The Kirengellids are a group of problematic Cambrian
fossil
A fossil (from Classical Latin , ) is any preserved remains, impression, or trace of any once-living thing from a past geological age. Examples include bones, shells, exoskeletons, stone imprints of animals or microbes, objects preserve ...
shells of
marine organisms. The shells bear a number of paired
muscle scars on the inner surface of the
valve
A valve is a device or natural object that regulates, directs or controls the flow of a fluid (gases, liquids, fluidized solids, or Slurry, slurries) by opening, closing, or partially obstructing various passageways. Valves are technically Pip ...
.
These fossils have conventionally been regarded as
monoplacophora
Shell of Monoplacophora
Monoplacophora , meaning "bearing one plate", is a polyphyletic class of molluscs with a cap-like shell, inhabiting deep sea environments. Extant representatives were not recognized as such until 1952; previously they wer ...
n
mollusc
Mollusca is a phylum of protostome, protostomic invertebrate animals, whose members are known as molluscs or mollusks (). Around 76,000 extant taxon, extant species of molluscs are recognized, making it the second-largest animal phylum ...
s, and possibly ancestral to
gastropod
Gastropods (), commonly known as slugs and snails, belong to a large Taxonomy (biology), taxonomic class of invertebrates within the phylum Mollusca called Gastropoda ().
This class comprises snails and slugs from saltwater, freshwater, and fro ...
s or
cephalopod
A cephalopod is any member of the molluscan Taxonomic rank, class Cephalopoda (Greek language, Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral symm ...
s. They were presumed to be exogastric on the presumption that their larger muscle scars were anterior, but it may be dangerous to compare these scars with molluscan musculature.
[ In any case, they coiled in the opposite direction to '' Romaniella''.][ However, their ]calcitic
Calcite is a carbonate mineral and the most stable polymorph of calcium carbonate (CaCO3). It is a very common mineral, particularly as a component of limestone. Calcite defines hardness 3 on the Mohs scale of mineral hardness, based on scratc ...
shells, the position of the muscle scars, and putative association with secondary shell elements, make a brachiopod
Brachiopods (), phylum (biology), phylum Brachiopoda, are a phylum of animals that have hard "valves" (shells) on the upper and lower surfaces, unlike the left and right arrangement in bivalve molluscs. Brachiopod valves are hinged at the rear e ...
affinity possible, by analogy with the mobergellans: a group of phosphatic shells from the same time period, with a similar set of muscle scars.[ There is also strong similarity to the contemporary brachiopod group, the Craniopsids. In the case of this diagnosis, a simple lophophore apparatus is postulated to sit between the muscle scars and the edges of the shell.]
Included taxa
After [
* ''Kirengella'' Rozov, 1968 (Upper Cambrian)
** † ''Kirengella alta'' Whitfield 1889
** ''Kirengella ayaktchica'' - type species
** ''Kirengella expansus''
** † ''Kirengella kultavasaensis'' Doguzhaeva 1972
** ''Kirengella oregonensis''
** ''Kirengella pyramidalis''
** † ''Kirengella rectilateralis'' Berkey 1898
** † ''Kirengella stabilis'' Berkey 1898
** ''Kirengella washingtonense''
* ''Hypseloconus'' (Upper Cambrian)
* ''Lenaella'' (Tremadoc / Lower Ordovician)
* ''Nyuella'' (Tremadoc / Lower Ordovician)
* ''Romaniella'' (Arenig / late Lower Ordovician)
* ''Moyerokania'' (Arenig / late Lower Ordovician)
* ''Angarella'' (Arenig / late Lower Ordovician)
* ''Pygmaeoconus'' (Llanvirn / early Middle Ordovician)
]
References
* S. N. Rozov. 1975. ''A new order of the Monoplacophora''. Paleontological Journal 15(1):39-43
* G.P. Wahlman. 1992. Middle and Upper Ordovician symmetrical univalved mollusks (Monoplacophora and Bellerophontina) of the Cincinnati Arch region. United States Geological Survey Professional Paper 1066(O):1-123
Cambrian animals
{{paleo-mollusc-stub