Old Earth Ministries Online Earth History Curriculum

Presented by Old Earth Ministries (We Believe in an Old Earth...and God!)

This curriculum is presented free of charge for use by homeschooling families.

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Chapter 10 - The Jurassic Period

Lesson 51: Plesiosaurs


     A plesiosaur was a type of carnivorous aquatic (mostly marine) reptile. After their discovery, plesiosaurs were somewhat fancifully said to have resembled "a snake threaded through the shell of a turtle", although they had no shell. The common name "plesiosaur" is applied both to the "true" plesiosaurs (Superfamily Plesiosauroidea), which include both long-necked (elasmosaurs) and short-necked (polycotylid) forms, and to the larger taxonomic rank of Plesiosauria, which includes the pliosaurs. The pliosaurs were the short-necked, large-headed plesiosaurians that were the apex predators for much of the Mesozoic. There were many species of plesiosaurs, while most of them were not as large as Elasmosaurus.

Chapter 10 - The Jurassic Period


 Lesson 49 - Jurassic Overview

 Lesson 50 - Morrison Formation

 Lesson 51 - Plesiosaurs

 Lesson 52 - Species In-Depth - Archaeopteryx




Dolichorhynchops, a short-necked, long-jawed plesiosaur, National Museum of Natural History, Washington D.C.   (Picture Source


     Plesiosaurs appeared at the start of the Jurassic Period and thrived until the K-T extinction, at the end of the Cretaceous Period. While they were Mesozoic reptiles that lived at the same time as dinosaurs, they were not dinosaurs.

     The first plesiosaur skeletons were found in England by Mary Anning, in the early 1800s, and were amongst the first fossil vertebrates to be described by science. Many have been found, some of them virtually complete, and new discoveries are made frequently. One of the finest specimens was found in 2002 on the coast of Somerset (England) by someone fishing from the shore. This specimen, called the Collard specimen after its finder, was on display in Taunton Museum in 2007. Another, less complete skeleton was also found in 2002, in the cliffs at Filey, Yorkshire, England, by an amateur paleontologist. The preserved skeleton is displayed at Rotunda Museum in Scarborough.

     Many museums have plesiosaur specimens. Notable among them is the collection of plesiosaurs in the Natural History Museum, London, which are on display in the marine reptiles gallery. Several historically important specimens can be found there, including the partial skeleton from Nottinghamshire reported by Stukely in 1719 which is the earliest written record of any marine reptile. Other specimens include those purchased from Thomas Hawkins in the early 19th century.

     Specimens are on display in museums in the UK, including New Walk Museum, Leicester, The Yorkshire Museum, The Sedgwick Museum in Cambridge, Manchester Museum, Warwick Museum, Bristol Museum and the Dorset Museum. A specimen was put on display in Lincoln Museum (now The Collection) in 2005. Peterborough Museum holds an excellent collection of plesiosaur material from the Oxford Clay brick pits in the area. The most complete known specimen of the long-necked plesiosaur Cryptoclidus, excavated in the 1980s can be seen there.

     Plesiosaurs had a broad body and a short tail. They retained their ancestral two pairs of
Restoration of a Plesiosaurus dolichodeirus pair, one catching a fish. (Picture Source)
 limbs, which evolved into large flippers. Plesiosaurs evolved from earlier, similar forms such as pistosaurs or very early, longer-necked pliosaurs. There are a number of families of plesiosaurs, which retain the same general appearance and are distinguished by various specific details. These include the Plesiosauridae, unspecialized types which are limited to the Early Jurassic period; Cryptoclididae, (e.g. Cryptoclidus), with a medium-long neck and somewhat stocky build; Elasmosauridae, with very long, inflexible necks and tiny heads; and the Cimoliasauridae, a poorly known group of small Cretaceous forms. According to traditional classifications, all plesiosaurs have a small head and long neck but, in recent classifications, one short-necked and large-headed Cretaceous group, the Polycotylidae, are included under the Plesiosauroidea, rather than under the traditional Pliosauroidea. Size of different plesiosaurs varied significantly, with an estimated length of Trinacromerum being three meters and Mauisaurus growing to twenty meters.

     Unlike their pliosaurian cousins, plesiosaurs (with the exception of the Polycotylidae) were probably slow swimmers. It is likely that they cruised slowly below the surface of the water, using their long flexible neck to move their head into position to snap up unwary fish or cephalopods. Their four-flippered swimming adaptation may have given them exceptional maneuverability, so that they could swiftly rotate their bodies as an aid to catching prey.
     Contrary to many reconstructions of plesiosaurs, it would have been impossible for them to lift their head and long neck above the surface, in the "
swan-like" pose that is often shown. Even if they had been able to bend their necks upward to that degree (which they could not), gravity would have tipped their body forward and kept most of the heavy neck in the water.

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