Short answers, pulled from the story.
The first plesiosaur fossil was discovered in 1719 by William Stukeley and brought to his attention by Robert Darwin. This specimen, later identified as Plesiosaurus dolichodeirus, was found in a stone slab used to reinforce a watering hole in Elston, Nottinghamshire. The stone plate is now housed in the Natural History Museum as specimen NHMUK PV R.1330.
Henri Marie Ducrotay de Blainville named the order Plesiosauria in 1835. This naming followed the formal recognition of plesiosaurs which began in 1821 when William Conybeare and Henry Thomas De la Beche described a partial skeleton. The discovery of these fossils in the early nineteenth century sparked a renewed interest in paleontology.
Edward Drinker Cope reconstructed a plesiosaur skeleton in 1867 by reversing the vertebral column relative to the body as a whole. He mistakenly identified the neck vertebrae as the tail and the tail vertebrae as the neck, leading to the erroneous naming of the group Streptosauria. Joseph Leidy later corrected this error by placing the skull against the presumed last tail vertebra, which fitted perfectly.
Plesiosaurs showed two main morphological types with long necks and small heads or short necks and large heads. Long-necked plesiosauromorphs were relatively slow and caught small sea animals, possibly using their long necks to surprise schools of fish. Short-necked pliosauromorphs were apex predators and fast hunters of large prey with skulls up to three meters long.
Plesiosaurs breathed air and bore live young, with a fossil of a pregnant Polycotylus latippinus proving they gave birth to a single large juvenile. The group became extinct as a result of the K-T event at the end of the Cretaceous period, approximately 66 million years ago. This extinction event marked the end of these ancient marine reptiles.