 Because the cladistic paradigm only recognises monophyletic taxa as natural groups, and because thecodonts are a paraphyletic group (they include among their descendants animals that are not thecodonts), the term is no longer used as a formal name by most paleontologists, but it can still be found in older (and even fairly recent) books as a convenient shorthand for the basal archosaurs.Traditionally, the order Thecodontia Owen, 1859 was divided into four suborders, the Proterosuchia (early primitive forms, another paraphyletic assemblage), Phytosauria (large crocodile-like semi-aquatic animals), the Aetosauria (armoured herbivores), and the Pseudosuchia (see e.g., Alfred Sherwood Romer's "Vertebrate Paleontology" and Edwin H. Colbert's "Evolution of the Vertebrates").Of these, only phytosaurs and aetosaurs constitute monophyletic groups, and the term "Pseudosuchia" was simply a catch-all term for any species that didn't fit in one of the other three sub-orders.