What today's baleen whales can do, a small marine reptile was apparently able to do an amazing 250 million years ago, report paleontologists: Hupehsuchus nanchangensise sifted small animals out of the water at that time, according to the examination of newly discovered fossils. The morphological features are strikingly similar to those of today's baleen whales. It is therefore an impressive example of parallel evolution, say the researchers: the two groups of animals came up with the concept independently of one another at a large time interval.
The fascination of evolution: fossils reflect how living beings conquered water, land and air over millions of years, and in the process also produced sophisticated nutritional concepts. Interestingly enough, there were always “returners”: land animals that had previously evolved from aquatic animals later developed into aquatic creatures again. The most famous example are today's marine mammals, which are descended from land animals. But there were such comebacks much earlier in the history of evolution: Some rulers of the medieval sea world, such as the ichthyosaurs, plesiosaurs or mosasaurs, also emerged from terrestrial reptiles.
These were mostly predators of larger prey. But have some marine reptiles also sifted small animals out of the water - similar to today's baleen whales? The marine mammals have special adaptations for this: they use sieve-like structures in their mouths, through which they push water and food that they have previously sucked into a throat pouch. So far, there is little evidence that certain Mesozoic marine reptiles may have used similar techniques. But now the "patent" is emerging very clearly, and in a very early marine reptile at that, reports the scientists led by Zi-Chen Fang from the China Geosciences University in Wuhan.
Amazingly old and specially adapted
Hupehsuchus nanchangensise was a reptile about a meter long whose remains were known from earlier fossil finds in China. The animal lived there 249 to 247 million years ago, and its skeletal features already clearly identified it as a sea creature descended from ancient land creatures. "Hupehsuchus was related to ichthyosaurs and has been known for 50 years, but its lifestyle has not been fully understood until now," says Fang. This was because no well-preserved skull fossils were available. But that has changed: The new results are based on the examination of two newly discovered Hupehsuchus fossils, in which the heads are preserved in detail. Researchers have now been able to take a close look at the structures and compare them with the morphological characteristics of various modern-day aquatic animals.
"The two new Hupehsuchian skulls revealed that the animal's long snout was composed of unfused, strap-like bones, with a wide space between them that ran the full length of the snout," says senior author Long Cheng of the Center of Chinese Geology service in Wuhan. "This construction is otherwise only found in modern baleen whales, where the loose structure of the mouth and especially the lower jaw allows them to support a huge neck area, which can inflate enormously when swimming forward and swallow small prey," explains the paleontologist.
Evidence of baleen-like soft structures
Although the researchers could not find any traces of baleen-like structures, there was indirect evidence that similar soft-tissue elements may have once existed in Hupehsuchus. "The clue lies in the absence of teeth," says co-author Li Tian of the Geosciences University. "Modern baleen whales, unlike toothed whales like dolphins and orcas, don't have teeth. Instead, the filter feeders have grooves along the jaws to support baleen curtains - long thin strips of keratin. Hupehsuchus had exactly the same grooves and notches on the edges of its jaws, so we suspect baleen-like structures were also present there,” says Tian.
"We were amazed to discover these adaptations in such an early marine reptile," says Fang. According to the team, this is a particularly interesting case of parallel evolution. One speaks of this when similar adaptations to a certain way of life have arisen in the course of the evolutionary history of unrelated living beings. As for other features of Hupehsuchus, the features of its body indicate that it was likely a rather slow swimmer, the researchers say. They say this suggests that the marine reptiles behaved similarly to bowhead whales, probably swimming near the sea surface with their mouths open to scavenge their food from the water.
The fact that Hupehsuchus developed this diet so early on may have had to do with the intense competition for food in its era, the researchers say. "Hupehsuchus lived in the early Triassic and was part of a massive and rapid oceanic repopulation," explains co-author Michael Benton of the University of Bristol. “This was a time of turmoil, just three million years after the great mass extinction at the end of the Permian that wiped out most of life. It is fascinating to discover how quickly these marine reptiles emerged and shaped the marine ecosystems of the time," says the paleontologist.
Source: University of Bristol, professional article: Ecology and Evolution, doi: 10.1186/s12862-023-02143-9