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Microfossil Mania!

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An ongoing account of additions to my burgeoning collection of Foraminifera and Ostracoda.

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Rumi

 

Since the upload of Part 1 succeeded, I'll now offer up Part 2, a look at two interesting taxa from the family Globigerinidae.  This family contains most of the taxa that we associate with the idea of "planktonic forams", perhaps due to our familiarity with the "globigerina oozes" that form a significant part of the floor of the modern world oceans.

 

Globigerinoides ruber (d’Orbigny, 1839) is one of the two “red” species of globigerinids, as the specific epithet indicates.  It is well-known that the color of individual specimens varies from white to pinkish-red, and it is typically the case that only some of its globular chambers exhibit the red coloration.  I have specimens with all white chambers, one red chamber, two red chambers, etc., and have a single individual that is all red.  Interestingly, the intensity of the color seems to increase with the number of chambers affected, so the all red specimen is very red indeed -- it is also a little smaller than average.  Here is a typical specimen seen from the umbilical side, in a slightly oblique view, showing the primary aperture and one red chamber:

 

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The genus Globigerinoides differs from Globigerina in that its species exhibit secondary apertures, formed at the junctions of the spiral suture with intercameral sutures:

 

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Here is the spiral side of the same specimen, again presented in an oblique view, with two supplementary apertures, two red chambers at the left, and a pale pink one at the right.  The top, final chamber is white, as is most frequently the case.  This taxon is the commonest foram in the sample, by a large margin. 

 

The other red globigerinid is Globoturborotalita rubescens (Hofker, 1956).  According to the World Foraminifera Database, it also occurs in the Gulf of Mexico, but I have seen no specimens in my sample as yet.  This taxon shows four chambers in the umbilical view, rather than three, and lacks the secondary apertures.

 

A second interesting globigerinid, quite different from the preceding, is Globigerinella siphonifera (d’Orbigny, 1839).  This genus exhibits planispiral forms, rather than trochospiral -- all of the chambers are in the same plane.  (Actually, the test begins growth in a trochospire, but quickly switches growth pattern to planispiral.)

 

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There is a primary aperture at the base of the final chamber, and in fully mature specimens like this one, the initial chambers enter the final one through the primary aperture:

 

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The final chamber appears to be “gobbling up” the initial chambers, like the snake that swallows its own tail.

 

In Part 3 of this entry, I’ll examine three taxa from the Family Globorotaliidae.  Stay tuned.......

 

 

 

Rumi

Planktonic Foraminifera are particularly important in biostratigraphic studies and correlation, as they are ubiquitous in marine deposits, and evolve rapidly.  They first appeared in Middle Jurassic time, and thus have a long geological history.  There are many phylogenetic and correlational studies available, and their rapid evolution makes them exceptionally useful as temporal markers, or guide fossils.

 

I am currently looking at planktonic Foraminifera from a deep-water sample that was collected from the Dry Tortugas Islands, off of the coast of southern Florida.  The sample was dredged from a depth of 215 meters, due south of the islands.  This is an interesting area, as it represents the eastern extremity of the Gulf of Mexico, as well as the northern edge of the Caribbean Sea.  The sample is a very rich one, with numerous species of benthic Foraminifera, as well as a few ostracodes.  There is a good selection of planktonic forams -- I have thus far identified ten species, and would like to discuss one of these, a member of the Family Pulleniatinidae.

 

Pulleniatina obliquiloculata (Parker & Jones, 1862) is a rather unusual looking taxon, starting with a trochospiral growth pattern, but switching to a streptospiral pattern for its final chambers.  It is globulose, and quite shiny, making it easy to recognize.  It took me some time to locate a specimen for imaging, as most specimens have their aperture clogged with matrix.

 

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The aperture is low, but very broad, and the apertural surface of the chamber below it is strongly pustulose.  If this image were rotated toward the viewer a bit it would be clear that a thin area just above the lip of the aperture (seen here as an imperforate band) also bears pustules, although they are not as strong as those beneath the aperture.  For those interested in taxonomy, this species is the generotype of Pulleniatina.

