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Archaeocyatha

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Archaeocyatha (/ˈɑːrkioʊsaɪəθə/, 'ancient cups') is a taxon of extinct, sessile, reef-building[2] 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).[3] In other regions of the world, they appeared much later, during the Atdabanian, and quickly diversified into over a hundred families.

Archaeocyatha
Temporal range: Tommotian - Mid Cambrian (possible Ediacaran records[1])
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Porifera
Clade: †Archaeocyatha
Vologdin, 1937
Synonyms
  • Cyathospongia Okulitch, 1935
  • Pleospongia Okulitch, 1935

They became the planet's first reef-building animals and are an index fossil[4] for the Lower Cambrian worldwide.

Preservation

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The remains of Archaeocyatha are mostly preserved as carbonate structures in a limestone matrix. This means that the fossils cannot be chemically or mechanically isolated, save for some specimens that have already eroded out of their matrices, and their morphology has to be determined from thin cuts of the stone in which they were preserved.

Geological history

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Archeocyathids from the Poleta formation, eastern California
 
Branching form archaeocyath from Rowland's Reef in Nevada

Today, the archaeocyathan families are recognizable by small but consistent differences in their fossilized structures: Some archaeocyathans were built like nested bowls, while others were as long as 300mm. Some archaeocyaths were solitary organisms, while others formed colonies. In the beginning of the Toyonian Age around 516 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.[5] Their rapid decline and disappearance coincided with a rapid diversification of the Demosponges.

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.[6]

Antarcticocyathus was considered the only late Cambrian archaeocyath, but its reinterpretation as a lithisid sponge[7] means that there are now no archaeocyaths post the mid-Cambrian.

Morphology

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1 – Gap (intervallum) 2 – Central cavity 3 – Internal wall 4 – Pore (all the walls and septa have pores, not all are represented) 5 – Septum 6 – External wall 7 – Rhizoid

The typical archaeocyathid resembled a hollow horn coral. Each had a conical or vase-shaped porous skeleton of calcite similar to that of a sponge. The structure appeared like a pair of perforated, nested ice cream cones. Their skeletons consisted of either a single porous wall (Monocyathida), or more commonly as two concentric porous walls, an inner and outer wall separated by a space. Inside the inner wall was a cavity (like the inside of an ice cream cup). At the base, these pleosponges were held to the substrate by a holdfast. The body presumably occupied the space between the inner and outer shells (the intervallum).

Ecology

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Archaeocyath, in situ at the Flinders Ranges.
See also: Sponge reef

Flow tank experiments suggest that archaeocyathan morphology allowed them to exploit flow gradients, either by passively pumping water through the skeleton, or, as in present-day, extant sponges, by drawing water through the pores, removing nutrients, and expelling spent water and wastes through the pores into the central space.[citation needed]

The size of the pores places a limit on the size of plankton that archaeocyaths could have consumed; different species had different sized pores, the largest large enough to conceivably consume mesozooplankton, possibly giving rise to different ecological niches within a single reef.[8]

Although archaeocyaths have commonly been thought of as stenobionts narrowly adapted to carbonate-dominated marine settings, they were also present in siliciclastic-dominated environments as well.[9]

Distribution

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The archaeocyathans inhabited coastal areas of shallow seas. Their widespread distribution over almost the entire Cambrian world, as well as the taxonomic diversity of the species, might be explained by surmising that, like true sponges, they had a planktonic larval stage that enabled their wide spread.

Taxonomy

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Restoration of Antarcticocyathus webberi

Their phylogenetic affiliation has been subject to changing interpretations, yet the consensus is growing that the archaeocyath was indeed a kind of sponge,[10] thus sometimes called a pleosponge. But some invertebrate paleontologists have placed them in an extinct, separate phylum, known appropriately as the Archaeocyatha.[11] However, one cladistic analysis[12] suggests that Archaeocyatha is a clade nested within the phylum Porifera (better known as the true sponges).

