Xilousuchus sapingensis, unearthed in the 1970s from the Heshanggou Formation of the Ordos Basin of China (late Early Triassic), oldest known member of Archosauria. This drawing depicts the skull and 10 neck vertebrae of Xilousuchus sapingensis. The elongated spines on rearward vertebrae indicate the presence of a "sail" on the animal's back. (Credit: Sterling Nesbitt)

Reconstruction of Xilousuchus sapingensis, based on the fossil. (Credit: Sterling Nesbitt)