 

I am submitting this short blog entry to see if the recent problems with uploading to the forum have been fixed.  If so, I'll be submitting other entries on this sample.

 

Rumi

The Lomita Marl Member of the San Pedro Formation is a well-known source for Middle Pleistocene marine fossils, and its beautifully preserved molluscan fauna has been treasured by fossil fanatics for decades.  There are outcrops in the city of San Pedro, California, although many of the "classic" localities have been destroyed by urban development.  It is well-exposed in the Lomita Quarry, located in the Palos Verdes Hills northwest of the city.  It has been dated at 400,000 to 570,000 years ago, about equivalent to the Santa Barbara Formation, which occurs further north along the California coast near the city of the same name.

 

The Lomita Marl is also an extremely rich source for microfossils, as ostracodes and forams are both very abundant and easy to extract from the matrix.  Most taxa in these two groups are still extant  off the southern coast of the state, but a significant proportion of the fauna appears to be extinct.  (One must hedge here, as the ostracode fauna of the Pacific coast of the United States is not very well known; the forams are better documented.)  A small sample of washed residues has given me the opportunity to begin study of this interesting fauna, and I hope to show some images of taxa from both groups on this blog.  This first entry will look at four ostracode taxa, selected simply because they are relatively easy to identify.  (Much of the ostracode fauna is known only in "open nomenclature", as in "Aurila sp. A", meaning that the species has not been recognized or is undescribed.)

 

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Bythocypris elongata Le Roy, 1943 is easy to recognize.  It is common, and appears to be the only member of the genus to be found in the Lomita.  It is a member of the family Bythocyprididae, which are smooth, and some would say "uninteresting" as a consequence.  As is normal in the family, the anterior end of the valve is broader and a bit more inflated than the posterior end.

 

The remaining three taxa are all members of the large family Hemicytheridae, a group with interesting surface ornamentation:

 

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Aurila driveri (Le Roy, 1943) is one of the several members of the genus to be found in the Lomita, and the only one (as far as I am concerned), that is easily recognizable.  The high-arched dorsum and strong ventral flange place it in the large genus Aurila, and the prominent anterio-ventral teeth are characteristic only of this species.  The caudal process is low on the posterior margin, and bears fine denticles.

 

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Australicythere californica (Hazel, 1962) is relatively large at roughly one millimeter in length, and is more elongate than most hemicytherids.  There is no caudal process, but typically 3-4 large posterio-ventral teeth.  The lower half of the anterior margin has some small denticles, rather worn on this specimen.  The valve outline is quite distinctive for this species.

 

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Hemicythere hispida Le Roy, 1943 is probably the easiest ostracode from the Lomita to identify, and is quite abundant.  This image does not do it justice, due to the lack of 3-D.  Under a stereo microscope it looks almost "furry", as the entire valve surface is covered with round-ended tubercles.  (The lack of 3-D here is due to the excess white matrix obscuring all but the ends of the tubercles.)  This species also has a particularly prominent eye tubercle, seen here at the anterior edge of the dorsal margin -- under the microscope this tubercle appears somewhat shiny, rather like glass.  (I had to sacrifice the shine to get decent illumination of the rest of the valve.)

 

To make these images, the specimens were simply laid flat on the inside of the lid of a micromount box.  Not very sophisticated, but it gives a nice black background -- at the expense of making the specimen a bit more difficult to illuminate evenly.  And it's quick and simple...........

 

That's it for this entry.  I will try to illustrate some of the many forams to be found in the Lomita in a future blog entry.

