Formerly living animals morphed into Flatland by a projective transformation applied by a heavy vehicle.

To help you identify these instances of roadkill (aka road pizza), consult Flattened Fauna: A Field Guide to Common Animals of Roads, Streets, and Highways by Roger M. Knutson, 1987, Ten Speed Press, Berkeley, California, ISBN 0-89815-186-4. The introduction to this useful book says "Why an animal is on the road and what it was doing there a few hours or days earlier are recorded in its flat remains as surely as the history of a tree is recorded in its annual rings."

This is a scholarly treatise which includes diagrams (two-dimensional, naturally!) of the fauna and their Latin names in the Linnaean system. For example, the well-known dead skunk in the middle of the road is identified as Mephitis mephitis.