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109-449: Mixosauridae was an early group of ichthyosaurs , living between 247.2 and 235 million years ago, during the Triassic period. Fossils of mixosaurs have been found all over the world: China , Timor , Indonesia , Italy , Germany , Spitsbergen , Switzerland , Svalbard , Canada , Alaska , and Nevada . Mixosauridae was named by Georg Baur in 1887 as a family-level group to contain

218-514: A Konservat-Lagerstätte , meaning not only the quantity, but also the quality was exceptional. The skeletons were very complete and often preserved soft tissues, including tail and dorsal fins. Additionally, female individuals were discovered with embryos. In the early twentieth century, ichthyosaur research was dominated by the German paleontologist Friedrich von Huene , who wrote an extensive series of articles, taking advantage of an easy access to

327-446: A t e s {\displaystyle n.states} , c i occupies a range from 1 to ( n . s t a t e s − 1 ) / ( n . t a x a − ⌈ n . t a x a / n . s t a t e s ⌉ ) {\displaystyle (n.states-1)/(n.taxa-\lceil n.taxa/n.states\rceil )} . The retention index (RI)

436-443: A dorsal fin . Their heads were pointed, and the jaws often were equipped with conical teeth to catch smaller prey. Some species had larger, bladed teeth to attack large animals. The eyes were very large, for deep diving. The neck was short, and later species had a rather stiff trunk. These also had a more vertical tail fin, used for a powerful propulsive stroke. The vertebral column, made of simplified disc-like vertebrae, continued into

545-445: A metric to measure how consistent a candidate cladogram is with the data. Most cladogram algorithms use the mathematical techniques of optimization and minimization. In general, cladogram generation algorithms must be implemented as computer programs, although some algorithms can be performed manually when the data sets are modest (for example, just a few species and a couple of characteristics). Some algorithms are useful only when

654-467: A pre-Adamite believing that ichthyosaurs were monstrous creations by the devil: Memoirs of Ichthyosauri and Plesiosauri of 1834 and The Book of the Great Sea-Dragons of 1840. The first work was illustrated by mezzotints by John Samuelson Templeton. These publications also contained scientific descriptions and represented the first textbooks of the subject. In the summer of 1834, Hawkins, after

763-450: A "primitive" group of ichthyosaurs. In 1904, Boulenger considered Ichthyosauria as splittable into three divisions, with Mixosaurus an early member of the group leading to the wide-finned Ichthyosaurus . In 1908, Merriam remarked that it was difficult to reconstruct the interrelationships of ichthyosaurs with confidence. However, he considered that all well-known Triassic ichthyosaurs at the time were too specialized to have been ancestral to

872-541: A basal, or low, position in the diapsid tree. More analyses result in their being Neodiapsida , a derived diapsid subgroup. Since the 1980s, a close relationship was assumed between the Ichthyosauria and the Sauropterygia , another marine reptile group, within an overarching Euryapsida , with one such study in 1997 by John Merck showing them to be monophyletic archosauromorph euryapsids. This has been contested over

981-417: A better understanding of their anatomy. Owen had noticed that many fossils showed a downward bend in the rear tail. At first, he explained this as a post mortem effect, a tendon pulling the tail end downwards after death. However, after an article on the subject by Philip Grey Egerton , Owen considered the possibility that the oblique section could have supported the lower lobe of a tail fin. This hypothesis

1090-530: A certain branch of the evolutionary tree. This also allows one to clearly indicate all relationships between the several subgroups in a cladogram . In 1999, a node clade Ichthyopterygia was defined by Motani as the group consisting of the last common ancestor of Ichthyosaurus communis , Utatsusaurus hataii and Parvinatator wapitiensis ; and all its descendants. Within Motani's phylogeny, the Ichthyopterygia were

1199-537: A character in a phylogenetic analysis as they do not contribute anything to our understanding of relationships. However, homoplasy is often not evident from inspection of the character itself (as in DNA sequence, for example), and is then detected by its incongruence (unparsimonious distribution) on a most-parsimonious cladogram. Note that characters that are homoplastic may still contain phylogenetic signal . A well-known example of homoplasy due to convergent evolution would be

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1308-422: A dataset, the degree to which each character carries phylogenetic information, and the fashion in which additive characters are coded, rendering it unfit for purpose. c i occupies a range from 1 to 1/[ n.taxa /2] in binary characters with an even state distribution; its minimum value is larger when states are not evenly spread. In general, for a binary or non-binary character with n . s t

1417-538: A distinctive build compared to "ichthyosaurs proper" that Motani excluded them from the Ichthyosauria and placed them in a basal position in a larger clade , the Ichthyopterygia . However, this solution was not adopted by all researchers. The basal forms quickly gave rise to ichthyosaurs in the narrow sense sometime around the boundary between the Early Triassic and Middle Triassic ; the earliest Ichthyosauria in

1526-523: A dorsal fin, and short flippers containing many phalanges. The sister group of the Mixosauria were the more advanced Merriamosauria . By the Late Triassic , merriamosaurs consisted of both the large, classic Shastasauria and more advanced, "dolphin-like" Euichthyosauria . Experts disagree over whether these represent an evolutionary continuum, with the less specialised shastosaurs a paraphyletic grade that

1635-421: A giant lizard. In October 1805, a newspaper article reported the find of two additional skeletons, one discovered at Weston by Jacob Wilkinson , the other, at the same village, by Reverend Peter Hawker. In 1807, the last specimen was described by the latter's cousin, Joseph Hawker . This specimen thus gained some fame among geologists as 'Hawker's Crocodile'. In 1810, near Stratford-upon-Avon , an ichthyosaur jaw

