Ichthyosauria

Ichthyosauria Temporal range: Ma PreꞒ Ꞓ O S D C P T J K Pg N
Skeleton of Ichthyosaurus somersetensis
Life restoration of Ophthalmosaurus
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Reptilia
Clade:	† Eoichthyosauria
Order:	†Ichthyosauria Blainville, 1835
Subgroups
See text

Ichthyosauria (Ancient Greek for "fish lizard" –

Ichthyosaurian species varied from 1 to 20 metres (3 to 66 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 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 the lower lobe of the tail fin. Ichthyosaurians were air-breathing, warm-blooded, and bore live young. They may have had a layer of blubber for insulation.

History of discoveries

Early finds

The first known illustrations of ichthyosaur bones, vertebrae, and limb elements were published by the Welshman Edward Lhuyd in his Lithophylacii Brittannici Ichnographia of 1699. Lhuyd thought that they represented fish remains.^[3] In 1708, the Swiss naturalist Johann Jakob Scheuchzer described two ichthyosaur vertebrae assuming they belonged to a man drowned in the Universal Deluge.^[4] In 1766, an ichthyosaur jaw with teeth was found at Weston near Bath. In 1783, this piece was exhibited by 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.^[5] 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; the teeth had been seen as those of sea lions.^[6]

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 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.^[7] This specimen thus gained some fame among geologists as 'Hawker's Crocodile'. In 1810, near Stratford-upon-Avon, an ichthyosaur jaw 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.

The first complete skeletons

In 1811, in

In 1814, the Annings' specimen was described by Professor

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 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

.

In 1835, the order Ichthyosauria was named by Henri Marie Ducrotay de Blainville.^[17] In 1840, Richard Owen named an order Ichthyopterygia as an alternative concept.^[18]

Popularisation during the 19th century

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 the strange build of the animals, especially the large

scleral rings in the eye sockets,^[19] 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.^[20] Not all were convinced that ichthyosaurs had gone extinct: Reverend George Young found a skeleton in 1819 at Whitby; in his 1821 description, he expressed the hope that living specimens could still be found.^[21] 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, a pre-Adamite believing that ichthyosaurs were monstrous creations by the devil: Memoirs of Ichthyosauri and Plesiosauri of 1834^[22] and The Book of the Great Sea-Dragons of 1840.^[23] 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 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 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.^[24]

Ichthyosaurs became even more popular in 1854 by the rebuilding at

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 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 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.

Later 19th-century finds

During the nineteenth century, the number of described ichthyosaur genera gradually increased. New finds allowed for 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

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 the many specimens found in his country. The amount of anatomical data was hereby vastly increased.^[31] 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 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 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 a larger number of articles and also brought the group to the attention of the general public.^[32] 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.^[33] In 2003, McGowan and Motani published the first modern textbook on the Ichthyosauria and their closest relatives.^[34]

Evolutionary history

Origin

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 was described that had been discovered in China with characteristics suggesting an amphibious lifestyle.

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 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 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.^[45]

The proposed relationships are shown by this cladogram:

Early Ichthyopterygia

The earliest ichthyosaurs are known from the Early and Early-Middle (

These very early "proto-ichthyosaurs" had such 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.^[40] However, this solution was not adopted by all researchers.

Later Triassic forms

The basal forms quickly gave rise to ichthyosaurs in the narrow sense sometime around the boundary between the

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

, which include Leptonectes and Eurhinosaurus, had longer bodies and long snouts.

Few ichthyosaur fossils are known from 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.^[52]

However, new finds from the Cretaceous indicate that ichthyosaur diversity in the Late Jurassic must have been underestimated.

Cretaceous

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 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 the sit-and-wait ambush strategies of the mosasauroids proved superior.^[53] This model thus emphasised evolutionary stagnation, the only innovation shown by Platypterygius being its ten fingers.^[54]

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 the Jurassic-Cretaceous boundary including Acamptonectes, Sveltonectes, Caypullisaurus, and Maiaspondylus.^[55] In 2013, a Cretaceous basal thunnosaurian was revealed: Malawania.^[56] Indeed, likely a radiation during the Early Cretaceous occurred due to an increase of coastlines when the continents further broke up.^[57]

The demise of the ichthyosaurs has been described as a two-step process.

The following cladogram is based on Motani (1999):^[33]

An alternative terminology was proposed by Maisch & Matzke in 2000, trying to preserve the traditional, more encompassing content of the concept Ichthyosauria. They defined a node clade Ichthyosauria as the group consisting of the last common ancestor of Thaisaurus chonglakmanii, Utatsusaurus hataii, and Ophthalmosaurus icenicus, and all its descendants.^[61] Ichthyosauria sensu Motani might materially be identical to a clade that Maisch & Matzke in 2000 called Hueneosauria, depending on the actual relationships.

Cladogram based on Maisch and Matzke (2000)^[61] and Maisch and Matzke (2003)^[62] with clade names following Maisch (2010):^[37]

Description

Size

Ichthyosaurs averaged about 2–4 m (6.6–13.1 ft) in length. Some individual specimens were as short as 0.3 m (1 ft); some species were much larger: the Triassic

This sea-going reptile with terrestrial ancestors converged so strongly on fishes that it actually evolved a dorsal fin and tail in just the right place and with just the right hydrological design. These structures are all the more remarkable because they evolved from nothing—the ancestral terrestrial reptile had no hump on its back or blade on its tail to serve as a precursor.[68]

Diagnostic traits

Derived ichthyosaurs in the narrow sense, as defined by Motani in 1999, differ from their closest basal ichthyopterygian relatives in certain traits. Motani listed a number of these. The external nostril is located on the side of the skull, and is hardly visible from above. The upper rim of the eye socket consists of a bone bar formed by the prefrontal and the postfrontal bones. The postorbital in side view is excluded from the supratemporal fenestra. The opening for the parietal eye is located on the border of the parietal and the frontal bone. The lateral wing of the pterygoid is incompletely and variably ossified. The ulna lacks the part behind the original shaft axis. The rear dorsal vertebrae are disc-shaped.^[33]

Skeleton

Skull

Basal Ichthyopterygia already had elongated, triangular skulls. With ichthyosaurs in the narrow sense, their snouts became very pointy. The snout is formed by the

Teeth

Ichthyosaur teeth are typically conical. Fish-eating species have long and slender tooth crowns that are slightly recurved. Forms specialised in catching larger prey have shorter, broader, and straighter teeth; sometimes, cutting edges are present.

dentine shows prominent vertical wrinkles. Durophagous forms have teeth with deep vertical grooves and wrinkles in the enamel.^[69]

