Fossil Discovery Suggests Amphibians Once Lived Entirely at Sea
Paleontologists have unearthed the first fossil evidence of an amphibian that may have spent its entire life in saltwater, challenging long-held understandings of the class.
Paleontologists have discovered the first fossil evidence suggesting that amphibians may have once lived exclusively in marine environments. The findings, based on two nearly complete, 237-million-year-old skeletons unearthed in China, point to a three-foot-long creature named Gerrothorax maritimus that inhabited the ocean floor during the Late Triassic period.
This discovery is significant because modern amphibians are largely confined to freshwater or moist terrestrial habitats, with fewer than 2% able to tolerate salinity due to their permeable skin, which is crucial for gas and water exchange. The existence of Gerrothorax maritimus challenges the definition of amphibians as creatures that can navigate both land and water.
The skeletons were found approximately 19 miles from the nearest ancient shorelines, leading researchers to theorize that these ancient amphibians spent their entire lives at sea. This would make them an extreme outlier in the amphibian class.
Researchers hypothesize that Gerrothorax maritimus survived in a marine environment due to its bony carapace, which may have prevented saltwater absorption through the skin. Instead, the creature likely ingested seawater and filtered out the salt through its digestive system, possibly aided by its gills. Its robust armor and squat head shape suggest it was an ambush predator that used suction to capture prey on the seafloor.
The integrity of the fossilized remains, particularly the preservation of delicate structures like fingers, supports the theory that these animals died and sank to the ocean floor relatively quickly in their habitat, rather than being washed out to sea after death. Analysis of strontium levels in the fossils further aligns with those found in ancient ocean environments.
During the Late Triassic, the marine ecosystem where these fossils were found was also populated by species like turtles, ichthyosaurs, and other marine reptiles. The presence of Gerrothorax maritimus adds a unique element to our understanding of this prehistoric marine biodiversity. The study was published in the journal Nature Ecology and Evolution.