Rumi

 

One of the problems I experience in studying microfossils is that of orienting a specimen so that crucial characters are visible.  An example: for identification it is often necessary to check the shape of the tooth in the aperture of taxa in the family Hauerinidae.  The tooth can be long or short, plain or bifid, present or missing, etc.  The aperture is on the end of the test, so it isn't possible to look into it when the test is lying flat -- which it always does when the test is lying in a tray under the scope.  Of course, it is possible to use a little glue on the opposite end and manipulate it into a vertical position: but this is a lot easier said than done!  However, there is a much easier way to look at such things -- use a mechanical two-axis stage, which will allow you to turn a specimen to literally any position under the stereo 'scope.  One of my holiday gifts this year was just such a stage, of the type most commonly used by entomologists to examine pinned insects.

 

To use the stage, I have a size 0 insect pin from which I removed the head with side-cutter pliers.  I put a small drop of gum tragacanth on the resulting blunt end of the pin, and touch it to the side of the specimen I wish to examine, where it quickly dries.  I stick the sharp end of the pin into the soft rubber plug of the rotating arm of the stage, and I'm set to go.  I can alter the orientation of the specimen by rotating either of the two axles of the stage; by rotating the whole stage around its vertical axis I get the third "axle".  The pin is not too distracting, and only the little area under the glue is not visible.  This works quite well!

 

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In this image, the aperture is at the upper end, toward the top.  (Oops, mispelled "hauerinid", drat...)  Two chambers are visible on this side, and there are three chambers visible on the opposite side.  One can't see the tooth in the aperture, par for the course when the test is lying flat.  Let's look at another specimen, mounted on the mechanical stage:

 

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I rotated this specimen by 90 degrees from its "flat" position, and now the aperture is perfectly placed for inspection.  The long tooth in the aperture is clearly visible, as is the thickening of the lip.

 

Another example using different orientations: here the specimen is perched on top of the pin.

 

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The genus Lenticulina is planispiral and involute, and the aperture is at the upper end of the exposed face of the final chamber.  The aperture is radiate; i.e., composed of several thin slits in the shape of an asterisk.  This can be difficult to see.  In this image the position of the aperture is marked by the arrow, but the nature of the aperture is not at all clear.  Rotating the test by 90 degrees to get a profile view gives us a better look, and this profile view is also most useful in species identification:

 

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In this image, the test is mounted on the pin, which is glued to the underside of the specimen.  So why is the pin not visible?  To light specimens under the 'scope I use a two-arm fiber optic illuminator -- careful adjustment of the twin light heads can "eliminate" the pin with shadows.  (Any remaining reflections from the pin are easily removed with image processing software.)  If the pin were visible, it would extend downward to the lower edge of the image.  Eliminating the pin makes the specimen appear to "float in midair", but at the expense of a weakly illuminated underside.

This image shows the involute structure nicely, the apertural face, the swollen center of the test, the thin peripheral keel, and the pale aperture area at the right end.  The aperture itself is still not well revealed, however.  Let's adjust the orientation a little more:

 

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Turning the right end of the test upward toward the objective lenses, and boosting the magnification a bit, brings the radiate aperture into better view.  Three of the radial slits, filled with contrasting matrix, are fairly clearly shown.  Further rotation upward toward the objectives would provide a fuller view of the aperture, but this view is sufficient to demonstrate that the aperture is indeed radiate in structure. 

 

This method of mounting a specimen on a pin is totally non-destructive: to remove the specimen from the pin one just immerses it in a drop of water, where the gum tragacanth will quickly dissolve, leaving the specimen completely undamaged.

 

Hopefully this blog entry will encourage others to explore ways to alter the orientation of their specimens, whether for identification purposes or photo-imaging.

 

Rumi

While picking specimens of Foraminifera from the Taylor Marl, of the Texas Cretaceous Gulfian Series, I found several fragments of a taxon that I could not recognize.  However, today I found a nearly complete specimen of what is obviously the same organism.