Postcrania

Vertebral column

Basal Ichthyopterygia, like their land-dwelling ancestors, still had

Amniota and makes discerning ichthyosaur vertebrae from those of other marine reptiles easy. The only process that kept its function was the spine at the top, serving as an attachment for the dorsal muscles. However, even the spine became a simple structure. The neural arch, of which it was an outgrowth, typically no longer fused to the vertebral centre.^[69]

The neck is short, and derived species show a reduction in the number of

cervical vertebrae. The short neck positions the skull close to the trunk, usually in a slight oblique elevation to it. Derived species usually also have a reduced number of dorsals, the total of presacral vertebrae totalling about forty to fifty. The vertebral column is little differentiated. Basal Ichthyopterygia still have two sacral vertebrae, but these are not fused. Early Triassic forms have a transversely flattened tail base with high spines for an undulating tail movement. Derived forms have a shorter tail with the characteristic kink at the end; a section of wedge-shaped vertebrae, itself supporting the fleshy upper tail fin lobe, forced the tail end into the lower fin lobe.^[69]

As derived species no longer have transversal processes on their vertebrae—again a condition unique in the Amniota—the parapophyseal and diapophysael rib joints have been reduced to flat facets, at least one of which is located on the vertebral body. The number of facets can be one or two; their profile can be circular or oval. Their shape often differs according to the position of the vertebra within the column. The presence of two facets per side does not imply that the rib itself is double-headed: often, even in that case, it has a single head. The ribs typically are very thin and possess a longitudinal groove on both the inner and the outer sides. The lower side of the chest is formed by

plastron. Usually two gastralia are present per dorsal rib.^[69]

Appendicular skeleton

The

Breast bones or sterna are absent.^[69]

Basal forms have a forelimb that is still functionally differentiated, in some details resembling the arm of their land-dwelling forebears; the

metacarpals.^[69]

A strongly derived condition show the

hyperphalangy, also known from the Plesiosauria, mosasaurs, and the Cetacea. The high number of elements allows the flipper to be shaped as a hydrofoil. When a high number of fingers is present, their identity is difficult to determine. It is usually assumed that fingers were added at both the front and at the rear, perhaps to a core of four original fingers. If fingers are added, often the number of metacarpals and carpals is also increased; sometimes even an extra lower arm element is present. Earlier, ichthyosaurs were commonly divided into "longipinnate" and "latipinnate" forms, according to the long or wide shape of the front flippers, but recent research has shown that these are not natural groups; ichthyosaur clades often contain species with and without elongated forelimbs.^[69]

The ichthyosaur

pubic bone, are not fused and often do not even touch each other. Also, the left and right pelvic sides no longer touch; only basal forms still have sacral ribs connecting the ilia to the vertebral column. The hip joint is not closed on the inside. The pubic bone typically does not connect to the ischium behind it; the space in between is by some workers identified as the fenestra thyreoidea;^[69] other researchers deny that the term is applicable given the general loose structure of the pelvis.^[37] Some later species have a connected pubic bone and ischium, but in this case, the femoral head no longer articulates with the hip joint. Triassic species have plate-like pubic bones and ischia; in later species these elements become elongated with a narrow shaft and can form a single rod.^[69]

Typically, the hindlimbs are shorter than the forelimbs, possessing a lesser number of elements. Often, the rear flipper is only half the length of the front flipper. The thighbone is short and broad, often with a narrow waist and an expanded lower end. The tibia, fibula and

metatarsals are merged into a mosaic of bone discs supporting the hydrofoil. Three to six toes are present. The toe phalanges also show hyperphalangy; exceptionally, Ophthalmosaurus shows a reduced number of phalanges.^[69]

Soft tissue

The earliest reconstructions of ichthyosaurs all omitted dorsal fins and caudal (tail) flukes, which were not supported by any hard skeletal structure, so were not preserved in many fossils. Only the lower tail lobe is supported by the vertebral column. In the early 1880s, the first body outlines of ichthyosaurs were discovered. In 1881, Richard Owen reported ichthyosaur body outlines showing tail flukes from Lower Jurassic rocks in Barrow-upon-Soar, England.^[75] Other well-preserved specimens have since shown that in some more primitive ichthyosaurs, like a specimen of Chaohusaurus geishanensis, the tail fluke was weakly developed and only had a dorsal tail lobe, making the tail more paddle-like.^[76] Over the years, the visibility of the tail lobe has faded away in this specimen.^[77]

The presence of dorsal fins in ichthyosaurs has been controversial. Finely preserved specimens from the Holzmaden Lagerstätten in Germany found in the late 19th century revealed additional traces, usually preserved in black, of the outline of the entire body, including the first evidence of dorsal fins in ichthyosaurs. Unique conditions permitted the preservation of these outlines, which probably consist of bacterial mats, not the remains of the original tissues themselves.^[78] In 1987, David Martill argued that, given the indirect method of conservation by bacteria, these outlines were unlikely to have been reliably preserved in any fine detail. He concluded that no authentic dorsal fins had been discovered. After displaced skins flaps from the body would have initially been misinterpreted as fins, fossil preparators later came to expect such fins to be present, and would have identified any discolouration in the appropriate position as a dorsal fin or even have falsified such structures. The lack of a dorsal fin would also explain why ichthyosaurs, contrary to porpoises, retained hind flippers, as these were needed for stability.^[79] Other researchers noted that, while the outlines might have been sharpened and smoothed by preparators because fossil bacterial mats usually have indistinct edges, many of the preserved dorsal fins were probably authentic and at least somewhat close to the true body outline. At least one specimen, R158 (in the collections of the Paleontologiska Museet, Uppsala University), shows the expected faded edges of a bacterial mat, so it has not been altered by preparators, yet still preserves a generally tuna-like body outline including a dorsal fin.^[77] In 1993, Martill admitted that at least some dorsal fin specimens are authentic.^[78]

The fossil specimens that preserved dorsal fins also showed that the flippers were pointy and often far wider than the underlying bones would suggest. The fins were supported by fibrous tissue. In some specimens, four layers of collagen are visible, the fibres of the covering layers crossing those of the collagen below.^[80]

In 2017, from the German Posidonia Shale the discovery was reported of 182.7-million-year-old vertebrae of Stenopterygius in a carbonate nodule, still containing collagen fibers, cholesterol, platelets, and red and white blood cells. The structures would not have been petrified, but represent the original organic tissues of which the biomolecules could be identified. The exceptional preservation was explained by the protective environment offered by the nodule. The red blood cells found, were one-fourth to one fifth the size of those of modern mammals. This would have been an adaptation for an improved oxygen absorption, also in view of the low oxygen levels during the Toarcian. The cholesterol had a high-carbon-13 isotope component which might indicate a higher position in the food chain and a diet of fish and cephalopods.^[81]

In 2018, evidence of blubber was discovered with Stenopterygius.^[82]

Skin and colouration

Typically, fossils that preserve it suggest that the skin of ichthyosaurs was smooth and elastic, lacking scales.

