File:Fossiliferous dolostone with ostracods 2.jpg
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editDescriptionFossiliferous dolostone with ostracods 2.jpg |
English: Dolostone is a crystalline-textured chemical sedimentary rock composed of dolomite (CaMg(CO3)2 - calcium magnesium carbonate). Most dolostones form by chemical alteration of previously-existing limestones. They tend to be fine-grained, vuggy (= having irregularly-sized and irregularly-shaped holes), and have poorly preserved fossils.
The small ovoid fossils in this dolostone sample are ostracods, often jokingly called "lima beans". Ostracods have an Ordovician to Holocene fossil record. Some Cambrian fossils (e.g., bradoriids) were formerly assigned to ostracods. True ostracods are small crustaceans with a calcified, bivalved, hinged carapace ("shell"). Most are microfossil-sized, but some are much larger. Many forms have considerable sexual dimorphism - females can have a different shell form compared with males. Such adult female ostracods are called heteromorphs. The pre-adult ostracods and male adults are called tecnomorphs. Most ostracods are filter feeders, but some are detritus feeders. They principally consume diatoms (= tiny, 1-celled, photosynthesizing protists) and other small "algal"; forms. Marine, brackish, and freshwater ostracods are known - they can be benthic (on the seafloor) or nektonic (free-swimming). Even terrestrial ostracods are known, but they are rare - they live on water drops on leaves in some jungles. Ostracods occur in large numbers in aquatic settings, but they are not very good swimmers - they are virtually defenseless against fish. Ostracods are common fossils and have biostratigraphic utility. They are often used by petroleum companies to date sedimentary rocks. They are probably the most economically significant crustacean group. In Mesozoic and Cenozoic rocks, ostracods are second only to foraminifera in abundance and biostratigraphic importance. Ostracod shells often have prominent ornamentation, consisting of lobes, spines, and processes. The ornamentation is used for taxonomic differentiation. Paleozoic ostracods tend to have more ornamentation than later forms. Some ostracods are just smooth "lima beans". The hinge line is on the dorsal side of the shell and typically consists of a simple groove or edge. Interlocking teeth structures, as in bivalves or brachiopods, are not present. Generally, there are five pairs of adductor muscles, which are used to close the shell - their presence will leave muscle scars on the shell's interior. Ostracod shells usually have tiny holes through which sensory hairs extended. Transparent to translucent portions of the shell are where eyespots occur. Some ostracods have only one eyespot. Classification: Animalia, Arthropoda, Crustaca, Ostracoda Stratigraphy: unknown, but possibly from the Silurian of Ohio Locality: out-of-place sample from Pickerington, northwestern Fairfield County, central Ohio, USA See info. at: en.wikipedia.org/wiki/Ostracod |
Date | |
Source | https://www.flickr.com/photos/47445767@N05/53247329909/ |
Author | James St. John |
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This image was originally posted to Flickr by James St. John at https://flickr.com/photos/47445767@N05/53247329909. It was reviewed on 11 October 2023 by FlickreviewR 2 and was confirmed to be licensed under the terms of the cc-by-2.0. |
11 October 2023
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Camera manufacturer | Canon |
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Camera model | Canon PowerShot D10 |
Exposure time | 1/400 sec (0.0025) |
F-number | f/3.2 |
ISO speed rating | 80 |
Date and time of data generation | 17:56, 9 October 2023 |
Lens focal length | 8.295 mm |
Width | 4,000 px |
Height | 3,000 px |
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Pixel composition | RGB |
Orientation | Normal |
Number of components | 3 |
Horizontal resolution | 180 dpi |
Vertical resolution | 180 dpi |
Software used | Adobe Photoshop Elements 20.0 (Macintosh) |
File change date and time | 19:38, 9 October 2023 |
Y and C positioning | Co-sited |
Exif version | 2.21 |
Date and time of digitizing | 17:56, 9 October 2023 |
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APEX shutter speed | 8.65625 |
APEX aperture | 3.34375 |
APEX exposure bias | −0.66666666666667 |
Maximum land aperture | 3.34375 APEX (f/3.19) |
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Flash | Flash did not fire, compulsory flash suppression |
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Focal plane resolution unit | inches |
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File source | Digital still camera |
Custom image processing | Normal process |
Exposure mode | Manual exposure |
White balance | Auto white balance |
Digital zoom ratio | 1 |
Scene capture type | Standard |
Lens used | 6.2-18.6 mm |
Date metadata was last modified | 15:38, 9 October 2023 |
Unique ID of original document | 80BFEAB93E1BD09FD68B06405C96DF11 |