Hi. I am doing a report on the plesiosaurus. I need to know how much they weighed.

Obviously, in deaing with an extinct animal we know only from the bones, estimates of weight can only be approximate. Plesiosaurs varied widely in size, the smallest being about a metre long, probably weighing around 30 kilos. The largest, the pliosaurs reached lengths of about 15 metres. I have made a rough estimate of the weight of such an animal as around 25 tonnes. The large, long-necked elasmosaurs were longer than this - up to 18 metres - but less heavily built, and probably weighed around 8 tonnes.