Editing Archaeocyatha (section)

== Geological history ==
[[File:Archeocyathids.JPG|thumb|Archeocyathids from the [[Poleta formation]], eastern California|left]]
[[File:Branching archaeocyath.jpg|thumb|Branching form archaeocyath from Rowland's Reef in Nevada]]
Today, the archaeocyathan families are recognizable by small but consistent differences in their [[fossil]]ized structures: Some archaeocyathans were built like nested bowls, while others were as long as 300mm. Some archaeocyaths were solitary organisms, while others formed [[Colony (biology)|colonies]].  In the beginning of the [[Toyonian]] Age around 516 [[mya (unit)|mya]], the archaeocyaths went into a sharp decline. Almost all species became [[extinct]] by the Middle Cambrian, with the final-known species, ''[[Antarcticocyathus]] webberi'', disappearing just prior to the end of the Cambrian period.<ref>The last-recorded archaeocyathan is a single species from the late (upper) Cambrian of Antarctica.</ref> Their rapid decline and disappearance coincided with a rapid [[Adaptive radiation|diversification]] of the [[Demosponges]]. As for the earliest archaeocyathan, the Ediacaran sponge ''[[Arimasia]]'' from the [[Nama Group]] may be within the clade and specifically allied with Monocyathea, however this is unclear.<ref name=arimasia/>

The archaeocyathids were important reef-builders in the early to middle Cambrian, with reefs (and indeed any accumulation of carbonates) becoming very rare after the group's extinction until the diversification of new taxa of coral reef-builders in the [[Ordovician]].<ref name=Munnecke2010>{{Cite journal| last1 = Munnecke | first1 = A.| last2 = Calner | first2 = M.| last3 = Harper | first3 = D. A. T.| author-link3 = David Harper (palaeontologist)| last4 = Servais | first4 = T.| title = Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis| journal = Palaeogeography, Palaeoclimatology, Palaeoecology| volume = 296| issue = 3–4| pages = 389–413| year = 2010| doi = 10.1016/j.palaeo.2010.08.001| bibcode = 2010PPP...296..389M}}</ref>

''Antarcticocyathus '' was considered the only late Cambrian archaeocyath, but its reinterpretation as a lithisid sponge<ref>{{Cite journal | doi = 10.1080/08912963.2022.2155818| title = Limiting the known range of archaeocyath to the middle Cambrian: Antarcticocyathus webersi Debrenne et al. 1984 is a lithistid sponge| year = 2022| last1 = Lee| first1 = Jeong-Hyun| journal = Historical Biology| pages = 1–5| s2cid = 254628199}}</ref> means that there are now no archaeocyaths post the mid-Cambrian.