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 spherical bryozoan from the Upper Ordovician of northeastern Estonia

October 2nd, 2015

1 Esthoniopora Kukruse 585Way back in July 2007 we had our first Team Estonia doing geological field research. Andrew Milligan (’08) and I, with our friend Dr. Olev Vinn of the University of Tartu, explored the Upper Ordovician of the northeastern part of the country, perilously close to the Russian border. Most of our work was stratigraphic and related to echinoderms, but I picked up several of these beautiful spherical bryozoans. This specimen comes from the Kiviõli Member, Viivikonna Formation, Kukruse Stage, Upper Ordovician, of Kohtla-Nõmme Quarry (N 59.35665º E 27.22343º). You won’t find the quarry on a map, though, because it was soon afterwards erased by continual mining. Now it is a grassy field. Since we are studying bryozoans this week in my Invertebrate Paleontology course, I’m bringing these specimens to the blog.

2 Esthoniopora subsphaericaThis is what two specimens of this bryozoan look like before cutting. They have the size and shape of golf balls.

3 Esthoniopora subsphaericaHere are the same two specimens cut in half and polished to show the growth rings and tubular zooecia (which held the feeding zooids of the living bryozoan).

4 Esthoniopora subsphaericaIn this closer view you can see the polygonal outlines of the zooecia, now filled with calcite. In the lower right is a boring that cut through the skeleton soon after the bryozoan’s death on the Ordovician seafloor. It has a bit of sediment that filled the boring except for the very center, which apparently held the body of the borer.

This bryozoan is the trepostome Esthoniopora subsphaerica (Bassler, 1911). Bassler originally called it Hemiphragma subsphaericum, which is a nod to its abundant hemiphragms (curving partitions in the zooecial tubes). As bryozoans go, this one has a fairly simple structure with no exozone, endozone, monticules or spines. How it lived on the seafloor with such a spherical shape is a bit of a mystery. A slightly flattened patch is probably where the sphere contacted the sediment. The borings in these bryozoans were studied by Wyse Jackson and Key (2007).

5 Ray BasslerThe species author, Raymond S. Bassler (1878-1961), was an American paleontologist prominent in the study of bryozoans and other encrusting organisms. He was born in Philadelphia and became very interested in fossils from childhood. He received his bachelor’s degree from that paleontological bastion the University of Cincinnati in 1902, followed quickly by his master’s (1903) and PhD (1905) degrees from George Washington University, where he served as a professor for over forty years. He also began work at the United States National Museum in Washington in 1910, rising through the ranks to become Head Curator in 1929. His main interests were bryozoans from the Cenozoic of the Gulf and Atlantic coasts, on which he had long collaborations with the French bryozoologist Ferdinand Canu. He also worked closely with Charles Schuchert, Carl Ludwig Rominger, and Edward Oscar Ulrich. Ray Bassler died in 1961.

References:

Bassler, R.S. 1911. The Early Paleozoic Bryozoa of the Baltic Provinces. Bulletin of the US National Museum 77: 1-382.

Koromyslova, A.V., Fedorov, P.V. and Ershova, V.B. 2009. New records of bryozoans from the Lower Ordovician of the Leningrad Region and intercolonial variability in Esthoniopora lessnikowae (Modzalevskaya). Paleontological Journal 43:39–45.

Wyse Jackson, P.N. and Key, M.M. 2007. Borings in trepostome bryozoans from the Ordovician of Estonia: two ichnogenera produced by a single maker, a case of host morphology control. Lethaia 40: 237-252.

