Coronary artery established through amniote evolution

Coronary arteries are part of the vascular system that nourishes the heart; they are generally considered a synapomorphy of jawed vertebrates. However, the so-called coronary arteries originated from different body parts in amniotes and other groups, and the evolution of these arteries remains unclear. Here we propose that the amniote coronary arteries were newly obtained, overriding the ancestral arterial systems. In mouse (Mus musculus) and quail (Coturnix japonica) embryos, the amniote-type coronary arteries are established by the reconstitution of the transient vascular plexus (aortic subepicardial vessels; ASVs) on the outflow tract and the primitive coronary plexus during the development. In contrast, amphibians (Xenopus laevis, Hyla japonica, Lithobates catesbeianus, and Cynops pyrrhogaster) retain the ASV-like vasculature as extrinsic cardiac arteries throughout their lives and have no primitive coronary plexus. A comparison of zebrafish (Danio rerio) and chondrichthyans (Lamna sp., Narke japonica, and Deania calcea) suggested that their hypobranchial arteries correspond morphologically to the ASVs and also serve as heart-feeding arteries throughout their lives. Thus, the coronary artery of adult amniotes is an evolutionary novelty that has acquired new anatomical connections through the addition of a new developmental process to the ancestral pattern. This change is probably related to the modification of branchial arteries, highlights the drastic morphological changes underlying the physiological transition in amniote evolution.