Solnhofen Plattenkalk, rocks which were capable of preserving even the finest detail. Minuscule scales seemed to be visible in this specimen.^[84]

The colouration of ichthyosaurs is difficult to determine. In 1956,

Mary Whitear reported finding melanocytes, pigment cells in which reddish-brown pigment granules would still be present, in a skin specimen of a British fossil, R 509.^[85] Ichthyosaurs are traditionally assumed to have employed countershading (dark on top, light at the bottom) like sharks, penguins, and other modern animals, serving as camouflage during hunting.^[73] This was contradicted in 2014 by the discovery of melanosomes, black melanin-bearing structures, in the skin of ichthyosaur specimen YORYM 1993.338 by Johan Lindgren of Lund University. It was concluded that ichthyosaurs were likely uniformly dark coloured for thermoregulation and to camouflage them in deep water while hunting. This is in contrast to mosasaurids and prehistoric leatherback turtles, which were found to be countershaded.^[86][87] However, a 2015 study doubted Lindgren and colleagues' interpretation. This study noted that a basal layer of melanosomes in the skin is ubiquitous in reptile coloration, but does not necessarily correspond to a dark appearance. Other chromatophore structures (such as iridiophores, xanthophores, and erythrophores) affect coloration in extant reptiles but are rarely preserved or identified in fossils. Thus, due to the unknown presence of these chromatophores, YORYM 1993.338, could have been countershaded, green, or various other colors or patterns.^[88]

In 2018, Lindgren and his colleagues also supported that ichthyosaurs would have been countershaded, on the basis of distributional variation of melanophores that contain eumelanin found on the specimen of Stenopterygius.[82]

Gastroliths

faeces, are very common, though, already being sold by Mary Anning

.

Paleobiology

Ecology

Apart from the obvious similarities to fish, ichthyosaurs also shared parallel developmental features with dolphins,

lamnid sharks, and tuna. This gave them a broadly similar appearance, possibly implied similar activity levels (including thermoregulation), and presumably placed them broadly in a similar ecological niche. Ichthyosaurs were not primarily coastal animals; they also inhabited the open ocean. They have been found in all Mesozoic oceans. This is even true of the earliest Ichthyopterygia, making identification of a certain area as their place of origin impossible.^[90]

Feeding

ammonoids

Ichthyosaurs were carnivorous; they ranged so widely in size, and survived for so long, that they are likely to have had a wide range of prey. Species with pointed snouts were adapted to grab smaller animals. McGowan speculated that forms with protruding upper jaws, in the Eurhinosauria, would have used their pointy snouts to slash prey, as has been assumed for

macropredator, capable of killing prey its own size,^[96] and Himalayasaurus and several species of Temnodontosaurus also shared adaptations for killing very large prey.^[97] These food preferences have been confirmed by coproliths which indeed contain the remains of fishes and cephalopods. Another confirmation is provided by fossilised stomach contents. Buckland in 1835 described the presence in a specimen of a large mass of partly digested fishes, recognisable by their scales.^[98] Subsequent research in 1968 determined that these belonged to the fish genus Pholidophorus, but also that cephalopod beaks and sucker hooks were present. Such hard food particles apparently were retained by the stomach and regularly regurgitated.^[99] Carcasses of drowned animals were eaten as well: in 2003 a specimen of Platypterygius longmani was reported having, besides fishes and a turtle, the bones of a land bird in its stomach.^[100]

Some early ichthyosaurs were

ram feeders, gathering food by constantly swimming forwards with a wide-open mouth.^[102]

Typical ichthyosaurs had very large eyes, protected within a

electro-sensory organs might have been present.^[104]

Ichthyosaurs themselves served as food for other animals. During the Triassic their

Plesiosauria and Thalattosuchia. This is again confirmed by stomach contents: in 2009 e.g., a plesiosaur specimen was reported with an ichthyosaur embryo in its gut.^[106]

Locomotion

In ichthyosaurs, the main propulsion was provided by a lateral movement of the body. Early forms employed an

thunniform

movement, in which the last third of the body, respectively, the tail end, is flexed only. The trunk in such species is rather stiff.

The tail was bi-lobed, with the lower lobe being supported by the caudal vertebral column, which was "kinked" ventrally to follow the contours of the ventral lobe. Basal species had a rather asymmetric or "heterocercal" tail fin. The asymmetry differed from that of sharks in that the lower lobe was largest, instead of the upper lobe. More derived forms had a nearly vertical symmetric tail fin. Sharks use their asymmetric tail fin to compensate for the fact that they are negatively buoyant, heavier than water, by making the downward pressure exerted by the tail force the body as a whole in an ascending angle. This way, swimming forwards will generate enough lift to equal the sinking force caused by their weight. In 1973, McGowan concluded that, because ichthyosaurs have a reversed tail fin asymmetry compared to sharks, they were apparently positively buoyant, lighter than water, which would be confirmed by their lack of gastroliths and of

swimming bladder), they could also regulate their buoyancy. The tail thus mainly served for a neutral propulsion, while small variations in buoyancy were stabilised by slight changes in the flipper angles.^[108] In 1992, McGowan accepted this view, pointing out that shark tails are not a good analogy of derived ichthyosaur tails that have more narrow lobes, and are more vertical and symmetric. Derived ichthyosaur tail fins are more like those of tuna fish and indicate a comparable capacity to sustain a high cruising speed.^[109] A comparative study by Motani in 2002 concluded that, in extant animals, small tail fin lobes positively correlate with a high beat frequency.^[110] Modern researchers generally concur that ichthyosaurs were negatively buoyant.^[111]

In 1994,

water resistance or drag. Their smooth skin and streamlined bodies prevented excessive turbulence. Their hydrodynamic efficiency, the degree to which energy is converted into a forward movement, would approach that of dolphins and measure about 0.8. Ichthyosaurs would be a fifth faster than plesiosaurs, though half of the difference was explained by assuming a 30% higher metabolism for ichthyosaurs. Together, within Massare's model these effects resulted in a cruising speed of slightly less than five kilometres per hour.^[112] However, in 2002, Motani corrected certain mistakes in Massare's formulae and revised the estimated cruising speed to less than two kilometres per hour, somewhat below that of modern Cetacea.^[113]

However, as the speeds estimated for plesiosaurs and mosasaurids were also revised downwards, ichthyosaurs maintained their relative position.

