acritarch

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acritarch

[′ak·rə‚tark]
(paleontology)
A unicellular microfossil of unknown or uncertain biological origin that occurs abundantly in strata from the Precambrian and Paleozoic.
References in periodicals archive ?
The lower boundary of the Middle Cambrian on the East European Craton was traditionally drawn near the appearance level of the acritarchs Baltisphaeridium latviense, B.
Acritarchs and Tasmanitids from the Chhidru Formation, Uppermost Permian of West Pakistan.
An acritarch assemblage sampled from the North Alton Formation indicates a Jiangshanian (mid-Furongian) age (White et al.
The Doushantuo formation shales and phosphorites, dated to 570 Ma, elegantly preserve acritarchs, multicellular algae, and significantly, animal embryos of uncertain affinity.
One or a few species of phytoplankton monopolizes nutrients at the expense of others," said Porter, explaining the die-off of diverse acritarchs.
In addition, palynologic analysis reveals the presence of land spores, acritarchs, chitinozoans, and scolecodonts.
A good fossil record exists for the dinophytes, proof of the group's antiquity; the remains of dinophytes similar to contemporary species are known from the Silurian and similar forms, such as some acritarchs, are even older, dating from the Cambrian period or before (see volume 1, p.
Palynodebris Characteristics Amorphous organic matter Unstructured, irregularly-shaped, light brown to medium brown masses; usually gel- like (Figure 2A) Marine palynomorphs Scolecodonts (chitinous mouth parts of marine annelid worms) and acritarchs (cysts of marine algal phytoplankton, Figure 2G) Black debris Opaque particles with sharp angular outlines; lath-shaped, sometimes more equidimensional (Figure 2E) Yellow-brown debris Structureless particles of yellow to light brown color; attributable to highly degraded herbaceous material (Figure 2A) Black-brown debris Unstructured dark brown to nearly black particles; attributable to highly degraded woody material Cuticles Platy epidermal fragments of leaves, roots, etc.
Paleontologists call these acritarchs, a catch-all category of unicellular eukaryotic fossils.
One of the best-studied core sections in sense of biostratigraphically useful fossils is Ruhnu (500), which has yielded detailed data on the distribution of ostracods, conodonts, chitinozoans, but also acritarchs.