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.
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
And of course, pictures.
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.
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.
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.
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Artist reconstruction with one in front having part of the skeleton removed to show the soft polyp inside the skeleton
Artist reconstruction with one in front having part of the skeleton removed to show the soft polyp inside the skeleton