Namacalathus
| Namacalathus | ||||
|---|---|---|---|---|
Namacalathus hermanastes |
||||
| Temporal occurrence | ||||
| Ediacarium | ||||
| 549 to 542 million years | ||||
| Locations | ||||
| Systematics | ||||
|
||||
| Scientific name | ||||
| Namacalathus | ||||
| Grotzinger , Watters & Knoll , 2000 | ||||
| species | ||||
|
||||
Namacalathus is an extinct species of Ediacarium of uncertain assignment that lived between 549 and 542 million years BP .
etymology
The generic name Namacalathus is a word creation composed of Nama , derived from the Nama group in which the fossil was discovered, and the ancient Greek κάλαθος (kálathos) meaning (lily-shaped) basket or wine goblet . The species name hermanastes comes from the ancient Greek words ἕρμα (hérma) reef, shoal, sunken stone and νάστης (nástēs) Be, inhabitants in allusion to the stromatolite reefs in which the organism lived.
Initial description
Namacalathus hermanastes was first scientifically described in 2000 by John P. Grotzinger and colleagues.
Occurrence
The type locality of Namacalathus is in the Nama group in central and southern Namibia , especially at Driedoornvlagte . Further occurrences are limited to Canada ( Byng Formation , Miette Group ), Oman and Siberia (western Siberia platform ).
Taphonomy
Namacalathus fossils are preserved as calcitic cavity fillings in an also calcitic matrix. Because of this chemical similarity and the fragile nature of the inclusions (with wall thicknesses less than 100 micrometers), it proved impossible to remove them as a whole from the matrix. The reconstruction of the morphology is therefore based on a tomographic reconstruction. For this purpose, a plate with inclusions was sanded down in 25 micrometer steps, its surface was photographed and then the shape was reconstructed on the computer from the series of these images. Based on fossils fragmented shortly before embedding, a later mineralization of an exclusively organic wall appears unlikely.
morphology
Namacalathus resembles a chalice that sits on an elongated stem. The handle is around 30 millimeters long and 1 to 2 millimeters in diameter. It narrows towards the top and is completely hollow inside. The chalice sits on the thinner top. It is open at the top and has an inverted edge. There are six or seven openings on the outside called windows . The walls of the cup bend into the window openings, which are elongated and widen upwards. The cup size varies between 2 and 25 millimeters, but averages 6.1 millimeters. The height to diameter ratio of the cup varies between 0.7 and 1.3. The fossil is moderately calcified ( calcite crystals ), but the original structure of the skeleton cannot be reconstructed. The walls of Namacalathus are only 0.1 millimeters thick and are therefore often deformed by the sediment load. The windows in the living organism may have been filled with organic matter, but the chalice was probably open at the top.
Since the three-dimensional shape of Namacalathus is relatively complex and the wall thickness is very thin, the fossils appear in two-dimensional sections in very different geometries, including open and closed circular sections, irregular hexagons and heptagons, and even heart and moon-shaped shapes.
Taxonomy
The fossils found in Siberia in the Vostok 3 well are considered to be a new species because of their significantly reduced size. The perforated cup measures only 110 to 230 μm and the stem 30 μm in diameter. The walls of the bowl are only 10 μm thick.
The general taxonomic position of Namacalathus is still uncertain. Depending on the processor, the fossil was previously placed among the sponges (Porifera), the cnidarians (Cnidaria), the algae or the protists . Grotzinger and colleagues (2000) advocate an interpretation as a sessile cnidarians due to the structure and the functional structure. Most experts now follow this view. Brusca and Brusca (1990) interpret the six or seven windows as the starting point of tentacles arranged radially around the central mouth opening. It is also possible that septa or gonads were attached at these points, which, with their disintegration, caused the window openings to loosen.
Socialization
In the Nama group, Namacalathus is regularly associated with not quite as common cloudina , other, less well-preserved taxa and trace fossils .
Habitat
The fossils of the Nama group occur in huge stromatolite reefs belonging to the thrombolite facies. Namacalathus was a benthic organism that was attached to the seabed or possibly also in the reefs growing algae mats with its stem .
Age
Dating with the uranium-lead method showed an age of 549 to 542 million years BP for fossil-containing sedimentary rocks from Namibia and Oman. This corresponds to the outgoing Ediacarium .
meaning
Together with Cloudina , Namacalathus is the oldest known taxon in the fossil record , in which a calcified skeleton can be detected - a characteristic that was to appear later in the metazoa of the Lower Cambrian .
Individual evidence
- ↑ a b Grotzinger, JP, Watters, WA and Knoll, AH: Calcified metazoans in thrombolite-stromatolite reefs of the terminal Proterozoic Nama Group, Namibia . In: Paleobiology . tape 26 (3) , 2000, pp. 334-359 , doi : 10.1666 / 0094-8373 (2000) 026 <0334: CMITSR> 2.0.CO; 2 .
- ↑ Hofmann, HJ and Mountjoy, EW: Namacalathus-Cloudina assemblage in Neoproterozoic Miette Group (Byng Formation), British Columbia: Canada's oldest shelly fossils . In: Geology . tape 29 (12) , 2001, pp. 1091-1094 , doi : 10.1130 / 0091-7613 (2001) 029 <1091: NCAINM> 2.0.CO; 2 .
- ↑ Amthor, JE, Grotzinger, JP, Schroder, S., Bowring, SA, Ramezani, J., Martin, MW and Matter, A .: Extinction of Cloudina and Namacalathus at the Precambrian-Cambrian boundary in Oman . In: Geology . tape 31 (5) , 2003, pp. 431-434 , doi : 10.1130 / 0091-7613 (2003) 031 <0431: EOCANA> 2.0.CO; 2 .
- ^ AE Kontorovich et al: The first section of Vendian deposits in the basement complex of the West Siberian petroleum megabasin (resulting from the drilling of the Vostok-3 parametric borehole in the Eastern Tomsk region) . In: Doklady Earth Sciences . tape 425 (1) , 2009, pp. 219-222 , doi : 10.1134 / S1028334X09020093 .
- ^ Wesley Andres Watters: Digital Reconstructions of Fossil Morphologies, Nama Group, Namibia. Thesis, Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, 2000.
- ^ Susannah M. Porter: Seawater Chemistry and Early Carbonate Biomineralization . In: Science . tape 316 (5829) , 2007, pp. 1302 , doi : 10.1126 / science.1137284 .
- ↑ Watters, WA and Grotzinger, JP: Digital reconstruction of calcified early metazoans, terminal Proterozoic Nama Group, Namibia . In: Paleobiology . tape 27 (1) , 2001, p. 159-171 , doi : 10.1666 / 0094-8373 (2001) 027 <0159: DROCEM> 2.0.CO; 2 .
- ↑ AE Kontorovich et al: A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3) . In: Russian Geology and Geophysics . tape 49 (12) , 2008, pp. 932-939 , doi : 10.1016 / j.rgg.2008.06.012 .
- ^ Brusca, RC and Brusca, GJ: Invertebrates . In: Sinuaer Assoc. Sunderland, Massachusetts 1990, p. 922 .