 

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Frondicularia christneri Carsey, 1926 does not look much like a typical member of the genus.  The overall shape of the test is fairly normal, but the sutures form a rather unusual pattern, and they are raised above the test surface and slightly thickened (limbate).  The test is rimmed, and the sides are flat.  (It is this rimmed edge which produces limbate sutures when additional chambers are added.)  Note that the final chamber, bearing the terminal aperture, occupies the entire right edge of the test.  (The lower left corner of the test has been broken away, which creates the obvious asymmetry.)  This unusual structure is not unique within the genus, however; Michael's Foraminifera Gallery website shows at least one other taxon with the same type of limbate sutures.

 

In his 1954 Handbook of Cretaceous Foraminifera of Texas, Frizzell transferred this species to the genus Kyphopyxa, a move that is neither cited nor  recognized in the World Foraminifera Database.  In her original description of the species, Carsey noted that it is more typical of the Austin Chalk, although not rare in the Taylor Marl.  I have a sample of the Austin Chalk, and will be looking for this taxon when I get to it.

Rumi

Another Foram From The Pecan Gap Chalk

When I was preparing my previous entry on nodosariid forams from the Pecan Gap Chalk, I originally included a specimen that I had identified as a member of the genus Dentalina.  This identification was incorrect, and I edited the entry to remove that specimen.  Here it is again, with what I hope is the correct identification!

 

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The genus Strictocostella is a member of the family Stilostomellidae, and this species is illustrated in Frizzell's "Handbook of Cretaceous Foraminifera of Texas" as a member of the genus Stilostomella.  He also listed it as occurring in the Pecan Gap Chalk.  Better images can be found on the World Foraminifera Database -- they show specimens with some very small spines around the bases of each chamber, almost what one might call "hispid".  The drawing in Frizzell does not show this feature, nor does my specimen.  I have not yet looked at Cushman's original description, but I am reasonably confident that this difference is within the range of natural variation.  (I have seen this kind of variation on images of other stilostomellids.)

 

I like it when I "Live and Learn!"  And I'm glad that I caught the error.............

Rumi

I have recently been studying a sample of washed residues from the Pecan Gap Chalk Formation of the Cretaceous Gulfian Series, from an outcrop in the vicinity of Austin, Texas.  Most of the Gulfian formations are richly fossiliferous, and the Pecan Gap is no exception.  It has abundant, well-preserved microfossils, particularly forams and ostracodes.  In this blog entry I would like to show some forams of the family Nodosariidae, which I find of particular interest.  All belong to the genus Frondicularia, which has compressed, biserial tests.

 

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Frondicularia archiaciana d'Orbigny, 1840 is one of the maddeningly similar "narrow" forms within the genus, whose identification often requires close attention to the contours of the test outline.  The biserial growth form of the test appears in most  members of the genus as inverted chevrons when the image is oriented with the aperture uppermost.  This structure is more-or-less apparent depending on the relative transparency of the individual test, and it shows quite well in this image.  What one is seeing are the suture lines between the chambers.  The aperture in members of the Nodosariidae is radiate; this type of aperture does not stand up very well to post-depositional forces, and is very frequently broken away -- true of all four specimens in this entry.

 

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Frondicularia frankei Cushman, 1936 is one of a group of taxa within the genus in which the base of the test is not compressed.  In profile, the base appears to be bulbous, with rather wide "ripples" oriented lengthwise.  The upper 3/4 of the test is compressed, and appears quite flat in profile.  The basal spine is one of the distinguishing characters of this species, although many others show such a spine also.

 

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Frondicularia intermittens Reuss, 1865 is another taxon of the "narrow" group, in which the chevrons produced by the biserial structure are less apparent.  A few bright, length-wise streaks show that the sutures separating the chambers are depressed.

 

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The largest of the nodosariids that I have found thus far is Frondicularia mucronata Reuss, 1845.  The larger, more ovoid appearance of this taxon is due in part to the greater length of the individual chambers, which also gives the "inverted chevron effect" a somewhat different character.  The specific epithet is from the small basal tooth on the initial chamber (proloculus) of the test.

