Kjellesvig-Waering designated H. ( Nanahughmilleria ) norvegica as the type species of
3936-453: The 16th century. Roman naturalist Pliny the Elder wrote of " tongue stones ", which he called glossopetra . These were fossil shark teeth, thought by some classical cultures to look like the tongues of people or snakes. He also wrote about the horns of Ammon , which are fossil ammonites , whence the group of shelled octopus-cousins ultimately draws its modern name. Pliny also makes one of
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4032-739: The 19th century that certain fossils were associated with certain rock strata led to the recognition of a geological timescale and the relative ages of different fossils. The development of radiometric dating techniques in the early 20th century allowed scientists to quantitatively measure the absolute ages of rocks and the fossils they host. There are many processes that lead to fossilization , including permineralization , casts and molds, authigenic mineralization , replacement and recrystallization, adpression, carbonization , and bioimmuration. Fossils vary in size from one- micrometre (1 μm) bacteria to dinosaurs and trees, many meters long and weighing many tons. A fossil normally preserves only
4128-413: The 8th century AD. In medieval China, the fossil bones of ancient mammals including Homo erectus were often mistaken for " dragon bones" and used as medicine and aphrodisiacs . In addition, some of these fossil bones are collected as "art" by scholars, who left scripts on various artifacts, indicating the time they were added to a collection. One good example is the famous scholar Huang Tingjian of
4224-608: The Devonian. In the Carboniferous, the distribution of Adelophthalmus became approximately circumequatorial (around the Equator ). Out of the 33 species referred to Adelophthalmus , 23 (69%) were from the Carboniferous alone, reaching its peak diversity in the Late Carboniferous and becoming the most common of all eurypterids of the Late Paleozoic . This quick diversification may be due to their morphology, converting
4320-615: The Preservation of Favoured Races in the Struggle for Life , the oldest animal fossils were those from the Cambrian Period, now known to be about 540 million years old. He worried about the absence of older fossils because of the implications on the validity of his theories, but he expressed hope that such fossils would be found, noting that: "only a small portion of the world is known with accuracy." Darwin also pondered
4416-566: The Proterozoic and deeper still in the Archean is only "recounted by microscopic fossils and subtle chemical signals." Molecular biologists, using phylogenetics , can compare protein amino acid or nucleotide sequence homology (i.e., similarity) to evaluate taxonomy and evolutionary distances among organisms, with limited statistical confidence. The study of fossils, on the other hand, can more specifically pinpoint when and in what organism
4512-556: The Silurian alone. Many eurypterid groups are first recorded from the Silurian, such as Pterygotioidea, Mycteropoidea , Stylonuroidea and Adelophthalmoidea itself. The most primitive members of Adelophthalmoidea evolved in Laurussia (an ancient supercontinent , also known as Euramerica). In fact, the most basal species of the clade so far ( Eysyslopterus patteni ) has been recovered from Ludlovian (around 427-423 mya ) deposits of
4608-466: The adelophthalmids in one of the most able swimmers among the eurypterids. The amalgamation (union) of Pangaea into a global supercontinent was also an important factor. The pterygotoids were also successful swimmers, but they went extinct in the Middle Devonian, long before the formation of Pangea. Although Unionopterus also appeared in the Carboniferous, this genus is very little known and
4704-413: The beach, indicating the fossils were once living animals. He had previously explained them in terms of vaporous exhalations , which Persian polymath Avicenna modified into the theory of petrifying fluids ( succus lapidificatus ). Recognition of fossil seashells as originating in the sea was built upon in the 14th century by Albert of Saxony , and accepted in some form by most naturalists by
4800-714: The beginning of recorded history. The fossils themselves are referred to as the fossil record. The fossil record was one of the early sources of data underlying the study of evolution and continues to be relevant to the history of life on Earth . Paleontologists examine the fossil record to understand the process of evolution and the way particular species have evolved. Fossils have been visible and common throughout most of natural history, and so documented human interaction with them goes back as far as recorded history, or earlier. There are many examples of paleolithic stone knives in Europe, with fossil echinoderms set precisely at
4896-415: The carapace from the basal genera to the derived Adelophthalmus . The position of its eyes has led some researchers to question whether Eysyslopterus is an adelophthalmid at all or a sister taxon of Adelophthalmidae, but more fossils are required to either prove or disprove its phylogenetic position within the family or outside it. The cladogram below presents the inferred phylogenetic positions of most of