Ichthyosaurs had fin-like limbs of varying relative length. The standard interpretation is that these, together with the dorsal fin and tail fin, were used as control surfaces for

Queensland lungfish and the Amazon river dolphin, which he presumed also used their long fins for propulsion. Riess expounded upon this hypothesis in a series of articles.^{[115][116][117]} This alternative interpretation was generally not adopted by other workers. In 1998, Darren Naish pointed out that the lungfish and the river dolphin actually do not use their fins in this way and that e.g. the modern humpback whale has very long front flippers, supported by a mosaic of bones, but that these nevertheless mainly serve as rudders.^[118] In 2013, a study concluded that broad ichthyosaur flippers, like those of Platyptergygius, were not used for propulsion but as a control surface.^[119]

Diving

Many extant lung-breathing marine vertebrates are capable of deep diving. There are some indications about the diving capacity of ichthyosaurs. Quickly ascending from a greater depth can cause decompression sickness. The resulting bone necrosis has been well documented with Jurassic and Cretaceous ichthyosaurs, where it is present in 15% and 18% of specimens, respectively, but is rare in Triassic species. This could be a sign that basal forms did not dive as deeply, but might also be explained by a greater predation pressure during the later epochs, more often necessitating a fast flight to the surface.^[120] However, this last possibility is contradicted by the fact that, with modern animals, damage is not caused by a limited number of rapid ascension incidents, but by a gradual accumulation of non-invalidating degeneration during normal diving behaviour.^[121]

Additional evidence is provided by the eyes of ichthyosaurs that among vertebrates are both relatively and absolutely the largest known. Modern leopard seals can dive to up to 1 km (0.62 mi) hunting on sight. Motani suggested that ichthyosaurs, with their relatively much larger eye sockets, should have been able to reach even greater depths.^[122] Temnodontosaurus, with eyes that had a diameter of twenty-five centimetres, could probably still see at a depth of 1,600 metres.^[123] At these depths, such eyes would have been especially useful to see large objects.^[103] Later species, such as Ophthalmosaurus, had relatively larger eyes, again an indication that diving capacity was better in late Jurassic and Cretaceous forms.

Metabolism

Similar to modern

vascularisation.^[124] Early Triassic species already show these traits.^[125][126] In 2012, it was reported that even the very basal form Utatsusaurus had this bone type, indicating that the ancestors of ichthyosaurs were already warm-blooded.^[127] Additional direct proof for a high metabolism is the isotopes of oxygen ratio in the teeth, which indicates a body temperature of between 35 and 39 °C, about 20° higher than the surrounding seawater.^[128][129] Blubber is consistent with warm-bloodedness as the insulating qualities require the animal to generate its own heat.^[82]

Indirect evidence for endothermy is provided by the body shape of derived ichthyosaurs, which with its short tail and vertical tail fin seems optimised for a high cruising speed that can only be sustained by a high metabolism: all extant animals swimming this way are either fully warm-blooded or, like sharks and tuna, maintain a high temperature in their body core.[130] This argument does not cover basal forms with a more eel-like body and undulating swimming movement. In 1996, Richard Cowen, while accepting endothermy for the group, presumed that ichthyosaurs would have been subject to Carrier's constraint, a limitation to reptilian respiration pointed out in 1987 by David Carrier: their undulated locomotion forces the air out of the lungs and thus prevents them from taking breath while moving.^[131] Cowen hypothesised that ichthyosaurs would have overcome this problem by porpoising: constantly jumping out of the water would have allowed them to take a gulp of fresh air during each jump.^[132] Other researchers have tended to assume that for at least derived ichthyosaurs Carrier's constraint did not apply, because of their stiff bodies, which seems to be confirmed by their good diving capacity, implying an effective respiration and oxygen storage system. For these species porpoising was not a necessity. Nevertheless, ichthyosaurs would have often surfaced to breathe, probably tilting their heads slightly to take in air, because of the lower position of the nostrils compared to that of dolphins.^[133]

Reproduction

Ichthyosaurs were

oviparous, ancestors, viviparity is not as unexpected as it first appears. Air-breathing marine creatures must either come ashore to lay eggs, like turtles and some sea snakes, or else give birth to live young in surface waters, like whales and dolphins. Given their streamlined and transversely flattened bodies, heavily adapted for fast swimming, it would have been difficult, if not impossible, for ichthyosaurs to move far enough on land to lay eggs. This was confirmed as early as 9 December 1845 when naturalist Joseph Chaning Pearce reported a small embryo in a fossil of Ichthyosaurus communis. The embryo, with a length of eleven centimetres, was positioned in the birth canal of its two-and-a-half metre long mother, with its head pointed to the rear. Pearce concluded from the fossil that ichthyosaurs had to have been viviparous.^[134]

Later, from the Holzmaden deposits numerous adult fossils were found containing

Harry Govier Seeley, heading a special British paleontological committee studying the problem of ichthyosaur reproduction, concluded that birth was given in the water and that fossils containing fetuses in the birth canal probably represented cases of premature death of the juvenile, causing the demise of the mother animal as well.^[135] A comparison has been made with dolphins and whales, whose young need to be born tail-first to prevent drowning; if the juvenile is born head-first, it dies and the mother with it if the corpse gets stuck in the birth canal.^[136] However, an alternative explanation is that such fossils actually represent females that had died for other reasons while pregnant, after which the decomposition gasses drove out the fetuses head-first. In 2014, a study reported the find of a fossilized Chaohusaurus female that had died while giving birth to three neonates. Two had already been expelled while a third was present in the birth canal. The fossil also documented that early ichthyosaurs were also born head first, perhaps opposed to later genera. As Chaohusaurus is a very basal ichthyopterygian—previously, the most basal genus of which fetuses were known, had been Mixosaurus—this discovery suggests that the earliest land-dwelling ancestors of ichthyosaurs had already been viviparous.^[137][138]

A comprehensive multi-author study published in 2023 examined the evolution of fetal orientation of ichthyosaurs based on known specimens of gravid female ichthyosaurs. Specimens of basal ichthyosaurs, Chaohusaurus and Cymbospondylus, showed evidence of head-first birth, while Mixosaurus had evidence of both head-first and tail-first birth based on three specimens. More derived ichthyosaurus including Stenopterygius, Besanosaurus, Qianichthyosaurus and Platypterygius showed evidence of tail-first birth. This indicates that while basal ichthyosaurs were born with head-first, merriamosaurian ichthyosaurs had preference of tail-first birth over head-first birth. The authors asserted that the derived ichthyosaurs' preference of tail-first birth may have been because it was easy for the female to push on the cranium rather than the pelvis when giving birth, or because it could reduce maternal energy expenditure on trim control. They disagreed with the "increased asphyxiation risk" hypothesis for tail-first birth preference, given that Mixosaurus showed evidence of both fetal orientation of head-first and tail-first birth; if this was indeed the reason, there should have been a higher preference for tail-first births caused by strong stabilizing selection for this trait much earlier in the evolutionary history of every aquatic, viviparous tetrapod clades, which isn't the case.^[139]

