| Diodorus Temporal range: Late Triassic,
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| Holotype right dentary bone of the lower jaw in outer and inner view (A) and close-up of an assigned tooth (B) | |
Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | †Ornithischia (?) |
| Family: | †Silesauridae |
| Clade: | †Sulcimentisauria |
| Genus: | †Diodorus Kammerer, Nesbitt, & Shubin, 2012 |
| Species: | †D. scytobrachion
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| Binomial name | |
| †Diodorus scytobrachion Kammerer, Nesbitt, & Shubin, 2012
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Diodorus is a genus of silesaurid dinosauromorph (member of a clade that includes the dinosaurs) that lived during the Late Triassic in what is now Morocco. Fossils were discovered in the Timezgadiouine Formation of the Argana Basin, and were used to name the new genus and species Diodorus scytobrachion. The genus name honors the mythological king Diodorus and the ancient historian Diodorus Siculus; the specific name is ancient Greek for 'leathery arm' and also honors the mythographer Dionysius Scytobrachion. The holotype specimen is a partial dentary bone (front of the lower jaw), and assigned specimens include isolated teeth, two humeri (upper arm bones), a metatarsal (foot bone), and femur (thigh bone).
Diodorus is estimated to have been up to 2.3 m (7.5 ft) long, and features thought to be shared by most silesaurs include a beak-like front of the lower jaw, leaf-shaped teeth, long limbs, and a quadrupedal posture. Diodorus differs from other silesaurids in having forward-tilted teeth that decrease in size towards the front of the jaw, and in having a distinct ridge on the side of the jaw running parallel to the tooth socket margin. The Meckelian groove is distinct in that it expands in height towards the back, and the dentary is distinguished by being bowed at the underside. The femur measures 92 mm (3.6 in) in length and the femoral head has a rather straight front edge instead of rounded like in most other archosaurs. As in other silesaurids, but unlike all other archosaurs, there is a distinct notch below the femur's head.
Within the clade Silesauridae, Diodorus has been grouped in Sulcimentisauria. Silesauridae is generally considered a sister group of the dinosaurs within the wider group Dinosauromorpha; some subsequent studies have suggested it was either a group of ornithischian dinosaurs or a paraphyletic (unnatural) group, consisting of basal (early diverging) ornithischians instead of being a sister group to all of Dinosauria. Although most silesaurids are inferred to have been herbivorous based on the shape of their teeth, coprolites (fossil dung) assigned to Silesaurus contain beetles, which shows they were not strictly plant-eaters. Their long forelimbs and short hindlimbs indicate they were quadrupedal, but they could probably also run bipedally. The Timezgadiouine Formation is probably late Carnian in age, dating to about 230 million years ago, which would make Diodorus one of the few silesaurids known from this time.