The "spider" hunting scene billions of years ago was "photographed" in amber

Ecological studies on fossil spider species in Cretaceous amber

Research author: Zhai Shihan team

First author: Zhai Shihan

Second author: Guo Zhongbin, Huang Bonan, Li Zhengxin, Shen Letian, Wang Jie, Wang Hao, Wang Yuchenzi (in alphabetical order)

Affiliation: Beijing Institute of Technology

summary:

Order Ricinulei, arthropod spiders, from the scarcity of fossil specimens and their ecological and behavioral data to the small distribution and number of existing populations, no matter from which aspect, arthropod spiders are creatures of great research value and exploration significance.

This study mainly focuses on the scarcity of ecological and behavioral data on segmented spiders, and is an exploration and discovery as well as the supplement of relevant evidence.

The author took advantage of the research characteristics of amber fossil specimens, where biological remains can be preserved in a three-dimensional, clear and intuitive manner. Based on the research subject of the fossil specimens and the relationship between them and other organisms, he accurately recorded information evidence on certain ecological behaviors of arthropod spiders, and also made some new discoveries. Through specimens in paleontological fossils, he provided detailed and reliable evidence for some of the research results achieved by modern arthropods, providing strong evidence for further research on arthropods in the future.

Keywords:

Arachnid spider, Cretaceous period, amber fossil

Animalia, Arthropoda, Chelicerata, Arachnida, Stalked Gnaphaloma, Ricinulei, Arachnostomatids. A species of spiders found in the Carboniferous strata hundreds of millions of years ago, with a few populations still living in remote areas of Africa and some parts of America.

Figure 1: World distribution map of three living genera of arthropod spiders

The spider, from the name, may be a spider, but it is actually a small group of arachnids that is completely different from the order Araneae. The living species are usually only half a centimeter to one centimeter long. It is closely related to the XiPhosura in the ocean and is a sister group to the modern Limulidae. Some of its appearance features and six-leggedness in the larval stage are similar to creatures in the orders Acariformes and Parasiformes.

Articulated spiders, whether fossil or living, are extremely rare. There are currently 83 known living species in the world, and 18 fossil species (including two found in amber from the Cretaceous period in Burma). There are a total of 101 living and fossil species.

Since most of the fossil specimens of Arthralgia come from the Carboniferous rock layers, the number of species is rare, and they are all extinct species, so the fossil specimens of Arthralgia spiders presented to the world are almost incomplete in limbs. Even though the specimens in the Cretaceous amber fossils fill this gap in terms of completeness, reliable and powerful evidence that can show the ecological behavior of Arthralgia spiders is extremely scarce. Before this paper was written, the research on Arthralgia creatures in the domestic and even international academic fields was still in the stage of inferential definition of the living habits and behaviors of ancient Arthralgia creatures based on the living species of Arthralgia spiders as a reference, using speculation or comprehensive description methods.

Figure 2: Hand-drawn reconstruction of specimen 1

The two fossil specimens of arthropod spiders studied by the author were collected in October 2017. They are both from amber in the middle and late Cretaceous strata in the northern Kachin region of Myanmar, dating back about 99 million years ago. Both specimens have special ecological behavior scene manifestations, and the behaviors occurred in pure natural states at different growth stages.

Figure 3: The holotype and dorsal type of the two specimens

Specific morphological characteristics of the specimen:

Specimen 1, female nymph ♀. Body length 2 mm. ① Body is short and thick. ② Eyeless. There are two round protrusions similar to dielectric membrane photoreceptors near the skull of the carapace. ③ The carapace is nearly square, with a movable skull on the front edge. ④ The abdomen is clearly segmented, with a pedicel formed at the front end of the abdomen. There are two shallow longitudinal lines that run through the transverse segments of the abdomen, forming a grid-like texture, and there is a protrusion at the very end of the abdomen. ⑤ The skull is slightly upturned, and the left chelicerae and mouth can be seen. The chelicerae are divided into two parts, the chelicerae and the chelicerae. ⑥ A pair of pedipalps, each pedipalp is divided into six segments, namely [1 base segment, 2 trochanter, 3 leg segment, 4 tibia, 5 palm segment and 6 claws (the upper claw has an immovable finger and the lower claw has a movable finger)]. ⑦Eight walking legs, each leg is divided into eight segments, namely [1 coxa, 2 trochanter, 3 femur, 4 knee, 5 tibia, 6 metatarsal, 7 tarsal, 8 tarsal claw]; the number of segments of the tarsal segments is different, the first leg has 1 segment, the second leg has 4 segments, the third leg has 3 segments, and the fourth leg has 2 segments. ⑧: The chest has umbilical texture. ⑨The first abdominal segment can be tilted up and has a pair of reproductive pores. ⑩Both the dorsal and ventral surfaces have nipple-like protrusions of varying sizes.

