How were anemones "hunted" 520 million years ago?

Recently, the team of Shu Degan, an academician of the Chinese Academy of Sciences and a professor at Northwest University, cooperated with the Ou Qiang team of China University of Geosciences (Beijing) to report the earliest known direct evidence of macrophagic predation behavior in the form of a research report in the newly published "The Innovation".

The paper reports on a rare coral fossil found in the early Cambrian Chengjiang biota (about 520 million years ago), the "Nailiana elegans", which belongs to the genus "Nailiana" and has a lotus-like appearance.

According to Ou Qiang, the overall morphology of the genus is close to that of the modern anemone, with 8 slender, smooth tentacles on its top edge, which surround the central mouth; the cylindrical body has a primitive digestive circulation cavity inside; and the longitudinal stripes on the surface of the trunk indicate the presence of an internal diaphragm.

The paper reported on more than 10 specimens of the anemone. "One of the specimens is particularly precious, recreating the hunting scene of the anemone preying on tongue-shaped shellfish brachiopods." Shudgan said.

The base of the tentacles of this anemone is wrapped in a well-preserved jade case of tongue shellfish, which is the relationship between predation and predation.

Shu Degan introduced that modern tongue-shaped shellfish brachiopods are commonly known as "sea bean sprouts", most of the time the camp bottom of the inflorescence life, in addition to the top three clusters of ring bristles slightly exposed to the surface of the seabed, the body is all hidden in the submersible; if stimulated by the outside world, it will quickly shrink to the depths of the submerged cavity. As a result, modern anemones have little chance of preying on tongue-shaped shellfish.

However, studies have shown that Cambrian tongue-shaped shellfish burrow only the back of the fleshy stem into the soft mud of the seabed, like a swaying "kite" filtering in the seawater. Therefore, compared with modern anemones, the probability of Cambrian anemone preying on tongue-shaped shellfish brachiopods is greatly increased.

The vast majority of modern spiny animals such as sea anemones prey on highly toxic stinging cells. They will not take the initiative to attack, but adopt a predatory strategy of "waiting for the rabbit". Anemones are usually like blooming anemones, with slender tentacles swaying slowly with the currents of the ocean, while small prey once touches the anemone tentacles, the densely packed spines on the surface of the latter will fire a thousand arrows, instantly paralyzing and poisoning the prey.

"We speculate that it is likely that the anemone also used the thorn cells that touched the surface of the face to prey, and this efficient method of predation has continued to this day." Shudgan said.

The results of the analysis showed that the anemone was a primordial branch of the order Phytophthora australis (six-shot corals + eight-shot corals). The researchers deduced that the ancestral type of corals may be eight-radiative symmetry, monomeric, exoskeleton-free hydra type, which entrenched benthic predatory life, while the coral group ecology, skeletal system and other symmetries evolved later.

Shudgan pointed out that obtaining nutrients by devouring is one of the essential characteristics of animals. Phagocytosis first occurred in single-celled protozoa — fossil mineralized exoskeletons used by protozoa for defense about 700 million years ago is the earliest known indirect evidence of microphagic predation. Multicellular epizoans may have been the first to obtain nutrients through surface penetration or filtration, while more complex and energy-intensive macrophagic predations theoretically appeared later—the late Ediacaran exoskeletons are indirect evidence of the earliest known macrophagic predations. The presence of nosodontic worms and hairy jaws (535 million years ago) in the earliest small shell fossils of the Cambrian Period provides more indirect evidence of macrophagic predation.

"The fossil record of brachiopods devoured by the anemone (520 million years ago) reported in this paper shows the earliest known direct evidence of macrophagic predation." "It also gives us a glimpse into a real-life scene of the cambrian marine ecosystem food web," Shudegan said. ”

The paper notes that macrophagic predation in early Cambrian animals was already very common. Taking the Chengjiang biota as an example, many animal phylums such as stingrays, gill-dragging animals, and leaf-legged animals have evolved a variety of strange "weapons and equipment" to improve the efficiency of predation. The life-and-death "arms race" between predators and prey undoubtedly increases the morphological diversity of various groups of animals. Macrophagic predation not only exacerbated the selection pressure, but may also accelerate the emergence of animal phyla in the early Cambrian, thus becoming one of the triggers and main drivers of the Cambrian life explosion. In the 30 million years from the emergence of post-mezoan exoskeletons to the outbreak of the Chengjiang biota, cambrian marine ecosystems have established complex food webs similar to modern marine ecosystems. (Zhang Xingyong)

Source: China Science Daily