Enigmatic Allonia Guanshan Fauna Chancelloriid Fossil

Allonia phrixothrix

Phylum Incertae sedis, Class Coeloscleritophora, Order Chancellorida, Family Chancelloridae

Geologic Time: Early/Middle Cambrian

Size (25.4 mm = 1 inch): Fossil Is 20 mm across by 35 mm long (with spines) on a 48 mm by 80 mm matrix

Fossil Site: Guanshan Fauna, Lower most part of Wulongqing Formation, Caijiachong Valley, Yieyatoung, Gangtoucun Village, Xiamacun Town, Kunming City, Yunnan Province, China - Near and similar to the Chengjiang Biota

Code: CF429

Price: $475.00

Allonia phrixothrixDescription: This fine Chancelloriid fossil comes from what has been termed the “Guanshan Fauna”, found in the Wulongqing Formation. The Guanshan Fauna shares many genera with the slightly older Chengjiang Biota, but differs at the species level. With the discovery of the Chengjiang Biota in 1984 a window on the Cambrain Explosion in China was opened. The diversity of soft-tissue fossils is astonishing: algae, medusiforms, sponges, priapulids, annelid like worms, echinoderms, arthropods (including trilobites), hemichordates, chordates, and the first agnathan fish make up just a small fraction of the total. Numerous problematic forms are known as well, some of which may have represented failed attempts at diversity that did not persist to the present day.

This is an unusual and enigmatic animal known as a chancellorid of the genus Allonia. The order is named after Chancelloria, another genus of this strange group of animals. Their precise assignment as to phylum is still much in dispute. Chancelloria was believed by C.D. Walcott to be a heteractinellid sponge, a position acceded to by most researchers until some 30 years ago when it was noted that the supposed spicules were actually sclerites. As such they must have been secreted from the inside, rather than being tissue-covered. These sclerites appear to have function like chain mail armor, affording protection to the animal. Like sponges, however, they are thought to have been filter feeders. Typically, only individual sclerites are preserved; a near complete specimen such as this is a rare occurrence. Look at my other postings for a large member of the genus from the Burgess Shale.

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