Namacalathus
Encyclopedia
NamacalathusNama, from the geological group where it was described, + Greek
κάλαθος, kalathos, meaning "basket in the shape of a lily", or "wine goblet" is a problematic metazoan fossil
occurring in the latest Ediacaran
. The single species N. hermanastesGreek ἕρμα, herma, "sunken rock, reef", + νάστης, nastes, "inhabitant" was first described in 2000 from Nama Group of central and southern Namibia
. The animal is more likely to be a Cnidarian than a sponge or primitive Bilateria
n.
A U–Pb zircon age from the fossiliferous rock in Namibia
and Oman
provides an age for the Namacalathus zone in the range from 549 to 542 Ma, which corresponds to the Late Ediacaran
.
These organism and Cloudina are the oldest known evidence in the fossil record of the emergence of calcified skeletal formation in metazoans, a prominent feature in animals appearing later in the Early Cambrian.
There are only four occurrences of Namacalathus (Namibia, Canada
, Oman, Siberia
) known to date, all of which are found in association with Cloudina fossils.
Among the late Precambrian fossil assemblage in the Nama group, Namibia, Namacalathus far outnumber Cloudina and other poorly preserved taxa and ichnofossils
found in the formation. The Nama Group fossils occur within thrombolitic facies
of immense Proterozic stromatolitic reefs. Namacalathus lived a benthic existence with its stalk attached to the sea floor or possibly to algal mats growing on the reef surface.
Siberian specimens from the borehole Vostok 3 were designated as new species, because they have, unlike the type species N. hermanastes, a significantly smaller size. Most specimens show sections of the perforated cup, ranging from 110 to 230 μm in diameter; one specimen (with a cup 120 μm across) has a stalk (30 μm in diameter). The walls of the cup are 10 μm thick.
Because the three dimensional shape of Namacalathus is complex, and the wall is so thin, the fossils appear as a two dimensional sections in a wide variety shapes, including closed and open circles, irregular hexagons or heptagons, as well as heart and moon shapes.
Ancient Greek
Ancient Greek is the stage of the Greek language in the periods spanning the times c. 9th–6th centuries BC, , c. 5th–4th centuries BC , and the c. 3rd century BC – 6th century AD of ancient Greece and the ancient world; being predated in the 2nd millennium BC by Mycenaean Greek...
κάλαθος, kalathos, meaning "basket in the shape of a lily", or "wine goblet" is a problematic metazoan fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
occurring in the latest Ediacaran
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
. The single species N. hermanastesGreek ἕρμα, herma, "sunken rock, reef", + νάστης, nastes, "inhabitant" was first described in 2000 from Nama Group of central and southern Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
. The animal is more likely to be a Cnidarian than a sponge or primitive Bilateria
Bilateria
The bilateria are all animals having a bilateral symmetry, i.e. they have a front and a back end, as well as an upside and downside. Radially symmetrical animals like jellyfish have a topside and downside, but no front and back...
n.
A U–Pb zircon age from the fossiliferous rock in Namibia
Namibia
Namibia, officially the Republic of Namibia , is a country in southern Africa whose western border is the Atlantic Ocean. It shares land borders with Angola and Zambia to the north, Botswana to the east and South Africa to the south and east. It gained independence from South Africa on 21 March...
and Oman
Oman
Oman , officially called the Sultanate of Oman , is an Arab state in southwest Asia on the southeast coast of the Arabian Peninsula. It is bordered by the United Arab Emirates to the northwest, Saudi Arabia to the west, and Yemen to the southwest. The coast is formed by the Arabian Sea on the...
provides an age for the Namacalathus zone in the range from 549 to 542 Ma, which corresponds to the Late Ediacaran
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
.
These organism and Cloudina are the oldest known evidence in the fossil record of the emergence of calcified skeletal formation in metazoans, a prominent feature in animals appearing later in the Early Cambrian.
There are only four occurrences of Namacalathus (Namibia, Canada
Canada
Canada is a North American country consisting of ten provinces and three territories. Located in the northern part of the continent, it extends from the Atlantic Ocean in the east to the Pacific Ocean in the west, and northward into the Arctic Ocean...
, Oman, Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
) known to date, all of which are found in association with Cloudina fossils.
Among the late Precambrian fossil assemblage in the Nama group, Namibia, Namacalathus far outnumber Cloudina and other poorly preserved taxa and ichnofossils
Trace fossil
Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...
found in the formation. The Nama Group fossils occur within thrombolitic facies
Facies
In geology, facies are a body of rock with specified characteristics. Ideally, a facies is a distinctive rock unit that forms under certain conditions of sedimentation, reflecting a particular process or environment....
of immense Proterozic stromatolitic reefs. Namacalathus lived a benthic existence with its stalk attached to the sea floor or possibly to algal mats growing on the reef surface.
Morphology
It has a unique shape with a cup on a stalk. The stalk is hollow all the way through and tapered from the bottom, ranging from 1 to 2 mm in diameter, and reaching 30 mm in length. The narrower top of the stalk connects to the cup. The cup is hollow and has a large hole in the top with the shell curving over forming a cup lip. Around the side of the globe are six or seven symmetrically arranged holes, called "windows". The wall curves inwards around each window in a formation called window lips. Each hole is slightly elongated vertically and expanded on the higher side. The size of the cup varies from two to about 25 mm, but averages 6.1 mm. The ratio of the height of the cup to the diameter is from 0.7 to 1.3. The fossil is lightly calcified, preserved as calcite crystals; its original morphology is unknown. The walls in Namacalathus are only 0.1 mm thick, and often deformed by the weight of the sediment. The windows were probably originally filled with organic matter during life, but the cup was likely to be open.Siberian specimens from the borehole Vostok 3 were designated as new species, because they have, unlike the type species N. hermanastes, a significantly smaller size. Most specimens show sections of the perforated cup, ranging from 110 to 230 μm in diameter; one specimen (with a cup 120 μm across) has a stalk (30 μm in diameter). The walls of the cup are 10 μm thick.
Because the three dimensional shape of Namacalathus is complex, and the wall is so thin, the fossils appear as a two dimensional sections in a wide variety shapes, including closed and open circles, irregular hexagons or heptagons, as well as heart and moon shapes.