Compared with

placental mammals or plesiosaurs, ichthyosaur fetuses tend to be very small and their number per litter is often high. In one female of Stenopterygius seven have been identified, in another eleven. The fetuses have at most a quarter of the length of the mother animal.^[140] The juveniles have about the same body proportions as adult individuals. The main ontogenetical changes during growth consist in the fusion and greater robustness of the skeletal elements.^[141]

Crocodiles, most sea turtles and some lizards determine the sex of their offspring by manipulating the temperature of the developing eggs' environment; i.e. they do not have distinct sex chromosomes. Live-bearing reptiles do not regulate sex through incubation temperature. A study in 2009, which examined 94 living species of reptiles, birds and mammals, found that the genetic control of sex appears to be crucial to live birth. It was concluded that with marine reptiles such control predated viviparity and was an adaptation to the stable sea-climate in coastal regions.^[142] Genetics likely controlled sex in ichthyosaurs, mosasaurs and plesiosaurs.^[143]

Social behaviour and intelligence

Ichthyosaurs are often assumed to have lived in herds or hunting groups.

morphotypes. Individuals with a longer snout, larger eyes, a longer trunk, a shorter tail, and longer flippers with additional phalanges, could have represented the females; the longer trunk may have provided room for the embryos.^[144]

Generally, the brain shows the limited size and elongated shape of that of modern cold-blooded reptiles. However, in 1973, McGowan, while studying the natural

telencephalon was not very small. The visual lobes were large, as could be expected from the eye size. The olfactory lobes were, though not especially large, well-differentiated; the same was true of the cerebellum.^[71]

Pathologies

Though fossils revealing ichthyosaur behavior remain rare, one ichthyosaur fossil is known to have sustained bites to the snout region. Discovered in Australia, and analyzed by

pliosaurid (known from the same habitat), which severed its tail. The ichthyosaur then sank to the depths, drowning and eventually becoming fossilized in the deep water. The find was revealed to the public in the National Geographic special Death of a Sea Monster.^[147]

Geological formations

The following is a list of

geological formations

in which ichthyosaur fossils have been found:

Name	Age	Location	Notes
Agardhfjellet Formation	late Tithonian	Norway	Cryopterygius, Janusaurus, Palvennia
Antimonio Formation	late Carnian	Mexico	Shastasaurus pacificus, Toretocnemus californicus
Besano Formation	Middle Triassic	Italy   Switzerland	Besanosaurus, Cymbospondylus buchseri, Mikadocephalus, Mixosaurus cornalianus, Mixosaurus kuhnschnyderi, Phalarodon fraasi, Phalarodon major, Tholodus, Wimanius
Blue Lias	Sinemurian	UK	Ichthyosaurus communis, Leptonectes tenuirostris, Temnodontosaurus platyodon
Charmouth Mudstone Formation	Sinemurian	UK	Ichthyosaurus anningae, Leptonectes spp, Temnodontosaurus platyodon
Clearwater Formation	early Albian	Canada	Athabascasaurus
Favret Formation (Fossil Hill Member)	Anisian	USA	Cymbospondylus nichollsi, Phalarodon callawayi, Phalarodon fraasi, Thalattoarchon
Franciscan Formation	Jurassic	USA	Ichthyosaurus californicus and Ichthyosaurus franciscanus
Guanling Formation	Anisian	China	Barracudasauroides, Contectopalatus, Xinminosaurus
Hosselkus Limestone	late Carnian	USA	Californosaurus, Shastasaurus pacificus, Toretocnemus californicus, Toretocnemus zitteli
Jialingjiang Formation	Olenekian	China	Chaohusaurus zhangjiawanensis
Katrol Formation[148][149]	Kimmeridgian	India	Indeterminate "Ichthyosaurs"[150]
Khao Thong Hill	Early Triassic	Thailand	Thaisaurus
Kimmeridge Clay	Kimmeridgian	UK	Brachypterygius extremus, Nannopterygius
Loon River Formation	early Albian	Canada	Maiaspondylus
Los Molles Formation	early Bajocian	Argentina	Chacaicosaurus, Mollesaurus
Lower Greensand	Early Aptian	UK	Ichthyosaurus sp.
Luning Formation	late Carnian	USA	Shonisaurus popularis
Marlstone	Lower Jurassic	UK	Ichthyosaurus sp.
Muschelkalk	Middle Triassic	Germany	Contectopalatus, Cymbospondylus germanicus, Cymbospondylus parvus, Omphalosaurus peyeri, Omphalosaurus wolfi, Phalarodon major, Phantomosaurus, Tholodus
Nanlinghu formation	late Olenekian	China	Chaohusaurus geishanensis
Nyalam	Norian	China	Himalayasaurus
Opalinuston Formation	early Aalenian	Germany	Stenopterygius aaleniensis
Osawa Formation (upper)	Olenekian	Japan	Utatsusaurus
Oxford Clay	Callovian	UK	Ophthalmosaurus icenicus
Paja Formation	Aptian	Colombia	Muiscasaurus, Kyhytysuka
Pardonet Formation	middle Norian	Canada	Callawayia, Hudsonelpidia, Macgowania, Shonisaurus/Shastasaurus sikkanniensis
Posidonia Shale	early Toarcian	Germany	Eurhinosaurus longirostris, Hauffiopteryx, Stenopterygius quadriscissus, Stenopterygius triscissus, Stenopterygius uniter, Suevoleviathan disinteger, Suevoleviathan integer
Prida Formation (Fossil Hill Member)	Anisian	USA	Cymbospondylus petrinus, Omphalosaurus nettarhynchus, Omphalosaurus nevadanus, Phalarodon fraasi
Ringnes Formation	Oxfordian-Kimmeridgian	Canada	Arthropterygius
Solnhofen Limestone	Tithonian	Germany	Aegirosaurus
Speeton Clay	Hauterivian	UK	Acamptonectes
Sticky Keep Formation	late Olenekian	Norway	Grippia, Isfjordosaurus, Omphalosaurus merriami, Pessopteryx, Quasianosteosaurus
Strawberry Bank, Ilminster	early Toarcian	UK	Hauffiopteryx, Stenopterygius triscissus
Sulphur Mountain Formation	late Olenekian – Anisian	Canada	Gulosaurus, Parvinatator, Phalarodon fraasi, Utatsusaurus
Sundance Formation	Bathonian - Oxfordian	USA	Baptanodon
Toolebuc Formation	Albian	Australia	Platypterygius
Tschermakfjellet Formation	Ladinian – Carnian	Norway	Cymbospondylus sp., Mikadocephalus, Phalarodon callawayi, Phalarodon fraasi
Vaca Muerta	Tithonian	Argentina	Caypullisaurus
Xiaowa Formation	Carnian	China	Guanlingsaurus, Guizhouichthyosaurus tangae, Guizhouichthyosaurus wolonggangense, Qianichthyosaurus

