2024-01-06 15:28:36
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Researchers have discovered very well preserved fossils of Fearbeast koprii (meaning “beast of terror”), carnivorous worms that lived more than 518 million years ago in northern Greenland. Particularly imposing, these worms would have almost occupied the top of the food chain in Cambrian marine ecosystems (541 million to 485.4 million years ago). They would likely have been among the first carnivorous animals to colonize the marine water column during this period.
The transition from the Ediacaran (the last period of the Precambrian) to the Cambrian, around 540 million years ago, was marked by an exceptional expansion in animal diversity (a period known as the Cambrian Explosion ). This evolutionary explosion coincided with the colonization of new spaces, including the marine water column. In aquatic ecology, this term designates the compartments and the different ecological niches present in a volume of water located between the bottom and the surface.
The explosion of biodiversity during the transition to the Cambrian gave rise to a remarkable evolution converging towards predation. Animals such as euarthropods (the crown group of current arthropods), for example, have evolved morphologically so as to develop better “tools” for capturing their prey. “ We already knew that primitive arthropods were the dominant predators in the Cambrian, such as the bizarre-looking anomalocarids
[ressemblant à des crevettes, avec de grandes pinces recourbées] »,
noted Jakob Vinther of the University of Bristol, co-lead author of the new study. However, the species of carnivorous worms discovered by the researchers appears much more primitive.
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The fossils of Fearbeast koprii, described in the journal Science Advances, would be distant relatives of chaetognaths (arrow worms, or sagittarius worms), whose living descendants currently occupy our oceans and feed on zooplankton. “ Our research shows that these ancient ocean ecosystems [du Cambrien] were quite complex, with a food chain that allowed the existence of several levels of predators “, explains Vinther.
Almost at the top of the food chain
Discovered in sediments from the Sirius Passet site in northern Greenland, the T. koprii are flattened worms with fins, a distinct head with long antennae and massive jaws. Although only regarding thirty centimeters long, they were very imposing for their time and were probably among the largest swimming animals of the early Cambrian.
Fossil of Timorebestia koprii — the largest known specimen, measuring almost 30 cm long. © Jakob Vinther
According to experts, their size might have placed them near the top of the food chain at this time, hence their name “beasts of terror”. “ Les Timorebeast were giants of their time and would have been near the top of the food chain. This makes them equivalent in importance to some of the major carnivores of modern oceans, such as sharks and seals. “, explains Vinther.
One of the fossils, which was in an excellent state of preservation, revealed the diet of these strange worms. X-ray scans showed that the majority of their gut contents contained Isoxys, small bivalve arthropods that were an important food source for many animals of the time. Although they had long spikes on the front and back of their bodies, probably to deter predators, these arthropods were still consumed in abundance by T. koprii. One of the fossils also showed remains of Isoxys in the jaw area.
By bombarding the fossils with T. koprii Using electron beams, researchers noticed that they had a nerve center known as the ventral ganglion in their abdomen. This organ, unique to chaetognaths, would have helped them control their locomotor muscles. Although their jaw differs significantly, the presence of this specific organ confirms that the newly discovered fossils are distant relatives of modern sagittarius worms.
The latter have external mobile hooks to grasp prey. This difference might provide valuable information regarding the appearance of the first jawed predators. Additionally, ganglia are also present in Amiskwia, a lineage related to chaetognaths.
3D digital model of T. koprii gen. Reconstruction showing internal and external anatomy (red, musculature; blue, ventral ganglion; black, maxillary apparatus; green, intestine). (A) Lateral view. (B) Dorsal view. (C) Ventral view. (D) Ventral view excluding musculature. © Tae-Yoon S. Park et al.
Furthermore, their link with chaetognaths suggests that they are much older than arthropods. If the latter are traced in the fossil record as dating from 521 to 529 million years ago, the sagittarius worms are traced back to at least 538 million years ago.
According to Vinther, “we can therefore assume that these are in all likelihood predators which dominated the oceans before the appearance of arthropods”. The expert estimates that this domination would have lasted between 10 to 15 million years, before other, more prosperous predatory lineages appeared. The team plans to find more clues in the coming years regarding how the ecosystems housing these animals evolved.
Source : Science Advances
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