1744-406: A large number of good specimens, mixosaurid anatomy is well understood. Mixosaurids show a variety of adaptations for life in the water, with their limbs modified into fins and their deep, streamlined bodies. Mixosaurids were not as dolphin -shaped as the later parvipelvians , but they were also not eel -shaped like the earliest ichthyopterygians. Mixosaurids are among the smaller ichthyosaurs, with

1853-457: A larger clade. The incongruence length difference test (ILD) is a measurement of how the combination of different datasets (e.g. morphological and molecular, plastid and nuclear genes) contributes to a longer tree. It is measured by first calculating the total tree length of each partition and summing them. Then replicates are made by making randomly assembled partitions consisting of the original partitions. The lengths are summed. A p value of 0.01

1962-705: A larger number of articles and also brought the group to the attention of the general public. The new method of cladistics provided a means to exactly calculate the relationships between groups of animals, and in 1999, Ryosuke Motani published the first extensive study on ichthyosaur phylogenetics . In 2003, McGowan and Motani published the first modern textbook on the Ichthyosauria and their closest relatives. Two jawbones of gigantic ichthyosaur were discovered in 2016 and 2020 in Lilstock and Somerset respectively, UK. Simple scaling would suggest that this ichthyosaur has an estimated total length of up to 26 meters (82 feet),

2071-475: A lost skeleton. Conybeare considered that Ichthyosaurus had priority relative to Proteosaurus . Although this is incorrect by modern standards, the latter name became a "forgotten" nomen oblitum . In 1821, De la Beche and Conybeare provided the first systematic description of ichthyosaurs, comparing them to another newly identified marine reptile group, the Plesiosauria . Much of this description reflected

2180-425: A mixosaurid, however, the very fragmentary nature of its remains make its relationships unclear, and it has also been proposed to be related to various other ichthyopterygians. Additionally, a specimen potentially belonging to the toretocnemid Qianichthyosaurus was initially misidentified as a species of Mixosaurus , M. guanlingensis . The number of mixosaurid genera is controversial. Traditionally, Mixosaurus

2289-523: A more derived member of Ichthyosauria than the mixosaurids. Moon also noted that the "intermediate grade" ichthyosaurs could be divided into two subgroups, with mixosaurids and Cymbospondylus part of the early grade, paraphyletic to the later grade which gave rise to the later ichthyosaurs. The relative positions of mixosaurids and Cymbospondylus remain unresolved. Cladogram following Ji and colleagues, 2016. Cymbospondylidae Mixosauridae Shastasauridae Euichthyosauria Cladogram following

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2398-433: A revived interest in the group, leading to an increased number of named ichthyosaurs from all continents, with over fifty genera known. Ichthyosaurian species varied from 1 to 26 metres (3 to 85 ft) in length. Ichthyosaurians resembled both modern fish and dolphins. Their limbs had been fully transformed into flippers, which sometimes contained a very large number of digits and phalanges . At least some species possessed

2507-566: A shallow ocean during the Triassic. Several of these are in the collection of the University of California Museum of Paleontology. After a slack during the middle of the century, with no new genera being named between the 1930s and the 1970s, the rate of discoveries picked up towards its end. Other specimens are embedded in the rock and visible at Berlin–Ichthyosaur State Park in Nye County . In 1977

2616-404: A shastasaurid. In 2008, Maisch and colleagues noted that toretocnemids shared multiple features with mixosaurids, and suggested that the two groups might be closely related, rather than the toretocnemids having branched off later. As they did not run an analysis to test this hypothesis, however, they considered it provisional. Maisch did not follow this hypothesis in his 2010 review, though he used

2725-473: A skeleton in 1819 at Whitby ; in his 1821 description, he expressed the hope that living specimens could still be found. Geologist Charles Lyell , to the contrary, assumed that the Earth was eternal so that in the course of time the ichthyosaur might likely reappear, a possibility lampooned in a famous caricature by De la Beche. Public awareness was increased by the works of the eccentric collector Thomas Hawkins ,

2834-520: A taxation by William Buckland and Gideon Mantell , sold his extensive collection, then the largest of its kind in the world, to the British Museum. However, curator Koenig quickly discovered that the fossils had been heavily restored with plaster, applied by an Italian artist from Lucca ; of the most attractive piece, an Ichthyosaurus specimen, almost the entire tail was fake. It turned out that Professor Buckland had been aware of this beforehand, and

2943-498: A total length of under 1 metre (3.3 ft) in the smallest species, making them among the smallest of ichthyosaurs. While typically around 2 metres (6.6 ft) long at maximum, fragmentary fossils suggest that some mixosaurids could have grown as long as 5 metres (16 ft), though the poor quality of preservation makes these larger sizes contentious. Mixosaurids are very specialized ichthyosaurs, and possess many distinctive features. Ichthyosaur See text Ichthyosauria

3052-513: A young girl, secured the torso of the same specimen. Their mother, Molly Anning, sold the combined piece to squire Henry Henley for £23. Henley lent the fossil to the London Museum of Natural History of William Bullock . When this museum was closed, the British Museum bought the fossil for a price of £47/5s; it still belongs to the collection of the independent Natural History Museum and has