Wooster’s Fossil of the Week: A new crinoid genus from the Silurian of Estonia

March 13th, 2015

Velocrinus CD-interray lateralIt is my pleasure to introduce a new Silurian crinoid genus and species: Velocrinus coniculus Ausich, Wilson & Vinn, 2015. The image above is a CD-interray lateral view of the calyx (or head), with the small anal plate in the middle-top. (This will make more sense below.) The scale bar is 2.0 mm, so this is a small fossil. It was captured by the Crinoid Master himself (my friend and colleague Bill Ausich) from the Middle Äigu Beds of the Kaugatuma Formation (Upper Silurian, Pridoli) at the Kaugatuma Cliffs of Saaremaa Island, Estonia. It is described in the latest issue of the Journal of Paleontology. Here’s a link to the abstract. (This is the first issue produced by Cambridge University Press, so we’re honored to be part of publishing history.)
Velocrinus E-ray lateralHere is another view of the calyx, this time looking laterally at the E-ray.
AusichWilsonVinn_Fig3This figure explains the calyx views we see above. It is a plate diagram of Velocrinus coniculus. Imagine it as what the crinoid would look like if we could separate all its preserved ossicles and lay them out. The radial plates are black; the anal plate is shown stippled and marked with an “X”; the other letters indicate the particular rays. The artwork, and the images above, are from Bill Ausich.

The genus Velocrinus is defined this way in the paper: “Crotalocrinitid with a calyx cone shaped, lacking stereomic overgrowths, comprised of relatively large plates; infrabasals not fused, visible in lateral view; two anal plates; primaxil minute, not visible in lateral view; fixed brachials present; free arms not laterally linked; anus on tegmen; (nature of tegmen plating unknown).” This certainly is opaque to most readers. Trust us — it separates this new genus from all described before. Velocrinus is derived from the Latin term velo, which means to cover or conceal (think “veil”). It refers to the tiny primibrachials, which are not visible in lateral view. The species name coniculus refers to the cone-shaped calyx.
Kaugatuma070511Velocrinus coniculus is known only from the Kaugatuma Cliffs locality on Saaremaa Island. This is one of my favorite outcrops in Estonia. The extensive bedding-plane exposures are rare in the region. They show hundreds of holdfasts (essentially roots) of crinoids, some very large. The deposit was a relatively high-energy carbonate sand shifting through a forest of tall crinoids rooted in the sediment. Palmer Shonk (’10) did an excellent Senior Independent Study with rocks and fossils we collected from this place. The site shown above, by the way, was the location of a Soviet amphibious landing in November 1944.
KaugatumaCrinoidStem070511This is a close look at a bedding plane of Middle Äigu Beds of the Kaugatuma Formation. The crinoid stems are robust and abundant. Oddly enough, we’re still not sure what genus is represented by the large stems and holdfasts. The calyx of Velocrinus coniculus is far too small to have been associated with them. I suppose this means we need another expedition to Estonia!

This is the 1000th post in the Wooster Geologists blog.

References:

Ausich, W.I., Wilson, M.A. and Vinn, O, 2012. Crinoids from the Silurian of western Estonia. 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 Fossil of the Week: A stromatoporoid from the Silurian of Estonia

January 30th, 2015

Densastroma pexisumStromatoporoids are extinct sponges that formed thick, laminated skeletons of calcite. They can be very common in Silurian and Devonian carbonate units, sometimes forming extensive reefs. The stromatoporoid above is Densastroma pexisum (Yavorsky, 1929) collected from the Mustjala Member of the Jaani Formation (Silurian, Wenlock) exposed on Saaremaa Island, Estonia. It was part of Rob McConnell’s excellent Senior Independent Study he completed in 2010.
Densastroma pexisum sectionStromatoporoids are rather featureless lumps until you cut a section through them. Then you see their characteristic laminae of calcite. Looking very close you might also glimpse the tiny vertical pillars between the laminae. Identifying the species of stromatoporoid always involves a thin-section or acetate peel to discern the forms of the pillars and laminae.

