Final answer:
The dinosaur described has characteristics that align with a saurischian, such as Herrerasaurus, being a bipedal walker. Conflicting traits like 'small' with 'large size' and 'short tail' with typical long tailed bipedal dinosaurs complicate the exact identity.
Step-by-step explanation:
The characteristics described suggest a dinosaur that is a mixture of traits, some conflicting such as 'small' and 'large size.' It is clear that this dinosaur is classified as a saurischian, meaning it has a 'lizard-hipped' pelvis. This group is distinguished from Ornithischia, the 'bird-hipped' dinosaurs. While a bird-hipped dinosaur would not be a saurischian, the description alludes to an archosaur lineage which could include traits leading to the evolution of birds. Herrerasaurus, for instance, fits several listed characteristics such as being bipedal and a 'walker', with its legs positioned under the pelvis.
Dinosaurs that walked on two legs often had long tails to counterbalance their long necks, which is curious as the dinosaur in question is described with a 'short tail.' Dewclaws might be seen in theropods, which also fall under the saurischian category. However, birds are known for their 'S-shaped' neck and a short tail or pygostyle, similar to some of these character descriptions.