 

Hopefully, readers have enjoyed looking at these little fossils.  If so, stay tuned -- I'll be writing more about microfossils from the Texas Gulfian Series, and will also upload an entry on Pleistocene Ostracoda from the San Pedro Formation of California in the near future.

Rumi

Some Centric Fossil Diatoms

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.

 

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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.

 

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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:

 

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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.

 

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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:

 

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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.

 

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A common triangular form.  There are many genera of triangular centric diatoms.  And other radial shapes are possible, too:

 

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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..............................

 

 

 

Rumi

In 1958, Louis S. Kornicker and John Imbrie wrote a brief paper on the holothurian sclerites of the Florena Shale in which they described four species.  I have found 3 specimens of one of these, Microantyx permiana Kornicker and Imbrie, 1958.  Two of these  specimens were badly broken, but one is in fair condition.

 

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The sclerites are wheel-shaped with short spokes, and the openings between the spokes are roughly triangular.  In this dorsal view we can see a distinctive trait of this taxon: the central area has four deep depressions.  (The upper one in this view is largely filled with matrix, unfortunately.)  The dorsal surface is virtually flat.  Individual specimens are typically very close to circular, but this one seems to have a marginal chip that disturbs the symmetry.

 

M_permiana2.jpg

 

The ventral surface is slightly cup-shaped, the marginal rim being raised above the level of the spokes.  The central area is more strongly raised, producing a central, conical hub.

 

The diameter of Kornicker and Imbrie's specimens ranged from 0.17 - 0.27 mm., the average being 0.23 mm.  This specimen is thus somewhat larger than any of theirs.

 

Kornicker, Louis S., and John Imbrie, 1958, "Holothurian Sclerites from the Florena Shale (Permian) of Kansas," Micropaleontology, vol. 4, no. 1, pp. 93-96, pl. 1.

Rumi

In this entry I would like to show two of the commonest Foraminifera from my sample of the Florena Shale.  The most common forams by far are the fusulinids, but as these are not identifiable without thin sections, they will have to wait until I'm equipped to deal with them.  Excepting the fusulinids, the commonest foram is Globivalvulina bulloides (Brady, 1876):

 

G_bulloides.jpg

 

This taxon has an enrolled biserial structure, and in spiral view it typically exhibits one large and two smaller chambers, the sutures between them forming a rough T-shape.  In the umbilical view the triangular projection into the umbilical area is characteristic.  The many specimens show several different growth stages, but all are easily identifiable.

 

The second most common non-fusulinid is Tetrataxis corona Cushman and Waters, 1928:

 

T_corona.jpg

 

This taxon is looks much like a Chinese straw hat: a very low cone, with a concave umbilical area.  Chambers are added marginally, typically four per whorl, hence the generic name.  Specimens vary greatly in size, representing various growth stages.  The larger ones very frequently exhibit chipped or broken edges, probably due to postmortem damage.

 

Rumi

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.

 

A_centronotus.jpg

 

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.

 

C_parva.jpg

 

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................!

Rumi

I recently received some samples of washed residues from various shales and marls noted for their microfossil content.  One of the best of these is from southern Kansas, of Permian (Wolfcampian) age, from the Council Grove Group, Beattie Limestone Formation, Florena Shale Member.  The sample is amazingly rich, and I have recovered numerous species of Foraminifera and Ostracoda, as well as many nice bryozoan fragments.  In this blog entry I would like to show one of the more interesting microfossils that the Florena Shale is particularly noted for: the oogonia of charophytes, members of the algal family Characeae, commonly known as Stoneworts.  These large green algae live in relatively shallow, fresh to brackish waters -- although the tiny oogonia can easily wash down streams to the sea, where they will settle to the bottom in quiet, shallow areas.  (An excellent example is provided by The Fleet, a brackish lagoon on the southern coast of Dorset, England, where charophyte oogonia are abundant in bottom samples.)  Charophytes have been around for a long time, the earliest known oogonia coming from Devonian shales.

