Researchers have recently discovered an endoparasitic tapeworm fossil from mid-Cretaceous Myanmar amber that is approximately 100 million years old.

The discovery was made by researchers from the Nanjing Institute of Geology and Palaeontology in Jiangsu province, part of the Chinese Academy of Sciences, in collaboration with researchers from Yunnan University, Germany, the United Kingdom and Myanmar.

This study, published in the journal Geology, provides evidence not only of the first partial body fossil of a tapeworm, but also, arguably, the most convincing body fossil of a flatworm, thus providing new information on the early evolution of tapeworms.

Tapeworms are a large class within the Platyhelminth phylum, with about 5,000 species described so far. They infect all major groups of vertebrates, including humans and livestock, and are found in nearly all marine, freshwater and terrestrial ecosystems. Their sizes vary, ranging from less than 1 millimeter to more than 30 meters in length.

The order Trypanorhyncha is the most diverse tapeworm group in the marine realm and comprises one of the most ubiquitous and readily recognized parasites of marine fish. Their adults are usually found in the stomachs and intestines of sharks and rays.

Previous studies on the molecular biology estimated that Trypanorhyncha tapeworms probably originated around the Triassic and Jurassic period boundary about 200 million years ago, but their own fossils have never been found.

"The fossil record of tapeworms is extremely sparse due to their soft tissues and endoparasitic habitats, which greatly hampers our understanding of their early evolution," said Wang Bo, a lead researcher of the study.

However, he added that his team had "reported the first body fossil of a tapeworm".

According to the researchers, this fossil displays unique external and internal features that are most consistent with the characteristics of extant Trypanorhyncha tapeworms.

The study also provides an exceptional example of a marine endoparasite trapped in amber, shedding new light on the taphonomy of amber and restoring paleoenvironment.

Previous studies had shown that internal structures could be preserved intact as in extant forms, but such studies all focused on arthropods. By using a high-resolution micro computed tomography, the researchers discovered that the interior of the current fossil is consistent with the Trypanorhyncha tapeworm.

"Our results show that amber can preserve the internal structure of helminths such as tapeworms on geologic time scales," Wang said.

Some trichomes and a scale insect were also preserved in the amber specimen, clearly indicating a terrestrial or onshore environment at the time of entrapment in the resin. In addition, many grains of sand were evenly distributed throughout the amber, suggesting that the fossil was entombed in a sandy environment.

One possible scenario for the deposition of the tapeworm in the amber is that its elasmobranch host was stranded by a tide or storm, and then was bitten by a higher-level terrestrial predator or scavenger. When the host was ingested by the predator, the tapeworm was pulled away, dislodged from the intestine, and stuck to nearby resin.

"Our study further supports the hypothesis that the amber was probably deposited in a paralic paleoenvironment, and also highlights the importance of amber research in paleoparasitology," Wang said.

Xinhua