Conulariida are an extinct group of Medusozoa Cnidaria known from fossils spanning from the latest Ediacaran up until the Triassic.
Structure
The conulariids are
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.
[Waggoner, B.M. & D. Smith (1994): The Conulariida, Mystery fossils. University of California Museum of Paleontology web page [1]] 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.
The fine structure of their shell comprises multiple lamellae of alternately organic-rich and organic-poor layers.
Fossil record
With the inclusion of the possible
Ediacaran conulariid
Vendoconularia, which may or may not be a conulariid at all,
and the definite late Ediacaran conulariid
Paraconularia,
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.
In North America, conulariids are generally more common in rocks of Ordovician and Carboniferous age.
Lifestyle
Conulariids were
Benthic zone animals that were sessile and attached to a substrate at the base of the theca, older individuals may have become recumbent (tipped over).
They are generally proposed to have been predators, using tentacles to ensnare prey.
Phylogeny
About 20 genera and 150 species are known,
but except for local occurrences, Conulariids are relatively uncommon.
The conulariids were originally thought to be 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 Ediacaran biota.
It is now also thought that the conulate Trilobozoa 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 three-fold symmetry.
Until the 1930-ies affinities of conulariids were unknown.
Pearls
Conulariids produced
within their shells, similar to the way
molluscs such as oysters, other
, and some
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.
List of genera
Bibliography
External links
-
http://www.uga.edu/strata/cincy/fauna/conulariida/Conularia.html