See also

• List of ichthyosaurs
• Timeline of ichthyosaur research
• Dolphin

References

1. ^ Southampton, University of. "Fossil Saved from Mule Track Revolutionizes Understanding of Ancient Dolphin-Like Marine Reptile". Science Daily. Retrieved 15 May 2013.
2. ^ Naish, Darren. "Malawania from Iraq and the Cretaceous Ichthyosaur Revolution (part II)". Scientific American – Blog. Retrieved 15 May 2013.
3. ^ Lhuyd, E., 1699, Lithophylacii Brittannici Ichnographia, sive Lapidum aliorumque Fossilium Brittanicorum singulari figurà insignium, London
4. ^ J. J. Scheuchzer, 1708, Piscium Querelae et Vindiciae, Zürich: Gessner
5. ^ Walcott, John, 1779, Descriptions and Figures of Petrifications Found in the Quarries, Gravel-Pits etc. Near Bath. Collected and Drawn by John Walcott, Esq., S. Hazard, Bath, pp. 51
6. ^ Evans, M., 2010, "The roles played by museums, collections, and collectors in the early history of reptile palaeontology", pp. 5–31 in: Richard Moody, E. Buffetaut, D. Naish, D. M. Martill (eds). Dinosaurs and Other Extinct Saurians: A Historical Perspective. Geological Society of London
7. ^ Hawker, J., 1807, Gentleman's Magazine, 77: 7–8
8. ^
   S2CID 111132066
   .
9. doi:10.1098/rstl.1816.0023
   .
10. S2CID 110990973
    .
11. S2CID 186211659
    .
12. doi:10.1098/rstl.1819.0015
    .
13. doi:10.1098/rstl.1819.0016
    .
14. ^ C. König, 1825, Icones Fossilium Sectiles, London
15. S2CID 129545314
    .
16. ^ De la Beche, H. T.; Conybeare, W. D. (1821). "Notice of the discovery of a new animal, forming a link between the Ichthyosaurus and crocodile, together with general remarks on the osteology of Ichthyosaurus". Transactions of the Geological Society of London. 1. 5: 559–594.
    S2CID 84634727
    .
17. ^ De Blainville, H. M. D. (1835). "Description de quelques espèces de reptiles de la Californie, précédée de l'analyse d'une système générale d'Erpetologie et d'Amphibiologie" [Description of some species of reptile of California, preceded by the analysis of a general system of herpetology and amphibiology]. Nouvelles annales du Muséum d'histoire naturelle (in French). 4. Paris: 233–296.
18. ^ Owen, R (1840). "Report on British fossils reptiles". Report of the British Association for the Advancement of Science. 9: 43–126.
19. ^ John Glendening, 2013, Science and Religion in Neo-Victorian Novels: Eye of the Ichthyosaur, Routledge
20. doi:10.12929/jls.02.1.02
    .
21. ^ Young, G. (1821). "Account of a singular fossil skeleton, discovered at Whitby in February 1819". Wernerian Natural History Society Memoirs. 3: 450–457.
22. ^ Hawkins, T. H., 1834, Memoirs on Ichthyosauri and Plesiosauri; Extinct monsters of the ancient Earth, Relfe and Fletcher, London
23. ^ Hawkins, T. H., 1840, The Book of the Great Sea-dragons, Ichthyosauri and Plesiosauri, Gedolim Taninum of Moses. Extinct Monsters of the Ancient Earth, W. Pickering, London
24. ^ McGowan, C., 2001, The Dragon Seekers: How an Extraordinary Circle of Fossilists Discovered the Dinosaurs and Paved the Way for Darwin, Basic Books
25. S2CID 129527838
    .
26. ^ Owen, R., 1840, "XXXVI.—Note on the Dislocation of the Tail at a certain point observable in the Skeleton of many Ichthyosauri", Transactions of the Geological Society of London, Series 2, Volume 5, 511–514
27. ^ Von Jäger, G. F., 1824, De ichthyosauri sive proteosauri fossilis speciminibus in agro bollensi in Wirttembergia repertis. Stuttgart, Cotta, 14 pp
28. ^ Von Theodori, C. (1843). "Über einen kolossalen Ichthyosaurus trigonodon". Gelehrte Anzeigen der Bayerischen Akademie der Wissenschaften. 16: 906–911.
29. ^ Bronn, H. G. (1844). "Über Ichthyosauren in den Lias-Schiefern der Gegend von Boll in Württemberg". Neues Jahrbuch für Mineralogie, Geognosie, Geologie und Petrefaktenkunde. 1844: 385–408.
30. ^ Von Jäger, G. F. (1852). "Über die Fortpflanzungsweise des Ichthyosaurus". Gelehrte Anzeigen der Bayerischen Akademie der Wissenschaften. 34: 33–36.
31. ^ Von Huene, F., 1922, Die Ichthyosaurier des Lias und ihre Zusammenhänge, Berlin, Gebrüder Borntraeger, VI+114 pp., 22 plates
32. ^ McGowan, C., 1983, The successful dragons: a natural history of extinct reptiles, Samuel Stevens & Company, 263 pp
33. ^
    doi:10.1080/02724634.1999.10011160
    .
34. ^ C. McGowan and R. Motani, 2003, Ichthyopterygia — Handbuch der Paläoherpetologie Part 8. Verlag Dr. Friedrich Pfeil, München. 175 pp.
35. S2CID 4392798
    .
36. ^ Huene, F. von (1937). "Die Frage nach der Herkunft der Ichthyosaurier". Bulletin of the Geological Institute Uppsala. 27: 1–9.
37. ^ ^{a b c d} Michael W. Maisch (2010). "Phylogeny, systematics, and origin of the Ichthyosauria – the state of the art" (PDF). Palaeodiversity. 3: 151–214.
38. doi:10.1111/j.1469-7998.1961.tb05908.x
    .
39. doi:10.1127/njgpa/200/1996/361
    .
40. ^
    S2CID 4416186
    .
41. doi:10.1080/02724634.1997.10011028
    .
42. PMID 23535642
    .
43. PMID 35984885
    .
44. S2CID 248452940
    .
45. S2CID 4392798
    .
46. PMID 36917937
    .
47. ^ (Maisch and Matzke 2000),
48. doi:10.1139/cjes-38-6-983
    .
49. ^ Motani, R.; Manabe, M.; Dong, Z-M. (1999). "The status of Himalayasaurus tibetensis (Ichthyopterygia)" (PDF). Paludicola. 2 (2): 174–181. Archived from the original (PDF) on 2017-08-11. Retrieved 2017-11-17.
50. ^ "The sea dragons bounce back".
51. PMID 21536898
    .
52. ^ (Motani 2000).
53. doi:10.1127/njgpa/213/1999/355
    .
54. doi:10.1127/njgpa/228/2003/421
    .
55. ^ Fischer, V., 2012, "A severe drop in Eurasian ichthyosaur diversity prior to their late Cenomanian extinction: local or global signal?", 4th International Geologica Belgica Meeting 2012. Moving Plates and Melting Icecaps. Processes and Forcing Factors in Geology
56. PMID 23676653
    .
57. doi:10.3390/geosciences2020011
    .
58. ^
    PMID 26953824
    .
59. PMID 22235274
    .
60. S2CID 45794618
    .
61. ^ ^{a b} Michael W. Maisch; Andreas T. Matzke (2000). "The Ichthyosauria" (PDF). Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie und Paläontologie). 298: 159. Archived from the original (PDF) on 2014-11-05. Retrieved 2017-10-08.
62. doi:10.1127/njgpa/229/2003/317
    .
63. S2CID 130274656
    .
64. doi:10.1139/e96-077
    .
65. PMID 29630618
    .
66. ISSN 1932-6203
    .
67. ^ Motani, Ryosuke (15 November 2000), Size of Ichthyosaurs, archived from the original on 6 February 2007, retrieved 21 May 2012
68. ^ Stephen Jay Gould, 1993, "Bent out of Shape", Essay 5 in: Eight Little Piggies, W. W. Norton & Co, pp 479
69. ^
    S2CID 85352593
    .
70. ^ Romer, A.S. (1968). "An ichthyosaur skull from the Cretaceous of Wyoming". Contributions to Geology. 7: 27–41.
71. ^
    doi:10.5962/p.313822
    .
72. doi:10.1130/0016-7606(1990)102<0409:taaeot>2.3.co;2
    .
73. ^ ^{a b} Taylor, M.A. (1987). "Reptiles that took on the sea". New Scientist. 1 (1): 46–51.
74. S2CID 32222934
    .
75. ^ Owen R., 1881, A Monograph of the Fossil Reptilia of the Liassic Formations. Part III, Ichthyopterygia, pp. 83–134. London: Palaeontographical Society
76. ^
    S2CID 4323012
    .
77. ^
    S2CID 54742104
