Large Chengjiang Biota Halichondrites Demosponge Fossil

Halichondrites sp.

Porifera, Demospongia, Halichondritdae

Geological Time: Early Cambrian (~525 million years ago)

Size: matrix 155 mm by 75 mm

Fossil Site: Chengjiang Maotianshan Shales, Quiongzhusi Section, Yu’anshan Member, Heilinpu Formation, Mafang Village, Kunming, Anning, Yunnan Province, China

HalichondritesDescription: This is a large member of the Demospongia, the most diverse of modern-day sponges. Greater than 90% of the extant 5,000 known species of sponges are desmosponges. Such a representation in the fossil record is not maintained where less than half the known genera are of this type, a consequence of the fact that the skeletons do not fossilize readily. Demosponge skeletons are composed of spongin fibers and/or siliceous spicules. Sponges are known from the late Precambrian, with few localities contributing to the fossil record over time. The Chengjiang Biota is one such fossil lagerstatte. 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 one is known as Halichondrites, a genus known also from the slightly younger Burgess Shale. It was shaped like a long tube, and had numerous long spicules that formed a hairy thatched appearance. It was one of the largest sponges of the Cambrian. This matrix section has numerous examples of the spicules preserved.

Also see: Chengjiang Biota

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