Sunday at the University of Tartu Natural History Museum — this time as tourists

August 5th, 2018

Tartu, Estonia — Bill Ausich and I returned to the Natural History Museum today to tour the public exhibits. It was hard to not make it into a study trip, though, for our research. I suppose since our “work” is so enjoyable it is difficult to separate it from a holiday. Above, for example, is a display of our favorite rhombiferan, Echinosphaerites aurantium of the Estonian Upper Ordovician.

There is a display about the Kalana Lagerstätte that we are studying.

Here is the museum description of the Lagerstätte.

And a close-up of some crinoids (“meriliilia”, sea lilies) from the Kalana.

It is a fun museum with a very thorough geology section, including meteorites you can touch (a favorite of mine). It has what is now an old-fashioned style of emphasizing actual specimens that Bill and I appreciated. There is a large biology section with much taxidermy and mounted skeletons. One of the featured exhibits is a rare “rat king” (see below), which you must look up!

Back to work in the University of Tartu Geology Department

August 3rd, 2018

Tartu, Estonia — Today Bill Ausich and I returned to the geology lab on the university campus to continue our work on the Kalana Lagerstätte crinoids. There is Bill above working on specimens.

I spent most of the day working with this beautiful Leica photomicroscope (model S9i). It is the most intuitive photomicroscope I have ever seen. The images are superb. I want.

Here I am at the microphotography station, looking wistfully outside.

We don’t have anything new to report today, so here’s an image of one of the best Kalana crinoids.

This is my favorite specimen because it is squashed in a way that separated the calyx plates to make them easier to see.

The calyx is on the left side of this specimen. The pinnules from the arms are preserved so well here they look like hair. Note the small angular fossil just below the crinoid on the right. These are common in the Lagerstätte, often appearing to be attached to crinoids. We think they may be green algae, possibly like the modern Hydrodictyon but marine — and with larger cells. Another mystery in this fossil assemblage.

We’ve now completed a week in Tartu. The Kalana crinoid project has gone especially well. Thank you to graduate student Viirika Mastik who collected most of the Kalana crinoids, and to her supervisor Oive Tinn. They have helped us immensely in the lab.

Back to the paleontology lab in Tartu, Estonia

August 1st, 2018

Tartu, Estonia — Disconcertingly it says “chemistry”, but there really is a geology department inside this building on the University of Tartu campus.

The Geology Department is part of the Institute of Ecology and Earth Sciences. We are very impressed with their facilities and friendly academics.

Here again is the lab room loaned to us for our stay. Bill is working in the back. The crinoid-rich specimens from the Kalana Lagerstätte at the Kalana Quarry (Silurian, Llandovery, Aeronian) are spread out through the room. We are very fortunate to have such space.

This is my workstation with my trusty laptop. The Leica microscope is fantastic.

We are examining the crinoids preserved on this dolomicritic limestone slabs that were carefully collected by university staff from Kalana Quarry in central Estonia. The crinoids are quickly apparent because their beautiful hair-like pinnulate arms are visible.

I’ll write more paleontological details later, but here is the part-counterpart of the best specimen of what will be a new crinoid taxon. From the bottom is the cylindrical stem, followed upwards by the conical calyx, and then the long arms with thin extensions called pinnules. You can also see some black smears of carbonaceous material on the right. These specimens are compressed and mostly decalcified. Their preservation is still a bit mysterious to us.

This is why we’re here so far from home!

Here is an image of the Kalana Quarry, where the Lagerstätte is found, from this wonderful Estonian geology website.

Fieldwork in Estonia, with a bonus visit to Narva

July 31st, 2018

Tartu, Estonia — Today Bill and I had a spectacular geology and culture field trip in northeastern Estonia. As you can see in the images, the weather was excellent, if a little warm. Our Estonian hosts took us from Tartu to several places north and east to the border with Russia. Our fieldwork in an oil shale quarry is shown above, but first our journey there —

Lake Peipsi (or Lake Peipus) is near Tartu. It is one of the largest freshwater lakes in Europe, with the Russian border running down its center. We stopped briefly for this view. It looks like one of North America’s Great Lakes from here. There is much history along these shores.

This is the Kiviõli Concentration Camp Holocaust Memorial near our collecting site today. The 20th century history of this region, especially during World War II, is notably grim and brutal. Relatively little has been published on the German concentration camps in Estonia.