 

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This is a relatively large specimen from the Florena Shale, very typical in appearance.  The plants are called Stoneworts because they slowly secrete calcium carbonate, which eventually coats the leaves and stems, and particularly the reproductive products, the oogonia.  These are quite small, roughly egg-shaped, with a prominent spiral structure due to the shape of strip-like cells which grow to encase the delicate reproductive cells.  These strip-like cells vary in number, a valuable taxonomic trait.  This taxon, Catillochara moreyi (Peck, 1934), like all late Paleozoic forms, has five spirals.  (To count them, one needs to look at the specimen in end view, where the strip-like cells converge to a point, or small pit -- depending on which end one looks at.  On this specimen the point is to the right.)  Whole specimens like this one are typically white, because we are looking at a relatively thick outer coating of calcium carbonate.  Interestingly, the spiral-forming strips are coal black, and are usually well-preserved inside the outer coating.

 

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This smaller specimen is broken, and the black spiral "egg case" beneath is readily apparent.  Holocene specimens from The Fleet look exactly the same when broken, or when the outer coating has yet to develop.

 

In further entries to this blog I will show off a few of the more interesting ostracodes and forams.

 

Rumi

About a month or so ago I received a sample of "microfossil dirt" from the Gene Autry Shale Member of the Golf Course Formation, which crops out in Johnston County, Oklahoma, in the Ardmore Basin. The Golf Course Formation is of Lower Pennsylvanian (Morrowan) age. The sample contains abundant foraminifera, although it is not rich in numbers of species. There are also some good ostracodes. Preservation is quite variable: a few specimens are essentially perfect, but most show varying degrees of crushing or recrystallization.

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The commonest foram in the sample is Ammodiscus semiconstrictus Waters, 1927. Most specimens are almost perfectly circular, like the one on the left, while others show deformation to a more-or-less oval shape, like the one on the right. Size of these specimens shows much variation: the larger specimen in this image is 1.0 mm in greatest width, and a few are a bit larger. Some tiny specimens are only 0.2 mm in width. The test is finely arenaceous, and seems to be composed mainly of tiny bits of carbonate mud. This wall composition is typical of all but one of the foraminifera specimens I have found in this sample thus far.

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Another common species in the sample is Hyperammina bulbosa Cushman & Waters, 1927. These are never found intact. The test shows only two chambers, a sac-like proloculus followed by a long, straight tubular chamber. In this image we see three proloculi, with the straight tubular chamber broken off at some distance away. (The specimen on the left is 1.8 mm long.) Fragments of the tubular chambers are very abundant, more so than the proloculi. (Each individual has only one proloculus, but the tubular chamber can easily be broken into 5-10 pieces, making such fragments more abundant.) A fairly long fragment of this sort is shown at the bottom of the image. These tubes may be slightly irregular, and occasionally show fine, transverse growth lines. The tubular chambers do not contain septa, however.

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Less common is Nodosinella glennensis Harlton, 1927. This is a robust, uniserial species with a round, terminal aperture. The subglobular chambers are typically crushed at right angles to the growth axis, as seen in the image on the left. (Length of this specimen is 2.2 mm.) The image on the right shows a terminal chamber, broken off from the remainder of the test, with the terminal aperture clearly indicated. This final chamber was only partially crushed.

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More rarely, one finds a specimen that has been crushed parallel to the axis of growth. This produces a form that looks like a stack of coins. In this image, the early chambers are on top, and the test is resting on its terminal face. (If you turn it over, the aperture is present in the center of the terminal face.)

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I suspect that this last image shows a specimen of the same species that has not been crushed. Chambers have been broken off of both ends, but the size and uniserial construction are correct. It looks very much like Harlton's original illustrations of the species, which was described from relatively undeformed specimens.

