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514 myo fossils provide answers regarding origins of skeletal structure

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  • 514 myo fossils provide answers regarding origins of skeletal structure

    A question that has been vexing researchers for quite some times may have finally been answered, namely what did the first animals to develop a skeleton look like. It's not what you probably expect. The answer was provided by examining four specimen of exceptionally well-preserved fossils unearthed in 2017 at a site in the Gaoloufang section in Kunming in eastern Yunnan Province, China. The fossils are tube-like creatures called Gangtoucunia aspera that lived roughly 514 mya and contained fossilized soft tissues, including the gut and mouthparts.

    Gangtoucunia resembled modern scyphozoan jellyfish polyps, with a hard tubular structure anchored to an underlying substrate, but there are differences. Most importantly, unlike their modern counterparts, the tube of Gangtoucunia was made of calcium phosphate, the mineral that makes up teeth and bones.

    The fossils also show that Gangtoucunia's mouth was fringed with a ring of smooth, unbranched tentacles about 5mm (0.2") long which were probably used to sting and capture prey and could retract back into the tube to avoid predators. They also demonstrated that they had a gut that has only a single opening, partitioned into internal cavities.

    Also, these are features are only found today in modern jellyfish, anemones and their close relatives known as cnidarians, meaning they're not closely related to worms as previous thought.

    Source: 500 million year-old fossils reveal answer to evolutionary riddle



    An exceptionally well-preserved collection of fossils discovered in eastern Yunnan Province, China, has enabled scientists to solve a centuries-old riddle in the evolution of life on earth, revealing what the first animals to make skeletons looked like. The results have been published today in Proceedings of the Royal Society B.

    The first animals to build hard and robust skeletons appear suddenly in the fossil record in a geological blink of an eye around 550-520 million years ago during an event called the Cambrian Explosion. Many of these early fossils are simple hollow tubes ranging from a few millimetres to many centimetres in length. However, what sort of animals made these skeletons was almost completely unknown, because they lack preservation of the soft parts needed to identify them as belonging to major groups of animals that are still alive today.

    The new collection of 514 million year old fossils includes four specimens of Gangtoucunia aspera with soft tissues still intact, including the gut and mouthparts. These reveal that this species had a mouth fringed with a ring of smooth, unbranched tentacles about 5 mm long. It's likely that these were used to sting and capture prey, such as small arthropods. 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.

    These are features found today only in modern jellyfish, anemones and their close relatives (known as cnidarians), organisms whose soft parts are extremely rare in the fossil record. The study shows that these simple animals was among the first to build the hard skeletons that make up much of the known fossil record.

    According to the researchers, Gangtoucunia would have looked similar to modern scyphozoan jellyfish polyps, with a hard tubular structure anchored to the underlying substrate. The tentacle mouth would have extended outside the tube, but could have been retracted inside the tube to avoid predators. Unlike living jellyfish polyps however, the tube of Gangtoucunia was made of calcium phosphate, a hard mineral that makes up our own teeth and bones. Use of this material to build skeletons has become more rare among animals over time.

    Corresponding author Dr Luke Parry, Department of Earth Sciences, University of Oxford, said: 'This really is a one-in-million discovery. These mysterious tubes are often found in groups of hundreds of individuals, but until now they have been regarded as 'problematic' fossils, because we had no way of classifying them. Thanks to these extraordinary new specimens, a key piece of the evolutionary puzzle has been put firmly in place.'

    The new specimens clearly demonstrate that Gangtoucunia was not related to annelid worms (earthworms, polychaetes and their relatives) as had been previously suggested for similar fossils. It is now clear that Gangtoucunia's body had a smooth exterior 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 section in Kunming, eastern Yunnan Province, China. Here, anaerobic (oxygen-poor) conditions limit the presence of bacteria that normally degrade soft tissues in fossils.

    PhD student Guangxu Zhang, who collected and discovered the specimens, said: 'The 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 three more specimens with soft tissue preservation, which was very exciting and made me rethink the affinity of Gangtoucunia. The soft tissue of Gangtoucunia, particularly the tentacles, reveals that it is certainly not a priapulid-like worm as previous studies suggested, but more like a coral, and then I realised that it is a cnidarian.'

    Although the fossil clearly shows that Gangtoucunia was a primitive jellyfish, this doesn't rule out the possibility that other early tube-fossil species looked very different. From Cambrian rocks in Yunnan province, the research team have previously found well-preserved tube fossils that could be identified 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 seems to have become increasingly common in the Cambrian, which might be an adaptive response to increasing predation pressure in the early Cambrian. This study demonstrates that exceptional soft-tissue preservation is crucial for us to understand these ancient animals.'


    Source

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    The entire paper, Exceptional soft tissue preservation reveals a cnidarian affinity for a Cambrian phosphatic tubicolous enigma can be read by clicking the hyperlink although the abstract can also be read below


    Abstract

    Exoskeletal dwelling tubes are widespread among extant animals and early fossil assemblages. Exceptional fossils from the Cambrian reveal independent origins of tube dwelling by several clades including cnidarians, lophophorates, annelids, scalidophorans, panarthropods and ambulacrarians. However, most fossil tubes lack preservation of soft parts, making it difficult to understand their affinities and evolutionary significance. Gangtoucunia aspera (Wulongqing Formation, Cambrian Stage 4) was an annulated, gradually expanding phosphatic tube, with occasional attachments of multiple, smaller juveniles and has previously been interpreted as the dwelling tube of a ‘worm’ (e.g. a scalidophoran), lophophorate or problematicum. Here, we report the first soft tissues from Gangtoucunia that reveal a smooth body with circumoral tentacles and a blind, spacious gut that is partitioned by septa. This is consistent with cnidarian polyps and phylogenetic analysis resolves Gangtoucunia as a total group medusozoan. The tube of Gangtoucunia is phenotypically similar to problematic annulated tubular fossils (e.g. Sphenothallus, Byronia, hyolithelminths), which have been compared to both cnidarians and annelids, and are among the oldest assemblages of skeletal fossils. The cnidarian characters of G. aspera suggest that these early tubular taxa are best interpreted as cnidarians rather than sessile bilaterians in the absence of contrary soft tissue evidence.




    And of course, pictures.


    3070fb79-c2a1-46d0-abd2-81ba9669eecb.jpg
    Artist reconstruction with one in front having part of the skeleton removed to show the soft polyp inside the skeleton

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