This is the oil shale mine we visited near Põhja-Kiviõli in northern Estonia. The oil shales, in the form of kukersite, are the brown units in the top half of the outcrop. The shales are dug from these pits and then separated from the limestones, which appear light gray. The pits fill quickly with water, so there are massive pumps continually working nearby.

A closer view of an oil shale outcrop. These units are Late Ordovician in age (Sandbian) and nearly unique to Estonia. They are very rich in organic material — up to 55% of the rock. The oil shales are used in a variety of ways for energy and petroleum products.

Finding specimens of the spherical rhombiferan echinoderm Echinosphaerites was one of our goals for this trip. Here is one in limestone. The best are those that are in the oil shale because they pop free of the matrix. We didn’t find very many, though.

Giant bryozoans were surprisingly common in the oil shales. This is the base of a large trepostome. We found many of these bryozoans with beautiful borings. It was a good collecting site.

Here are our delightful Estonian hosts at lunch following fieldwork. From left to right: Olev Vinn (a colleague since 2006), Ingrid Vinn, and Mare Isakar.

Much to our surprise we were able to go to the storied easternmost Estonian city of Narva. This was very much a treat. Narva sits along the Narva River, which is the border with Russia. The city has a high concentration of Russian-speakers and a distinct Estonian-Russian culture. Its history has been, needless to say, complex even to present times.

This is Hermann Castle, also called Narva Castle, the focus of our visit. Hermann Castle is the blocky, high structure. To the right is visible another castle on the other side of the Narva River (see below).

This is that Russian castle opposite the Hermann Castle on the castle on the other bank of the Narva River. It is the Ivangorod Fortress. It makes for quite a striking boundary at the western edge of Russia.

The Narva River between the two castles, looking upstream. The Ivangorod Fortress is on the left. This is effectively the boundary between East and West in Europe.

The Narva border crossing bridge between Estonia on the left and Russia on the right. This is the view from the top of the Hermann Castle. At this point my phone gave me a message: “Welcome to the Russian Federation”.

The interior of the Hermann Castle is a museum. I thought these stone cannon balls were geologically interesting, considering that earlier this summer I saw their equivalents in Wales. Note my foot for scale.

On the way back to Tartu, we visited the town of Sillamäe on the Baltic coast. During Soviet times factories in Sillamäe extracted uranium oxides from local oil shales and then from other ores mined throughout the Soviet Empire. Because of the high concentration of scientists and engineers, this town was built with, shall we say, higher architectural and aesthetic standards than the usual Soviet constructions. It was a “closed town” forbidden to foreigners or even most Estonians.

This is a 1987 statue in Sillimäe celebrating its atomic achievements. By then this town produced almost 100,000 tons of uranium oxides for Soviet nuclear weapons and energy plants. It all stopped in 1989, and when Estonia reclaimed the area two years later there were serious contamination problems to solve. [Update: Cheryl Rofer, Los Alamos National Laboratory (retired), added a comment and a link to her story about the clean-up: Averting a Baltic Sea Disaster. It is an excellent read!)

What a rich trip this was. Thank you again to Olev, Ingrid and Mare.

Starting work in Estonia

July 30th, 2018

Tartu, Estonia — Ah, fossils at last! Bill Ausich and I are here to explore several topics, but the main one is describing the crinoids in a Silurian (Aeronian) Konservat Lagerstätte at Kalana Quarry in central Estonia. Much more on this later, but above is one of the crinoids, from the stem to the calyx to the pinnulate arms. The preservation is very odd, with most of the original calcite dissolved away and considerable carbonization and, maybe, some recrystallization. (Much of the list of preservation modes we teach!)

We’re working in a beautiful teaching lab at the University of Tartu. We have plenty of space to lay out the specimens collected by the geologists here. (These particular quarry beds are no longer accessible.) The microscopes are new and the best student models I’ve seen.

Today was mostly orientation for us in the lab. After dinner we walked down to the Emajõgi River, which runs through the campus and has been very important in Estonian history. Its name means “Mother River”. Beautiful.

