size dimorphism. Marugán-Lobón and colleagues studied the relationships between the presence and absence of long tail feathers and the lengths of various long bones of the arms and limbs, using a once more enlarged sample of 130 specimens. While confirming that the tail feathers are unrelated to body size, their presence corresponds to different proportions of the forelimb compared to the hind limb. The authors concluded that the meaning of the observed distributions of both the tail feathers and the body size remains contentious. Chiappe and colleagues, in their 2008 study, concluded that limb bones growth was almost isometric, meaning that skeletal proportions did not change during growth. This was contested by Peters and Peters in 2009, who observed that wing bones tended to be proportionally longer in very small individuals, as seen in modern chicken, and thus grew allometrically. Chiappe and colleagues, in their 2010 comment, responded that proportional variation is present across the whole size range, and that the presence of allometry was not conclusively demonstrated by the analyses presented by Peters and Peters. Possible medullary bone A 2013 histological study by Anusuya Chinsamy and colleagues found medullary bone within the long bones of a short tailed specimen (DNHM-D1874), while three long-tailed specimens lacked medullary bone. In modern birds, medullary bone only forms temporarily in females, where it functions as a calcium reservoir for eggshell production. Therefore, these authors suggested short-tailed specimens to be females, and long-tailed specimens to be males. The female specimen had already passed its rapid growth phase, although it was still significantly smaller than the maximum size reached by Confuciusornis exemplars. At least two lines of arrested growth (growth lines that form annually) could be identified, demonstrating an extended growth over several years; the studied female would have been in its third year. Long tail feathers were confirmed to occur in small individuals, the smallest of which was only around 23% the mass of the largest specimens. Assuming that the occurrence of tail feathers indicates sexual maturity, the authors concluded that the latter must have occurred well before the animals reached their final size, unlike in birds but similar to non-avian dinosaurs. In a 2018 study, Jingmai O'Connor and colleagues questioned the identification of medullary bone, arguing that the purported medullary bone was only found in the forelimb, while in modern birds it is mostly present in the hind limb. Furthermore, the tissue in