Specimen 2, female larva ♀. Body length 1 mm. The basic structure and morphology are almost identical to specimen 1. Differences: ①Only six walking legs grow on both sides of the thorax, and the fourth walking leg grows in the nymph stage. ②The number of segments of the walking leg tarsus is different. ③The first walking leg tarsus has 1 segment, the second walking leg tarsus has 2 segments, and the third walking leg tarsus has 2 segments.

Figure 4: Enlarged view of the head of the segmented spider nymph in specimen 1

Figure 5: Magnified view of the abdomen of the segmented-bellied spider nymph in specimen 1

Figure 6: Observation of the four tarsal segments of the segmented-bellied spider nymph in specimen 1

Figure 7: Observation of the tarsus of the legs of the larvae of the middle-segmented spider in specimen 2

The author carefully observed the limb structures of the fossil spiders in Cretaceous amber, and consulted a large number of scientific literature on spiders, and found a foreign scientific paper published in the 1970s. Among them, the morphological structure of the larvae, nymphs and adults of the spiders (mainly the changes in the tarsal segments on the four pairs of legs) was carefully compared and verified. Not only did it determine the exact growth stage of the fossil spiders in Cretaceous amber, but it also verified the accuracy and practicality of this scientific paper. From another perspective, it is a scientific and rigorous research and demonstration of all aspects of living species, which can provide strong evidence support for the restoration of the fine structure and morphology of ancient species, especially extinct species, and can be a very trustworthy reference.

Two fossil specimens of arthropod spiders in Cretaceous amber. What is shown is that arthropod spiders do almost the same thing in two different growth stages, the larval stage and the nymphal stage, that is, predation. The larval stage arthropod spider preys on a mosquito belonging to the class Insecta and the order Diptera. This mosquito appears right in front of the larval arthropod spider, and the first step on the right side suppresses and controls it. And from the degree of damage to the mosquito's body and the distance it was pushed out, it can be clearly seen that the mosquito has been eaten clean. Because there is a very obvious wound mark on the mosquito's chest and back, left by the skin and flesh being turned outward after being eaten. There is also a scar on the mosquito's head, which should be some kind of sharp object that quickly cuts the mosquito's head from the mouthparts to the antennae. From these subtle observational evidence, we can roughly infer the scene of the predation at that time. A spider larva quietly approaches a mosquito, and when it reaches the effective attack range, it quickly swings its second leg and uses the acceleration inertia of the club-shaped tarsus to drive the tarsal claw at the end of the leg to scratch the mosquito's head. The mosquito dies before it can react. The spider uses the claws at the end of the pedipalps to tear and the chelicerae to cooperate, eating away the mosquito's chest tissue.

The hunting scene of the nymphal spider is more intuitive and thrilling. The entanglement and strangulation, the strength confrontation, the legs of both sides are entangled, and the fierceness is fully revealed. It is a posture of fighting for life. Because no matter which side loses the battle, it means the end of death. In a fight scene where the two sides are almost evenly matched, how to judge whether the nymphal spider is the winner? The reason needs to be analyzed from their body structure and hunting skills. Insecta, Hemiptera stink bug is a kind of insect that is good at flying and has a quick reaction. Especially the one fighting with the spider in the specimen should belong to the genus of Assassinidae, with extremely strong hunting ability, and some species even hunt Arachnidae. It can be regarded as an out-and-out cold-faced killer. The stink bug in the specimen picture already has the idea of ​​killing the spider with one blow. Because the stink bug has raised its strong and hard iron spear-like beak to a certain angle, which is a posture that the beak will not show when the stink bug is in normal activity (the normal dominance of the beak can be referred to the author's other Cretaceous stink bug specimens). How did the segmented-abdomen spider nymph face such a dangerous and critical situation? The segmented-abdomen spider in the specimen gave a perfect answer. The segmented-abdomen spider used the advantage of the extra-long limb structure of the left second leg to block the stink bug, especially the lethal beak, at a safe distance. At the same time, it used the third leg to assist in the attack, firmly hooking the left limb of the stink bug with the capture leg to prevent the stink bug from retreating and escaping. Moreover, even the pedipalps with relatively short limbs have been facing the enemy to the greatest extent, ready to join the battle at any time. The fourth leg is the main walking leg of the segmented-abdomen spider. At the moment of life and death, it also participated in it and blocked the attack route of the stink bug's beak. The skull is slightly opened, and the left chelicerae have been exposed. Such a strategic measure of both offense and defense, defense and attack, really makes the author amazed. Such a wonderful and shocking scene of predation battles between arthropod spiders has never appeared in ancient fossil species of arthropod spiders, and even in the process of scientific researchers raising living arthropod spiders, such a situation has never been actually observed and recorded.

