Development of the bony skeleton in the Taiwan salamander, Hynobius formosanus Maki, 1922 (Caudata: Hynobiidae): Heterochronies and reductions

Abstract

The development of the bony skeleton in a partially embryonized lotic-breeding salamander Hynobius formosanus is studied using the ontogenetic series from late embryos to postmetamorphic juveniles and adult specimen. Early stages of skull development in this species are compared with the early cranial ontogeny in two non-embryonized lentic-breeding species H. lichenatus and H. nigrescens. The obtained results show that skeletal development distinguishes H. formosanus from other hynobiids by a set of important features: 1) the reduction of provisory ossifications (complete absence of palatine and reduced state of coronoid), 2) alteration of a typical sequence of ossification appearance, namely, the delayed formation of vomer and coronoid, and 3) the absence of a separate ossification center of a lacrimal and formation of a single prefrontolacrimal. These unique osteological characters in H. formosanus are admittedly connected with specific traits of its life history, including partial embryonization, endogenous feeding until the end of metamorphosis and relatively short larval period.