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#17327980039754992-670: The deity Sopdu , the Morning Star, equivalent of Venus in Roman mythology. Fossils appear to have directly contributed to the mythology of many civilizations, including the ancient Greeks. Classical Greek historian Herodotos wrote of an area near Hyperborea where gryphons protected golden treasure. There was indeed gold mining in that approximate region , where beaked Protoceratops skulls were common as fossils. A later Greek scholar, Aristotle , eventually realized that fossil seashells from rocks were similar to those found on
5088-466: The dry northern climate zone of what is now Yan'an , Shaanxi province, China, led him to advance early ideas of gradual climate change due to bamboo naturally growing in wetter climate areas. In medieval Christendom , fossilized sea creatures on mountainsides were seen as proof of the biblical deluge of Noah's Ark . After observing the existence of seashells in mountains, the ancient Greek philosopher Xenophanes (c. 570 – 478 BC) speculated that
5184-415: The earlier known references to toadstones , thought until the 18th century to be a magical cure for poison originating in the heads of toads, but which are fossil teeth from Lepidotes , a Cretaceous ray-finned fish. The Plains tribes of North America are thought to have similarly associated fossils, such as the many intact pterosaur fossils naturally exposed in the region, with their own mythology of
5280-550: The earliest known stromatolites are over 3.4 billion years old. The fossil record is life's evolutionary epic that unfolded over four billion years as environmental conditions and genetic potential interacted in accordance with natural selection. The Virtual Fossil Museum Paleontology has joined with evolutionary biology to share the interdisciplinary task of outlining the tree of life, which inevitably leads backwards in time to Precambrian microscopic life when cell structure and functions evolved. Earth's deep time in
5376-464: The earth during earthquake and subsidences, and petrifies whatever comes into contact with it. As a matter of fact, the petrifaction of the bodies of plants and animals is not more extraordinary than the transformation of waters. From the 13th century to the present day, scholars pointed out that the fossil skulls of Deinotherium giganteum , found in Crete and Greece, might have been interpreted as being
5472-635: The eurypterids continued to exist represented by the stylonurids. The Russian hibbertopterid species Campylocephalus permianus persisted until the Changhsingian (around 254-252 mya, Late Permian) stage, being the last known eurypterid. No eurypterids are known from fossil beds higher than the Permian, indicating that they probably died out in the Permian–Triassic mass extinction event or shortly before. The adelophthamids are classified within
5568-478: The existence of a world previous to ours, destroyed by some kind of catastrophe. Interest in fossils, and geology more generally, expanded during the early nineteenth century. In Britain, Mary Anning 's discoveries of fossils, including the first complete ichthyosaur and a complete plesiosaurus skeleton, sparked both public and scholarly interest. Early naturalists well understood the similarities and differences of living species leading Linnaeus to develop
5664-410: The eye position. In the latter, the eyes were almost marginal, but were separated from margin by the marginal rim. The eyes of Herefordopterus were completely marginal, a characteristic present in all the pterygotioid genera. Although the eyes of Eysyslopterus were intramarginal, they were much closer to the margin than in its relatives, suggesting that the eyes gradually migrated towards the center of
5760-472: The first specimen of the species A. granosus at Jägersfreude in Saarland , Germany . The specimen would be described three years later by Jordan and Hermann von Meyer , who immediately recognized the eurypterid nature of the fossils by the great resemblance of the overall shape and form of the carapace and appendages with that of Eurypterus . One of the main differences that Jordan and von Meyer noticed
5856-727: The genera included in the three most derived superfamilies of the Eurypterina suborder of eurypterids (Adelophthalmoidea, Pterygotioidea and the waeringopteroids), as inferred by O. Erik Tetlie and Markus Poschmann in 2008, based on the results of a 2008 analysis specifically pertaining to the Adelophthalmoidea and a preceding 2004 analysis. Orcanopterus Waeringopterus Grossopterus Eysyslopterus Bassipterus Pittsfordipterus Nanahughmilleria Parahughmilleria Adelophthalmus Hughmilleria Herefordopterus Slimonia Erettopterus Pterygotus Type genus According to
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#17327980039755952-401: The group by over a hundred million years. Though the last swimming eurypterids and the final members of the traditionally more successful and numerous suborder Eurypterina, the adelophthalmids were not the last eurypterids. The stylonurines or the "walking eurypterids" were the last ones, surviving in the family Hibbertopteridae until the Permian–Triassic extinction event or shortly before
