The nine-metre long quadriped was discovered recently in Tazouda, 70 km from Ouarzazate in southeastern Morocco by a team of scientists from the north African kingdom, France, Switzerland and the United States.
Officially named "Tazoudasaurus Naimi", the newly discovered creature is key to understanding the evolutionary process of large vertebrates, said Philippe Taquet, head of the natural history museum in Paris.
The bones found in Tazouda include a jawbone with 17 teeth, said to be one of the oldest dinosaur remains ever found - aged about 180 million years.
A sauropod is a plant eater with a long neck and tail, but a disproportionately small head, and many species are believed to have walked slightly tip-toed.
Tazoudasaurus Naimi is the big brother of North American dinosaurs, said Dale Russell, chief researcher at the natural history museum in North Carolina.
Two-hundred-million years ago, the Atlantic Ocean did not exist, Russell said, putting Tazouda about "four hours by road" from North Carolina, where the US researcher works.