With its release in December 2022, our readers may by now have seen the new James Cameron Avatar film. The charismatic blue-skinned aliens making their long awaited second appearance since the first film released in 2009. Our main characters (now with teenagers of their own) seek refuge with the Reef Na’vi (Metkayina Clan) near the ocean. This new habitat is teeming with new marine animals and new forms of travel for the Na’vi. One of these bonded animal species is called the ‘Skimwing’ or ‘Tsurak’ in the Na’vi language.
The skimwing, hosting an alligator-like head and flying-fish based fins is a sight to behold. This post breaks down this unique creatures anatomy and morphology, and highlights some of the living fish and fossil species references that were used during its conceptualization.
FLYING FISH
At first glance, the skimwing’s ‘wings’ immediately reminds the viewer of flying fish (Exocoetidae) of Earth. There are currently 79 species of flying fishes currently described and they are so-named because they are able to propel themselves out of the water and glide across the surface.
Flying fishes have rigid bodies and strengthened linkages between their vertebral column and their cranium. This helps with stability and maintaining an aerodynamic shape during a glide. Similar to the skimwing’s ‘wings’, flying fishes have their pectoral fins extended while out of the water. They can also use their caudal (tail) fins to push up against the water for lift or for another glide. Both skimwings and some flying fishes have enlarged pelvic fins placed further back on the body and extend them out for additional lift and stabilization.
Unlike the skimwing, which can actually maintain ‘flight’ across the surface of the water, flying fishes are only known to have a maximum distance of about 400m. Additionally, flying fishes generally propel themselves out of the water to escape predation whereas skimwings- this movie creature does not.
DIFFERENCES
Other than the fact that flying fishes are approximately half a foot long and skimwings are large enough to carry an adult Na’vi there are additional differences between the two. Skimwings have a body shape more akin to a marlin or a sailfish than they do to the rigid body of a flying fish.
FINS
Flying fish pectoral fins are greatly enlarged and what are used for flying/gliding. Skimwing’s have small pectoral fins that are low on the body and are sometimes used for skimming the water and helps with stabilization and balance. The large ‘wings’ of skimwings are an additional set of limbs that, similar to many of the animals on Pandora are the 6th set of paired limbs. This is opposed to what we normally see on in terrestrial vertebrates on Earth, which is four. Although the skimwing shares numerous traits with fish, in the world of Pandora, the skimwing is more closely related to the mountain banshee (ikran) than it is to fish.
In addition to differences in the pectoral fins, skimwings have differences in their dorsal fins. Skimwings have a long dorsal fin, similar to the Bowfin (Amiidae) and Marlin (Istiophoridae) of Earth. Flying fishes have a shorter dorsal fin located posteriorly on their bodies. In addition to this one long dorsal fin, skimwings also have a pair of small dorsal fins just behind their pectoral ‘wings’ that their Na’vi riders use to tuck their feet under. No fish on Earth possess paired dorsal fins.
Lastly, the caudal fin. Although both skimwings and flying fishes have an elongated lower caudal fin lobe, flying fish caudal fins are considered homocercal. This means that their vertebrae end in the caudal peduncle (tail), and their caudal fin area is made up of rays. In flying fish the ventral lobe is elongated, which is sometimes called hypocercal. Alternatively, skimwing caudal fins are considered heterocercal, where their vertebrae extend into the lower lobe. Most fish species that possess heterocercal tails have vertebrae that extend into the upper lobe (e.g., sharks and sturgeon). Vertebrae extending into the lower lobe are not seen in any living fish species but this condition thought to be present in extinct marine reptiles called Mosasaurs and some lineages of extinct fishes.
BREATH THROUGH GILLS AND NOSTRILS
Skimwings have the ability to breath both through their gills while underwater, but also through their nostrils while in the air. The internal anatomy that allows these two different methods of gas exchange are not known, but there are some fishes that can something similar.
Most fish perform respiration via countercurrent exchange of oxygenated water over their gill filaments. Tiny capillaries that allow deoxygenated red blood cells to come very near to the water enable gas exchange.
Some fishes can actually breathe air from the surface of the water. Species that can do this, like snakeheads (Channidae), lungfishes (Ceratodontiformes), and bettas (Osphronemidae), have evolved different specialized organs to perform additional gas exchange. Some are obligate air breathers and possess “lungs” like lungfishes. Other fish species can use both gills and things like “labyrinth organs” in bettas, which are a species that live in small pools of stagnant water where sometimes oxygen levels in the water are too low to meet their respiratory needs. Interestingly, when fish do breathe air, the do not do so through their nostrils like most tetrapods can. Their olfactory system is separate from their respiratory system. Instead, fishes gulp air using their mouths. If you find this topic interesting, see our post from 2017 to learn more about fishes that can breathe air.
HEAD
Since we know that skimwings are in-fact not closely related to fishes, their heads looking distinctly non-fishy makes a bit more sense. Some cross between a gar (Lepisosteidae) and a gharial (Gavialidae), the skimwing’s sharp teeth dispersed along its very long snout are used in hunting fish and other in the case of the skimwing ‘small aerial creatures.’
CONCLUSIONS
The combined outward appearance of flying fish, marlin, and gar plus the internal workings of an air-breathing plus gill-using animal double the length of a great white shark makes for an imposing picture. Needless to say, skimwings seem to be great companions to the Na’vi and are certainly not an animal I would consider messing with!
The Fisheries Blog 