6048-546: The group, and of swimming eurypterids (the suborder Eurypterina) beyond the Late Devonian is entirely due to the survival, and subsequent success, of Adelophthalmus throughout the Devonian and Carboniferous . Adelophthalmus (and possibly Unionopterus ) represents the only known genus of swimming eurypterids beyond the extinction of the rest of the group in the Late Devonian, extending the temporal range of
6144-519: The hand grip, dating back to Homo heidelbergensis and Neanderthals . These ancient peoples also drilled holes through the center of those round fossil shells, apparently using them as beads for necklaces. The ancient Egyptians gathered fossils of species that resembled the bones of modern species they worshipped. The god Set was associated with the hippopotamus , therefore fossilized bones of hippo-like species were kept in that deity's temples. Five-rayed fossil sea urchin shells were associated with
6240-444: The limbs) long and an eighth podomere coarsely serrated. The body had a midsection second order differentiation present (that is, with lateral "extensions" in the seventh body segment ) and with a lanceolate (lance-shaped) telson (the posteriormost division of the body). The morphology of the group varies depending on how derived (evolutionary advanced) the genus was. In fact, from the basal ("primitive") Nanahughmilleria to
6336-535: The limits of fossilization. Fossils of two enigmatic bilaterians, the worm-like Markuelia and a putative, primitive protostome , Pseudooides , provide a peek at germ layer embryonic development. These 543-million-year-old embryos support the emergence of some aspects of arthropod development earlier than previously thought in the late Proterozoic. The preserved embryos from China and Siberia underwent rapid diagenetic phosphatization resulting in exquisite preservation, including cell structures. This research
6432-506: The loss of a feature which seems to have been lost separately in the two groups is not in line with common practice. Odd Erik Tetlie in an unpublished thesis of 2004 erected the superfamily Adelophthalmoidea and the family Nanahughmilleridae. Adelophthalmoidea was diagnosed as eurypterids with parabolic carapaces, small reniform eyes, appendages of variable spinosity and a lanceolate telson, among others. This superfamily would be formally described two years later by Tetlie and Peter Van Roy. On
6528-464: The more derived Adelophthalmus , a gradual decrease in the spinosity (possessing spines) of the appendages (limbs) and an increase in the size of the genital spatulae (a long, flat piece in the genital area) occurred. The even more primitive Pittsfordipterus probably did not even possess the latter. The first adelophthalmid fossils to be uncovered were those of the type genus , Adelophthalmus . The German paleontologist Hermann Jordan collected
6624-551: The most diverse eurypterid genus to date. However, many of these species are fragmentary and could represent synonyms of other species within Adelophthalmus or even species of other genera. It is possible that the large amount of species in Adelophthalmus will eventually provoke its separation into two or three separate genera. In 1948, the Ukrainian paleontologist and geologist Boris Isidorovich Chernyshev described
6720-466: The nanahughmillerids as part of Adelophthalmidae. In 2008, Nanahughmilleria patteni was recognized as a different and much more basal species, and therefore a new genus, Eysyslopterus , was named by Tetlie and Markus Poschmann. The carapace of Eysyslopterus and other basal members of the closely related Pterygotioidea ( Herefordopterus ) and the waeringopteroids ( Orcanopterus ) has been shown as almost identical, only differing between them by
6816-641: The nearly cosmopolitan (worldwide) genus Adelophthalmus was also present in the Rheno-Hercynian Terrane (western and central Europe), Siberia and in the Gondwana part of the current Australia . In the Silurian, most of the adelophthalmid genera would appear, but all went extinct soon after or in the Middle Devonian . The oldest representatives of the group were Parahughmilleria maria and Nanahughmilleria prominens , both from
6912-415: The new subgenus. At the same time, he erected a new genus, Parahughmilleria , with P. salteri as the type species. Kjellesvig-Waering based its new clade mainly on the presence of supplementary lobes ( distal lobes in a plate-like segment which contains the genital aperture called genital operculum), as well as in the intramarginal eyes. In 1964, Kjellesvig-Waering described the genital operculum of
7008-432: The other hand, Nanahughmilleridae was described to contain the adelophthalmoids with no or reduced genital spatulae and the second to fifth pair of prosomal (of the prosoma, "head") appendages of Hughmilleria -type. This family contained Nanahughmileria , Pittsfordipterus and perhaps Parahughmilleria . However, the clade has almost never been used in subsequent studies and lists of eurypterids, and instead, they classify
