Conulariida are an extinct group of medusozoancnidarians known from fossils spanning from the latest Ediacaran up until the Late Triassic.[1][2][3] They are almost exclusively known from their hard external structures (alternatively referred to as a theca, periderm or test), which were pyramidal in shape and made up of numerous lamellae.
The conulariids are fossils preserved as shell-like structures made up of rows of calcium phosphate rods, resembling an ice-cream cone with fourfold symmetry, usually four prominently-grooved corners.[4] New rods were added as the organism grew in length; the rod-based growth falsely gives the fossils a segmented appearance. Exceptional soft-part preservation has revealed that soft tentacles protruded from the wider end of the cone, and a holdfast from the pointed end attached the organisms to hard substrate. The prevailing reconstruction of the organism has it look superficially like a sea anemone sitting inside an angular, hard cone held perpendicular to the substrate. Conulariid shell is composed of francolite with carbonate ion concentration 8.1 wt%. The lattice parameters of conulariid apatite are a = 9.315(7) Å,
c = 6.888(3) Å.[5] The fine structure of their shell comprises multiple lamellae of alternately organic-rich and organic-poor layers.[6]
Close-up of a conulariid from the Mississippian of Indiana; scale in mm.Conularia milwaukeensis from the Middle Devonian of Wisconsin.A pair of Conularia niagarensis specimens from the Lower Silurian Waukesha Biota site in Wisconsin.
With the inclusion of the possible Ediacaran conulariid Vendoconularia, which may or may not be a conulariid at all,[7] and the definite late Ediacaran conulariid Paraconularia ediacara,[2] the Conulata fossil record begins with undeniable specimens in the Upper Ediacaran and extends without significant break through numerous major mass extinctions. The Conulariids finally disappear from the fossil record during the Late Triassic, by which time they were very rare, with only 8 documented occurrences across the entire Triassic. Their extinction may have been due to the rise of durophagous organisms as part of the Mesozoic marine revolution.[8]
In North America, conulariids are generally more common in rocks of Ordovician and Carboniferous age.
Life restoration of a conulariid, showing the soft-bodied anatomy
Conulariids were benthic animals that were sessile and attached to a substrate at the base of the theca, older individuals may have become recumbent (tipped over).[9] They are generally proposed to have been predators, using tentacles to ensnare prey.[10]
About 20 genera and 150 species are known,[11] but except for local occurrences, Conulariids are relatively uncommon.
The conulariids were originally thought to be anthozoan cnidarians. However, the lack of septa or other features diagnostic of anthozoans led researchers to abandon this hypothesis. Ivantsov and Fedonkin (2002) posit that the conulariids were ancestrally tri-radially symmetrical, as typified with Vendoconularia, typical of the structure seen in Vendozooans.[12] Conulariids are, however, technically a part of the Ediacaran biota as their fossil record starts at latest parts of that period.[2]
It is now also thought that the conulate trilobozoans derived their fourfold symmetry from a sixfold symmetry, as seen in Vendoconularia. This in turn, is thought to be originally derived from an ancestral disk-like trilobozoan three-fold symmetry.[citation needed]
Conulariids have generally been thought to be of Cnidarian affinity, occupying a position near the base of the Cnidarian family tree. However, since the 2010s, authors consider conulariids to be members of the subclade Medusozoa, though their exact placement within the clade is uncertain.[3]
Conulariids produced pearls within their shells, similar to the way molluscs such as oysters, other pelecypods, and some gastropods do today. These pearls give a clue as to the internal anatomy of the conulariid animal. But due to their calcium phosphate composition, their crystal structure, and their extreme age, these pearls tend to be rather unattractive for use in or as decorative objects.[13]
^Ford, Robert C.; Van Iten, Heyo; Clark, George R. (2016). "Microstructure and composition of the periderm of conulariids". Journal of Paleontology. 90 (3): 389. doi:10.1017/jpa.2016.63. S2CID133541791.
^Van Iten, H.; De Moraes Leme, J.; Coelho Rodrigues, S.; Guimaraes Simoes, M. (2005). "Reinterpretation of a Conulariid-Like Fossil from the Vendian of Russia". Palaeontology. 48 (3): 619–622. doi:10.1111/j.1475-4983.2005.00471.x. hdl:11449/31655. S2CID247733826.
^Iten, Heyo Van; Vyhlasová, Zdenka (2004-12-31), Webby, Barry D.; Paris, Florentin; Droser, Mary L.; Percival, Ian G. (eds.), "14. Conulariids", The Great Ordovician Biodiversification Event, Columbia University Press, pp. 119–123, doi:10.7312/webb12678-015, ISBN978-0-231-12678-6, retrieved 2023-06-25
Babcock, L. E. (1991). "The enigma of conulariid affinities". In A. M. Simonetta; S. Conway Morris (eds.). The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge: Cambridge University Press. pp. 133–143.
Van Iten, H. (1991). "Evolutionary affinities of conulariids". In A. M. Simonetta; S. Conway Morris (eds.). The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge: Cambridge University Press. pp. 145–155.