Wooster’s Fossils of the Week: Peanut worms from the Silurian of Illinois

February 3rd, 2017

1-lecthaylus-gregarius-5-copyThis week’s fossils are a set of cool sipunculan worms from the Lockport Shale Member of the Racine Formation (Wenlockian, Silurian) of Blue Island, Illinois (which, it turns out, is not an island.). This is Lecthaylus gregarius Weller, 1925. (There is a common misspelling of the genus name as “Lecathylus”, which is how it is labeled in our collection.) They are masses of partially-carbonized bodies and external molds in a very fine-grained matrix. They are well known from this particular fossil-lagerstätte (a fossil fauna of remarkable preservation) in northern Illinois.

The Phylum Sipuncula did not often make it into the fossil record because of their entirely soft bodies, but a few are preserved way back in the Cambrian Chengjiang and Burgess Shale faunas. They show virtually no evolutionary changes in their long run to today, at least not in their outer form. They are commonly known as “peanut worms”.

2-lecthaylus-gregarius-2This is an example of the preservation modes: a black carbon film that has mostly flaked away, leaving behind a detailed external mold of the squashed peanut worms.

3-lecthaylus-gregarius-1Sipunculan bodies are divided into a main thick posterior trunk and a narrow, retractable anterior “introvert”. We’re looking here at the anterior introvert of Lecthaylus gregarius.

4-lecthaylus-gregarius-3-copyThis is the squat trunk of Lecthaylus gregarius.

5-themiste_petricola_evertedHere is the modern sipunculan Themiste petricola with introvert extended. It is the same basic plan as the Silurian Lecthaylus gregarius. Image from Wikipedia courtesy of Tomás Lombardo and Guillermo A. Blanco.

6-themiste_petricola_invertedThe modern sipunculan Themiste petricola with its introvert retracted. Image from Wikipedia courtesy of Tomás Lombardo and Guillermo A. Blanco.

stuart-weller-1870-1927Lecthaylus gregarius was described and named by Stuart Weller (1870-1927), an American paleontologist and geologist. He was born in the small town of Maine, New York. He earned a Bachelor’s degree in geology at Cornell University in 1894 followed by a PhD at Yale in 1901. Shortly after his Cornell degree, though, Weller traveled to the University of Chicago, where he worked his way through the ranks from a research associate to a full professor of Paleontology and Geology in 1915. He was also the director of the Walker Museum at the University of Chicago, and in 1926 he was president of the Paleontological Society. One of his sons, J. Marvin Weller (1899-1976) had a remarkably similar career as a stratigrapher and paleontologist.

References:

Kluessendorf, J. 1994. Predictability of Silurian Fossil‐Konservat‐Lagerstatten in North America. Lethaia 27: 337-344.

Roy, S.K. and Croneis, C. 1931. A Silurian worm and associated fauna. Field Museum of Natural History, Geological Series IV(7): 229-247.

Weller, S. 1925. A new type of Silurian worm. Journal of Geology 33: 540-544.

Wooster’s Fossils of the Week: New Early Silurian crinoids from Estonia

September 16th, 2016

1 Hilliste crinoidsIt has been a good year for new fossil taxa on this blog. I’m pleased to present a fauna of Early Silurian crinoids from the Hilliste Formation (Rhuddanian) exposed on Hiiumaa Island, western Estonia. They are described in a paper that has just appeared in the Journal of Paleontology (early view) written by that master of Silurian crinoids, Bill Ausich of Ohio State University, and me, his apprentice.

Here’s the simplified caption for the above composite image: Rhuddanian crinoids from western Estonia: (1) Bedding surface comprised primarily of crinoid columnals and pluricolumnals; (2) Radial circlet of an unrecognizable calceocrinid; (3) Basal circlet of an unrecognizable calceocrinid; (4) Holdfast A: Virgate radices anchored in coarse skeletal debris; (5) Holdfast D: Simple discoidal holdfast cemented to a bryozoan; (6, 7, 8) Hiiumaacrinus vinni n. gen. and n. sp.: 6, D-ray lateral view of calyx, 7, E-ray lateral view of calyx, 8, basal view of calyx; (9) Holdfast B: Dendritic holdfast in coarse skeletal debris; (10) Eomyelodactylus sp. columnal; (11) Holdfast C: Simple discoidal holdfast cemented to a tabulate coral; (12) Two examples of Holdfast E: Stoloniferous holdfasts cemented to a tabulate coral; (13) Protaxocrinus estoniensis n. sp. lateral view of partial crown, top of radial plate indicated by line.