The two arthropod spiders at different growth stages preyed on insects from the order Insecta, the order Hemiptera, and the order Diptera, respectively. This is absolutely detailed and reliable visual evidence. From these evidences, it can be concluded that the broad interpretation that arthropods prey on small arthropods is highly correct, but lacks specific directionality. This problem has been successfully solved in this study. In the future, when introducing the predation habits of arthropods, it can be clearly marked that arthropod spiders mainly like to prey on small arthropods such as the order Hemiptera and Diptera of the order Insecta. An accurate answer from the "Arthropoda" to the "order" or even "family", "genus", and "species" level will be a major step forward in the field of arthropod research.

Figure 8: Predation scenes depicted in two specimens

During their study of the ecological behavior of the Cretaceous amber fossil spiders, the authors unexpectedly discovered a phenomenon that had never been discovered or recorded in related research fields at home and abroad: spiders can be parasitic.

Spiders, which belong to the same class of Arachnida, have been recorded and marked as parasitoids by parasitic wasps of the class of Insecta-Hymenoptera in research materials and literature pictures. However, due to various unfavorable factors in population size, distribution area and cognitive understanding, there are large gaps in the research field of the order of Gastropoda. This record of parasitoids will provide a more accurate and comprehensive supplement to the research data on fossil and living species of Gastropoda. This specimen of parasitoids of Gastropoda spiders is the most direct, accurate and objective physical evidence.

The spider larva in the Cretaceous amber fossil specimen has a parasitic egg that has begun to develop on the inner side of the second leg segment on the right (the picture is a ventral view). (Although the parasitic egg is only 100 microns, its obvious developmental morphology is still very typical and significant). Because this kind of external parasitic egg, like the internal parasitic egg, is not just a simple parasitic coexistence relationship like the Acarina organism, but it will suck the host's body dry and kill the host in the final adult stage. This phenomenon is called parasitism, and once this parasitism occurs, it is irreversible. The parasitized organism will die painfully in endless torture. Although the spider larva has an advantage in the process of preying on Diptera mosquitoes, it kills mosquitoes effortlessly and has a full meal, but it will never think that fate will play tricks on people, and its future fate will be miserable and sad. This is the true law of nature. The ancient pine sap ended all this in advance, and will forever freeze the tragic and high-spirited years. At the same time, it also left extremely precious three-dimensional images for the author and all those who study and pay attention to the Arthropoda.

Figure 9: Focus on the specimen of a spider being parasitized, and a reference to the phenomenon of parasitism (another specimen, a parasitic wasp being parasitized)

These fossil specimens, which record the most intuitive and wonderful moments of the ecological behavior of Gastropoda, will to the greatest extent promote the rapid development of Gastropoda research in a more sound direction.

Through this study, the number of changes in the walking legs (tarsal segments) of Arthralgias was determined, which can be used as a basis for determining the growth stage of fossil Arthralgias.

Through this study, more specific categories of predators in the natural predation habits of Gastropoda were identified, from the broad scope of the phylum Small Arthropoda to a substantial streamlining and compression of the orders, families and genera.

Through this study, it was discovered for the first time that Gastropoda organisms can be parasitized.

Through this study, the specific morphological details of the predation behavior of the segmented spider were revealed for the first time.

This provides evidence for applying modern research results on arthropods to the determination of limb details of ancient arthropod spiders.

It provides strong physical ecological behavioral evidence for the time node between the fossil species and the living species of the Artemisia.

It provides a number of physical evidence supports the study of the ecological behavior of the Ardeidae, and also fills many research gaps in this field.

It provides accurate basis and real images for paleontological evolution and ecological behavior.

It provides a reference for whether the living area, climate, ecological environment and many other factors of the living Artemisia are beneficial to the continuation of the population.

References:

[1] Mark S. Harvey (Australia). The female of Ricinoides westermannti (Guerin-Meneville), with notes on those of R. afzetti (Thorell) and R. karschii (Hansen & S^rensen) (Ricinulei)[J]. Bull.Br.arachnol.Soc. (1984)6 (5), 205-210

[2] Ligia R. Benavides, Savel R. Daniels, Gonzalo Giribet. Understanding the real magnitude of the arachnid order Ricinulei through deep Sanger sequencing across its distribution range and phylogenomics, with the formalization of the first species from the Lesser Antilles[J]. Journal of Zoological Systematic Evolutionary Research 2021.9.14

[3] Sara Kay Pittard, B.5. ComparaAtive External Morphology of ??? Stages of C??? Pelaezi

(ARACHNIDA. RICINULEI)[J]. 1970.8(NO.121)（Submitted to the graduate faculty of Texas Tech University in partial fulfillment of the requirements for the degree of masert of science approved）The paper was published 54 years ago. The manuscript is blurred and some words are difficult to recognize. It is temporarily represented by “???”