New fossils link ancient reptiles to whales

An unusual ancient marine reptile swallowed tons of shrimp-like animals using a feeding technique similar to that applied by some modern whales.

The reptile, called Hupehsuchus nanchangensislived in Earth’s oceans between 247 million and 249 million years ago, during the early from the Triassic period.

Fossils of the reptile were first found in China in 1972. However, researchers have struggled in recent decades to understand the animal’s eating behavior and lifestyle because none of the skulls were well preserved.

Luckily, two newly discovered fossils unearthed from China’s Jialingjiang Formation in Hubei Province include the nearly complete skeleton of one reptile and a large portion (from head to collarbone) of another.

The findings allowed the researchers to closely examine the Hupehsuchus nanchangensis and determined that the reptile had a toothless snout and a small, narrow skull. Its lower jaw was loosely attached to the rest of the skull, meaning the creature could expand its mouth, similar to what modern whales do to eat by filtering their food, so-called filter feeding.

The study detailing the findings was published Tuesday (8) in the journal “BMC Ecology and Evolution”.

“The new findings were more complete than the previous ones and showed that the long snout was composed of unfused bones, like strips, with a wide space between them running along the length of the snout,” said study co-author Long Cheng, professor at the Wuhan Center for Geological Survey of China. “This type of formation is only seen in modern baleen whales, where the loose structure of the snout and lower jaws allows them to support a huge throat region that opens wide as they swim forward, swallowing small prey.”

Evidence of filter feeding

The researchers compared the skull of the Hupehsuchus with 130 modern skulls of various aquatic animals, including 23 species of seals, 14 crocodilians, 52 toothed whales, 25 birds, platypus and 15 species of baleen whale. The team found that the creature had more in common with baleen whales than with other animals.

Bowhead and modern right whales are species that use filter-feeding techniques to eat, sifting material through plates of fins as they swim with their mouths open close to the ocean’s surface to absorb large amounts of plankton or small crustaceans called krill.

“The fin is made of keratin, forming a soft yet tough fibrous curtain hanging from the upper jaw of this type of whale,” according to the study. During filter feeding, the sturdy fin plates trap prey as the water is forced out.

But until now, there hasn’t been enough evidence in the fossils of ancient reptiles using filter feeding. Although no actual evidence of the fin was found on the skull of Hupehsuchus, the researchers noted a series of ridges around the palate where soft tissue may have helped with the feeding system. These are structures similar to those seen in baleen whales, which have strips of keratin instead of teeth.

“Modern baleen whales do not have teeth, unlike toothed cetaceans such as dolphins and killer whales,” explained study co-author Li Tian, ​​an assistant researcher at the Wuhan University of Geosciences of China.

“They have grooves along their jaws to support curtains of fins, which are long thin strips of keratin, the same protein that makes hair, feathers and nails. O Hupehsuchus it had the same ridges and notches along the edges of its jaws, and I think it evolved independently with some form of a fin.”

evolutionary revelations

the reptile Hupehsuchus it had a rigid body that made it a slow swimmer, so it probably expanded its throat when swimming to take large gulps of water, swallowing the shrimp-like prey of early Triassic oceans. It is possible that the marine reptile did not have this ability from the beginning. In fact, the creature may have evolved over time, developing the adaptive physical traits that made filter feeding possible if the level of competition for food was high, according to the study.

The discovery is an example of what scientists call convergent evolution, where similar traits evolve independently in different species.

“We were surprised to discover these adaptations in such an ancient marine reptile,” said study lead author Zichen Fang of the Wuhan Center. “Hupehsuchians were a unique group in China, closely related to ichthyosaurs and known for 50 years, but their way of life was not fully understood.”

Whales evolved about 15 million years after dinosaurs went extinct at the end of the Cretaceous period, 66 million years ago. And it took about 17 million years for them to evolve their filter-feeding adaptations, according to the study.

However, the same technique was quickly adapted, within about 5 million years, by marine reptiles that lived much earlier than whales.

“Hupehsuchians lived in China in the early Triassic, about 248 million years ago, and were part of a huge and rapid repopulation of the oceans,” explained study co-author Michael Benton, professor of vertebrate paleontology at the School of Earth Sciences. from the University of Bristol. “It was a time of turmoil that happened just three million years after the massive Permian-Triassic extinction that wiped out most life. It was incredible to discover how quickly these large marine reptiles arrived on the scene and completely changed marine ecosystems at the time.”