Volcanic eruptions triggered a catastrophic event known as “the Great Dying” 252 million years ago, resulting in a mass extinction. This event led to significant climate change and acid rain, causing a severe decline in marine life, with less than 5 percent of species surviving.
However, this event also provided an opportunity for the evolution of unique life-forms, including a small sea-dwelling reptile called Hupehsuchus nanchangensis. This reptile, which appeared a few million years after the Great Dying, fed by filtering, similar to contemporary baleen whales like bowheads. The findings of this discovery were published in the journal BMC Ecology and Evolution on Monday.
Unlike the large sea monsters that eventually evolved, Hupehsuchus was relatively small, measuring about three feet long, including its tail. Interestingly, it had a slender snout without teeth. Scientists, such as Cheng Long from the Wuhan Center in China, have long suspected that Hupehsuchus was a filter feeder, ingesting tiny zooplankton and filtering out seawater. However, no soft tissues for filtering meals, comparable to the baleen in modern whales, have been found in Hupehsuchus fossils. Additionally, the flattened slabs in which Hupehsuchus fossils are preserved have made it challenging to identify similarities with the skulls of contemporary filter-feeding whales.
The recent discovery of two new Hupehsuchus specimens from Hubei, China, including a complete skeleton and one of the head, neck, and clavicle, has changed the game. Both fossils offer a clear view of the skulls from above. Dr. Cheng, one of the authors of the study, noted the strange resemblance between the snout shape of H. nanchangensis and that of modern baleen whales. This inspired Dr. Cheng and his colleagues to compare the skulls of Hupehsuchus with 130 aquatic species, including baleen whales, toothed whales, seals, crocodiles, water birds, and platypuses. By mapping the skulls and examining their alignment with different prey sizes, they found that Hupehsuchus and its close relatives shared skull proportions with modern baleen whales, suggesting that they were also filter feeders.
Hupehsuchus likely skimmed near the water’s surface with its mouth open, similar to bowhead or right whales, due to its relatively rigid body. While the baleen-like tissue is soft and unlikely to fossilize, researchers observed grooves in the roof of Hupehsuchus’s mouth, which could have anchored such tissues.
Based on these findings, Hupehsuchus is now regarded as the earliest known filter-feeding, four-limbed vertebrate. Filter feeding was rare among marine reptiles but is prevalent in many modern whale species.
Nick Fraser, a paleontologist from National Museums Scotland who was not involved in the study, concurs with the conclusions. He finds the research compelling and believes that the study raises a larger question about how Hupehsuchus rapidly evolved its feeding method after the Great Dying.
Dr. Cheng emphasizes the significance of Hupehsuchus’s appearance, as it coincided with the aftermath of the mass extinction and the subsequent domination of reptilian predators in the age of dinosaurs. He describes it as more than just an evolutionary oddity but a testament to how rapidly large marine reptiles transformed marine ecosystems during that time.
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