[2] In 1974 however, Robert "Bob" Bakker and Peter Malcolm Galton successfully defended the monophyly of the Dinosauria, arguing that the Saurischia and Ornithischia were real sister groups.

Both sauropodomorphs and ornithischians are characterized by their “blunt, spoon-crowned teeth suitable for cropping plants” and these would not be an instance of convergent evolution, both groups adapting to a herbivorous mode of living, but a sign they were descended from a plant-eating common ancestor.

[6] In his 1988 book Predatory Dinosaurs of the World: A Complete Illustrated Guide he repeated his hypothesis that therizinosaurs were late-surviving basal sauropodomorphs.

[8] Bonaparte, Bakker, and Paul argued that ornithischians were descended from basal sauropodomorphs, with segnosaurs being transitional taxa as depicted in the phylogeny below.

They recovered a polytomy showing herrerasaurs, Eodromaeus, Daemonosaurus, theropods, and a clade that includes Guaibasauridae and Phytodinosauria as shown below:[12] †Marasuchus †Silesauridae †Herrerasauridae †Eodromaeus †Daemonosaurus Theropoda †Guaibasauridae †Ornithischia †Sauropodomorpha