The phrase "small dinosaurs" refers to dinosaurs that were not very big in size. They were smaller than the usual or average size of dinosaurs. Full definition
In the summer I can just fill up a box with dirt and let my toddler son play with it in the yard, small dinosaurs optional. (mommyscene.com)
Most scientists agree that birds evolved from small dinosaurs at least 150 million years ago, and the earliest known birds have wings and feathers that look much like those of modern birds. (sciencemag.org)
The scientists replicated ancestral molecular development to transform chicken embryos in a laboratory into specimens with a snout and palate configuration similar to that of small dinosaurs such as Velociraptor and Archaeopteryx. (sciencedaily.com)