3161-410: Is a character state that is shared by two or more taxa due to some cause other than common ancestry. The two main types of homoplasy are convergence (evolution of the "same" character in at least two distinct lineages) and reversion (the return to an ancestral character state). Characters that are obviously homoplastic, such as white fur in different lineages of Arctic mammals, should not be included as

3270-521: Is also sometimes treated as a separate genus, Barracudasauroides . Additionally, M. kuhnschnyderi was initially named as a separate genus, Sangiorgiosaurus , by Brinkmann in 1998, who sunk it into Mixosaurus later during the same year, an assignment agreed upon by other authors. While most researchers accept only Mixosaurus and Phalarodon as valid, in 2017, Moon cautioned that the standard concepts of Mixosaurus and Phalarodon may not be monophyletic . The following cladograms show two hypotheses for

3379-534: Is an order of large extinct marine reptiles sometimes referred to as "ichthyosaurs", although the term is also used for wider clades in which the order resides. Ichthyosaurians thrived during much of the Mesozoic era; based on fossil evidence, they first appeared around 250 million years ago ( Ma ) and at least one species survived until about 90 million years ago, into the Late Cretaceous . During

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3488-581: Is based on Motani (1999): Utatsusaurus [REDACTED] Parvinatator Chaohusaurus [REDACTED] Grippia [REDACTED] Cymbospondylus [REDACTED] Mixosauria [REDACTED] Shastasauria [REDACTED] Toretocnemus Californosaurus [REDACTED] Macgowania Cladogram The characteristics used to create a cladogram can be roughly categorized as either morphological (synapsid skull, warm blooded, notochord , unicellular, etc.) or molecular (DNA, RNA, or other genetic information). Prior to

3597-411: Is obtained for 100 replicates if 99 replicates have longer combined tree lengths. Some measures attempt to measure the amount of homoplasy in a dataset with reference to a tree, though it is not necessarily clear precisely what property these measures aim to quantify The consistency index (CI) measures the consistency of a tree to a set of data – a measure of the minimum amount of homoplasy implied by

3706-586: Is the use of genomic retrotransposon markers , which are thought to be less prone to the problem of reversion that plagues sequence data. They are also generally assumed to have a low incidence of homoplasies because it was once thought that their integration into the genome was entirely random; this seems at least sometimes not to be the case, however. Researchers must decide which character states are "ancestral" ( plesiomorphies ) and which are derived ( synapomorphies ), because only synapomorphic character states provide evidence of grouping. This determination

3815-526: Is usually done by comparison to the character states of one or more outgroups . States shared between the outgroup and some members of the in-group are symplesiomorphies; states that are present only in a subset of the in-group are synapomorphies. Note that character states unique to a single terminal (autapomorphies) do not provide evidence of grouping. The choice of an outgroup is a crucial step in cladistic analysis because different outgroups can produce trees with profoundly different topologies. A homoplasy

3924-618: The Carnian and Norian , Shastosauria reached huge sizes. Shonisaurus popularis , known from a number of specimens from the Carnian of Nevada, was 15 m (49 ft) long. Norian Shonisauridae are known from both sides of the Pacific. Himalayasaurus tibetensis and Tibetosaurus (probably a synonym ) have been found in Tibet . These large (10- to 15-m-long) ichthyosaurs have by some been placed into

4033-593: The Cenomanian-Turonian boundary approximately 90 million years ago. Scientists became aware of the existence of ichthyosaurians during the early 19th century, when the first complete skeletons were found in England. In 1834, the order Ichthyosauria was named. Later that century, many finely preserved ichthyosaurian fossils were discovered in Germany, including soft-tissue remains. Since the late 20th century, there has been

4142-424: The Early Triassic epoch , ichthyosaurs and other ichthyosauromorphs evolved from a group of unidentified land reptiles that returned to the sea, in a development similar to how the mammalian land-dwelling ancestors of modern-day dolphins and whales returned to the sea millions of years later, which they gradually came to resemble in a case of convergent evolution . Ichthyosaurians were particularly abundant in

4251-445: The Late Triassic and Early Jurassic periods, until they were replaced as the top aquatic predators by another marine reptilian group, the Plesiosauria , in the later Jurassic and Early Cretaceous , though previous views of ichthyosaur decline during this period are probably overstated. Ichthyosaurians diversity declined due to environmental volatility caused by climatic upheavals in the early Late Cretaceous, becoming extinct around

4360-653: The Society for Promoting Natural History as those of a crocodilian. In 1779, ichthyosaur bones were illustrated in John Walcott 's Descriptions and Figures of Petrifications . Towards the end of the eighteenth century, British fossil collections quickly increased in size. Those of the naturalists Ashton Lever and John Hunter were acquired in their totality by museums; later, it was established that they contained dozens of ichthyosaur bones and teeth. The bones had typically been labelled as belonging to fish, dolphins, or crocodiles;

4469-524: The 17-metre-long (56 ft) Triassic ichthyosaur Shonisaurus became the state fossil of Nevada. About half of the ichthyosaur genera determined to be valid were described after 1990. In 1992 Canadian paleontologist Elizabeth Nicholls uncovered the largest known specimen, a 23-metre-long (75 ft) Shastasaurus . The new finds have allowed a gradual improvement in knowledge about the anatomy and physiology of what had already been seen as rather advanced "Mesozoic dolphins". Christopher McGowan published

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4578-562: The Cretaceous indicate that ichthyosaur diversity in the Late Jurassic must have been underestimated. Traditionally, ichthyosaurs were seen as decreasing in diversity even further with the Cretaceous , though they had a worldwide distribution. All fossils from this period were referred to a single genus: Platypterygius . This last ichthyosaur genus was thought to have become extinct early in

