Archaeopteryx of "Archaeopteryx" bones appear poorly vascularized; in living vertebrates, poorly vascularized bone is correlated with slow growth rate. They also assume that all known skeletons of "Archaeopteryx" come from juvenile specimens. Because the bones of "Archaeopteryx" could not be histologically sectioned in a formal skeletochronological (growth ring) analysis, Erickson and colleagues used bone vascularity (porosity) to estimate bone growth rate. They assumed that poorly vascularized bone grows at similar rates in all birds and in "Archaeopteryx". The poorly vascularized bone of "Archaeopteryx" might have grown as slowly as that in a mallard (2.5 micrometres per day) or as fast as
Specimens of Archaeopteryx than flight. Pennaceous feathers thus represent an exaptation and were only later adapted for aerodynamic capabilities, a function that was apparently convergent among different groups within Avialae. In February 2014, the existence of a twelfth specimen was announced from an Altmannstein quarry near the Schamhaupten district of Bavaria. This specimen was unearthed by a private collector in 2010.. Based on a new diagnosis for the genus Archaeopteryx, by the German paleontologist Oliver Rauhut c.s., the Berlin, Eichstätt, Solnhofen, Munich, Daiting, Thermopolis, 11th, and 12th specimens can be referred to this genus with high certainty. Specimens of Archaeopteryx Archaeopteryx fossils from