Amniotic eggs were a big deal. They opened up a whole new world of opportunities for land-based egg-laying locations, and the extra membranes paved the way for bigger (and mostly better) eggs.⁠ ⁠ Scientists are still not sure of exactly when this happened, largely because egg membranes don’t make very good fossils, leaving scientists with no clear record of when or how amniotic eggs developed. Our best guess is that the last common ancestor of both tetrapods (four-limbed animals with a backbone) and the amniotes (four-limbed animals with a backbone that lay eggs with all those extra layers) lived around 370-340 million years ago, though some sources put the first amniote species as living closer to 312 million years ago. Today’s mammals, reptiles, and birds are all descendants of the first amniotes.⁠ ⁠ _____⁠ ⁠ The very first chicken in existence would have resulted from a genetic mutation (or mutations) taking place in a zygote produced by two almost-chickens (or proto-chickens). This...