Here is the abstract: “Rhuddanian crinoid faunas are poorly known globally, making this new fauna from the Hilliste Formation of western Estonian especially significant. The Hilliste fauna is the oldest Silurian fauna known from the Baltica paleocontinent, thus this is the first example of the crinoid recovery fauna after the Late Ordovician mass extinction. Hiiumaacrinus vinni n. gen. n. sp., Protaxocrinus estoniensis n. sp., Eomyelodactylus sp., calceocrinids, and five holdfast types are reported here. Although the fauna has relatively few taxa, it is among the most diverse Rhuddanian faunas known. Similar to other Rhuddanian crinoid faunas elsewhere, the Hilliste crinoid fauna contains crinoids belonging the Dimerocrinitidae, Taxocrinidae, Calceocrinidae, and Myelodactylidae; most elements of the new fauna are quite small, perhaps indicative of the Lilliput Effect.”
3 Hilliste diagramNo crinoid paper is complete without camera lucida drawings (scale bar for all figures is one mm): (1) Hiiumaacrinus vinni n. gen. and n. sp.; (2) Radial circlet of an unrecognizable calceocrinid; (3) Basal circlet of an unrecognizable calceocrinid; (4) Protaxocrinus estoniensis n. sp.
4 Olev062511There are two new species and one new genus here. Hiiumaacrinus vinni is named first after the lovely Estonian island where the species is found, and then after our good friend and colleague Olev Vinn (above) at the University of Tartu. Olev first introduced me to the Ordovician and Silurian of Estonia, and then was an excellent field companion for Bill and me on our Estonian field trips.
2 Hiiumaa mapA reminder where Hiiumaa Island is, and for that matter, the nation of Estonia.

5 HillisteQuarry071312Here is Hilliste Quarry on Hiiumaa Island. Still one of my favorite places to work. Very, very quiet.

6 HillisteAusich071112Here is Bill Ausich in the quarry during our 2012 expedition. The pose is known among paleontologists as “the Walcott“.

7 Holdfasts071112Here is one of the specimens collected by Bill in July of 2012. You may recognize this field scene as figure 12 in the top image of this post. These are two examples of crinoid holdfasts on a tabulate coral.

Please welcome Hiiumaacrinus vinni and Protaxocrinus estoniensis to the paleontological world!

References:

Ausich, W.I. and Wilson, M.A. 2016. Llandovery (Early Silurian) crinoids from Hiiumaa Island, Estonia. Journal of Paleontology (early view).

Ausich, W.I., Wilson, M.A. and Vinn, O. 2012. Crinoids from the Silurian of Western Estonia (Phylum Echinodermata). Acta Palaeontologica Polonica 57: 613‒631.

Ausich, W.I., Wilson, M.A. and Vinn, O. 2015. Wenlock and Pridoli (Silurian) crinoids from Saaremaa, western Estonia (Phylum Echinodermata). Journal of Paleontology 89: 72‒81.

Wooster’s Fossils of the Week: Symbiotic interactions in the Silurian of Baltica

June 17th, 2016

EcclimadictyonThis week’s fossils are from work Olev Vinn (University of Tartu, Estonia) and I did last summer that is soon to appear in the journal Lethaia. (An early electronic version of the manuscript has been available since November.) After numerous smaller studies describing symbiotic relationships recorded in Silurian fossils in the paleocontinent Baltica, we wrote a summary paper under Olev’s leadership. All the images are take by Olev and in the paper itself. I love this kind of study because it is about fossils as living, interacting organisms, not just static sets of characteristics.

For example, the top image is of the stromatoporoid Ecclimadictyon astrolaxum (a kind of hard sponge) with embedded rugosan corals (Palaeophyllum, with arrows) from the Jaagarahu Formation (Sheinwoodian) exposed at Abula cliff, Saaremaa Island, Estonia. The stromatoporoid and corals were growing together, each having their particular needs met and maybe even enhanced by the other.
syringoporidThe network of holes in this stromatoporoid from the Paadla Formation (Ludfordian) of Katri cliff, Saaremaa, represent the corallites of a syringoporid coral. Again, the coral and sponge formed an intergrown association.
ChaetosalpinxThis is a thin-section view of what was likely a soft-bodied worm (represented by Chaetosalpinx sibiriensis, noted by a white arrow) embedded in the tabulate coral Paleofavosites cf. collatatus from the Muksha Subformation (Homerian), Bagovitsa A, Podolia, Ukraine. Again, the worm was embedded in the living tissues of the host.

