Are Extreme Anatomical Modifications Required for Fish to Move Effectively on Land? Comparative Anatomy of the Posterior Axial Skeleton in the Cyprinodontiformes

Abstract

Many teleost fishes with no apparent modifications for life on land are able to produce effective terrestrial locomotor behaviors, including a ballistic behavior called the "tail-flip" jump. Cyprinodontiformes (killifishes, Teleostei: Atherinomorpha) that live at the water's edge vary in morphology and inclination to emerge onto land. Do fish with an amphibious predisposition have extensive modification of the propulsive region of the body when compared to fully aquatic relatives? We quantified body shape and anatomy of the caudal peduncle and tail (the propulsive organ on land and in water) in 11 cyprinodontiform species and two outgroup taxa (Atherinomorpha). We hypothesized that amphibious species would have longer, "shallower" bodies (larger body fineness ratios), deeper (proportionally larger) caudal peduncles, and more robust bones in the tail fin (larger ossified area of the hypural/epural bones) to facilitate locomotor movements on land. We found no evidence of convergence in body shape or skeletal anatomy among species known to make voluntary sojourns onto land. In fact, deep-bodied species, shallow-bodied species, and species with intermediate morphologies all are able to emerge from the water and move on land. It is possible that there are as-yet-undocumented subtle soft-tissue (muscle, tendon, and ligament) modifications that enhance terrestrial locomotor performance in species known to spend large periods of time on land. However, it is also possible that extreme anatomical changes are not required for aquatic cyprinodontiform species to produce effective locomotor movements when they emerge out of the water and move across the land. Anat Rec, 303:53-64, 2020.

Emersion and Terrestrial Locomotion of the Northern Snakehead (Channa argus) on Multiple Substrates

“…2013 ; Gibb et al. 2011 ; Mast 1915 ; Minicozzi et al. 2019 ; Perlman and Ashley-Ross 2016 ; Pronko et al.…”

“…Several cyprinodontiform species are able to tail-flip at TL up to 11 cm ( Bressman et al. 2016 ; Minicozzi et al. 2019 ), so the transition to crawling in snakeheads larger than 4.5 cm may not be because of size limitations.…”

Extreme Anatomy: Gear for the Pioneer

“…We will defer a detailed discussion of these creatures, the tetrapodomorphs (tetrapods and lobe‐finned fishes), to part 2 of our special issue (Molnar, Diogo, Hutchison, & Pierce, forthcoming). In this issue, Minicozzi, Kimball, Finden, Friedman, and Gibb (this issue) observe that to the present‐day bony fishes that thrive in shallow aquatic environments also engage in land‐specific locomotor behaviors. If you have ever observed fish trapped in tidal pools, depending on the species, they may not have been trapped at all.…”

“…They can use this specialized behavior to move from shallow pools, over a bank, and to the ocean. Minicozzi et al (this issue) ask whether cyprinodontiformes that exhibit this amphibious behavior have morphological adaptations such as proportionally more robust peduncles (muscular region closest to the tail). Their analysis found no such specializations in amphibious species compared to other cyprinodontiformes, and conclude that either more subtle adaptations may facilitate these behaviors, or that no special anatomical change is necessary for these terrestrial exploits.…”