The ancient ancestors of the human-sized coelacanth (see-leh-kanth) breathed with lungs, according to a new study. The modern coelacanth, like most fish, uses gills to get oxygen from the water, but its dinosaur-age ancestors also had a well-developed lung, allowing them to survive in low-oxygen shallow waters. It’s probable that during the Mesozoic Era, part of the coelacanth family moved to deeper waters, eventually losing their lung and relying solely on their gills to breathe.
The deep-water adaptation likely allowed the coelacanth to survive an asteroid that slammed into Earth, killing the dinosaurs and many of their fellow creatures. The shallow-water dwelling, gill- and lung-breathing coelacanths were likely caught in the destruction from the asteroid too; they disappeared from the fossil record about 66 million years ago, the researchers said. Fossils of the hulking fish date back to the Devonian period, about 410 million years ago, and the coelacanth was thought to be extinct until 1938, when they were found living off the coast of South Africa.
The research team studied one species of modern coelacanth at five stages of its growth. Modern-day coelacanths have vestigial lungs and small, hard plates that surround them. Fossil coelacanths have “calcified lungs” which could be the precursor to these small plates. It’s possible that the plates in ancient coelacanths were used to regulate lung volume. “Our results demonstrate the presence of a potentially functional, well-developed lung in the earliest known coelacanth embryo,” the study says.