7104-474: The pattern of diversification of life on Earth. In addition, the record can predict and fill gaps such as the discovery of Tiktaalik in the arctic of Canada . Paleontology includes the study of fossils: their age, method of formation, and evolutionary significance. Specimens are usually considered to be fossils if they are over 10,000 years old. The oldest fossils are around 3.48 billion years to 4.1 billion years old. The observation in
7200-410: The position of the eyes. Due to the intramarginal position of the eyes, Eysyslopterus has been classified within Adelophthalmidae, but it has also been suggested that it is the sister taxon (closest relative) of a clade formed by Adelophthalmoidea and Pterygotioidea. However, this can not be demonstrated until more fossil material is found. In 2023, Archopterus anjiensis , a new genus and species,
7296-407: The presence of epimera (lateral "extensions" of the segment) in the seventh segment. Tollerton commented that some species of Adelophthalmus that did not have spines in the appendages may be better placed in a new genus in the family Slimonidae (he mentioned the now invalid Slimonioidea). Although a new genus for spineless species could be phylogenetically supported, moving it to Slimonidae based on
7392-417: The presence of epimera in the postabdomen (body segments 8 to 12) and the large spatulae that has been associated with the genital operculum. Nanahughmilleria is placed as the sister taxon of this clade but more basal due to the increased spinosity of its appendage V and in the small size of the genital spatulae. Bassipterus and Pittsfordipterus are positioned as relatively more basal to this clade and form
7488-545: The problems involved in matching rocks of the same age across continents . Family-tree relationships also help to narrow down the date when lineages first appeared. For instance, if fossils of B or C date to X million years ago and the calculated "family tree" says A was an ancestor of B and C, then A must have evolved earlier. It is also possible to estimate how long ago two living clades diverged, in other words approximately how long ago their last common ancestor must have lived, by assuming that DNA mutations accumulate at
7584-443: The ratio of the radioactive element to its decay products shows how long ago the radioactive element was incorporated into the rock. Radioactive elements are common only in rocks with a volcanic origin, and so the only fossil-bearing rocks that can be dated radiometrically are volcanic ash layers, which may provide termini for the intervening sediments. Consequently, palaeontologists rely on stratigraphy to date fossils. Stratigraphy
7680-462: The relative ages of rock strata as determined by the early paleontologists and stratigraphers . Since the early years of the twentieth century, absolute dating methods, such as radiometric dating (including potassium/argon , argon/argon , uranium series , and, for very recent fossils, radiocarbon dating ) have been used to verify the relative ages obtained by fossils and to provide absolute ages for many fossils. Radiometric dating has shown that
7776-429: The sea and that they were still living when the strait of Gibraltar was cut through. In the mountains of Parma and Piacenza multitudes of shells and corals with holes may be seen still sticking to the rocks.... In 1666, Nicholas Steno examined a shark, and made the association of its teeth with the "tongue stones" of ancient Greco-Roman mythology, concluding that those were not in fact the tongues of venomous snakes, but
7872-423: The sea we see the oysters all together and also the shellfish and the cuttlefish and all the other shells which congregate together, found all together dead; and the solitary shells are found apart from one another as we see them every day on the sea-shores. And we find oysters together in very large families, among which some may be seen with their shells still joined together, indicating that they were left there by
7968-586: The skulls of the Cyclopes of Greek mythology , and are possibly the origin of that Greek myth. Their skulls appear to have a single eye-hole in the front, just like their modern elephant cousins, though in fact it's actually the opening for their trunk. In Norse mythology , echinoderm shells (the round five-part button left over from a sea urchin) were associated with the god Thor , not only being incorporated in thunderstones , representations of Thor's hammer and subsequent hammer-shaped crosses as Christianity
8064-410: The specialization of its genital appendage, with characteristics reminiscent of Eurypterus . In 1989, Victor P. Tollerton, Jr. described the family Adelophthalmidae along with many others, including Adelophthalmus , Parahughmilleria , Bassipterus and Unionopterus . This clade was based on the presence of spines in the second to fifth pair of appendages, a swimming leg of Adelophthalmus -type and
