March 5, 2024

500 Million Year-Old Fossils Solve a Centuries-Old Riddle in the Evolution of Life on Earth

Artists restoration of Gangtoucunia aspera as it would have appeared in life on the Cambrian seafloor, circa 514 million years back. The individual in the foreground has part of the skeleton eliminated to show the soft polyp inside the skeleton. Credit: Reconstruction by Xiaodong Wang
Researchers have finally solved a centuries-old riddle in the evolution of life on earth, revealing what the first animals to make skeletons appeared like. This discovery was possible due to an exceptionally well-preserved collection of fossils found in eastern Yunnan Province, China. The outcomes of the research study were released on November 2 in the clinical journal Proceedings of the Royal Society B.
During an occasion called the Cambrian Explosion around 550-520 million years ago, the very first animals to develop tough and robust skeletons appear unexpectedly in the fossil record in a geological blink of an eye. A number of these early fossils are simple hollow tubes varying from a few millimeters to many centimeters in length. Nevertheless, what sort of animals made these skeletons was nearly completely unidentified, because they do not have conservation of the pulps required to determine them as belonging to major groups of animals that are still alive today.
Fossil specimen (left) and diagram (right) of Gangtoucunia aspera preserving soft tissues, consisting of the gut and tentacle. Credit: Luke Parry and Guangxu Zhang
Four specimens of Gangtoucunia aspera with soft tissues still intact, consisting of the gut and mouthparts, are included in the new collection of 514 million-year-old fossils. The fossils likewise reveal that Gangtoucunia had a blind-ended gut (open only at one end), partitioned into internal cavities, that filled the length of the tube.

These are features found today only in modern jellyfish, anemones, and their close loved ones (referred to as cnidarians), organisms whose pulps are incredibly uncommon in the fossil record. The research study shows that these simple animals were amongst the first to construct the difficult skeletons that comprise much of the recognized fossil record.
According to the researchers, Gangtoucunia would have looked similar to modern-day scyphozoan jellyfish polyps, with a tough tubular structure anchored to the underlying substrate. The arm mouth would have extended outside television, but might have been retracted inside television to prevent predators. Unlike living jellyfish polyps, however, the tube of Gangtoucunia was made of calcium phosphate, a difficult mineral that makes up our own teeth and bones. Use of this material to build skeletons has actually become more unusual among animals gradually.
Close up photo of the mouth region of Gangtoucunia aspera showing the tentacles that would have been utilized to catch prey. Credit: Luke Parry and Guangxu Zhang
Corresponding author Dr. Luke Parry, Department of Earth Sciences, University of Oxford, stated: “This truly is a one-in-million discovery. These strange tubes are frequently discovered in groups of hundreds of individuals, but until now they have actually been considered problematic fossils, due to the fact that we had no other way of categorizing them. Thanks to these amazing brand-new specimens, an essential piece of the evolutionary puzzle has actually been put firmly in place.”
The new specimens clearly show that Gangtoucunia was not related to annelid worms (earthworms, polychaetes and their loved ones) as had been formerly recommended for similar fossils. It is now clear that Gangtoucunias body had a smooth outside and a gut partitioned longitudinally, whereas annelids have segmented bodies with transverse partitioning of the body.
The fossil was found at a site in the Gaoloufang area in Kunming, eastern Yunnan Province, China. Here, anaerobic (oxygen-poor) conditions restrict the existence of bacteria that generally break down soft tissues in fossils.
Fossil specimen of Gangtoucunia aspera maintaining soft tissues, including the gut and tentacles (left and middle). The illustration at the ideal illustrates the visible anatomical functions in the fossil specimens. Credit: Luke Parry and Guangxu Zhang
PhD student Guangxu Zhang, who gathered and found the specimens, said: “The very first time I discovered the pink soft tissue on top of a Gangtoucunia tube, I was surprised and confused about what they were. In the following month, I found 3 more specimens with soft tissue preservation, which was extremely exciting and made me reconsider the affinity of Gangtoucunia. The soft tissue of Gangtoucunia, particularly the tentacles, reveals that it is definitely not a priapulid-like worm as previous research studies recommended, however more like a coral, and after that I understood that it is a cnidarian.”
The fossil clearly reveals that Gangtoucunia was a primitive jellyfish, this doesnt rule out the possibility that other early tube-fossil types looked very different. From Cambrian rocks in Yunnan province, the research team has actually previously discovered well-preserved tube fossils that might be recognized as priapulids (marine worms), lobopodians (worms with paired legs, closely related to arthropods today), and annelids.
Co-corresponding author Xiaoya Ma (Yunnan University and University of Exeter) said: “A tubicolous mode of life appears to have actually become significantly common in the Cambrian, which might be an adaptive reaction to increasing predation pressure in the early Cambrian. This study demonstrates that exceptional soft-tissue conservation is important for us to comprehend these ancient animals.”
Reference: “Exceptional soft tissue preservation reveals a cnidarian affinity for a Cambrian phosphatic tubicolous enigma” by Guangxu Zhang, Luke A. Parry, Jakob Vinther and Xiaoya Ma, 2 November 2022, Proceedings of the Royal Society B Biological Sciences.DOI: 10.1098/ rspb.2022.1623.

Fossil specimen of Gangtoucunia aspera protecting soft tissues, consisting of the gut and tentacles (left and middle). PhD trainee Guangxu Zhang, who collected and discovered the specimens, stated: “The very first time I discovered the pink soft tissue on top of a Gangtoucunia tube, I was surprised and confused about what they were. In the following month, I discovered 3 more specimens with soft tissue conservation, which was very interesting and made me rethink the affinity of Gangtoucunia.

Four specimens of Gangtoucunia aspera with soft tissues still intact, consisting of the gut and mouthparts, are included in the brand-new collection of 514 million-year-old fossils. The fossils also show that Gangtoucunia had a blind-ended gut (open only at one end), partitioned into internal cavities, that filled the length of the tube.