Tiktaalik, the closest known fish ancestor to land tetrapods, had fins with armlike skeletal structures, a head that moved independently of its body, and spiracles on the top of its head.
"This Gogonasus fish shows similar adaptation for air breathing that we see in creatures much closer to tetrapods," said Jennifer Clack, a paleontologist and tetrapod expert at the University of Cambridge in England. Clack was not involved in the new study.
In more advanced tetrapods, spiracle structures became ears, Clack adds.
Long and colleagues also describe Gogonasus' fins in detail for the first time, showing they are stout and robust like those in early tetrapods.
"In simple terms, Gogonasus is a missing link between fishes that look like fish and the more amphibian-like elpistosteglians [tetrapod-like fishes such as Tiktaalik]," Long said.
Marine Dispersal
Prior to the discovery of Gogonasus, tetrapod-like fish were known mostly from the Northern Hemisphere, raising the question of how tetrapods got to the Southern Hemisphere.
"The marine environment of Gogonasus means that tetrapod-like fishes and tetrapods probably had more marine dispersal ability than previously thought," Long said.
The early tetrapod-like fish could have swum around the world, Cambridge's Clack adds.
However, Gogonasus may have evolved its tetrapod-like features independently of the first fishes to crawl out of water onto land, she says.
"It's possible the features we are seeing in Gogonasus—the air breathing and limb characters—are in fact evolved in parallel, in fact have nothing to do with those in tetrapods. They perhaps derived similar mechanisms quite independently," she said.
"We'll need a lot more work to sort that one out."
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