Recently, Chinese and foreign researchers have found 430 million-year-old Fossils of the Silurian mixed-winged horseshoe crab in South China. Directly calling this name may not have much concept, in fact, it is a family classification commonly known as the sea scorpion, and the scientific name of the sea scorpion should be called plate foot crab, which is closely related to our modern arachnids.
The fossil body found this time is 1 meter long and belongs to the mixed-winged horseshoe crab. The most different thing from the regular broad-winged horseshoe crab is that the third pair of mixed-winged horseshoe crabs have exaggerated long spines on the appendages, which seem to be used to fix prey, and this ancient animal will always crudely evolve some strange forms.
Scientists have named the hybrid-winged horseshoe crab found this time as the Xiushan dinosaur. The discovery of the Xiushan horseshoe crab is of great significance, this is the first time that Mixed-winged Horseshoe Crabs have been found in China, and the last time a mixed-winged horseshoe crab was found worldwide was 80 years ago. Moreover, the high completeness of the fossils this time helps scientists to study the diversity, geographical distribution and evolutionary history of the taxon.
Let's go back in time and go back to the Paleozoic era before the mass extinction.
At this time in Earth's history, between 541 million and 252 million years ago, arthropods are exploring extreme leaps from tiny to massive sizes.
They did succeed, and some Paleozoic arthropods at the time became the largest animals on earth. If we are lucky enough to swim in the Paleozoic ocean, we can easily spot one of the most terrifying of extinct arthropods: the plate-footed crab.
The largest species ever seen in the fossil record of the plate-footed crab is called Jaekelopterus rhenaniae, which is even more than 2.5 meters long, and its ecological niche at that time was actually similar to that of modern great white sharks.
These agile swimmers would arm their large appendages with multiple inward spikes as prey, and then they would squeeze between the tooth-like structures on their legs (called jaw spines) to squeeze the shell of the stacked nails that were common to animals at the time.
Plate-footed horseshoe crabs are even armed with a tail, which consists of a jagged, prickly tip. These predators will attack with a lateral impact of their jagged tails and kill their prey. When attacking, their ridge tip will bend strongly to one side, throwing out only one blow.
Unlike lobsters and shrimp, which can flip their broad tails up and down to help them swim, the tails of plate-footed horseshoe crabs are not elastic vertically, but are highly mobile horizontally.
This means that these plate-footed horseshoe crabs can wave their tails from side to side, encounter little hydraulic resistance and do not push themselves away from their intended targets, and their forelimbs quickly grab prey even if the tail attacks incorrectly.
Their extremely flexible arms and huge size made them the top predators of their time.
When the scientists 3D imaged the plate-footed horseshoe with CT scans, they found an unusual double respirator. Their gills are made of plates connected by tissue columns called trabeculae. More of these plates were found at the front of the gills than in the rear. Such gills don't seem to be gills that can fully function underwater, so how it breathes has been a mystery until studying the girders between its gills. Extant arachnids, such as scorpions and spiders, are known to have trabeculae.
The question of how broad-winged animals breathe underwater later turned into an explanation of how they breathed on land. The trabecular separates the creature's gills so that they don't collapse when it climbs out of the water, meaning it can breathe air.
Although the plate-footed crab has dominated the ocean for hundreds of millions of years, the predators who came after it have obviously absorbed a lot of experience, squeezing the ecological niche of the plate-footed crab from birth, and even hunting them.
So plate-footed horseshoe crabs will choose to go out of the ocean and crawl between shallower pools of water to lay their eggs, where they can protect themselves from predators. So, if these bizarre life forms are somewhere between land and sea, why do some of their offspring end up flying to land while others stay underwater?
The question remains to be studied, but such an option is indeed the case that their descendants have gained a foothold in several mass extinctions.
Future studies will revisit the site where the fossils of the plate-footed horseshoe were originally collected, hoping to find more complete fossils. This not only helps to better document the plate-footed horseshoe, but also contributes to a more complete understanding of the environment in which they live.
Ultimately, one thing is clear, there are still many secrets to be uncovered about these arthropods that dominated the prehistoric oceans.
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