4687-565: The Early Triassic. Since 1959, a second enigmatic group of ancient sea reptiles is known, the Hupehsuchia . Like the Ichthyopterygia, the Hupehsuchia have pointed snouts and show polydactyly , the possession of more than five fingers or toes. Their limbs more resemble those of land animals, making them appear as a transitional form between these and ichthyosaurs. Initially, this possibility

4796-649: The Early and Early-Middle ( Olenekian and Anisian ) Triassic strata of Canada , China , Japan , and Spitsbergen in Norway , being up to 246 million years old. These first forms included the genera Chaohusaurus , Grippia , and Utatsusaurus . Even older fossils show they were around 250 million years ago, just two million years after the Permian mass extinction. This early diversity suggests an even earlier origin, possibly late Permian. They more resembled finned lizards than

4905-557: The Jurassic-Cretaceous boundary including Acamptonectes , Sveltonectes , Caypullisaurus , and Maiaspondylus . In 2013, a Cretaceous basal thunnosaurian was revealed: Malawania . Indeed, likely a radiation during the Early Cretaceous occurred due to an increase of coastlines when the continents further broke up. The demise of the ichthyosaurs has been described as a two-step process. A first extinction event in

5014-489: The Late Triassic, ichthyosaurs attained the peak of their size and diversity. They occupied many ecological niches . Some were apex predators ; others were hunters of small prey. Several species perhaps specialised in suction feeding or were ram feeders ; also, durophagous forms are known. Towards the end of the Late Triassic, a decline of variability seems to have occurred. The giant species seemed to have disappeared at

5123-640: The Middle Jurassic. This might be a result of the poor fossil record in general of this epoch. The strata of the Late Jurassic seem to indicate that a further decrease in diversity had taken place. From the Middle Jurassic onwards, almost all ichthyosaurs belonged to the thunnosaurian clade Ophthalmosauridae . Represented by the 4 m-long (13 ft) Ophthalmosaurus and related genera, they were very similar in general build to Ichthyosaurus . The eyes of Ophthalmosaurus were huge, and these animals likely hunted in dim and deep water. However, new finds from

5232-579: The Welshman Edward Lhuyd in his Lithophylacii Brittannici Ichnographia of 1699. Lhuyd thought that they represented fish remains. In 1708, the Swiss naturalist Johann Jakob Scheuchzer described two ichthyosaur vertebrae assuming they belonged to a man drowned in the Universal Deluge . In 1766, an ichthyosaur jaw with teeth was found at Weston near Bath . In 1783, this piece was exhibited by

5341-587: The advent of DNA sequencing, cladistic analysis primarily used morphological data. Behavioral data (for animals) may also be used. As DNA sequencing has become cheaper and easier, molecular systematics has become a more and more popular way to infer phylogenetic hypotheses. Using a parsimony criterion is only one of several methods to infer a phylogeny from molecular data. Approaches such as maximum likelihood , which incorporate explicit models of sequence evolution, are non-Hennigian ways to evaluate sequence data. Another powerful method of reconstructing phylogenies

5450-526: The beginning of the Cenomanian eliminated two of the three ichthyosaur feeding guilds still present: the 'soft-prey specialists' and the 'generalists', leaving only an unspecialized apex predator group. The second extinction event took place during the Cenomanian-Turonian boundary event , a marine ' anoxic event ', after which just a single lineage survived, Platypterygius hercynicus , which then disappeared about 93 million years ago. Ichthyosaur extinction

5559-431: The character, "presence of wings". Although the wings of birds, bats , and insects serve the same function, each evolved independently, as can be seen by their anatomy . If a bird, bat, and a winged insect were scored for the character, "presence of wings", a homoplasy would be introduced into the dataset, and this could potentially confound the analysis, possibly resulting in a false hypothesis of relationships. Of course,

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5668-434: The characteristic data are molecular (DNA, RNA); other algorithms are useful only when the characteristic data are morphological. Other algorithms can be used when the characteristic data includes both molecular and morphological data. Algorithms for cladograms or other types of phylogenetic trees include least squares , neighbor-joining , parsimony , maximum likelihood , and Bayesian inference . Biologists sometimes use

5777-424: The creature to the fishes, as seemed to be confirmed by the flat shape of the vertebrae. At the same time, he considered it a transitional form between fishes and crocodiles, not in an evolutionary sense, but as regarded its place in the scala naturae , the "Chain of Being" hierarchically connecting all living creatures. In 1818, Home noted some coincidental similarities between the coracoid of ichthyosaurians and

5886-685: The dataset). The rescaled consistency index (RC) is obtained by multiplying the CI by the RI; in effect this stretches the range of the CI such that its minimum theoretically attainable value is rescaled to 0, with its maximum remaining at 1. The homoplasy index (HI) is simply 1 − CI. This measures the amount of homoplasy observed on a tree relative to the maximum amount of homoplasy that could theoretically be present – 1 − (observed homoplasy excess) / (maximum homoplasy excess). A value of 1 indicates no homoplasy; 0 represents as much homoplasy as there would be in

5995-427: The derived, "fish-shaped" ichthyosaurs. Utatsusaurus and Grippia were found to belong to the basal grade, but mixosaurids were instead recovered in the intermediate grade, together with the shastasaurids and Cymbospondylus . Thus, mixosaurids were found to be members of Ichthyosauria. The first of these analyses was done by Motani in 1999, who found mixosaurids to be more derived than Cymbospondylus but less so than

