A LOT OF PEOPLE think of dinosaurs as being massive creatures, big enough to reach the treetops, but there were also tiny dinosaurs, ones that would not even reach your knee. The biggest creatures ever to walk the Earth were the sauropod group of dinosaurs, which were all plant eaters. Brachiosaurus was the biggest sauropod that we know much about. Weighing about 70 tons, it was 22 m(70 ft) long, and stood at 12 m(39 ft) high about as tall as a four-storey building, or a big oak tree. Bones have recently been found belonging to dinosaurs that may have been even larger than Brachiosaurus. Named Supersaurus and ultrasaurus, they may have been a third larger than Brachiosaurus! When alive, ultrasaurus would have weighed as much as 20 large elephants. By contrast with these quite peaceful giants, the tiny dinosaurs like Compsognathus(far right) were mostly agile, crafty meat eaters, some no heavier than a cat