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Finally, we see Endothyra whitesidei Galloway & Ryniker, 1930, a specimen that is 1.1 mm in greatest width. This specimen was unique in the sample, and looks rather different from the others. It is amber in color, and slightly shiny. The Treatise on Invertebrate Paleontology describes all members of the superfamily Endothyracea as being calcareous imperforate, with some arenaceous material in the more "primitive" forms. I see no trace of arenaceous structure in this specimen, but it is certainly imperforate.

I continue to struggle with the whole question of wall composition. If you see sand grains or sponge spicules in the wall, then the specimen is clearly agglutinated. Calcareous, hyaline walls, with their (usually) obvious perforations are also easy to recognize. What is not clear to me is the distinction between the secreted calcareous (but imperforate) type of wall, and the agglutinated wall composed of fine calcareous particles in a secreted, calcareous cement. How would they look different?

Rumi

In picking out my sample of microfossils from the Middle Pliocene Coralline Crag Formation, Suffolk, England, I noted a few fragments of what appeared to be a species of the ostracode genus Pterygocythereis, a particularly spiny-looking genus of the family Trachyleberididae. I assumed it to be Pterygocythereis jonesi (Baird, 1850), the common species of the North Sea. As luck would have it, while finishing the picking of the last bit of the sample, up popped a complete valve, in almost perfect condition.

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To my surprise, it turned out not to be the common North Sea species; rather, it is Pterygocythereis siveteri Athersuch, 1972. The image does not do it justice, as even with image stacking software, the great length of the alae and the 3-D spininess are not very apparent. (Published dorsal views of the complete carapace are quite impressive!) Further cleaning of the specimen should greatly improve its appearance.

In the standard book on the recent Ostracoda of Great Britain, we find the following: "British records of P. siveteri are sub-Recent, and there are, as yet, no live records outside the Mediterranean." (Athersuch, Horne and Whittaker 1989: 146) Presence of this species thus provides further evidence that the Middle Pliocene sea around southern Great Britain was warmer than it is now, and that the ostracode fauna was essentially Lusitanian, characteristic of the modern Mediterranean Sea and of the Atlantic Ocean off the northwest coast of Africa.

The genus Pterygocythereis today is commonly encountered in the sublittoral zone, down to a depth of about 200 meters. Faunal studies of the Coralline Crag have suggested that it was deposited in a high energy environment with a maximum depth of about 20 meters, which seems to fit. However, this species is rather rare in the Coralline Crag, suggesting that it may not have been a member of the original, local biocoenosis.

Athersuch, J., D. J. Horne, and J. E. Whittaker, 1989, Marine and Brackish Water Ostracods, The Linnaean Society of London.

Rumi

I have always enjoyed looking at ostracodes of the family Trachyleberididae, for their varied and complex structures, and interesting ornamentation. The family seemingly first appeared in the Middle Jurassic, became abundant during the Cretaceous, and remains abundant in the seas of today.

About a month ago, in an exchange of microfossil material with an Italian friend, I received a sample of material from the Coralline Crag of southeastern England, a well-known and extensively studied Middle Pliocene (Zanclean) marine deposit of cross-bedded sands. The deposit averages about 12 meters in thickness, varies from weakly to more strongly consolidated, and is highly fossiliferous. The name comes from an abundance of bryozoans, which early scholars mistakenly thought were corals. Ostracodes and foraminifera are both abundant. Faunal studies have suggested that the sea was a bit warmer when this formation was laid down, perhaps more closely resembling the Mediterranean Sea, or the Atlantic Ocean off the northwest coast of Africa. Hence the Coralline Crag contains many species that do not much resemble those found in the marine littoral deposits of modern-day England.

I have recovered quite a few species of both forams and ostracodes from my sample, and am just beginning the identification process. The species I want to show off in this entry is the first I have identified, chosen to be investigated first because it is both common and showy. The taxon is correctly known as Cletocythereis jonesi Wood et al., although it was previously known by various other names through misidentification. It is a typical trachyleberidid, although with much coarser surface sculpture than most. The valves are subquadrate and rather thick, with an amphidont hinge.

