Final answer:
The word 'dinosaur' means 'terrible lizard,' a term that symbolizes their formidable presence and size but is not indicative of their biological relationship to modern-day lizards. Dinosaurs were extremely diverse, with more than 1,000 species, and birds are their only living descendants.
Step-by-step explanation:
The term dinosaur literally means 'terrible lizard'. This name reflects their impressive size and their distinction from the lizards we are familiar with today. Although the term suggests dinosaurs were gigantic lizards, they actually were a unique group of reptiles. They were not only large but also diverse, encompassing over 1,000 non-avian species that roamed the Earth predominantly during the Mesozoic Era, an era that is often referred to as the Age of Reptiles.
Dinosaurs had a distinctive upright posture that set them apart from lizards. They included both the Saurischia, or 'lizard-hipped' dinosaurs, and the Ornithischia, or 'bird-hipped' dinosaurs. The former had a simple, three-pronged pelvis while the latter had a more bird-like pelvis. It's interesting to note that birds are the only living descendants of dinosaurs, specifically theropod dinosaurs. This evolution illustrates the dynamic and complex nature of dinosaur biology and their dominance on Earth until the catastrophic Cretaceous-Tertiary extinction event.