In this extended simile, the story compares the Tyrannosaurus to medieval weapons and gadgets:
Each lower leg was [...] sheathed over in a gleam of pebbled skin like the mail of a terrible warrior. [...] Its mouth gaped, exposing a fence of teeth like daggers. [...] Its armored flesh glittered like a thousand green coins. The coins, crusted with slime, steamed.
Each of these similes relates to medieval warriors and knights, using objects like coins, daggers, and chain mail as points of comparison. In using ancient similes, the narrator emphasizes the true archaism of prehistoric times and therefore how many years into the past the Machine transported the hunters. Knights are a representation of history, pulling the reader out of the story's futuristic setting and into the past. However, the comparisons are somewhat ironic, since the Middle Ages were actually closer to the year 2055 than they were to prehistoric times.
The similes also assume layered meanings. The Tyrannosaurus is like a "terrible warrior" because there is nothing heroic about the hunting expedition, especially given how Eckels runs away from the dinosaur at first sight. There are no heroics in killing without reason. Comparing the Monster's flesh to a thousand coins highlights the exorbitant prices that people like Eckels pay to use the Time Machine and hunt dinosaurs.