| Archaeocyatha Temporal range:
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Scientific classification 
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| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Porifera |
| Clade: | †Archaeocyatha Vologdin, 1937 |
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Archaeocyatha (/ˈɑːrkioʊsaɪəθə/, 'ancient cups') is a taxon of extinct, sessile, reef-building[1] marine sponges that lived in warm tropical and subtropical waters during the Cambrian Period. It is believed that the centre of the Archaeocyatha origin is now located in East Siberia, where they are first known from the beginning of the Tommotian Age of the Cambrian, 525 million years ago (mya).[2] In other regions of the world, they appeared much later, during the Atdabanian, and quickly diversified into over a hundred families.
They became the planet's first reef-building animals and are an index fossil[3] for the Lower Cambrian worldwide.
- ^ Archaeocyathid reef structures ("bioherms"), although not as massive as later coral reefs, might have been as deep as ten meters (Emiliani 1992:451).
- ^ Maloof, A.C. (2010). "Constraints on early Cambrian carbon cycling from the duration of the Nemakit-Daldynian–Tommotian boundary $$\delta$$13C shift, Morocco". Geology. 38 (7): 623–626. Bibcode:2010Geo....38..623M. doi:10.1130/G30726.1. S2CID 128842533.
- ^ Anderson, Dr. John R. "Paleozoic Life". Georgia Perimeter College. Archived from the original on 20 July 2011. Retrieved 6 July 2010.