Volcanic eruptions set off a mass extinction 252 million years in the past that scientists name “the Great Dying.” The ensuing local weather change and acid rain hit life within the oceans onerous, with lower than 5 % of marine species making it out alive.

But that occasion gave strange new life-forms the opportunity to evolve, together with a small sea-dwelling reptile that filter-fed a lot as bowheads and different baleen whales do as we speak. The discovery was reported on Monday in the journal BMC Ecology and Evolution.

The reptile in query, Hupehsuchus nanchangensis, arrived on the scene just a few million years after the Great Dying. Unlike the large sea monsters that ultimately developed, it was about three toes lengthy, together with its tail. And in contrast to lots of its kinfolk, Hupehsuchus had no tooth in its skinny snout.

In the many years because it was first found in 1972 in Hubei Province in southern China, scientists have puzzled over how Hupehsuchus may need been in a position to snag its meals. Cheng Long, a paleontologist on the Wuhan Center, China Geological Survey, has suspected for years that Hupehsuchus may need been a filter feeder, gulping mouthfuls of tiny zooplankton and straining out the seawater. However, tender tissues for filtering meals, similar to the bristles that make up fashionable whales’ baleen, haven’t been discovered. Additionally, Hupehsuchus fossils are usually preserved in flattened slabs. The angles and high quality of preservation of the specimens’ skulls have made it troublesome to establish similarities to the skulls of recent filter-feeding whales.

That modified with the invention of two new Hupehsuchus specimens, additionally from Hubei: one full skeleton, and one of many head, neck and clavicle. Crucially, each fossils give a transparent view of the skulls from above.

“When we first saw these specimens, we thought they were very strange,” Dr. Cheng, an writer of the brand new paper, wrote in an e-mail. “We thought that the snout shape of H. nanchangensis was similar to that in modern baleen whales.”

Inspired by the skulls’ similarities, Dr. Cheng and his colleagues in contrast Hupehsuchus skulls with these of 130 fashionable aquatic species, together with baleen whales, toothed whales, seals, crocodiles, water birds and platypuses. The researchers mapped the skulls and charted methods they aligned with totally different sizes of prey. Hupehsuchus and its shut kinfolk’ cranium proportions overlapped with fashionable baleen whales’ skulls, indicating that the traditional reptiles had been filter feeders, too.

Hupehsuchus’s comparatively stiff physique meant that it in all probability skimmed alongside close to the floor with its mouth open, like a bowhead or proper whale, relatively than diving deep like a humpback. While baleen is a tender tissue and thus is much less prone to fossilize, the researchers famous the presence of grooves within the roof of Hupehsuchus’s mouth, which can have anchored baleen-like tissues.

Based on these findings, Hupehsuchus seems to be the earliest identified instance of a filter-feeding, four-limbed vertebrate. While filter feeding is seen in lots of fashionable whales, it was uncommon in marine reptiles.

Nick Fraser, a paleontologist at National Museums Scotland who was not concerned with the research, mentioned that he was persuaded by its conclusions. “I think they’ve got it right, how these animals fed,” Dr. Fraser mentioned. What’s extra, he mentioned, Dr. Cheng and his colleagues opened up an even bigger query, of how Hupehsuchus developed its methodology of feeding comparatively rapidly within the wake of the Great Dying.

“The evolution of this type of very, very specialized feeding mechanism took at least 30 million years in whales,” Dr. Fraser mentioned. Reptiles like Hupehsuchus creating filter feeding in simply three million years after the Great Dying implies that “there was a heck of a lot of evolution going on.”

Dr. Cheng mentioned that the timing of Hupehsuchus’s look, proper on the heels of the mass extinction and precipitating a takeover of the oceans by reptilian predators within the period of the dinosaurs, made it extra than simply an evolutionary oddity. “It’s been amazing to discover how fast these large marine reptiles came on the scene and entirely changed marine ecosystems of the time,” he mentioned.