6104-421: The direction of Richard Owen. Among them were three models of an ichthyosaur. Although it was known that ichthyosaurs had been animals of the open seas, they were shown basking on the shore, a convention followed by many nineteenth century illustrations with the aim, as Conybeare once explained, of better exposing their build. This led to the misunderstanding that they really had an amphibious lifestyle. The pools in

6213-440: The early appearance of ichthyosaurs in the fossil record, and also their lack of clear affinities with other reptile groups, as anapsids were supposed to be little specialised. This hypothesis has become unpopular for being inherently vague because Anapsida is an unnatural, paraphyletic group. Modern exact quantitative cladistic analyses consistently indicate that ichthyosaurs are members of the clade Diapsida . Some studies showed

6322-589: The end of the Norian. Rhaetian (latest Triassic) ichthyosaurs are known from England, and these are very similar to those of the Early Jurassic . A possible explanation is an increased competition by sharks , Teleostei , and the first Plesiosauria . Like the dinosaurs, the ichthyosaurs and their contemporaries, the plesiosaurs, survived the Triassic–Jurassic extinction event , and quickly diversified again to fill

6431-620: The evolutionary relationships between different mixosaurid species. Cladogram following Jiang and colleagues, 2006. Mixosaurus panxianensis Mixosaurus cornalianus Mixosaurus kuhnschnyderi Phalarodon atavus Phalarodon fraasi Phalarodon callawayi Cladogram following the preferred tree of Moon, 2017. Barracudasauroides panxianensis Mixosaurus xindianensis Phalarodon fraasi Contectopalatus atavus Phalarodon callawayi Mixosaurus cornalianus Mixosaurus kuhnschnyderi In his 1887 description, Baur recognized mixosaurids as

6540-612: The fishes or dolphins to which the later, more familiar species were similar. Their bodies were elongated and they probably used an anguilliform locomotion, swimming by undulations of the entire trunk. Like land animals, their pectoral girdles and pelves were robustly built, and their vertebrae still possessed the usual interlocking processes to support the body against the force of gravity. However, they were already rather advanced in having limbs that had been completely transformed into flippers. They also were probably warm-blooded and viviparous . These very early "proto-ichthyosaurs" had such

6649-426: The genus Barracudasaurus was proposed, before the referred specimens were reassigned to M. panxianensis , among others. Grippia was once considered a junior synonym of Mixosaurus , however, restudy has revealed that the two genera are significantly different, and Grippia is now understood to instead be a basal ichthyopterygian, not a mixosaurid. The very poorly-known Tholodus has also been proposed to be

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6758-518: The genus Shonisaurus . The gigantic Shonisaurus sikanniensis (considered as a shastasaurus between 2011 and 2013) whose remains were found in the Pardonet Formation of British Columbia , has been estimated to be as much as 21 m (69 ft) in length. Ichthyotitan , found in Somerset , has been estimated to be as much as 26 m long—if correct, the largest marine reptile known to date. In

6867-410: The group, he redefined it as being all ichthyosaurs more closely related to Mixosaurus cornalianus than Ichthyosaurus communis for consistency. There are six species of mixosaurids widely accepted as valid: Mixosaurus cornalianus , Mixosaurus kuhnschnyderi , Mixosaurus panxianensis , Phalarodon atavus , Phalardon callawayi , and Phalarodon fraasi . An additional species, Mixosaurus luxiensis ,

6976-437: The insights of their friend, the anatomist Joseph Pentland . In 1835, the order Ichthyosauria was named by Henri Marie Ducrotay de Blainville . In 1840, Richard Owen named an order Ichthyopterygia as an alternative concept. The discovery of a hitherto unsuspected extinct group of large marine reptiles generated much publicity, capturing the imagination of both scientists and the public at large. People were fascinated by

7085-740: The inventory number NHMUK PV R1158 (formerly BMNH R.1158). It has been identified as a specimen of Temnodontosaurus platyodon . In 1814, the Annings' specimen was described by Professor Everard Home , in the first scientific publication dedicated to an ichthyosaur. Intrigued by the strange animal, Home tried to locate additional specimens in existing collections. In 1816, he described ichthyosaur fossils owned by William Buckland and James Johnson . In 1818, Home published data obtained by corresponding with naturalists all over Britain. In 1819, he wrote two articles about specimens found by Henry Thomas De la Beche and Thomas James Birch. A last publication of 1820

7194-419: The larger parent clade of a smaller stem clade Ichthyosauria that was defined as the group consisting of Ichthyosaurus communis and all species more closely related to Ichthyosaurus than to Grippia longirostris . Motani's concept of the Ichthyosauria was thus more limited than the traditional one that also contained basal forms, such as Grippia , Utatsusaurus , and Parvinatator . The following cladogram

7303-415: The largest known to date marine reptile. The fossils of this individual were dated to be 202 million-year-old. The origin of the ichthyosaurs is contentious. Until recently, clear transitional forms with land-dwelling vertebrate groups had not yet been found, the earliest known species of the ichthyosaur lineage being already fully aquatic. In 2014, a small basal ichthyosauriform from the upper Lower Triassic

7412-492: The late Permian or the earliest Triassic. However, establishing their position within the amniote evolutionary tree has proven difficult, due to their heavily derived morphology obscuring their ancestry. Several conflicting hypotheses have been posited on the subject. In the second half of the 20th century, ichthyosaurs were usually assumed to be of the Anapsida , seen as an early branch of "primitive" reptiles. This would explain