8160-428: The species H. ( N. ) phelpsae and suggested that this part of the body could have great phylogenetic importance in the future. Two years later, together with the American paleontologist Kenneth Edward Caster, he raised H. ( N. ) phelpsae to the generic level under the name Pittsfordipterus . They also described a new genus and species, Bassipterus virginicus . It differs essentially from other adelophthalmids by
8256-414: The stem of the name of the type genus[…]." In 2019, it was proposed that all ranks above genus should use the genus category as the nomenclatural type. This proposal was subsequently adopted for the rank of phylum. Fossil A fossil (from Classical Latin fossilis , lit. ' obtained by digging ' ) is any preserved remains, impression, or trace of any once-living thing from
8352-467: The sudden appearance of many groups (i.e. phyla ) in the oldest known Cambrian fossiliferous strata. Since Darwin's time, the fossil record has been extended to between 2.3 and 3.5 billion years. Most of these Precambrian fossils are microscopic bacteria or microfossils . However, macroscopic fossils are now known from the late Proterozoic. The Ediacara biota (also called Vendian biota) dating from 575 million years ago collectively constitutes
8448-451: The teeth of some long-extinct species of shark. Robert Hooke (1635–1703) included micrographs of fossils in his Micrographia and was among the first to observe fossil forams . His observations on fossils, which he stated to be the petrified remains of creatures some of which no longer existed, were published posthumously in 1705. William Smith (1769–1839) , an English canal engineer, observed that rocks of different ages (based on
8544-524: The world was once inundated in a great flood that buried living creatures in drying mud. In 1027, the Persian Avicenna explained fossils' stoniness in The Book of Healing : If what is said concerning the petrifaction of animals and plants is true, the cause of this (phenomenon) is a powerful mineralizing and petrifying virtue which arises in certain stony spots, or emanates suddenly from
8640-480: The world, provoking a decrease in number of the genus. A. sellardsi from the Artinskian (around 290-284 mya, Early Permian) epoch of Kansas , United States , was the last species of Adelophthalmus and therefore of all the suborder Eurypterina. The genus expanded the temporal range of the suborder by about 100 million years and turned its family to the longest lasting single family of eurypterids. Nevertheless,
8736-458: Was adopted, but also kept in houses to garner Thor's protection. These grew into the shepherd's crowns of English folklore, used for decoration and as good luck charms, placed by the doorway of homes and churches. In Suffolk , a different species was used as a good-luck charm by bakers, who referred to them as fairy loaves , associating them with the similarly shaped loaves of bread they baked. More scientific views of fossils emerged during
8832-534: Was described based on a single specimen found in the Ordovician -aged Wenchang Formation of Zhejiang , China , representing the oldest known record of the Adelophthalmidae, extending the stratigraphic record of the family some 10 million years older from the early Silurian into the late Ordovician. The eurypterids as a group peaked in diversity during the Silurian, of the approximately 250 valid species accounted for as of 2024, around 139 (≈56 %) were from
8928-446: Was one of the most diverse taxonomically eurypterid clades, with about 40 species described. The sister group of Adelophthalmoidea, Pterygotioidea, surpassed this amount with around 50 described species, becoming the most diverse superfamily to date. These sister-clades are the most derived in the Eurypterina and make up more than a third of all the species of eurypterids, with almost 100 species between both of them. The cladogram below
9024-408: Was real. Georges Cuvier came to believe that most if not all the animal fossils he examined were remains of extinct species. This led Cuvier to become an active proponent of the geological school of thought called catastrophism . Near the end of his 1796 paper on living and fossil elephants he said: All of these facts, consistent among themselves, and not opposed by any report, seem to me to prove
9120-532: Was the apparent lack of eyes, which gives name to Adelophthalmus (meaning "no obvious eyes") and the entire superfamily. This feature is now assumed to be due to a preservational artifact and that was not present in Adelophthalmus , nor in any other adelophthalmid. Since then, a total of 33 species have been described, some of which have been historically classified within other genera ( Anthraconectes , Glyptoscorpius , Lepidoderma and Polyzosternites , all now synonymous with Adelophthalmus ), making Adelophthalmus
9216-408: Was the largest arthropod ever discovered. The adelophthalmids were small swimming eurypterids with a parabolic (approximately U-shaped) carapace (the dorsal plate of the head, Unionopterus possibly representing an exception) and with intramarginal (occurring within the margin) eyes . The swimming leg (sixth limb ) was of Adelophthalmus -type, that is, with a seventh podomere (segments of
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