This timeline of ichthyosaur research is a chronological listing of events in the history of paleontology focused on the ichthyosauromorphs, a group of secondarily aquatic marine reptiles whose later members superficially resembled dolphins, sharks, or swordfish. Scientists have documented ichthyosaur fossils at least as far back as the late 17th century. At that time, a scholar named Edward Lhuyd published a book on British fossils that misattributed some ichthyosaur vertebrae to actual fishes; their true nature was not recognized until the 19th century. In 1811, a boy named Joseph Anning discovered the first ichthyosaur fossils that would come to be scientifically recognized as such. His sister, Mary Anning, would later find the rest of its skeleton and would go on to become a respected fossil collector and paleontologist in her own right.

Early researchers recognized ichthyosaurs as marine reptiles, but major aspects of their anatomy and behavior needed to be resolved. They were frequently portrayed as leaving the water to bask on rocks and with straight tails. Although a bend in ichthyosaurs' tail vertebrae was seen from the earliest specimens, scholars assumed the bend reflected damage incurred to the animal's carcass after death. This bend was so common, however, that scholars eventually realized that it was natural and supported a shark-like tail fin. Scientists came to realize that ichthyosaurs were too adapted to leave the water even to lay eggs. Evidence for live birth in ichthyosaurs dates back as far as 1846, when Chaning Pierce reported an apparent fossil Ichthyosaurus embryo to Sir Richard Owen.

Ichthyosaur discoveries continued to be made into the 20th century. In 1928, Simeon Muller discovered the remains of 40 gigantic ichthyosaurs in Nevada. However, these remains would not be excavated until Charles Camp and Samuel Welles of Berkeley led an expedition for the purpose in the mid 1950s. These fossils would take more than a decade to excavate, and the results of Camp's examination of the bones would not be published until a year after his 1975 death. These giant ichthyosaurs were named Shonisaurus popularis and their final resting place is now known as Berlin-Ichthyosaur state park.

Other notable late 20th century advances in ichthyosaur research include the recognition of a new genus of ichthyosaur called Eurhinosaurus longirostris that had been misclassified as a species of Ichthyosaurus since 1854. In 1986 Christopher McGowan would describe another, similar animal serendipitously discovered in England as Excalibosaurus, after King Arthur's mythical sword. The late 1990s and early 21st century would see scholarly debate regarding the cause of the ichthyosaurs' extinction, especially regarding the potential role played by competition with the mosasaurs which had evolved around the time. 17th century

1699 Edward Lhuyd published a book called Lithophylacii Britannici Ichonographia about British fossils housed in Oxford's Ashmolean Museum. The book contained illustrations of unrecognized ichthyosaur vertebrae misidentified as belonging to fishes. 120 copies of the book were produced.

19th century

1810s

1811 Joseph Anning discovered the first scientifically recognized ichthyosaur remains.

1812 Mary Anning found the rest of the original ichthyosaur skeleton discovered by her brother Joseph.

1814 An anatomist with the Royal College of Surgeons named Sir Everard Home described the ichthyosaur discovered by the Annings. He thought it formed a "link between fishes and crocodiles".

1818 König described the new genus Ichthyosaurus.

1819 Everard Home changed his mind about the relationships of Ichthyosaurus. Instead of linking fishes with crocodiles, he concluded that it linked salamanders and lizards. He tried to rename it Proteosaurus after the salamander genus Proteus, but his original name had priority and is still considered official.

1820s

1822 Conybeare described Ichthyosaurus communis and I. intermedius along with the species that would later come to be known as Leptonectes tenuirostris and Temnodontosaurus platyodon.

1823 Mary Anning or a member of her family discovered a complete Ichthyosaurus skeleton in Lyme Regis. The find aroused widespread curiosity about ancient life throughout Britain.

1824 The Reverend George Young discovered an ichthyosaur fossil in Whitby, Yorkshire. He also described the specimen, noting that it shared traits with crocodiles, fishes, and dolphins. Young speculated that ichthyosaurs might still be discovered alive as more of the world's seas and oceans are explored.

1830s

1830 Henry de la Beche illustrated a work titled "Duria Antiquior", meaning "Ancient Dorset" for fossil hunter Mary Anning. This work, which prominently features plesiosaurs, has been regarded as the first attempt to accurately reconstruct the Mesozoic world through an artistic medium.

1834 Thomas W. Hawkins published a book titled Memoirs of Ichthyosauri and Plesiosauri. He sold it in subscription format for L2.10, an exorbitantly high price for the period. The book included illustrations by landscape painter John Samuelson Templeton, although many of these inaccurately portray ichthyosaurs with straight tails and leaving the water to bask on rocks.

1840s

1840 Owen described the new species "Ichthyosaurus" acutirostris.

1843 Theodori described the new species that would later become known as Temnodontosaurus trigonodon.

1844 Bronn described the species that would later become known as Suevoleviathan integer.

1846 Chaning Pearce discovered that a specimen of Ichthyosaurus communis contained the skeleton of another, tiny I. communis partially protruding from the larger individual's pelvis. After discussing the fossil with Sir Richard Owen, Pearce concluded that the specimen was a female killed and preserved in the act of giving birth.

