The largest known type of dinosaur is Argentinosaurus. Argentinosaurus was a massive, long-necked sauropod dinosaur that lived during the Late Cretaceous period, approximately 90 to 100 million years ago. While estimates of its size vary, it is believed to have reached lengths of around 98 to 115 feet (30 to 35 meters) and weighed anywhere between 70 and 100 tons. This makes it one of the largest land animals to have ever existed.