Hippostrich

Hippostrich is a future descendant of ostriches that escaped from zoos and private farms. They are herbivores that feed on grass and underwater plants, and fill a similar niche to African hippos. Unlike modern ostriches, they are semi-aquatic, in a similar fashion to African hippos. They are about the same height as their ancestors, but are larger and weigh three times as much as their ancestors due to their semi-aquatic life.

Evolution
After the Late Holocene ended, humans are now gone, so ostriches have escaped from zoos and private farms. Ostriches eventually become more and more semi-aquatic, while also becoming more herbivorous. As an effect of these features, they also grew much bigger than any bird alive today. Ostriches had evolved into hippostriches.