Did bird embryos have gill slits?

Yes, bird embryos do have gill slits. This is because birds are descended from reptiles, which evolved from fish. Fish have gill slits, which are openings in the throat that allow water to flow over the gills. The gills extract oxygen from the water and remove carbon dioxide.

As birds evolved from reptiles, they lost their gills and developed lungs. However, bird embryos still retain some of the features of their reptilian ancestors, including gill slits. These gill slits are visible as small indentations on the sides of the neck of a bird embryo. They eventually disappear as the embryo develops.

The presence of gill slits in bird embryos is a reminder of the evolutionary history of birds. It is a fascinating example of how the features of an organism can change over time.