Phylogenetic relationships of the animal groups parasitized by species of the order Oxyurida. Most animal groups that consume large quantities of plant material (cellulose) are parasitized by pinworms (in red). Generally, these parasites are found in all the representatives of a family group over the complete geographic distribution of the family. Different pinworm species identified in one host group are morphologically very similar, indicating host-parasite cospeciation. However, some groups have not been shown to harbor oxyurids (in green and indicated by a question mark) even though the feeding habits and digestive tract seem appropriate. The question also can be asked regarding the presence of pinworms in herbivorous dinosaurs.