"Because their maximum diameter falls within the width range of the rings, these animals can be identified as potential prey of the fungus," the authors wrote.
"Once trapped, the nematodes were probably penetrated and digested by infestation hyphae," they added. While the rings resemble those found in modern trapping fungi, "the fossils cannot be assigned to any recent carnivorous fungus."
This suggests different groups thrived in the age of the dinosaurs, the researchers said, "and that trapping devices were developed independently multiple times in the course of Earth history."
Nematode-eating fungi expert Philip Jacobs, based in Germany, described the study as "a really amazing report."
Jacobs noted that the fossil fungus also shows evidence of buds known as blastospores, which are not seen in modern nematode-preying species.
And while none of the nematodes are seen actually inside the trapping rings, "it seems very probable that [the rings] were indeed capturing organs," Jacobs said.
However, George L. Barron, of the Department of Environmental Biology at the University of Guelph, Canada, is more skeptical of the amber findings.
"The presence of nematodes could be coincidental and nothing to do with predation," Barron said in an email.
"Nematodes are commonly found mixed up within organic debris with nonpredatory fungal hyphae."
Barron said the rings of the fungus "are nicely shaped, and it is very tempting to suggest their function as primitive trapping devices," but he added that such features represent "a giant step on the evolutionary scale."
"Someday someone might find the definitive proof in amber, showing a nematode captured in a ring, or a nematode by itself with a ring encircling its body," he added.
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