Agmata

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Agmata
Temporal range: Early Cambrian–Middle Cambrian
StadtmuseumBerlin GeologischeSammlung SM-2012-1604.jpg
Volborthella
Scientific classification Red Pencil Icon.png
Kingdom: Animalia
Phylum: Agmata
Yochelson, 1977 [1]
Taxa

Volborthellida

Agmata is a proposed extinct phylum of small animals with a calcareous conical shell. They were originally thought to be cephalopods or annelid worms. The living animals filled up to five-sixths of their shell with laminae, angled layers composed of grains of quartz or calcium carbonate detritus from the environment cemented together, with larger grains near the shell wall and smaller grains near the center. A very fine tube ran through the center of the shell. The grains may be of quartz or calcium carbonate, but are of specific shapes and materials that are rare in the surrounding rock. Though the body of the living animal is not preserved, it had to be able to find, choose, and retrieve rare grains from its environment to build the laminae.

The phylum's name comes from the Greek word for "fragments", referring to these fine fragments and grains of detritus. [1] It was proposed by the paleontologist and geologist Ellis L. Yochelson  [ de ] (1928–2006) in 1977 to house the agglutinating Early Cambrian fossils Salterella and Volborthella , with the Middle Cambrian Ellisell yochelsoni later included. [2] The poorly known Middle Cambrian fossil Vologdinella was also considered for inclusion, as it has superficial resemblance to the Agmata, but was later excluded from the group. [3]

Currently, the phylum contains only one family, Salterellidae; a second family, Volborthellidae, was originally included but later became a synonym of the former. No orders, classes or superfamilies are used within the phylum, despite the order "Volborthellida" being previously proposed for Volborthella before the phylum's own proposal. The reasoning for this was that taxa of these ranks were not seen as necessary in a phylum with very few genera. [1] [3]

The genera within the group are clearly different: Salterella had a pointed shell made of calcium carbonate with a thin outer layer and a thick inner layer, and secreted a calcium carbonate cement to hold its grains in place. Volborthella was the older genus, had a blunter shell with a shallower opening, and cemented grains in place with organic material that also may have formed the outside surface of the shell. [4]

Fossils are found in large numbers in some areas. Paleontologists have offered several different ideas of how these animals lived: filter-feeding with the points of the shells embedded in the substrate, grazing actively like snails, or lying on their sides on the substrate. Volborthella is found in silt and clay deposits, and apparently lived on tidal mudflats. Attempts to reconcile these genera as members of any other group have been rejected due to basic differences in structure, but not all paleontologists accept them as a phylum; Jones (2007) considers the shell an agglutinating test parallel to that of foraminifers. Yochelson considered Agmata to be complex multicellular animals.

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Salterella is an enigmatic Cambrian genus with a small, conical, calcareous shell that appears to be septate, but is rather filled with stratified laminar deposits. The shell contains grains of sediment, which are obtained selectively by a manner also observed in foramanifera. The genus was established by Elkanah Billings in 1861, and was named after the English palaeontologist John William Salter.

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<span class="mw-page-title-main">Salterellidae</span> Extinct family of enigmatic fossils

Salterellidae is a family of enigmatic fossil genera from the Early to Middle Cambrian. It was originally created for the genus Salterella by Charles Doolittle Walcott, who placed it in the group Pteropoda. It was later placed in Agmata, a proposed extinct phylum by Ellis L. Yochelson which is accepted by some other authors.

Ellisell is a Middle Cambrian genus of fossils from Denmark. It contains only one species, Ellisell yochelsoni. Both the genus and species are named after the paleontologist and geologist Ellis L. Yochelson (1928–2006), who had turned 60 at the time the fossils were first described. The genus was originally placed in the family Salterellidae of the phylum Agmata; this placement was rejected by Yochelson & Kisselev (2003), but was restored by Peel (2016). Ellisell is distinguished from Salterella by its slowly expanding conch and the resulting cylindrical apertural cavity, compared to the latter's more rapidly expanding conch and cone-shaped apertural cavity.

<span class="mw-page-title-main">Foraminifera test</span>

Foraminiferal tests are the tests of Foraminifera.

References

  1. 1 2 3 Yochelson, Ellis L. (1977). "Agmata, a Proposed Extinct Phylum of Early Cambrian Age". Journal of Paleontology . 51 (3): 437–454. JSTOR   1303675.
  2. Peel, John S. (2016). "Anatase and Hadimopanella selection by Salterella from the Kap Troedsson formation (Cambrian Series 2) of North Greenland". GFF . 139 (1): 70–74. doi:10.1080/11035897.2016.1227365. S2CID   132731070.
  3. 1 2 Yochelson, Ellis L.; Kisselev, Gennadii N. (2003). "Early Cambrian Salterella and Volborthella (Phylum Agmata) re‐evaluated". Lethaia . 36 (1): 8–20. doi:10.1080/00241160310001254.
  4. Jones, Tom Dunkley (2007). "Salterella and Volborthella from the Early Cambrian of Spitsbergen: The Evolution of Agglutinating Organisms during the Neoproterozoic-Cambrian Transition". Micropaleontology. 53 (4): 331–342. doi:10.2113/gsmicropal.53.4.331. ISSN   0026-2803. JSTOR   4499786.