Figure 4
From: Avian tail ontogeny, pygostyle formation, and interpretation of juvenile Mesozoic specimens
A ventral furrow in caudal vertebrae is a common extant avian trait. A ventral furrow or concave surface in extant avians shelters the ventral tail vasculature. This vasculature includes the branched aorta artery, as well as caudal veins11. (A) A transverse paraffin section of a 7–8 week old chicken juvenile pygostyle stained with alcian blue and picrosirius red; blood vessels are noted by the black arrowheads. A ventral caudal furrow is evident in the proximal caudal vertebrae in (B) a red-tailed hawk, Buteo jamaicensis skeletal tail (MOR 1230), especially in the pygostyle region, and in the entire tail in (C) a golden eagle, Aquila chrysaetos (MOR 116) (ventral views). (D) Enlarged ventrolateral view of the golden eagle pygostyle, showing the deeply recessed furrow. MOR is the abbreviation for the Museum of the Rockies.
