This is the icon set that I chose to dissect. Essentially it is primarily animals with a few nature icons to make a whole. They are made to look like origami.
As you can see, the majority of the icons are animals. All of which seem prehistoric, though I do not know how old penguins and squirrels are. But for the majority of the set, the pattern seems to be ancient prehistoric animals in order to make the set.
For the coloring of the icons one color was chosen for each and then contrast was added by giving a light and dark version of that color. For example, orange and light orange, red and light red, etc.
Finally, in order to give it the shape of an origami, triangles were primarily used in order to make the shapes. This includes distorting them, resizing, adjusting angles etc.