system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How did Dolphins go from being land animals to water animals?
gpt
We beleive right now that dolphins and whales originated from a pig like creature who lived in and around water 48 million yesrs ago. You can look at what we believe is the closest land relative to the dolphins, hippos, and sort if imagine how the ancestor lived. Some evolutionary biologists assume that the ancestor took the next step and over generations became better and better fit for the shallow ocean environment of the time until it became completely aquatic.