Vertebral Column Variation of Mudskippers (Gobiidae: Oxudercinae): Early Stages of Water-to-land Transition

Carrying a gravitational load requires modifications of the skeletal system during water-to-land transition of vertebrates. Early stages of the transition are little known due to incomplete and scattered fossil deposits which can be fulfilled by examining extant amphibious fishes facing analogous conditions. In the present study, we compared vertebral morphometrics of eight oxudercine gobies (Parapocryptes serperaster, Pseudapocryptes elongatus, Oxuderces nexipinnis (low terrestrial); Boleophthalmus boddarti and Scartelaos histophorus (moderate terrestrial), Periophthalmus chrysospilos, Periophthalmodon schlosseri, and Periophthalmodon septemradiatus (high terrestrial)) to gain understanding of the vertebral modifications during land invasion. Results show that the higher terrestrial species possess higher flexibility of the vertebral column, heavy ossification of the neural and haemal spines in the caudal region, and the dorsal twisting feature of the caudal base which could serve effective terrestrial locomotion and allow to perform various body postures. The flexibility of the anterior portion of the caudal region could serve the tail standing and leaping of some mudskippers. We tentatively presume that terrestrial locomotion of oxudercine gobies is endowed by flexibility of the vertebral column and heavy ossification of the caudal vertebrae.