Animal with First-Ever Skeleton Revealed by Fossils 500 Million Years Old

Scientists have been able to solve a long-standing puzzle in the evolution of life on earth by revealing the appearance of the first animals to make skeletons thanks to an amazingly well-preserved collection of fossils dating back 500 million years that was found in eastern Yunnan Province, China.

Sudden Appearance

In a geological flash, between 550 and 520 million years ago, during the Cambrian Explosion, the first animals to develop strong, hard skeletons appear in the fossil record. Many of these ancient fossils are just plain hollow tubes that range in length from several millimeters to a few centimeters.

Due to the lack of preservation of the soft parts required to distinguish them as belonging to the main groups of animals that remain alive today, it was almost impossible to determine what kind of organisms made these skeletons.

Gangtoucunia Aspera

There are four Gangtoucunia aspera specimens in the new collection of 514 million-year-old fossils that still have their soft tissues, such as their guts and mouthparts, in tact. These prove that the mouth of this species was fringed by a ring of 5 mm long, smooth, unbranched tentacles. These were probably used to catch and sting prey, like little arthropods.

The fossils also demonstrate that Gangtoucunia had an internal cavity-partitioned blind-ended gut that occupied the tube's entire length and was only open at one end.

These characteristics are only present in contemporary jellyfish, anemones, and their close relatives, which are soft-bodied organisms that are extremely uncommon in the fossil record. The research demonstrates that these primitive creatures were among the first to develop the hard skeletons that compose the majority of the fossil record.

According to the researchers, with a tough tubular structure rooted to the underlying substrate, Gangtoucunia would have resembled modern scyphozoan jellyfish polyps. The mouth of the tentacle would have protruded from the tube but could have been drawn back inside to evade predators.

The Gangtoucunia tube was made of calcium phosphate, a hard mineral that also makes up human teeth and bones, unlike living jellyfish polyps. It has become less common for animals to use this material to construct skeletons over time.

Key Piece from Problematic Fossils

Dr. Luke Parry, the corresponding author of the study from the University of Oxford's Department of Earth Sciences, said that these mysterious tubes are generally observed in groups of hundreds, but up until recently, there was no way to classify them, so they were thought to be "problematic" fossils. These remarkable new specimens have helped to solidly anchor a crucial piece of the evolutionary puzzle.

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Not A Worm but a Cnidarian

According to the University of Oxford, the new specimens unequivocally show that, contrary to what had previously been hypothesized for related fossils, Gangtoucunia was never related to annelid worms such as earthworms, polychaetes, and their relatives. It is now evident that annelids have segmented bodies with transverse body partitioning, whereas Gangtoucunia had a smooth exterior and a gut divided longitudinally.

The fossil was discovered at a location in Kunming, located in the eastern Yunnan Province, China, in the Gaoloufang neighborhood. The fossil was discovered at a location in Kunming, located in eastern Yunnan Province, China, in the Gaoloufang village. Conditions that are anaerobic or oxygen-poor, such as those in this area, restrict the presence of bacteria that typically break down soft tissues in fossils.

Guangxu Zhang, a PhD student who discovered and collected the specimens, was surprised and unsure of what they were when he first noticed the pink soft tissue on the upper end of a Gangtoucunia tube.

He discovered three more specimens bearing soft tissue preservation the following month, which was extremely exciting and caused him to reconsider Gangtoucunia's affinities. He realized that Gangtoucunia is a cnidarian when he noticed that its soft tissue, especially the tentacles, clearly shows it is not a priapulid-like worm as past studies suggested. Instead, it looks more like coral.

Primitive Jellyfish

Although the fossil unequivocally demonstrates that Gangtoucunia was a prehistoric jellyfish, it is still possible that some early tube-fossil species had very different appearances. The research team has previously discovered well-preserved tube fossils from Cambrian rocks in Yunnan province that could be classified as priapulids or marine worms, lobopodians, which are worms with paired legs that are closely related to modern arthropods, and annelids.

Xiaoya Ma, a co-corresponding author from Yunnan University and the University of Exeter, said that the Cambrian appears to have seen a rise in the prevalence of tubicolous life forms, which could have been an adaptive reaction to the early Cambrian's increased predation pressure. This study shows that excellent soft-tissue preservation is essential for our understanding of these extinct animals, Phys Org reports.

The Proceedings of the Royal Society B published the paper early this month.

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