The tarsometatarsus conformation and foot types in birds are unique traits within vertebrates. We investigate how the tarsometatarsus and the zygodactyl foot are formed during development in the monk parakeet (Myiopsitta monachus). Using bones, whole mount specimens stained for cartilage and bone, and histological sections, we focus on the osteology and morphogenesis of the tarsometatarsus. We also compare the tarsometatarsus development between the altricial monk parakeet with the precocial chicken. The results and conclusions we reached are: (1) the hypotarsus, a character of phylogenetic significance, is monocanaliculate in the adult; (2) digit I retroversion is consequence of the displacement of the articulation site of the metatarsal 1 and its torsion; (3) digit IV retroversion is linked to the development of the trochlea accesoria; (4) in ovo, the ossification and fusion of the metatarsals 2-4 begin in their mid-diaphysis and extends cylindrically to both proximal and distal directions; and (5) the differences in the development of the tarsometatarsus between the monk parakeet and the chicken evidence heterochronies, probably related with their different types of development.

中文翻译：

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制作鹦鹉合趾足：僧鹦鹉（Myiopsitta monachus）跗跖骨的骨骼学和形态发生

鸟类的跗跖构造和足部类型是脊椎动物的独特特征。我们调查跗跖骨和合子足是如何在和尚鹦鹉 (Myiopsitta monachus) 发育过程中形成的。使用骨骼、软骨和骨骼染色的整体标本以及组织切片，我们专注于跗跖骨的骨学和形态发生。我们还比较了晚熟和尚鹦鹉与早熟鸡之间跗跖骨的发育。我们得出的结果和结论是：（1）在成虫中具有系统发育意义的下睑板是单管的；(2) 趾I后倾是第一跖骨关节位移位和扭转的结果；(3) 数字IV后倾与滑车的发育有关；(4) 在卵内，2-4 跖骨骨化和融合开始于它们的骨干中部，并呈圆柱形向近端和远端方向延伸；(5)和尚鹦鹉与鸡证据异时性跗跖骨发育的差异，可能与其发育类型不同有关。