We found 13 such symbiotic associations in the Silurian of Baltica. Most of these interactions involved large skeletal organisms like stromatoporoids and corals, which provided stable hosts for smaller sessile filter-feeders and micro-predators. This work is part of a larger study looking at evolutionary trends in symbiotic associations during the Paleozoic.

References:

Tapanila, L. 2005. Palaeoecology and diversity of endosymbionts in Palaeozoic marine invertebrates: trace fossil evidence. Lethaia 38: 89–99.

Vinn, O. and Wilson, M.A. 2016. Symbiotic interactions in the Silurian of Baltica. Lethaia 49: 413–420.

Vinn, O., Wilson, M.A. and Motus, M.-A. 2014. Symbiotic endobiont biofacies in the Silurian of Baltica. Palaeogeography, Palaeoclimatology, Palaeoecology 404: 24–29.

Wooster’s Fossil of the Week: A striated brachiopod from the Silurian of New York

November 13th, 2015

6 StriispiriferCalebsSometimes it is a Fossil of the Week simply because it is new to me. The brachiopods above are abundant in a thin layer of shells within the Lewiston Member of the Rochester Shale (Silurian, Wenlockian) in western New York State. They are well exposed in the magnificent Caleb’s Quarry a few colleagues and I visited this past summer.
2 Striispirifer niagarensis Bed 9 Mbr D

3 Striations Sheinwoodian 585I find this spiriferid brachiopod fascinating because of the fine striations it shows on its fold and sulcus (where the shell bends at its middle). I’ve never seen these before on a brachiopod. The species is Striispirifer niagarensis (Conrad, 1842). I know of no functional interpretation of these fine lines other than that they might have provided some micro-topography to dissuade encrusting organisms. (I observed, in fact, no encrusters on these shells, but that may be coincidence.) The Striispirifer shell pavement consists mostly of isolated valves, but there are occasionally clusters of articulated shells in living position. It appears likely this is a storm lag of shells that was later colonized by the same brachiopods composing it.
4 Conrad description niagaraensisWe met the species author Timothy Abbott Conrad (1803-1877) earlier in this blog. He described this brachiopod originally as Delthyris niagaraensis in 1842 (above). (The third “a” in the species name was dropped by James Hall in his species lists.) This name held for over a century until G. Arthur Cooper and Helen Muir-Wood discovered that the genus was also in use for another brachiopod named in 1828 by Johan Wilhelm Dalman. This made “Delthyris” a homonym, or a name for a taxon identical in spelling to another such name for a different taxon. We can’t have that, of course, since every genus name must be unique (at least among the animals). Cooper and Muir-Wood (1951) gave the later genus (the junior homonym) the new name Striispirifer. Paul Taylor and I recently had our own adventure with a homonym we inadvertently created.
5 Helen Muir Wood 1955 Jill DarrellHelen Muir-Wood (1896-1968) was one of the most prominent brachiopod experts of the 20th Century. The image above may be the first one of her online. (Thanks to Jill Darrell of the Natural History Museum, London, for providing it. Come to think of it, the earlier image of Rousseau Hayner Flower in this blog is likely the first picture of him on the web.) Muir-Wood was born in Hampstead, England, and educated at Bedford College, University of London (a college for women at the time). She joined the professional staff at the British Museum (Natural History) in 1922 and spent the next 43 years of her career there. She was a systemacist to the core, apparently intolerant of any work with with fossils outside of describing and classifying them. Although she did no fieldwork of her own, from her position at the museum she was able to study brachiopods from around the world. She pioneered the techniques of describing brachiopod internal structures and eventually had to her credit hundreds of new and redescribed taxa. She was awarded the Lyell Medal in 1958 for her achievements, and in 1965 received the Order of the British Empire. She was remarkably successful and her work is still heavily cited to this day.

References:

Ager, D. 1969. Helen Marguerite Muir-Wood. Proceedings of the Geologists’ Association 80: 122-124.

Brett, C.E. 1983. Sedimentology, facies and depositional environments of the Rochester Shale (Silurian; Wenlockian) in western New York and Ontario. Journal of Sedimentary Research 53: 947-971.

Conrad, T.A. 1842. Observations on the Silurian and Devonian Systems of the United States, with descriptions of new organic remains. Journal of the Academy of Natural Sciences of Philadelphia 8: 228–280.

