Osteology of the Asian narrow‐mouth toad Kaloula borealis (Amphibia, Anura, Microhylidae) with comments on its osteological adaptation to fossorial life

Abstract

AbstractOsteology of vertebrates plays an indispensable role in taxonomy, form‐function evolution and ecological adaptations. The Asian narrow‐mouth toad genus Kaloula is an interesting group that is known for many species having a fossorial life. However, to date, there has been no comprehensive osteological account of Kaloula. Herein, we present the osteology of K. borealis with the help of micro‐CT scanning and double‐staining technologies, which is the first detailed osteological description of the genus. Osteological comparisons with other members of Microhylinae indicate that K. borealis is characterized by the following traits: skull obviously wider than long; suture between frontoparietals narrow; parasphenoid posterior to vomer; premaxilla, maxilla and vomer edentate; clavicles absent; procoracoids small; omosternum and sternum cartilaginous; crista femoris present and large; femur longer than tibiofibula; prehallux including one element. Remarkably, the species possesses a series of osteological specializations that probably are adaptations for the hindlimbs‐first burrowing and a fossorial life, including stout hindlimb, robust crista femoris, tibiofibula shorter than femur, enlarged prehallux, long anterior ramus of the pterygoid and branched bronchial processes of the cricoid. These findings will contribute to the systematics of microhylids and evolutionary interpretations of the osteological adaptation to fossorial life.