GASTROINTESTINAL TRACT DIAGRAMS
The narwhal's digestive tract may be compared to that of the Atlantic white-sided dolphin (Lagenorhynchus acutus). This species also consumes fish and squid, and inhabits the sub-Arctic waters of the north Atlantic ocean. (www.arkive.org)
Stevens & Hume, Atlantic white-sided dolphin, www.cnsweb.org
Anja Reckendorf, Atlantic white-sided dolphin, http://www.ffh-anhang4.bfn.de
The emperor penguin's digestive tract can be modeled by that of the red-tailed hawk (Buteo jamaicensis). The red-tailed hawk is a carnivorous bird that eats rodents and small mammals. (www.arkive.org)
Unlike the red-tailed hawk, the emperor penguin does not have a crop. Instead, they store food in the stomach and regurgitate it to feed the chicks. Since the emperor penguin does not have teeth, it will store rocks in the gizzard for mechanical breakdown. (Olsen et al. 2002)
Stevens & Hume, red-tailed hawk, www.cnsweb.org