specimen
Ecological restoration map of Chimera Spider of Ying's study by Huang Diying's team
■ Zhang Wenjing, a reporter of this newspaper
Speaking of spiders, everyone will certainly not be unfamiliar. Spiders belong to the arachnid order of arthropods and are one of the most common animals in nature. According to statistics, the total number of spiders in the world today is as heavy as 478 Titanic ships, and it eats about 400 million to 800 million tons of prey every year, more than the total weight of the world's population. Many species of spiders are the most abundant predatory predators in terrestrial ecosystems and play an important role in maintaining the stability of agroforestry ecosystems.
We are very familiar with the appearance of modern spiders, but what did spiders look like more than 100 million years ago? How are they different from modern spiders? How can this difference reveal the evolutionary mystery of spiders? In February this year, two international research teams led by Wang Bo and Huang Diying, researchers at the Nanjing Institute of Geology and Paleontology of the Chinese Academy of Sciences, published two papers "back to back" in the same issue of the British sub-journal Nature Ecology and Evolution, reporting on the mysterious 100 million-year-old "long-tailed spider" found in Burmese amber, the Ying's Chimera spider. This spider looks really different from modern spiders.
These spiders are a bit weird
Faced with four 100 million-year-old "elderly" Burmese amber fossils, the researchers carefully observed them carefully with optical microscopes, laser confocal microscopes and high-resolution CT for three-dimensional stereoscopic presentation. Under the microscope, the shapes of several small animals in golden amber gradually became clear and vivid.
These small things are only two or three millimeters long, and the body is divided into a cephalothorax and an abdomen, with 6 eyes and 8 walking feet. Like a spider, but not certain. Because although these are the distinctive features of spiders, they are not unique to them, and some other arachnids such as scorpions also have them. It wasn't until the well-developed spuns in its abdomen were observed that the researchers finally determined that these were indeed spiders from ancient times. "One of the most important features of determining whether a creature is a spider is that it has glands that produce spider silk." Huang Diying explained.
The next discovery surprised and excited the researchers, these spiders actually have a slender tail whisker, which can reach more than 1.5 times the length of their body, and the tail whisker is divided into more than 70 segments, each with a slender ring of bristles.
It should be known that living spiders do not have a long tail, and only in a small number of spiders, there is still a short protrusion, called the hip plate. But two or three hundred million years ago, spiders still had tails.
Previously, in the Devonian strata of New York, which dates back more than 300 million years, researchers have found fragments of fossils with the unique claw structure and long tail whiskers of spiders. In the Permian formation of Russia about 270 million years ago, researchers have found a relatively complete fossil that can be seen dragging a long tail behind its butt. Therefore, some scientists have established an extinct order of the arachnid order, the Ural arachnid order.
Since then, researchers have not found any fossils of long-tailed spiders until the appearance of these pieces of amber.
"They have a lot of hairs on their tails, probably sensory hairs. In addition, the tail is straight, can not swing freely, and there are no venom glands. Therefore, it may belong to the perceptual organ, which is used to perceive the environment and odors in the rear, etc. Wang Bo introduced.
From the morphological characteristics of the spiders retained in the amber, researchers can infer the picture of the life of these spiders 100 million years ago - in the dense jungle, under the roots of the trees, in the dirt, the spider hides in a small coiled silk hole, the hole is covered with the silk they spit out, as soon as a small worm sticks up, they will quickly extend their claws to turn it into a delicacy in the abdomen, and if an enemy is coming, its tail will feel it in order to escape. Female spiders generally hide in the hole, while male spiders swim outside. "This is also the reason why we now find more males than females, which is the opposite of the number of males and females we have found in the spider fossils in the past." Huang Diying said.
Why tails are so important
The amber spider found this time has a spinning vessel, which confirms its identity as a spider. The long, well-preserved tail inside amber is enough to prove its antiquity, after all, the tail is a feature that living spiders do not have.
Because these spiders reflect a mixture of the biological characteristics of the multiple arachnids possessed by the new species, they are named "Chimera spiders". Among them, the Chimera is a monster with a lion's head, a sheep's body, and a snake's tail in ancient Greek mythology, and the species name Ying is derived from the surname of the specimen provider.
Why are the researchers so excited about the multi-species arachnid biometrics embodied in the Chimera spider, especially its long tail? Is a thin tail really that important? This also begins with the initial evolution of arachnids.
The ancestors of arachnids were marine animals that resembled scorpions or horseshoe crabs, landed on land around the Ordovicians (about 450 million years ago) to the Silurians (420 million years ago), and then quickly differentiated into many different taxa. Figuring out the kinship between these taxa is not an easy task, and their evolutionary history is questionable due to the fragmentation of fossil evidence.
Of all these taxa, the Ural spider is thought to be closestly related to modern spiders. In addition to their similar appearance, they all have silk tubes that can produce spider silk and weave cobwebs. However, there are also significant differences between the two. "Modern spiders have long spinning vessels, and each section of the spinning vessel has a spinning gland; the woolly spider's spinning glands are irregularly arranged at the back of the body, and there are no knotted spuns." Huang Diying said.
As a recent "relative", the Ural spider is obviously of great significance for the study of the origins of modern spiders. But these animals have long since become extinct, and fossils are unusually rare. Before the discovery of the Chimera spider, only two ural spider fossils were found in the United States and Russia, some of which were very poorly preserved.
The Chimera spider of Ying's in the amber found this time is nearly perfectly preserved, providing researchers with many valuable details. The researchers found that they had both the distinctive elongated tail whiskers of the Ural spider and the multi-knotted spun and silk gland structure almost identical to that of modern spiders. "This not only postpones the extinction of the long-tailed spider from about 250 million years ago to more than 100 million years ago." More importantly, this suggests that it is a transitional link between ancient and living spiders, making up for an important link in the evolution of spiders and providing key evidence for solving the mystery of spider origin and evolution. Huang Diying said. But he also stressed that whether the Chimera spider belongs to the order spider or appears as a separate order, more fossils and further research are needed.
More secrets have yet to be solved
As for why the spider's tail gradually disappeared, researchers can only speculate. "Maybe it's because the spider weavers later became more powerful." The Chimera spider should not have the ability to weave a complex web, it may be a hole in the ground, weaving an irregular web around the hole. With the evolution of spiders, the ability to weave webs has become stronger and stronger, and if they move on the web, the tail has played a hindrance role. At the same time, its living environment is also changing. We speculate that the long tail is a perceptual organ, sensing prey, predators, and so on. As the spider's ability to weave webs strengthens, it can sense the surrounding situation through the webs it weaves, so gradually it does not need such a long tail. Wang Bo said.
Spider fossils have always been difficult to preserve, and only specially buried fossil points can preserve the body and detailed characteristics of spiders, such as the Daohugou biota in the middle of the Jurassic Period in China. "Spiders are more difficult to preserve in rocks because spiders mainly live in woods and soil, and the probability of being buried in fossils in lakes is relatively small." In addition, spiders are small and have softer bodies, making it relatively more difficult for this species to preserve in fossils. Wang Bo introduced. This amber can preserve the spider intact, and undoubtedly explores a new way for spider research. But Wang Bo said that although there is a lot of amber, its large number appeared more than 100 million years ago, and there is very little more ancient amber, and even less spider amber.
Currently, researchers have a total of 5 pieces of amber with spiders in their hands, of which 4 spiders are males. Huang Diying said that team members are stepping up their research on the only female individual, hoping to reveal more mysteries about spiders.
Wang Bo's team studied the restoration of the Chimera spider
China Science Daily (2018-03-02 4th Edition Nature)