Do hot river birds feed on seeds? Scientists have been “misled” for 20 years

The reconstruction of the Hot River Bird .jpg

Rehe Bird Restoration Picture Painted by Han Zhixin and Wang Yifan

Twenty years ago, paleontologists at the Institute of Vertebrate Paleontology and Paleoanthropology of the Chinese Academy of Sciences (hereinafter referred to as the Institute of Paleovertebrates) first reported a new primitive bird fossil in Nature, the primitive hot river bird. It is the only primitive bird with a long bony tail other than Archaeopteryx, and its taxonomic location and unique body structure make it world-famous when discovered.

Another special feature of the Hot River Bird when it was first discovered was that many fossil plant seeds were preserved in its body. Among the fossils of Mesozoic birds found in the past, there is little direct evidence of feeding habits. Since then, numerous similar specimens have been published, so the Hot River Bird has been considered a seed-eating bird for a living.

Recently, the team of Marie Curie, postdoctoral fellow Hu Han of the School of Earth Sciences of the University of Oxford, and Zhou Zhonghe, academician of the Chinese Academy of Sciences and researcher of the Institute of Paleovertebrate, collaborated to publish a research result at eLife. They scanned and reconstructed a new specimen of the skull of one of the most primitive birds, the Hot River Bird, at the Synchrotron Radiation Center in Melbourne, Australia, and compared its skull and stomach contents with those of living birds in detail, overturning decades of paleontologists’ knowledge of their feeding habits.

The seed is still the fruit

The hot river bird has seeds in its belly, so there seems to be nothing wrong with speculating that it feeds on seeds. At the same time, in the case of only qualitative observation, previous paleontologists also felt that its head resembled a living bird that eats seeds such as parrots.

The type and manner in which animals feed is closely related to the shape of the skull. “However, due to the squash preservation of fossil specimens and the limitations of traditional research methods, scientists know very little about the skull morphology of the Hot River Bird.” Hu Han, the first author of the paper, pointed out.

In the new study, the researchers used advanced 3D scanning and reconstruction methods to reconstruct a hot river bird specimen in three dimensions and obtain morphological information as well as a three-dimensional model for subsequent analysis.

Collected in the Jiufotang Formation formation in Chaoyang, Liaoning Province, the specimen dates back about 120 million years, and it preserves a complete head, as well as a spine, belt and part of the hind limbs, which are classified into the original species of Rehe bird.

In addition, the researchers also sampled representative species of living birds, including fruit-eating and grain-eating, and reconstructed them in three dimensions for comparison between ancient and modern times.

Hu Han said that birds that eat seeds raw can be basically divided into two major types, one is to use the beak to open the seeds, and the other is to use the gastrospares to grind the seeds.

The analysis showed that the hot river bird did not have the high jaw that scientists had previously thought, and was significantly different in morphology from the grain-eating birds such as parrots that could open seeds, which ruled out the possibility that it would eat seeds by cracking open.

To test the possibility of another grain-eating option— using stomach stones to digest seeds, the researchers conducted a gastric volume analysis. The results showed that the seeds in the abdomen of living birds that used gastroliths to digest seeds still retained their overall morphology, but had different degrees of damage, and at the same time, the seeds and gastrolers mixed with each other and bonded tightly. In contrast, the seeds preserved by the hot river bird not only lack such damage, but are also more loosely preserved, and have never been preserved with the gastrolith, which is closer to the state of the seeds in the belly of the fruit-eating bird.

In fact, there is no significant difference in jaw morphology between the Hot River Bird and the live fruit-eating bird. Hu Han explained that for fruit-eating birds, the beak does not need to do too much treatment, so it is not surprising that there is no specialization of the beak.

So far, researchers have ample evidence that the Hot River Bird is actually a fruit-eating bird that is at least seasonal, and that the seeds in the belly are nothing more than the products left over from their indigestion. It is also the earliest fossil record of the ecological habit of birds eating fruit.

The earliest plant propagators

Many live birds have a specialized or seasonal fruit-eating habit, they eat plant fruits into the stomach, hard seeds can not be fully digested, will be excreted with their feces, fruit-eating birds have become an important medium for plants to spread seeds. But when exactly this habit appeared in the fossil record was previously unknown.

“The radiative evolution of birds during the Early Cretaceous period was an important event in the evolution of terrestrial ecosystems, which was followed by the flourishing and diversification of plant fruit structures that continued throughout the Cretaceous period.” Hu Han said that scientists have been speculating that there may be an evolutionary link between early birds and fruiting plants, but this speculation has never been proven because the fruit-eating records of fossil species are very difficult to determine.

The latest study of the hot river bird suggests that birds may have played the role of plant seeding mediums in the earliest stages of their evolution. Hu Han believes that as a propagator with a certain ability to fly and greatly increase its range of movement, early fruit-eating birds are likely to have assisted in the expansion of fruiting plants, and the high-quality food of fruits may also expand the evolutionary possibilities of early birds – the interaction between birds and plants may have an important place to be further explored in the Cretaceous land revolution.

It is worth mentioning that in this study, the representatives of live birds with different diets such as fruit-eating and grain-eating selected by scientists include two “star” species that have recently become extinct – the Carolina long-tailed parrot and the passenger pigeon.

(Akiko-e) .jpg

Four-panel manga Akiko-e

“In a sense, we are using recently extinct species to study ancient extinct species.” Hu Han told China Science Daily.

Since scientists cannot tell from the outside whether the specimen has a stomach volume inside, and it is not realistic to scan each specimen, the research team’s analysis of the gastric volume part is preferred to select samples from the specimens that have been scanned in the Oxford University database.

“These recently extinct species have a higher chance of being scanned than other relatively common species, so eventually our dataset includes these two star species.” In Hu Han’s view, this is also worth thinking about, “When humans lose a species, there may be much more information lost than we think.” (Source: China Science Daily Hu Minqi)

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