UNIVERSAL MAMMALIAN SHUNT VESTIGES. “Ductus arteriosus → ligamentum arteriosum. The ductus arteriosus (AKA ductus Botalli), a bypass from the pulmonary trunk to the aorta (i.e., the fourth to the sixth aortic arches), normally withers in the days following birth to become a shriveled band of tissue, the ligamentum arteriosum. This remnant, which connects the pulmonary trunk and aorta, can be found in all mammals.”
https://evolution-outreach.springeropen.com/articles/10.1186/s12052-014-0012-5