Elasmosauruses are long-necked, primeval reptiles that dwell in deep oceans and seas. Although not truly a dinosaur, elasmosauruses are often found in similar locations and are similarly titanic creatures. Keeping their massive bodies underwater, elasmosauruses use their long necks to catch prey and snorkel air to their massive lungs while remaining mostly hidden from the surface above. An elasmosaurus is 30 feet long and weighs 6,000 pounds.