Triassic fossils show evolution’s first take on flying fish
For a class of animals that require water to breathe, a surprising number of fish have figured out how to soar in the wild blue yonder, at least temporarily. With a slight bit of exaggeration, we call the 64 species of the exocoetidae family as flying fish, perhaps because “leaping and gliding fish” just doesn’t roll off the tongue so well. Despite living in tropical waters around the world, these fish still stand out as oddballs of evolution, defying common conceptions of how a fish conducts itself. What’s actually weirder is that jumping out of the water is such a normal idea for fish that our modern examples are actually all knock-offs, retreading evolutionary frontiers conquered over 200 million years ago.
Sailing over Triassic seas
Various fossils from China have been helping tell the story of Earth’s first round of flying, er, leaping fish, which popped up in the Triassic period over 230 million years ago. A species known as Potanichthys xingyiensis had so many anatomical features found in modern flying fish that scientists think it likely behaved like their modern doppelgangers as well. P. xingyiensis had wide, glider-like pectoral fins, a strong, asymmetrically-forked tail and even a lack of large scales on their skin. The nearly identical specializations strongly suggest that that these fish jumped and glided over the water to avoid predators, and probably favored the warmer temperatures of their modern counterparts as well.
Looking further back in time, we have Wushaichthys exquisitus, an older ancestor of the thoracopterids like P. xingyiensis. This fish wasn’t so obviously well-suited for gliding over the water, but it offered a look at how such specializations likely evolved in these ancient fish, as well as our modern exocoetidids. The first step seemed to be evolving a flattened head to swim close to the surface of the water, which was then followed by tail development that would enable punctuated leaps into the air. Fins likely evolved next, with the loss of scales only coming as a refinement to fish already accustomed to wriggling through the air.
Precursors but not progenitors
As strong a match as these ancient species are for modern flying fish, they’re not actually related. As far as we know, the world’s first iteration of flying fish all went extinct by the end of the Triassic period, and the fish flying over the water today can only be dated back 65 million years. Even if it seems unlikely that evolution would have effectively recreated these animals again, this isn’t the only case of such complete convergent evolution. Modern butterflies are also a rehashed animal, looking like near clones of some ancient lacewings that once flew alongside the dinosaurs of the Jurassic period. It’s weird to wrap your head around, but apparently throwing fish out of the water was such a successful answer to predatation that evolution ended up inventing it twice.
Source: How Flying Fish Took Flight? Fossils May Tell Us by Charles Q. Choi, Live Science