Some scientists contend
that many species of dinosaur had a metabolism more like a warm-blooded mammal's than a cold-blooded reptile's.
Option Elimination -
(A) that many species of dinosaur had a metabolism more like - ok. "had" past form of "have". The metabolism of a dinosaur is correctly compared with the metabolism of others. Moreover, the usage of the "contend that" is okay - The phrase is used to express an argument or a point of view. It is typically followed by a clause or statement that presents a claim. E.g., The author contends that the rise in oil prices will hurt the economy (true in today's context

). Another usage of contending is with. "Contend with" indicates dealing with or grappling with a problem. E.g., The company is contending with increased competition in the market. The idea is not to cram the idioms, just to share to be more careful. Otherwise, the options have enough other issues to eliminate and get the right option.
(B) that the metabolism of many dinosaur species were more like - a "were" SV issue.
(C) that the metabolisms of many species of dinosaurs were more like those of - "those" is wrong. "the metabolisms ...were like..." those" (the metabolisms) of a warm-blooded mammal's (metabolism)" and "a cold-blooded reptile's (metabolism).
(D) there were many species of dinosaurs that had metabolisms more like those of - "that" is wrong. Same as C.
(E) there were many dinosaur species that had a metabolism more like that of - "that" is wrong. Same as C.