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The surface is coarsely reticulate, with a strong sub-central tubercle, and dorsal and ventral ridges. The anterior margin is also reticulate, divided into elongate, transverse cells. The ventral ridge terminates posteriorly in a complex loop. The eye tubercle, just below the anterior dorsal margin, is large and shiny.

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Here is an interior view of the same right valve, unfortunately obscured by residual matrix. The ventral margin exhibits a strong concavity; the posterior dorsal corner is not broken, contrary to appearances, and is a close match to images of the type specimens.

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The hinge of the right valve has a strong, round anterior tooth. The posterior tooth is weaker, and the middle element is of the smooth groove-and-bar type; the right valve has the grooved element, and there is a corresponding thin bar in the left valve.

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This dorsal view shows the thickened central part of the carapace, due to the dorsal and ventral ridges, and the relatively flat anterior and posterior margins.

Personally, I think this is a really handsome microfossil -- considering that its largest dimension is only about 1 millimeter in length!

In future entries in this blog I hope to illustrate a few other ostracodes and forams from this interesting formation, if I am able to make more identifications. Fortunately, I have access to a good research library!

Two interesting references are:

Wilkinson, I. P., 1980, "Coralline Crag Ostracoda and their environmental and stratigraphical significance," Proceedings of the Geologists' Association 91:291-306.

Wood, A. M., R. C. Whatley, C. A. Maybury, and I. P. Wilkinson, 1992, "Three new species of cytheracean Ostracoda from the Coralline Crag at Orford, Suffolk," Journal of Micropaleontology 11:211-220.

Rumi

Finally, I Can Stop Whining!

In a number of recent posts to the Forum I have complained incessantly about my inability to locate microfossils here in my home state of Arizona. Well, no more! A sample that I processed over the weekend produced a few nice ostracodes, and I am optimistic about finding more. The locality is the well-known Kohl Ranch site, just northeast of Payson, Arizona, reputed to be the best spot for collecting invertebrate fossils in the state. The material comes from the "beta" member of the Naco Formation, a purplish, siliciclastic mudstone of Middle Pennsylvanian (Desmoinesian) age. The megafossils of this locality were listed by Brew and Beus (1976), and thirteen species of ostracodes were listed by Lundin and Sumrall (1999). (Several other publications deal with more specialized aspects of the fauna.) The reported fauna is representative of an offshore, shallow, marine environment, probably less than 20 meters in depth. (Brew and Beus 1976: 889)

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Two of the better specimens are shown in the attached photos. Both are complete single valves, and are partially pyritized. The male valve is a bit better preserved than the female, but both are adequate to show the basic features of the species -- which is the commonest one found in this particular sample. The ventral frill (velum) of the male is smaller, with a smaller posterior spine. The frill of the female is larger and incurved, presumably to form a brood pouch. This type of velum is characteristic of the family Hollinidae, although the various genera exhibit it in different degrees of development.

The remaining matrix on these specimens certainly detracts from their appearance, and I am going to try further cleaning with kerosene. Thus far the sample has simply been boiled with some sodium bicarbonate.

It is interesting that no other microfossils have been found in this formation. Although fusilinids are reported, I have seen no other forams at all, nor have I seen any conodonts.

A future entry in this blog will present some photos of the locality.

Brew, Douglas C. and Stanley S. Beus, 1976, "A Middle Pennsylvanian Fauna from the Naco Formation near Kohl Ranch, Central Arizona," Journal of Paleontology 50:888-906.

Lundin, Robert F. and Colin D. Sumrall, 1999, "Ostracodes from the Naco Formation (Upper Carboniferous) at the Kohl Ranch Locality, Central Arizona," Journal of Paleontology 73:454-460.

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