True archaeocyathans coexisted with other enigmatic sponge-like animals. Radiocyatha and Cribricyatha were two diverse Cambrian classes comparable to Archaeocyatha, alongside genera such as Boyarinovicyathus, Proarchaeocyathus, Acanthinocyathus, and Osadchiites.[13]

The clade Archaeocyatha have traditionally been divided into Regulares and Irregulares (Rowland, 2001):

However, Okulitch (1955), who at the time regarded the archaeocyathans as outside of Porifera, divided the phylum in three classes:

Notes

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  1. ^ Runnegar, Bruce; Gehling, James G.; Jensen, Sören; Saltzman, Matthew R. (October 2024). "Ediacaran paleobiology and biostratigraphy of the Nama Group, Namibia, with emphasis on the erniettomorphs, tubular and trace fossils, and a new sponge, Arimasia germsi n. gen. n. sp". Journal of Paleontology. 98 (S94): 1–59. doi:10.1017/jpa.2023.81.
  2. ^ Archaeocyathid reef structures ("bioherms"), although not as massive as later coral reefs, might have been as deep as ten meters (Emiliani 1992:451).
  3. ^ 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.
  4. ^ Anderson, Dr. John R. "Paleozoic Life". Georgia Perimeter College. Archived from the original on 20 July 2011. Retrieved 6 July 2010.
  5. ^ The last-recorded archaeocyathan is a single species from the late (upper) Cambrian of Antarctica.
  6. ^ Munnecke, A.; Calner, M.; Harper, D. A. T.; Servais, T. (2010). "Ordovician and Silurian sea-water chemistry, sea level, and climate: A synopsis". Palaeogeography, Palaeoclimatology, Palaeoecology. 296 (3–4): 389–413. Bibcode:2010PPP...296..389M. doi:10.1016/j.palaeo.2010.08.001.
  7. ^ Lee, Jeong-Hyun (2022). "Limiting the known range of archaeocyath to the middle Cambrian: Antarcticocyathus webersi Debrenne et al. 1984 is a lithistid sponge". Historical Biology: 1–5. doi:10.1080/08912963.2022.2155818. S2CID 254628199.
  8. ^ Antcliffe, Jonathan B.; Jessop, William; Daley, Allison C. (2019). "Prey fractionation in the Archaeocyatha and its implication for the ecology of the first animal reef systems". Paleobiology. 45 (4): 652–675. doi:10.1017/pab.2019.32. S2CID 208555519.
  9. ^ Yang, Aihua; Luo, Cui; Han, Jian; Zhuravlev, Andrey Yu.; Reitner, Joachim; Sun, Haijing; Zeng, Han; Zhao, Fangchen; Hu, Shixue (1 November 2024). "Niche expansion of archaeocyaths during their palaeogeographic migration: Evidence from the Chengjiang Biota". Palaeogeography, Palaeoclimatology, Palaeoecology. 653: 112419. doi:10.1016/j.palaeo.2024.112419. Retrieved 15 November 2024 – via Elsevier Science Direct.
  10. ^ Scuba divers have discovered living calcareous sponges, including one species that -- like the archaeocyathans -- is without spicules, thus morphologically similar to the archaeocyaths. Rowland, S.M. (2001). "Archaeocyatha: A history of phylogenetic interpretation". Journal of Paleontology. 75 (6): 1065–1078. doi:10.1666/0022-3360(2001)075<1065:AAHOPI>2.0.CO;2.
  11. ^ Debrenne, F. and J. Vacelet. 1984. "Archaeocyatha: Is the sponge model consistent with their structural organization?" in Palaeontographica Americana, 54:pp358-369.
  12. ^ J. Reitner. 1990. "Polyphyletic origin of the 'Sphinctozoans'", in Rutzler, K. (ed.), New Perspectives in Sponge Biology: Proceedings of the Third International Conference on the Biology of Sponges (Woods Hole) pp. 33-42. Smithsonian Institution Press, Washington, DC.
  13. ^ Treatise on Invertebrate Paleontology Part E, Revised. Porifera, Volumes 4 & 5: Hypercalcified Porifera, Paleozoic Stromatoporoidea & Archaeocyatha, liii 1223 p., 665 figs., 2015, available here. ISBN 978-0-9903621-2-8.

References

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  • Emiliani, Cesare. (1992). Planet Earth : Cosmology, Geology, & the Evolution of Life & the Environment. Cambridge University Press. (Paperback Edition ISBN 0-521-40949-7), p 451
  • Okulitch, V. J., 1955: Part E – Archaeocyatha and Porifera. Archaeocyatha, E1-E20 in Moore, R. C., (ed.) 1955: Treatise on Invertebrate Paleontology. Geological Society of America & University of Kansas Press, Lawrence, Kansas, 1955, xviii-E122.
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