Question

the paleozoic era is characterized by the presence of which organisms?
dinosaurs and reptiles
mammals and flowering plants
invertebrates, fish, and amphibians
humans and large mammals

Explanation:

The Paleozoic era (about 541 - 252 million years ago) is known for the diversification of life. Invertebrates (like trilobites) were abundant. Fish (including jawless and jawed fish) evolved and became common. Amphibians also emerged during this era as vertebrates started to adapt to life on land. Dinosaurs and reptiles were more prominent in the Mesozoic era. Mammals and flowering plants became more dominant later (mammals more so in the Cenozoic, flowering plants had some evolution but full dominance later). Humans and large mammals are much more recent (Cenozoic era for large mammals in a more modern sense and humans are very recent in geological time - Holocene epoch which is part of the Cenozoic).

Answer:

invertebrates, fish, and amphibians