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.[1] Plesiosaurs were actually discovered and described before dinosaurs.[2] 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.[3] 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.[4]
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.[5] Plesiosaur locomotion has been a source of continuous controversy among paleontologists.[6] 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.[7] However, a paper published in 1975 that once more found support for sea turtle-like swimming in plesiosaurs.[8] This conclusion reignited the controversy regarding plesiosaur locomotion through the late 20th century.[9] 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.[10]
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.[11]
1719
1811
1823
December
c. December
1829
March, mid
March 24
September
August
March 8
November
Spring
c. 1935
1950s
October
May
October
In his remarks on short-necked plesiosaur evolution, Carpenter argued that polycotylids were more closely related to long-necked plesiosaurs than pliosaurs.[90] He observed that Trinacromerum bentonianum seems to have existed from the late Cenomanian to the Turonian. This represents a span of time approximating 3.3 million years. He found Dolichorhynchops osborni to have had an even longer lifespan, from the middle Turonian to the early Campanian., or roughly 4 million years. His research also suggested that there was a span of time during the life of the Western Interior Seaway in which it was not inhabited by polycotylids.[29]
He also reported that the Dolichorhynchops specimen KUVP 40001 from the Pierre Shale of South Dakota may have achieved the extraordinary length of 23 feet.[34] The large size of the Pierre Shale Dolichorhynchops compared to those of the earlier Smoky Hill Chalk suggested to Carpenter that these plesiosaurs were evolving larger body sizes over time. In fact the Pierre Shale specimens of Dolichorhynchops were nearly as large as Brachauchenius lucasi.[78] Carpenter described a particularly large specimen of that latter taxon in this paper as well, specifically FHSM VP-321.[52] His study of Brachauchenius led him to concur with Williston that it was closely related to Liopleurodon ferox.[52]
November
They also noted that some of NJSM 15435's gastroliths were scarred by rounded chips and arc-shaped marks. These were likely inflicted by contact with other gastroliths during the churning of the animal's stomach, and constituted physical evidence that plesiosaurs used their gastroliths to help break down their food during digestion.[97] Cicimurri and Everhart disputed the hypothesis that plesiosaurs used their gastroliths for ballast on the grounds that swallowing and vomiting such stones would be relatively difficult for the long-necked forms and their feeding grounds may have been hundreds of miles from sources of stones.[98]
September
September 11
November
2001–2002
December 30
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