7521-545: The late Cretaceous, during the Cenomanian about 95 million years ago, much earlier than other large Mesozoic reptile groups that survived until the very end of the Cretaceous. Two major explanations have been proposed for this extinction including either chance or competition from other large marine predators such as plesiosaurs . The overspecialisation of ichthyosaurs may be a contributing factor to their extinction, possibly being unable to 'keep up' with fast teleost fish, which had become dominant at this time, against which

7630-410: The later latipinnates; often their features differed markedly or the mixosaurids were more specialized than their supposed descendants. Consequently, he named a new monotypic order for the mixosaurids, Mixosauroidea, and instead argued that the post-Triassic latipinnates evolved from the longipinnate line. Despite initially supporting the dichotomy, McGowan would go even further than Appleby in overturning

7739-453: The later species, pointing to the anatomy of the ribs in particular. Therefore, he proposed an early split between the Triassic ichthyosaurs and the post-Triassic ichthyosaurs. In the 1920s, von Huene proposed a classification scheme where ichthyosaurs were divided into two different groups, the latipinnates and longipinnates, which split from each other in the Triassic and both persisted into the Cretaceous. These divisions were based primarily on

7848-561: The latipinnate-longipinnate classification, considering that the differences separating the two groups were too ambiguous to be valid. The first cladogram of Ichthyopterygia was published by Mazin in 1981, in which mixosaurids were found to fall outside Ichthyosauria, though in a more derived position than Grippia . Based on these results, Mazin argued that heterodonty was the ancestral conidition in ichthyopterygians. Nicholls and colleagues in 1999 placed mixosaurids in Ichthyosauria, arguing based on tooth and shoulder girdle anatomy that they were

7957-440: The lower lobe of the tail fin. Ichthyosaurians were air-breathing, warm-blooded, and bore live young. Many, if not all, species had a layer of blubber for insulation. Like other ancient marine reptiles, such as those in the clades Mosasauria and Plesiosauria , the genera in Ichthyosauria are not part of the clade Dinosauria . The first known illustrations of ichthyosaur bones, vertebrae, and limb elements were published by

8066-517: The many specimens found in his country. The amount of anatomical data was hereby vastly increased. Von Huene also travelled widely abroad, describing many fossils from locations outside of Europe. During the 20th century, North America became an important source of new fossils. In 1905, the Saurian Expedition led by John Campbell Merriam and financed by Annie Montague Alexander , found twenty-five specimens in central Nevada , which were under

8175-599: The museum was forced to reach a settlement with Hawkins, and gave the fake parts a lighter colour to differentiate them from the authentic skeletal elements. Ichthyosaurs became even more popular in 1854 by the rebuilding at Sydenham Hill of the Crystal Palace , originally erected at the world exhibition of 1851 . In the surrounding park , life-sized, painted, concrete statues of extinct animals were placed, which were designed by Benjamin Waterhouse Hawkins under

8284-410: The name Mixosauria for a group containing mixosaurids and Wimanius . Further phylogenetic analyses were conducted since, often drawing from the analysis of Motani and that of Maisch and Matzke. In 2016, Ji and colleagues found mixosaurids to be more derived than cymbospondylids based on their analysis. However, in 2017, Moon recovered the mixosaurids as more basal. Additionally, Wimanius was found to be

8393-431: The new genus, Mixosaurus that he named in the same publication. The name Mixosauria has been used for a larger group containing Mixosauridae, but also as an equivalent term for Mixosauridae, resulting in Mixosauria being regarded as a junior synonym of Mixosauridae. Motani defined the clade Mixosauria as comprising all descendants of the last common ancestor of Mixosaurus cornalianus and M. nordenskioeldii , which

8502-525: The niches previously occupied by ichthyosaurs, although they had coexisted for 19 million years. The extinction was most likely the result of ecological change and volatility that caused changes in migration, food availability, and birthing grounds. This part of the Cretaceous was one in which many other marine extinctions occurred, including those of some types of microplankton , ammonites , belemnites , and reef-building bivalves . In modern phylogeny , clades are defined that contain all species forming

8611-705: The only reason a homoplasy is recognizable in the first place is because there are other characters that imply a pattern of relationships that reveal its homoplastic distribution. A cladogram is the diagrammatic result of an analysis, which groups taxa on the basis of synapomorphies alone. There are many other phylogenetic algorithms that treat data somewhat differently, and result in phylogenetic trees that look like cladograms but are not cladograms. For example, phenetic algorithms, such as UPGMA and Neighbor-Joining, group by overall similarity, and treat both synapomorphies and symplesiomorphies as evidence of grouping, The resulting diagrams are phenograms, not cladograms, Similarly,

8720-423: The park were at the time subjected to tidal changes , so that fluctuations in the water level at intervals submerged the ichthyosaur statues, adding a certain realism. Remarkably, internal skeletal structures, such as the scleral rings and the many phalanges of the flippers, were shown at the outside. During the nineteenth century, the number of described ichthyosaur genera gradually increased. New finds allowed for

8829-434: The preferred tree of Moon, 2017. Parvinatator wapitiensis Thalattoarchon saurophagis Xinminosaurus catactes Mixosauridae Pessopteryx nisseri Cymbospondylus spp. Phantomosaurus neubigi Besanosaurus leptorhynchus Californosaurus perrini Phalarodon major Qianichthyosaurus xingyiensis Wimanius odontopalatus Shastasauridae Euichthyosauria Thanks to

