Modern Express (reporter Aria) is only the size of a millimeter, has a large mouth, but has no tail and anus... The crinkle cysts lived in the ocean about 535 million years ago and is thought to be a close relative of human distant ancestors.
Recently, a research team composed of researchers from scientific research units inside and outside the United Nations has given a new interpretation of its kinship and evolutionary significance through in-depth research on microenvironed lithophyllaceae about 535 million years ago in southern Shaanxi. Recently, the relevant results were published online in the international top academic journal Nature.
With a mouth and no anus, 535 million years ago, the ancestors of mankind looked like this?
"Who am I and where am I from?" Where am I going? "Throughout the ages, these ultimate three questions have plagued countless people. With the tireless exploration of generations of scientists, the mystery of human origins has gradually been unveiled.
520 million years ago, the "world's first fish in the Chengjiang fauna - Kunming Fish Order" represented the "macro-type" human ancestors who had just created their minds and primitive spines. So, further on, what did the ancestors of mankind look like?
△ Scanning electron microscopy photos of a specimen of the crease cyst
The body structure is simple and oval; It looks weird, like a bag with only one opening; There is a "blood basin mouth", around which radial folds are developed, and the spines are symmetrically arranged with radiant protrusions... In 2017, Chinese scientists found fossils of crumb cysts in the Kuanchuanpu biota in southern Shaanxi, which is believed to be the earliest hindspeak.
Posterior-mouthed animals include echinoderms (sea lilies, starfish, sea urchins, etc.), hemizoans (intestinal gills and feather gills, etc.), cephalics (Wenchang fish, etc.), tails (sea squirts, etc.) and vertebrates (fish, frogs, crocodiles, dinosaurs, birds, tigers, pandas and humans, etc.).
△ Wrinkled cyst restoration diagram (painted by Yang Dinghua)
It is reported that the crumpled cysts previously lived in the ocean, and when they encountered food, they opened the retractable pouch and swallowed it together with water. The key feature that supports the crinkle cysts as a posterior-mouthed animal is the "gill hole" structure in the fossil, which is one of the original features of the posterior-mouthed animals. Since humans also belong to the post-mouth animals, the wrinkled cyst is considered to be one of the early ancestors of humans, which has attracted much attention from the academic community.
Crurised cysts are more closely related to molts
This time, through an in-depth study of more and more complete fossil specimens, the research team found that the two sides of the body of the crinkle cyst are symmetrically arranged with bone-bearing plates, and there are a large number of small spines on the reverse mouth surface. The structure that was once interpreted as a "gill hole" is likely to be a closed pore-like structure formed by the wear and tear of the bone-bearing plate during the fossilization process.
△ Location map of the cysticers system
"Some of the key features of the crinkle cyst, such as the developmental epidermis also known as the stratum corneum, the absence of cilia in the epithelium, and the structure of the radiation symmetrical arrangement of the terminal mouth and the annular mouth, indicate that it is more closely related to molting animals." The researchers note that the creases are more likely to be molts than hindspeakers.
Molting is also called peeling, and for some animals with hard carapace, it is also called shelling. For example, the crab that has just peeled off its skin, because the carapace is soft and the flesh is very delicious, is a blessing for those who love crabs and are too lazy to peel the shell.
Molts are a "large family" that includes pan-arthropods and cyclic neurozoa. Among them, in addition to crabs, roundworms, essies, tardigrades, trilobites, spiders, insects, centipedes, shrimp... These are also pan-arthropods. Cyclic neurozoa include gill trolls, snouts, roundworms and horse nematodes.
Fossils of various animals suddenly appeared in the Cambrian strata from about 540 million years ago to 530 million years ago, which is known as the Cambrian explosion. The Modern Express reporter learned that the earliest known fossils of molts appeared in the Cambrian "lucky period", but they were all cyclic neurozoa. The wrinkled cysts add a whole new type to the earliest known molts. However, the systematic position of the crablopods inside the molting animals has not been resolved. It may be the ancestral type of cyclic neurozoa, the ancestral type of pan-arthropods, or the ancestral type of molts.
In addition , molts generally have a " demoral " body , and their latest common ancestor may have been demodex-shaped. The "cystic" body structure of the wrinkled cyst is significantly different from the "demodex" body structure of other molting animals, suggesting that the "demodex" is not the only body type of molting animals, and the latest common ancestor of molts may not be worm.
The researchers say the origin of molt body structures still needs to be further studied on the interevolutionary relationship between the earliest known molts during the Cambrian "lucky period".
(Source: Nanjing Institute of Geology and Paleontology, Chinese Academy of Sciences, Editor Wei Rufei)
(Modern Express All Media)