    .
78. ^ ^{a b} Martill, D.M. (1993). "Soupy Substrates: A Medium for the Exceptional Preservation of Ichthyosaurs of the Posidonia Shale (Lower Jurassic) of Germany". Kaupia. 2: 77–97.
79. ^ Martill, D.M. (1987). "Prokaryote mats replacing soft tissues in Mesozoic marine reptiles". Modern Geology. 11: 265–269.
80. PMC 1690467
    .
81. PMID 29061985
    .
82. ^
    S2CID 54458324.{{cite journal}}: CS1 maint: multiple names: authors list (link
    )
83. doi:10.1080/002411601753293042 (inactive 2024-04-02).{{cite journal}}: CS1 maint: DOI inactive as of April 2024 (link
    )
84. S2CID 131190803. Archived
    (PDF) from the original on 2022-10-06.
85. doi:10.1080/00222935608655889
    .
86. S2CID 4468035
    .
87. ^ "Fossil pigments reveal the colors of ancient sea monsters". ScienceDaily.
88. S2CID 24966334
    .
89. S2CID 131465028
    .
90. JSTOR 1303861
    .
91. ^ Moore, C. (1856). "On the skin and food of ichthyosauri and teleosauri". Reports of the British Association for the Advancement of Science: 69–70.
92. ^ Pollard (1968). "The gastric contents of an ichthyosaur from the Lower Lias of Lyme Regis, Dorset". Palaeontology. 11: 376–388.
93. ^ Burgin (2000). "Euthynotus cf. incognitos (Actinopterygii, Pachycormidae) als Mageninhalt eines Fischsauriers aus dem Posidonieschiefer Suddeutschlands (unterer Jura, Lias Epsilon)". Eclogae Geologicae Helvetiae. 93: 491–496.
94. ^ Bottcher (1989). "Uber die Nahrung eines Leptopterygius (Ichthyosauria, Reptilia) aus dem suddeutschen Posidonienschiefer (Unterer Jura) mit Bemerkungen uber den Magen der Icthyosaurier". Stuttgarter Beiträge zur Naturkunde. 155: 1–19.
95. ISBN 978-0-88854-151-2. {{cite book}}: |journal= ignored (help
    )
96. PMID 23297200
    .
97. ^ C. McGowan. 1974. A revision of the longipinnate ichthyosaurs of the Lower Jurassic of England, with descriptions of two new species (Reptilia: Ichthyosauria). Life Sciences Contribution of the Royal Ontario Museum 97.
98. S2CID 128707639
    .
99. ^ Pollard, J.E. (1968). "The gastric contents of an ichthyosaur from the Lower Lias of Lyme Regis, Dorset". Palaeontology. 11: 376–388.
100. PMID 14667384
     .
101. PMID 21625429
     .
102. PMID 24348983
     .
103. ^
     PMID 22425154
     .
104. ^ Kear, B.P. and Barrett, P.M., 2007, "Reassessment of the English Cretaceous ichthyosaur Platypterygius campylodon", pp. 37–38 in Abstracts of Presentations: 55th Symposium of Vertebrate Palaeontology and Comparative Anatomy. The University of Glasgow Press, Glasgow
105. ISSN 0272-4634
     .
106. S2CID 40467872. Archived from the original
     on 2015-09-19. Retrieved 2019-11-30.
107. doi:10.5962/bhl.title.52086
     .
108. ^ Taylor, M.A. (1987). "A reinterpretation of ichthyosaur swimming and buoyancy". Palaeontology. 30: 531–535.
109. ^ McGowan, C (1992). "The ichthyosaurian tail: sharks do not provide an appropriate analogue". Palaeontology. 35: 555–570.
110. S2CID 4422615
     .
111. S2CID 129712910
     .
112. ^ Massare, J.A., 1994, "Swimming capabilities of Mesozoic marine reptiles: a review", In: L. Maddock et al. (eds.) Mechanics and Physiology of Animal Swimming, Cambridge, England: Cambridge University Press pp 133–149
113. S2CID 56387158
     .
114. ^ Riess, J., 1984, "How to reconstruct paleoecology? – Outlines of a holistic view and an introduction to ichthyosaur locomotion". In: Reif, W.-E. & Westphal, F. (eds) Third Symposium on Mesozoic Terrestrial Ecosystems, Short Papers. Attempto Verlag (Tübingen), pp. 201–205
115. ^ Riess, J., 1985, "Biomechanics of ichthyosaurs". In: Riess, J. & Frey, E. (eds) Principles of Construction in Fossil and Recent Reptiles. Konzepte SFB 230 Heft 4, pp. 199–205
116. ^ Riess, J (1986). "Fortbewegungsweise, Schwimmbiophysik und Phylogenie der Ichthyosaurier". Palaeontographica Abteilung A. 192: 93–155.
117. ^ Riess, J.; Tarsitano, S.F. (1989). "Locomotion and phylogeny of the ichthyosaurs". American Zoologist. 29: 184A.
118. ^ Naish, D (1998). "Did ichthyosaurs fly?". Dinosaur World. 4: 27–29.
119. S2CID 86387785
     .
120. S2CID 18970911
     .
121. S2CID 1692472
     .
122. S2CID 5432366
     .
123. doi:10.1080/02724634.1999.10011202
     .
124. S2CID 88171648
     .
125. ^ de Buffrénil, V.; Mazin, J.-M.; de Ricqlès, A. (1987). "Caractères structuraux et mode de croissance du femur d'Omphalosaurus nisseri, ichthyosaurien du Trias moyen de Spitsberg". Annales de Paléontologie. 73: 195–216.
126. doi:10.1016/j.crpv.2010.10.008
     .
127. ^ Nakajima, Y., Houssaye, A., and Endo, H., 2012, "Osteohistology of Utatsusaurus hataii (Reptilia: Ichthyopterygia): Implications for early ichthyosaur biology", Acta Palaeontologica Polonica
128. S2CID 206525584
     .
129. ^ Warm-Blooded Marine Reptiles at the Time of the Dinosaurs, Science Daily, 14 June 2010, retrieved 21 May 2012
130. S2CID 54742104
     .
131. S2CID 83722453
     .
132. ^ Cowen, R., 1996, "Locomotion and respiration in marine air-breathing vertebrates", In: D. Jablonski, D. H. Erwin, and J. H. Lipps (eds) Evolutionary Biology. University of Chicago Press
133. ^ Klima, M (1993). "Über einen möglichen Auftauchmodus bei den Ichthyosauriern". Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen. 188: 389–412.
134. doi:10.1080/037454809496438
     .
135. ^ Seeley, H.G.; Dawkins, Boyd W.; Moore, C. (1880). "Report on the mode of reproduction of certain species of Ichthyosaurus from the Lias of England and Würtemberg, by a Committee". Report of the British Association for the Advancement of Science. 1880: 68–76.
136. ^ Deeming, D.C.; Halstead, L.B.; Manabe, M.; Unwin, D.M. (1993). "An ichthyosaur embryo from the Lower Lias (Jurassic: Hettangian) of Somerset, England, with comments on the reproductive biology of ichthyosaurs". Modern Geology. 18: 423–442.
137. ^ "Ancient reptile birth preserved in fossil: Ichthyosaur fossil may show oldest live reptilian birth". ScienceDaily.
138. PMID 24533127
     .
139. PMID 37072698
     .
140. ^ Böttcher, R (1990). "Neue Erkenntnisse zur Fortpflanzungsbiologie der Ichthyosaurier (Reptilia)". Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie und Paläontologie). 164: 1–51.
141. S2CID 85601386
     .
142. S2CID 351047
     .
143. ^ Carroll, Sean B. (March 22, 2010). "For Extinct Monsters of the Deep, a Little Respect". The New York Times.
144. ^ Qing-Hua, Shang; Chun, Li (2013). "The sexual dimorphism of Shastasaurus tangae (Reptilia: Ichthyosauria) from the Triassic Guanling Biota, China". Vertebrata PalAsiatica. 51 (4): 253–264.
145. hdl:2440/70043
     .
146. ^ "Battle scars found on an ancient sea monster". ScienceDaily.
147. ^ James Woods, 2011, Death of a Sea Monster, DVD-R, National Geographic Channel, 45 m.
148. ^ Seidel, Jamie. "Indian Ichthyosaur fossil proves this ancient sea monster roamed the world". News Corp Australia Network. Retrieved 30 October 2017.
149. PMID 29069082
     .
150. ^ Michael, Greshko (25 October 2017). "Stunning Jurassic 'Sea Monster' Found in India". National Geographic. Archived from the original on October 29, 2017. Retrieved 25 October 2017.

