On November 18, the reporter learned that Professor Zhang Zhifei of the Early Life and Environment Innovation Research Team of Northwest University supervised the doctoral student Liu Fan, the joint research group of foreign young scientists Tim topper and Dr. Skovsted of the Swedish Natural History Museum carried out the latest observations and research findings on the soft tongue snail fossils found in the Chengjiang biota: negated the conclusion that the soft tongue snail belongs to the brachiopod crown group or the sister group of brachiopods, and believes that the soft tongue snail does not belong to the tentacle crown animal and is most likely close to the mollusk.
This achievement fills the gap in the anatomy of the mouth of the straight-tube snail fossil, and adds new key softstone evidence to the systematic analysis of the soft-tongued snail fossil that has been debated for nearly 200 years.
Three-slot snail restoration diagram (provided by the interviewee)
The soft-tongued snail is part of the Cambrian evolutionary fauna
It turns out that since 200 years, there has been a great controversy in the academic community about the biological properties of the invertebrate soft-tongue snail during the Cambrian outbreak. Some scholars believe that the soft-tongued snail is closely related to brachiopods, and even believe that the soft-tongued snail belongs to the sister taxon or crown group of brachiopods.
Teacher Zhang Zhifei introduced that there are about 38 living animal phylums on the earth, of which many animal phylums such as trilobites, ancient cups, and penstones have been extinct. The soft-tongued snail is also an extinct Paleozoic marine benthic invertebrate that flourished from the Cambrian explosion of life 540 million years ago and became extinct at the end of the Permian, making it a major component of the Cambrian evolutionary fauna.
The first report of this fossil comes from the Russian paleontologist Eichwald in 1840, although the early monographs described and revised some fossils are relatively vague, but it has great reference significance for later paleontologists.
Soft-tongue snails have been widely found and reported in Europe, North America, Australia and China. Its fossils generally preserve conical tubes, mouth caps and appendage structures, in the early Cambrian period, the soft-tongued snail underwent rapid evolutionary radiation events, that is, the Cambrian explosion, in the long 4.6 billion years of earth history evolution, almost all living animal fossils, including vertebrates, suddenly appeared in the early Cambrian (540 million years ago) strata, with high diversity. However, to this day, research on its biological properties and systematics is still controversial.
Brachiopods or molluscs? Both have research results to support this controversy specifically, Zhang Zhifei introduced, in 2017, paleontologist Moysiuk et al. found a wing-like tentacle structure in the soft tongue snail fossils in the Burgess Shale, Canada, and explained it as a ciliary ring homologous to the ciliary ring feeding structure of the tentacle crown animal. In addition, the soft-tongued snail has two shells, the mouth cover and the spinal canal, so it is believed that the soft-tongued snail should belong to the tentacle crown animals closely related to brachiopods. Subsequently, some scholars have found a "meat stem" structure similar to that of brachiopods in the fossils of straight-tube snails, thus further speculating that soft-tongued snails are closely related to brachiopods, and even believe that soft-tongued snails belong to sister groups or crown groups of brachiopods. However, through the fine observation and comparison of shell structure, some scholars have found that the soft-tongued snail has a similar flaky shell microstructure with the shells of molluscs of the same period, thus adhering to the relationship between soft-tongued snails and molluscs.
Negating the conclusion of "relatives" Experts at West University fill the research gap
So, what are the new findings of the early life and environmental innovation research team at Northwestern University? First, the team found that the straight tube snail fossil three-slot snail in the Chengjiang Fossil Bank (Cambrian 3rd order) preserves a fan-like arrangement of tentacle structures. Its tentacle-like feeding organs were found to be freely retractable and retractable inside and outside the edge of the ventral cap abdomen.
What does this mean? Zhang Zhifei introduced that the tentacle crown animals (brachiopods, broomworms and bryozoans) have horseshoe-shaped arrangement of tentacles, the mouth is located at the base of the tentacle crown, and the tentacles are arranged around the mouth (placed outside the crown of the tentacles). In the life of the tentacle crown animal, the base of the tentacle is stable and immovable, and with the swing of the tentacle, the filtered food flows into the mouth along the tentacle arm for filter feeding life. However, the tentacle-like structure of the soft tongue snail can move freely back and forth with the contraction of the internal organs of the body muscles, indicating that the tentacle-like structure of the soft tongue snail is significantly different from that of the tentacle crown animals such as brachiopods, and is not passive filter feeding life, but may be deposited for feeding; in addition, the tentacle structure of the soft tongue snail is not "around" the mouth distribution, so it does not meet the definition of ciliary rings of the crown of the tentacles; although there are similarities between the tentacle crown of the soft tongue snail and the shape of the tentacle crown of the brachiopod larval stage, However, the main function of the tentacles in the larval stage of brachiopods is to swim rather than filter feeding. These evidences suggest that the tentacle-like structure of the soft-tongued snail is different from the ciliary ring tentacle function of the tentacle crown animal and is not homologous. Therefore, the functional morphology of soft-tongued snail tentacles has shown that soft-tongued snails are not tentacle crown animals and are far related to brachiopods.
In addition, the early life and environmental innovation research team of Northwest University also observed the Yunnan meat stem snail in the Chengjiang biota and found that there was no fleshy stem attachment structure of brachiopods in the structure of the beginning of the spinal canal. Yunnan meat stem snail belongs to the soft tongue snail, and in 2018, researchers reported that at the end of its shell developed a "meat stem structure" similar to the flesh stem of brachiopods, thus supporting the soft tongue snail belonging to brachiopods. However, through our latest observations, we found that there is no 'meat stem-like' structure at the beginning of the yunnan meat stem snail shell, and the so-called meat stem is actually part of the fragments or residues of the cone shell shell, and this difference in preservation can also be corroborated by similar soft tongue snail fossils in other fossil libraries, thus negating the thesis that the soft tongue snail has a meat stem. Thus, new research denies that the soft-tongued snail belongs to brachiopods or their sister taxa.
The results were recently published online in the National Science Review. Today (November 18), it was reported by people's daily (overseas edition).
Source: Wen/Xi'an Newspaper all-media reporter Zhang Xiao
Edit: Mustard peanuts