Paleontologists regard the ornithosu-chians as ideal intermediaries between the 4-legged thecodontians and the 2-legged dinosaurs. One family in particular, the Lagosuchidae, is considered to contain the likely ancestors of the dinosaurs (below).
Ornithosuchians probably descended directly from some type of protero-suchian, the earliest-known group of ruling reptiles, during the Late Permian (see p. 96). They became extinct at the end of the Triassic, but not before they had produced the ancestral dinosaur stock (see pp. 90-91).
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