Matchless Passion Go-Saurer(1993)

Matchless Passion Go-Saurer is a mecha anime series about Earth's last defense against an invading alien empire. The Kikaika Empire sweeps through the solar system, conquering planets one by one and setting their sights on Earth. Standing alone against this threat is Eldran, an ancient warrior of light who grants a sixth-grade class three massive robotic dinosaurs capable of merging into the colossal robot Go-Saurer. The children must pilot their combined machine to repel the Kikaika's relentless assault and save their world. Blending action-packed battles with the unlikely heroism of young pilots, the series follows their struggle to master their giant robot and protect humanity from extinction.