Which of the following was a significant development during the Paleozoic Era?

The first reptiles emerged during the Paleozoic Era, making this a significant development in the history of life on Earth. This era, spanning from around 541 to 252 million years ago, saw a diversification of life forms and the evolution of many key vertebrate groups. Reptiles evolved from amphibian ancestors, adapting to terrestrial environments with their scaly skin, which helped them conserve water, and eggs that could be laid on land rather than in water, marking an essential step in the transition to life on land.

In contrast, the first mammals evolved later, during the Mesozoic Era, from therapsid ancestors. Flowering plants (angiosperms) also appeared after the Paleozoic, in the Mesozoic, and the first birds came about much later as well. Thus, the emergence of reptiles represents a crucial evolutionary milestone that laid the groundwork for a wide range of future terrestrial vertebrates.