BUENOS AIRES—Scientists have unearthed in Argentina’s Patagonian wilderness fossils of what may be the oldest-known member of the dinosaur group known as titanosaurs that includes the largest land animals in Earth’s history. Researchers said on Monday the fossils represent a dinosaur species named Ninjatitan zapatai that lived 140 million years ago during the Cretaceous Period. They identified Ninjatitan as a titanosaur, a group of long-necked plant-eating dinosaurs that walked on four pillar-like legs. The dinosaur’s incomplete skeletal remains were discovered south of the city of Neuquen. The researchers said Ninjatitan demonstrated that the titanosaurs as a group first appeared longer ago than previously known. “It is the oldest record known, not only from Argentina but worldwide,” study lead author Pablo Gallina, a researcher at the National Council for Scientific and Technical Research of Argentina (CONICET), told Reuters. “Titanosaurs are recorded on various sides of the world, but the oldest-known records …