The dinosaur known for its long front legs and enormous size is Brachiosaurus.
Unlike most sauropods, Brachiosaurus had forelimbs longer than its hindlimbs. This unusual proportion gave its body a steep, giraffe-like slope from the shoulders toward the hips and helped it browse on vegetation high above the ground. Its name means “arm lizard,” referring to those proportionately long arms.
Brachiosaurus lived in North America during the Late Jurassic, roughly 155.6 to 145.5 million years ago. It was a quadrupedal herbivore with a long neck, small skull, deep chest, and column-like limbs. Estimates place it at about 18–22 metres long, although its precise mass and maximum size remain uncertain because the genus is known from relatively limited fossil material.
A common mix-up involves Giraffatitan. Many famous museum reconstructions once labeled as Brachiosaurus are now assigned to Giraffatitan, an African relative. Brachiosaurus was once considered the largest land animal, but several giant titanosaurs, including Argentinosaurus, may have exceeded it in mass.