The duodenum /ˌduːəˈdiːnəm/ or /ˌduːˈɒdᵻnəm/ also known as dodecadactylum, is the first section of the small intestine in most higher vertebrates, including mammals, reptiles, and birds. In fish, the divisions of the small intestine are not as clear, and the terms anterior intestine or proximal intestine may be used instead of duodenum. In mammals the duodenum may be the principal site for iron absorption.