Enigmatic Allonia Burgess Shale Chancellorid

Allonia sp

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

Geological Time: Early Cambrian, (~520 million years ago)

Size (25.4 mm = 1 inch): Fossil is 62 by 25 mm on a on 115 by 80 mm matrix

Fossil Site: Stephen Formation, Burgess Shale, Burgess Pass, British Columbia, Canada

Fossil Code: JH34

Price: Sold

Allonia Burgess Shale ChancelloridDescription: 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 complete specimen such as this is a rare occurrence. Since the location has been declared a World Heritage site, only specimens from old collections such as this are available.

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