Search the Community: Showing results for tags 'ostracoda'.
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In this second entry I would like to show well-preserved specimens of two ostracodes: the very long-ranging taxon Amphissites centronotus (Ulrich and Bassler, 1906), and the Permian taxon Cornigella parva Kellett, 1933. The former belongs in the family Amphissitidae, while the latter is placed in the family Drepanellidae. This specimen is a relatively late instar, but not fully mature, as final instar specimens average about 50% larger. The species is very easy to recognize, the very large and prominent central node being quite distinctive. Additionally, there are two strong ventral flanges, the inner flange curving upward to the anterior cardinal angle. There is a fairly strong dorsal ridge, the ends curving abruptly downward to form anterior and posterior ridges, the former being the longer of the two. The flanges and ridges are considerably weaker on early instars, but the prominent central node is still unmistakable. So far as I am aware, this taxon occurs throughout the Pennsylvanian (and perhaps earlier), and disappears by mid-Permian time, a range in excess of 100 Ma. It has been assumed that this species was a free-swimming benthic form, as the prominent flanges would not be well-suited to an infaunal mode of life. Betty Kellett described two species of the genus Cornigella from the Fort Riley Limestone of the Chase Group, higher in the Permian section of Kansas: Cornigella parva Kellett 1933, and Cornigella binoda Kellett 1933. They differed in the number of lateral nodes, the former species having a larger number of nodes, while in the latter species only the two prominent dorsal nodes were present. However, Kellett noted that her specimens showed considerable variation, which she attributed to poor preservation and diagenetic crushing. She went so far as to suggest that the two described taxa might actually be the same. Looking at Florena specimens, which are well-preserved complete carapaces, I would agree with her suggestion. The lateral nodes exhibit varying degrees of development; although the two dorsal nodes are always strongly developed, the ventral and anterior nodes may be considerably weaker. The specimen shown here is very well-preserved, and the full (?) complement of lateral nodes is clearly represented. (Note that, since we are looking at a complete carapace, the posterior dorsal node of the right valve is also obvious, as is a hint of the anterior dorsal node.) This specimen is also of interest, in that it shows a lot of the surface sculpturing, not too obvious on other specimens. I have chosen the name C. parva for this taxon, as Kellett's description appears first on the page, and should thus have priority. I have not seen the description or illustrations of the generotype Cornigella minuta Warthin, 1930, which was described as having eight "prominent spines", one projecting well above the hinge line. Type specimens were from the Pennsylvanian Wetumka Formation of Oklahoma. I would follow Kellett's judgement in deciding that the Permian taxon was not conspecific with that of Warthin. I had hoped to illustrate a perfect carapace of Ectodemites pinguis (Ulrich and Bassler, 1906) from the Florena, which I had temporarily stored in a small black plastic tray (the lid of a micromount box) on my desktop. Unfortunately, when I went to retrieve it for photography, it had simply disappeared -- even though I thought it to be well covered! Now it's fodder for the vacuum cleaner, one of the hazards of microfossil collecting................!