1850s

1851 Gideon Mantell described the new species Ichthyosaurus longirostris based on fossil found in Whitby, Yorkshire. Its upper jaw was so much longer than its lower jaw that it resembled a swordfish. Meyer described the new genus and species Tholodus schmidi.

1852 Quenstedt described the species that would later become known as Contectopalatus atavus.

1853 Henry Coles reported that ichthyosaurs were covered by scales resembling tiny hairs or spines. However, these supposed scales were actually hooklets from the tentacles of the prehistoric cephalopods the ichthyosaur had eaten. Wagner described the species that would one day be known as Aegirosaurus leptospondylus.

1854 Sir Richard Owen inaccurately reconstructed Ichthyosaurus as straight-tailed and able to bask on rocks for an outdoor exhibit at Sydenham.

1858 Quenstedt described the species that would later come to be known as Stenopterygius quadriscissus and Stenopterygius triscissus.

1860s

1860 Sir Richard Owen tried to rename the Ichthyosauria the Ichthyopterygia. The first ichthyosaur fossils known from Australia were discovered in Queensland and named Ichthyosaurus australis.

1866 Oskar Fraas of Stuttgart's Museum of Natural History documented the bustling ichthyosaur excavations at Holzmaden.

1867 M'Coy described the species that would later come to be known as Platypterygius australis .

1868 Leidy described the genus Cymbospondylus and the species Cymbospondylus piscosus and Cymbospondylus petrinus .

1870s

1871 Hulke described the species that would later become known as Nannopterygius enthekiodon.

1874 Seeley described the new genus and species Ophthalmosaurus icenicus.

1876 Blake described the species that would one day come to be known as Temnodontosaurus crassimanus.

1879 Marsh described the species that would one day come to be known as Ophthalmosaurus natans.

1880s

1880 Harry Govier Seeley published an argument in favor of live birth in ichthyosaurs. Seeley noted that many ichthyosaur specimens from Britain and Germany contained miniature ichthyosaur skeletons inside them. While some researchers interpreted these remains as fossil stomach contents, Seeley observed that the smaller skeletons tend to be located too near the rear of the animal to be stomach contents. Instead, he interpreted the small skeletons as fetuses and the larger ones as pregnant females.

1881 Owen described the species Ichthyosaurus breviceps .

1886 Bassani described the species that would later come to be known as Mixosaurus cornalianus.

1887 Georg Baur published a paper speculating on the origins of ichthyosaurs. He concluded that ichthyosaurs were descended from relatives of the Sphenodontidae, the family that includes the modern tuatara. He reclassified the species Ichthyosaurus cornalianus and I. atavus into a new genus, Mixosaurus. He also erected a new family for this genus, the Mixosauridae.

1888 Lydekker described the species Ichthyosaurus conybeari and the species that would later come to be known as Brachypterygius cantabridgiensis.

1889 Lydekker described the genus Temnodontosaurus.

1890s

1895 Merriam described the new genus and species Shastasaurus pacificus.

20th century

1900s

1902 J. C. Merriam named the new species Shastasaurus alexandrae after Annie Alexander, the wealthy fossil enthusiast who financed much of his research and founded the Museum of Paleontology at Berkeley. He also described the species that would later come to be known as Californosaurus perrini.

1903 J. C. Merriam described the new genus Toretocnemus from Late Triassic rocks in California. Along with the genus, he described the species Toretocnemus californicus and Toretocnemus zitteli.

1904 Boulenger described the species that would later become known as Brachypterygius extremus. Jaekel described the new genus Stenopterygius.

1906 J. C. Merriam discovered the unusual remains of an animal with short jaws and button-shaped teeth in Nevada. He thought it was the first member of a new group of reptiles related to placodonts or rhynchosaurs but it would actually come to be recognized as ichthyosaurian and described as the genus Omphalosaurus.

1908 Broili described the species that would later come to be known as Platypterygius platydactylus.

1909 Abel erected the genus Eurhinosaurus for the species Ichthyosaurus longirostris.

1910s

1910 Some putative ichthyosaur limb bones were found in Spitsbergen. Carl Wiman would later refer these remains to the species Omphalosaurus nevadanus. Wiman also described the new genus and species Pessopteryx nisseri as well as the species that would one day be known as Isfjordosaurus minor. Andrews speculated that since many specimens of Ophthalmosaurus are toothless that it may have fed via suction feeding on soft foods like squid. Merriam described the new genus and species Phalarodon fraasi.

1916 Huene described the species now known as Phalarodon major. Huene described the new genus and species Pachygonosaurus robustus.

1920s

1922 German paleontologist Friedrich von Huene described the new genus Brachypterygius. He also described the genera Nannopterygius and Platypterygius.

1925 von Huene described a new species of Shastasaurus.

1926 von Huene erected the new genus Suevoleviathan for the species "Leptopterygius" disinteger.

1927 Huene described the species that would later come to be known as Platypterygius hauthali.

1928 Simeon Muller discovered the remains of 40 gigantic ichthyosaurs in Nevada.

1929 Wiman described the new genus and species Grippia longirostris.

1930s

1931 Huene described the new species Stenopterygius uniter as well as the species that would later become known as Temnodontosaurus nuertingensis .

1934 The most complete known ichthyosaur specimen from Australia, a Platypterygius was discovered in Queensland. Despite not being fully grown it was 18 feet in length. Kuhn described the genus Californosaurus.

1939