8938-436: The program settles on a local minimum rather than the desired global minimum. To help solve this problem, many cladogram algorithms use a simulated annealing approach to increase the likelihood that the selected cladogram is the optimal one. The basal position is the direction of the base (or root) of a rooted phylogenetic tree or cladogram. A basal clade is the earliest clade (of a given taxonomic rank[a]) to branch within

9047-405: The results of model-based methods (Maximum Likelihood or Bayesian approaches) that take into account both branching order and "branch length," count both synapomorphies and autapomorphies as evidence for or against grouping, The diagrams resulting from those sorts of analysis are not cladograms, either. There are several algorithms available to identify the "best" cladogram. Most algorithms use

9156-404: The sense Motani gave to the concept, appear about 245 million years ago. These later diversified into a variety of forms, including the still sea serpent -like Cymbospondylus , a problematic form which reached ten metres in length, and smaller, more typical forms like Mixosaurus . The Mixosauria were already very fish-like with a pointed skull, a shorter trunk, a more vertical tail fin,

9265-406: The sister taxon of a group composed of Utatsusaurus , Grippia , and Omphalosaurus . These two groups were placed in a suborder that was named Mixosauria. In 1999 and 2000, multiple major phylogenetic analyses of Ichthyopterygia were published. These studies all agreed upon a general framework, with three nested groups: the early "basal grade", followed by an intermediate grade, followed in turn by

9374-485: The sit-and-wait ambush strategies of the mosasauroids proved superior. This model thus emphasised evolutionary stagnation, the only innovation shown by Platypterygius being its ten fingers. Recent studies, however, show that ichthyosaurs were actually far more diverse in the Cretaceous than previously thought. Fragments previously referred to "Platypterygius" have been found to be from several different taxa. As of 2012, at least eight lineages are known to have spanned

9483-468: The sternum of the platypus . This induced him to emphasize its status as a transitional form, combining, like the platypus, traits of several larger groups. In 1819, he considered it a form between newts , like the olm , and lizards; he then gave a formal generic name: Proteo-Saurus . However, in 1817, Karl Dietrich Eberhard Koenig had already referred to the animal as Ichthyosaurus , "fish saurian" from Greek ἰχθύς , ichthys , "fish". This name at

9592-448: The strange build of the animals, especially the large scleral rings in the eye sockets, of which it was sometimes erroneously assumed these would have been visible on the living animal. Their bizarre form induced a feeling of alienation , allowing people to realise the immense span of time passed since the era in which the ichthyosaur swam the oceans. Not all were convinced that ichthyosaurs had gone extinct: Reverend George Young found

9701-571: The structure of the forelimb, though McGowan argued in 1972 that the two groups could be differentiated by skull proportions as well. Under this classification scheme, mixosaurids were classified as early latipinnates, with von Huene believing them to be the direct ancestors of Ichthyosaurus . The classification of ichthyosaurs into latipinnates and longipinnates persisted for many decades. However, in 1979, Appleby reassessed mixosaurid anatomy, and found it to be very specialized. These specializations did not suggest to him that mixosaurids were ancestral to

9810-402: The teeth had been seen as those of sea lions. The demand by collectors led to more intense commercial digging activities. In the early nineteenth century, this resulted in the discovery of more complete skeletons. In 1804, Edward Donovan at St Donats uncovered a four-metre-long (13 ft) ichthyosaur specimen containing a jaw, vertebrae, ribs, and a shoulder girdle. It was considered to be

9919-460: The term parsimony for a specific kind of cladogram generation algorithm and sometimes as an umbrella term for all phylogenetic algorithms. Algorithms that perform optimization tasks (such as building cladograms) can be sensitive to the order in which the input data (the list of species and their characteristics) is presented. Inputting the data in various orders can cause the same algorithm to produce different "best" cladograms. In these situations,

10028-407: The time was an invalid nomen nudum and was only published by Koenig in 1825, but was adopted by De la Beche in 1819 in a lecture where he named three Ichthyosaurus species. This text would only be published in 1822, just after De la Beche's friend William Conybeare published a description of these species, together with a fourth one. The type species was Ichthyosaurus communis , based on

10137-406: The tree. It is calculated by counting the minimum number of changes in a dataset and dividing it by the actual number of changes needed for the cladogram. A consistency index can also be calculated for an individual character i , denoted c i . Besides reflecting the amount of homoplasy, the metric also reflects the number of taxa in the dataset, (to a lesser extent) the number of characters in

10246-429: The true shastasaurs. The phylogenetic analysis run by Sander and Maisch and Matzke the next year instead found mixosaurids to be more basal than Cymbospondylus . Additionally, Maisch and Matzke argued that the poorly-known Wimanius was the sister taxon of Mixosauridae. Due to its fragmentary nature, however, both Motani and Sander considered the relationships of this genus provisional, with Sander instead considering it

10355-423: The user should input the data in various orders and compare the results. Using different algorithms on a single data set can sometimes yield different "best" cladograms, because each algorithm may have a unique definition of what is "best". Because of the astronomical number of possible cladograms, algorithms cannot guarantee that the solution is the overall best solution. A nonoptimal cladogram will be selected if