Diatoms are monocellular organisms which contain chlorophyll, and manufacture their own food in the same manner as plants, through the process of photosynthesis. They are one of the major producers of the Earth's oxygen. Their long geological history makes them very useful in the correlation of sedimentary rocks, and they are of equal value in reconstructing paleoenvironments. They are remarkably common everywhere there is any water at all! I have studied fossil marine diatoms for many years, as they are my primary interest in the microfossil world. Many of them are quite beautiful, and they are a favorite subject with many persons who enjoy photomicrography. My primary interest is in diatom taxonomy and evolution, not photography, so I'm afraid my images don't really do them justice. Centric diatoms exhibit radial symmetry, from circular to triangular, and all points between. Oval shapes are not uncommon. The oldest specimens of essentially modern diatom types are from the Cretaceous, and one of the very best localities is the Moreno Shale, which crops out in the Panoche Hills of California. Many diatomists have worked on this flora, and it is fairly well understood. Here we see two of the common taxa from this source. (The bar across the top of the Azpeitiopsis is a sponge spicule, not part of the diatom!) Diatom frustules are composed of secreted silica -- hence they are brittle, but can be virtually indestructible by chemical or diagenetic change in the right sort of environment. (One exception is a highly alkaline environment, which corrodes and ultimately dissolves biogenetic silica.) Other siliceous microfossils include some types of sponge spicules, silicoflagellates (another blog entry coming up perhaps), radiolarians, and ebrideans. At least one family of the foraminifera uses siliceous cement to form their tests. Diatom floras changed radically across the KT boundary, but they are still abundant in the Paleocene. Arguably the world's most famous locality for fossil diatoms is the region around Oamaru, New Zealand, and all collectors have many specimens from there. The age is Late Eocene - Early Oligocene. Somewhat earlier are the many great localities in Russia. Here is a Paleocene specimen from Simbirsk, Ulyanovskaya, Russia. Note that it deviates from pure centric form in that it is slightly ovoid. My own specialty is the diatoms of the Miocene. The United States is blessed with superb Miocene localities on both coasts, many well-known to members of this forum, because most of them can also produce superb shark teeth. The earliest known Miocene flora in the US comes from sites in Maryland: near Dunkirk, Nottingham, and other lesser known localities along the Patuxent River. All of these sites began to be explored in the mid-19th Century, because the diatoms are so perfectly preserved, to say nothing of abundant! These sites are in the lowest part of the Calvert Formation; indeed, there is an unconformity above them that lasted for a considerable period of time, and the diatom flora exhibits considerable changes across it. This part of the Miocene section belongs to the Burdigalian Stage, and age-equivalent diatoms are found also in bore holes and artesian wells at Atlantic City, New Jersey. An index fossil for the East Coast Burdigalian is the following taxon: This species of Actinoptychus evolved relatively quickly, and became extinct at the end of the Burdigalian. It is remarkably beautiful under the microscope, especially in color images, as fine structures in the silica serve as diffraction gratings. I regret that I have no color image in my photo library: I need to make a few! The Calvert Cliffs are rich in fossil diatoms, also, from the later, Middle Miocene. The above is but one example of the many marvelous specimens that can be found in the Calvert. If you're walking the beach for shark teeth, and have access to a microscope such as that used in microbiology or pathology labs, or even the type used in high school biology labs, grab a sample of the sediment. Soak it in water until it disaggregates into mud, let it settle until the water is just a bit cloudy, and put a drop on a microscope slide with a coverslip. A magnification of 100X should reveal diatom frustules (or fragments thereof) among the remaining, unsettled particles of silt. Diatomists all have their own protocols to get such specimens almost perfectly clean, and permanent slides made with a mountant of high refractive index can be utterly gorgeous. I am currently working most intensely on samples from the somewhat later Choptank Formation, that outcrops at Richmond, Virginia. This is another locality that produces excellent specimens: This is one of the most enduring taxa in the geological record, appearing from the early Paleogene right up until the present day, and it can be very abundant. A common triangular form. There are many genera of triangular centric diatoms. And other radial shapes are possible, too: So far as I am aware, this unique specimen is the earliest known example of this taxon, which is still found today in tropical waters. The breakage in the top "arm" is unfortunate, but what can I say: the specimen is, thus far, unique. One might expect modern contamination of the sample, were it not for the fact that the Richmond localities occur far from the contemporary ocean coast -- they are not "watered" by modern waves! That's it -- the 3.95 MB limit..............................
I have about 8 acres of coastal estuary in northern Nova Scotia, and decided to take a look at the estuary sediments to see if I could find any fossils. Yes, they are there! Microfossils and lots of other life including ostracoda. Using my hand lens I could see them very well. Will invest at sometime in a microscope and maybe I will see even more. Hand lens for scale for foraminifera and ostracod scale is in millimeters.
oilshale posted a fossil in CrustaceansLit.: World heritage nomination: Chengjiang Fossil Site (40MB, excellent overview with many pictures)