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: the biggest genera may have been too heavy to go on land at all, but smaller genera could've been capable. 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.
1848 The trustees of the British Museum of Natural History bought the type specimen of Plesiosaurus from the estate of the first duke of Buckingham, Richard Glenville. The museum catalogued the specimen as BMNH 22656.
1860s
1863 Carte and Bailey described the species now known as Rhomaleosaurus cramptoni.
1864 Jules Verne depicted a relict plesiosaur's defeat in combat against an ichthyosaur in Journey to the Center of the Earth.
1865 Owen described the species now known as Eretmosaurus rugosus and Microcleidus homalospondylus. Seeley described the species now known as Microcleidus macropterus. Owen described the species now known as Archaeonectrus rostratus.
1867 An army surgeon named Dr. Theophilus Turner discovered the fossils of a large animal in the Pierre Shale of Kansas, USA. The remains represented the first nearly complete plesiosaur specimen from North America. Turner gave some of its vertebrae to a member of the Union Pacific Railroad's survey named John LeConte. LeConte sent the vertebrae to Edward Drinker Cope for study. Cope recognized the find as a significant plesiosaur discovery and wrote to Turner asking him to excavate and ship the fossils to him. March, mid
Cope erected the new genus and species Elasmosaurus platyurus for the fossils sent by Turner in a rushed descriptive manuscript written within two weeks of obtaining them. March 24
Cope presented his findings regarding Elasmosaurus to a meeting of the Academy of Natural Sciences in Philadelphia, Pennsylvania.
1868 Cope described the new species Elasmosaurus platyurus. Cope's description of Elasmosaurus was formally published. September
William E. Webb and others collected and shipped a plesiosaur specimen to Cope.
1869 Seeley described the species now known as Liopleurodon pachydeirus and Peloneustes philarchus. Cope named the plesiosaur specimen collected by Webb Polycotylus latipinnis. August
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