An alligator embryo during organogenesis, with nerves, muscle tissues, and cell nuclei fluorescently labeled (green, orange, and blue, respectively)JOÃO FRANCISCO BOTELHO, YALE UNIVERSITY Alligator embryos share many characteristics with bird embryos, a hallmark of their shared evolutionary heritage. Their last common ancestor lived some 250 million years ago, and would have resembled a small dinosaur. Evolutionary biologists are comparing the development of chicken and alligator embryos to pinpoint stages where bird and crocodylian features emerge. 

This image was a winner of the Federation of American Societies for Experimental Biology’s 2017 BioArt Contest


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