Sources

• Ellis, Richard, (2003) Sea Dragons – Predators of the Prehistoric Oceans. University Press of Kansas.
  ISBN 0-7006-1269-6
  .
• Maisch, M. W.; Matzke, A. T. (2000). "The ichthyosauria" (PDF). Stuttgarter Beiträge zur Naturkunde, Serie B (Geologie und Paläontologie). 298: 1–159. Archived from the original (PDF) on 2014-11-05. Retrieved 2017-10-08.
• McGowan, Christopher (1992). Dinosaurs, Spitfires and Sea Dragons.
  ISBN 0-674-20770-X
  .
• McGowan, Christopher & Motani, Ryosuke (2003). "Ichthyopterygia, Handbook of Paleoherpetology, Part 8, Verlag Dr. Friedrich Pfeil.
• Motani, R. (1997). "Temporal and spatial distribution of tooth implantation in ichthyosaurs", in JM Callaway & EL Nicholls (eds.), Ancient Marine Reptiles. Academic Press. pp. 81–103.
• Motani, R (2000). "Rulers of the Jurassic Seas".
  PMID 11103459
  .
• Weedon, Graham, P. & Chapman, Sandra, D. (2022). Ichthyosaurs from the Early Jurassic of Britain.
  ISBN 978-1-8381528-6-4
  .

External links

Wikispecies has information related to Ichthyosauria.

Wikimedia Commons has media related to Ichthyosauria.

• USMP Berkeley's ichthyosaur introduction
• Ryosuke Motani's detailed Ichthyosaur homepage, with vivid graphics
• Eureptilia: Ichthyosauria – Palaeos
• Hauff Museum, Germany – exhibiting the finds of Holzmaden
• Current research on origins of Ichthyosauria, March 21, 2023, Atlas Obscura