The smallest dinosaur fossils ever found belong to Apatosaurus pusillus, known to archaeologists as the "pygmy bronto." Native to the western regions of what would later become the North American continent, pygmy brontos lived during the Lower and Middle Jurassic periods. Adult males stood around three quarters of an inch tall, measuring on average three inches in length from nose to tail. They roamed in great herds that often numbered in the hundreds. Vast though these herds were, they likely passed undetected through the plains, appearing to other animals as nothing more than a rustle in the grass. Indeed, evidence of pygmy brontos falling victim to predators is rare. They were herbivores, consuming what vegetation they could reach and standing atop one another — sometimes thirteen or fourteen at a time — to reach low-hanging leaves. Fossil records of Apatosaurus pusillus end abruptly 160 million years ago. Archaeologists believe that they were wiped out by the impact of a tiny asteroid.