10464-937: The vacant ecological niches of the early Jurassic. During the Early Jurassic, the ichthyosaurs still showed a large variety of species, ranging from 1 to 10 m (3 to 33 ft) in length. Many well-preserved specimens from England and Germany date to this time and well-known genera include Eurhinosaurus , Ichthyosaurus , Leptonectes , Stenopterygius , and the large predator Temnodontosaurus . More basal parvipelvians like Suevoleviathan were also present. The general morphological variability had been strongly reduced, however. Giant forms, suction feeders and durophagous species were absent. Many of these genera possessed streamlined, dolphin-like thunniform bodies, although more basal clades like Eurhinosauria , which include Leptonectes and Eurhinosaurus , had longer bodies and long snouts. Few ichthyosaur fossils are known from

10573-517: The years, with the Euryapsida being seen as an unnatural polyphyletic assemblage of reptiles that happen to share some adaptations to a swimming lifestyle. However, more recent studies have shown further support for a monophyletic clade between Ichthyosauromorpha , Sauropterygia, and Thalattosauria as a massive marine clade of aquatic archosauromorphs originating in the Late Permian and diversifying in

10682-641: Was announced, a small species with a short snout, large flippers, and a stiff trunk. Its lifestyle might have been amphibious. Motani found it to be more basal than the Ichthyopterygia and named an encompassing clade Ichthyosauriformes . The latter group was combined with the Hupesuchia into the Ichthyosauromorpha . The ichthyosauromorphs were found to be diapsids. The proposed relationships are shown by this cladogram: Hupehsuchia Cartorhynchus Ichthyopterygia The earliest ichthyosaurs are known from

10791-450: Was applied to its equivalent group Mixosauridae by Maisch and Matzke in 2000. This definition was emended by Ji and colleagues in 2016 by replacing Mixosaurus nordenskioeldii with Phalarodon fraasi , as the former had since been determined to not be diagnostic. The definition was changed again in 2017, this time by Moon. As the evolutionary relationships his analyses found would have resulted in many traditional mixosaurids falling outside of

10900-485: Was confirmed by new finds from Germany . In the Posidonia Shale at Holzmaden , dating from the early Jurassic , already in the early nineteenth century, the first ichthyosaur skeletons had been found. During the latter half of the century, the rate of discovery increased to a few hundred each year. Ultimately, over four thousand were uncovered, forming the bulk of ichthyosaur specimens displayed. The sites were also

11009-403: Was dedicated to a discovery by Birch at Lyme Regis. The series of articles by Home covered the entire anatomy of ichthyosaurs, but highlighted details only; a systematic description was still lacking. Home was very uncertain how the animal should be classified. Though most individual skeletal elements looked very reptilian, the anatomy as a whole resembled that of a fish, so he initially assigned

11118-479: Was described that had been discovered in China with characteristics suggesting an amphibious lifestyle. In 1937, Friedrich von Huene even hypothesised that ichthyosaurs were not reptiles, but instead represented a lineage separately developed from amphibians. Today, this notion has been discarded and a consensus exists that ichthyosaurs are amniote tetrapods , having descended from terrestrial egg-laying amniotes during

11227-482: Was evolving into the more advanced forms, or whether the two were separate clades that evolved from a common ancestor earlier on. Euichthyosauria possessed more narrow front flippers, with a reduced number of fingers. Basal euichthyosaurs were Californosaurus and Toretocnemus . A more derived branch were the Parvipelvia , with a reduced pelvis, basal forms of which are Hudsonelpidia and Macgowania . During

11336-509: Was found that was combined with plesiosaur bones to obtain a more complete specimen, indicating that the distinctive nature of ichthyosaurs was not yet understood, awaiting the discovery of far better fossils. In 1811, in Lyme Regis , along the Jurassic Coast of Dorset , the first complete ichthyosaur skull was found by Joseph Anning , the brother of Mary Anning , who in 1812 while still

11445-433: Was generally regarded as the only valid genus of mixosaurids, and this system of classification continued to be used into the 21st century. However, Phalarodon was also sometimes treated as a separate genus, a position which later became widely accepted. In 1998, Maisch and Matzke named a new genus, Contectopalatus , for P. atavus , and later maintained its distinctiveness from Mixosaurus and Phalarodon . M. panxianensis

11554-403: Was largely neglected because the Hupehsuchia have a fundamentally different form of propulsion, with an extremely stiffened trunk. The similarities were explained as a case of convergent evolution. Furthermore, the descent of the Hupehsuchia is no less obscure, meaning a possible close relationship would hardly clarify the general evolutionary position of the ichthyosaurs. In 2014, Cartorhynchus

11663-404: Was named in 2024. Mixosaurus xindianensis is sometimes also considered valid, but has also been treated as a species inquirenda . Other mixosaurid species have been proposed in the past but subsequently had their validity questioned or rejected. These include Mixosaurus nordenskioeldii , of which Phalarodon fraasi was traditionally seen a junior synonym, and Mixosaurus maotianensis , for which

11772-399: Was proposed as an improvement of the CI "for certain applications" This metric also purports to measure of the amount of homoplasy, but also measures how well synapomorphies explain the tree. It is calculated taking the (maximum number of changes on a tree minus the number of changes on the tree), and dividing by the (maximum number of changes on the tree minus the minimum number of changes in

11881-533: Was thus a pair of abrupt events rather than a long decline, probably related to the environmental upheavals and climatic changes in the Cenomanian and Turonian . Competition with early mosasaurs is unlikely to have been a contributing factor since large mosasaurs did not appear until 3 million years after the ichthyosaur extinction, filling the resulting ecological void left by the extinction of ichthyosaurs. Plesiosaurian polycoltylids perhaps also filled some of

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