Cooper, G.A. and Muir-Wood, H.M. 1951. Brachiopod homonyms. Journal of the Washington Academy of Sciences 41: 195-196.

Dalman, J.W. 1828. Uppställning och Beskrifning af de i sverige funne Terebratuliter. Kongl. Svenska Vetenskaps Academiens Handlingar, für 1827, 1828; Stockholm, tryckt hos P.A. Norstedt & söner, pp. 93, 99.

Williams, A. 1969. Helen Marguerite Muir-Wood. Proceedings of the Geological Society of London 1655: 123-125.

Wooster’s Fossil (Maybe) of the Week: Kinneyia ripples

October 23rd, 2015

1 Kinneyia_Grimsby_Silurian_Niagara_Gorge_585While hiking through the Niagara Gorge on a field trip in August, my friend Andrej Ernst of the University of Kiel found the above block of siltstone from the Grimsby Formation (Silurian) with unusual small-scale ripples in a patch. Carl Brett (University of Cincinnati) immediately identified it as a sedimentary structure/fossil known since 1914 as Kinneyia. This name was new to me. I had long called such features “elephant skin”, but I’ve now learned that these “sedimentary wrinkles” have a long and sometimes contentious history of study, and they have significant variability (see references).

Charles Doolittle Walcott (1850-1927) was one of the best known and productive invertebrate paleontologists. An American, he most famously discovered the Cambrian Burgess Shale in western Canada with its fantastic soft-tissue preservation. Walcott was especially fascinated with finding the earliest evidence of life, so he intently studied rocks older than the Cambrian (an interval we used to call the Precambrian). In 1914 he published a compendium of what we considered to be fossil algae, including Kinneyia. Below is his original description followed by his photographic image.
2 Walcott 1914 1073 Screen Shot 2015-08-22 at 6.42.01 PM4 Screen Shot 2015-08-22 at 6.42.57 PMWe now know that these curious structures are not fossilized algae, hence the name Kinneyia no longer has any biological use. (You may note that most authors do not italicize the name, emphasizing that it is no longer a valid taxon. I keep the style as a reminder of the name’s history.) These are ripples with sinuous, bifurcating, flat-topped crests. They are sometimes very complicated when the crests interfere with each other. Their flat tops (when well-preserved) suggest that there was something lying above them. Most workers on Kinneyia conclude that this was a microbial mat, so Walcott would be at least satisfied that life was involved. Did the Kinneyia ripples form as gas built up underneath a decaying mat? Are they made when the mat shrinks through desiccation? Experimental physicists have even gotten involved in the interpretations. Thomas et al. (2013) write: “Microbial mats behave like viscoelastic fluids. We propose that the key mechanism involved in the formation of Kinneyia is a Kelvin-Helmholtz type instability induced in a viscoelastic film under flowing water. A ripple corrugation is spontaneously induced in the film and grows in amplitude over time.”

Kinneyia is thus a sedimentary feature formed by physical processes mediated by life in the form of a microbial mat. What those processes were is the most interesting question now.

References:

Gerdes, G., Klenke, T. and Noffke, N. 2000. Microbial signatures in peritidal siliciclastic sediments: a catalogue. Sedimentology 47: 279-308.

Hagadorn, J.W. and Bottjer, D.J. 1997. Wrinkle structures: Microbially mediated sedimentary structures common in subtidal siliciclastic settings at the Proterozoic-Phanerozoic transition. Geology 25: 1047-1050.

Noffke, N., Gerdes, G., Klenke, T., Krumbein, W.E. 2001. Microbially induced sedimentary structures — a new category within the classification of primary sedimentary structures. Journal of Sedimentary Research A71: 649-656.

Porada, H., Ghergut, J. and Bouougri, E.H. 2008. Kinneyia-type wrinkle structures—critical review and model of formation. Palaios 23: 65-77.

Thomas, K., Herminghaus, S., Porada, H. and Goehring, L. 2013. Formation of Kinneyia via shear-induced instabilities in microbial mats. Philosophical Transactions of the Royal Society of London A: Mathematical, Physical and Engineering Sciences 371(2004), 20120362.

Walcott, C.D. 1914. Cambrian geology and palaeontology III No.2 – Precambrian, Algonkian algal flora. Smithsonian Miscellaneous Collections 64: 77-156.

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