This timeline of plesiosaur research is a chronologically ordered list of important fossil discoveries, controversies of interpretation, taxonomic revisions, and cultural portrayals of plesiosaurs, an order of marine reptiles that flourished during the Mesozoic Era. The first scientifically documented plesiosaur fossils were discovered during the early 19th century by Mary Anning. Plesiosaurs were actually discovered and described before dinosaurs. They were also among the first animals to be featured in artistic reconstructions of the ancient world, and therefore among the earliest prehistoric creatures to attract the attention of the lay public. Plesiosaurs were originally thought to be a kind of primitive transitional form between marine life and terrestrial reptiles. However, now plesiosaurs are recognized as highly derived marine reptiles descended from terrestrial ancestors.
Early researchers thought that plesiosaurs laid eggs like most reptiles. They commonly imagined plesiosaurs crawling up beaches and burying eggs like turtles. However, later opinion shifted towards the idea that plesiosaurs gave live birth and never went on dry land. Plesiosaur locomotion has been a source of continuous controversy among paleontologists. The earliest speculations on the subject during the 19th century saw plesiosaur swimming as analogous to the paddling of modern sea turtles. During the 1920s opinion shifted to the idea that plesiosaurs swam with a rowing motion. However, a paper published in 1975 that once more found support for sea turtle-like swimming in plesiosaurs. This conclusion reignited the controversy regarding plesiosaur locomotion through the late 20th century. In 2011, F. Robin O'Keefe and Luis M. Chiappe concluded the debate on plesiosaur reproduction, reporting the discovery of a gravid female plesiosaur with a single large embryo preserved inside her.
Prescientific
Associated remains of plesiosaurs and animals like the diving bird Hesperornis or the pterosaur Pteranodon may have inspired legends about conflict between Thunder Birds and Water Monsters told by the Native Americans of Kansas and Nebraska.
18th century
1719
William Stukeley described the first partial skeleton of a plesiosaur, brought to his attention by the great-grandfather of Charles Darwin, Robert Darwin of Elston.
19th century
1810s
1811
Mary Anning discovered some plesiosaur fossils in England.
1820s
1821
Henry De la Beche and William Conybeare are the first to name a plesiosaurian species: Plesiosaurus dolichodeirus.
1822
Parkinson coined the name Plesiosaurus priscus for some of the remains used by de la Beche and Conybeare as the basis for Plesiosaurus. This species is currently regarded as of dubious taxonomic value.
1823
December
Mary Anning discovered a nearly complete Plesiosaurus skeleton near Lyme Regis. This specimen would later be catalogued as BMNH 22656.
c. December
Around the same time as the discovery of BMNH 22656, another Plesiosaurus specimen was discovered at the same site. The specimen was donated to the Oxford University museum and is probably the specimen known today as OXFUM J.10304.
1824
Conybeare described the new species name Plesiosaurus dolichodeirus for the Plesiosaurus discovered by Anning. As the first species name given to a distinctive and well preserved Plesiosaurus skeleton it has come to be regarded as both the type specimen of Plesiosaurus dolichodeirus specifically and of the genus Plesiosaurus as a whole.
1829
Mary Anning collected the Plesiosaurus dolichodeirus specimen now known as BMNH R.1313.
1830s
1837
Buckland in Conybeare described the new species Plesiosaurus macrocephalus.
1839
De la Beche illustrated a work titled "Duria Antiquior", meaning "A More 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. von Meyer described Pistosaurus. Pistosaurus is believed to be a transitional form linking plesiosaurs to their basal sauropterygian forebears.
1840s
1840
Owen described the species now known as Colymbosaurus trochanterius, Eurycleidus arcuatus, and Thalassiodracon hawkinsii.
1841
Owen described the new species Pliosaurus brachydeirus, Pliosaurus brachyspondylus. and Polyptychodon interruptus.
1842
Sir Richard Owen formally named the pliosaurs.
1846
Stutchbury described the species now known as Atychodracon megacephalus.