In the upper left of the sectioned D. pexisum is an oval boring cut through the fabric of the stromatoporoid. This is likely the trace fossil Osprioneides kampto Beuck and Wisshak, 2008. This is the largest known Palaeozoic boring. It is relatively common in Silurian stromatoporoids of the Baltic region. Last year Olev Vinn, Mari-Ann Mõtus and I published a paper describing the same ichnospecies in large trepostome bryozoans from the Estonian Ordovician.
8 schematic drawing of Osprioneides kampto
This diagram of O. kampto is from Figure 8 of the Beuck et al. (2008) paper. The organism that made the boring was almost certainly a filter-feeding worm of some kind that gained a feeding advantage by placing itself high on a hard substrate.
Flügel in 7000 ts by Chris SchulbertDensastroma was originally named in 1958 by Erik Flügel (1934-2004). He combined the Latin densus with the Greek stroma, meaning “dense-layered”. (Yes, taxonomic purists will object to the mix of Latin and Greek in one name.) Flügel was a highly accomplished and diverse scientist who founded the Institute of Paleontology at the University of Erlangen-Nuremberg as well as the journal Facies. He is best known for his advocacy of detailed study of carbonate facies through petrography (“microfacies analysis“), developing a series of techniques and principles that I found very useful in my dissertation work. The above image is a fitting tribute to Erik Flügel made by Chris Schulbert. It is a portrait made of 7000 carbonate thin-sections!

References:

Beuck, L., Wisshak, M., Munnecke, A. and Freiwald, A. 2008. A giant boring in a Silurian stromatoporoid analysed by computer tomography. Acta Palaeontologica Polonica 53: 149-160.

Flügel, E. 1959. Die Gattung Actinostroma Nicholson und ihre Arten (Stromatoporoidea). Annalen des Naturhistorischen Museums in Wien 63: 90-273.

Freiwald, A. 2004. Erik Flügel: 1934–2004. Facies 50: 149-159.

Vinn, O., Wilson, M.A. and Mõtus, M.-A. 2014. The earliest giant Osprioneides borings from the Sandbian (Late Ordovician) of Estonia. PLoS ONE 9(6): e99455. doi:10.1371/journal.pone.0099455.

Wooster’s Fossils of the Week: A trace fossil from the Ordovician of Estonia

November 21st, 2014

Hyoliths03_585The fossils above have been in a previous post as examples of hyolith internal molds from the Middle Ordovician of northern Estonia. I collected them on my first visit to the Baltic countries in 2006. This week I want to recognize them again, but this time for the squiggly trace fossils you can just make out on their outer surfaces. These are the ichnospecies Arachnostega gastrochaenae Bertling, 1992. They are the subject of a paper that has just appeared in Palaeontologia Electronica entitled, simply enough, “The trace fossil Arachnostega in the Ordovician of Estonia (Baltica)“. The senior author is my Estonian buddy Olev Vinn. My Polish friend Michał Zatoń, my new Estonian colleague Ursula Toom, and I are co-authors.
399-861 copyAbove is an unpublished image of a gastropod internal mold from the Estonian Ordovician taken by Olev. It shows very well the variable branching nature Arachnostega. This trace was formed by a deposit-feeding organism mining organic material in a sediment-filled shell. It worked along the sediment-shell interface, probably because there was more nutrient value at that margin. The internal mold was formed when sediment filling the shell was cemented and the shell dissolved away, leaving the hard mold behind.
Screen Shot 2014-11-02 at 4.05.40 PMThis is Figure 3.1 in the new paper. Note the variation in the traces as well as the shells it inhabited. The caption as published: Arachnostega gastrochaenae Bertling in a gastropod from Haljala Regional Stage (Sandbian), Aluvere Quarry, northern Estonia. GIT 399-948-1. 2. Arachnostega gastrochaenae Bertling in a gastropod from the Kunda Regional Stage (Darriwilian), Kunda Ojaküla, northern Estonia. GIT 404-355-1. 3. Arachnostega gastrochaenae Bertling in a bivalve from the Haljala Regional Stage (Sandbian), Aluvere Quarry, northern Estonia. GIT 399-1590-1. 4. Arachnostega gastrochaenae Bertling in a bivalve from the Haljala Regional Stage (Sandbian), Aluvere Quarry, northern Estonia. GIT 399-1601-1. 5. Arachnostega gastrochaenae Bertling in a cephalopod from the Uhaku Regional Stage (Darriwilian), Püssi, northern Estonia. GIT 695-12-1.

Our paper analyzes the distribution of Arachnostega through the Ordovician of Baltica, a paleocontinent with a long history, including a collision with Avalonia (western Europe today, more or less) in the Late Ordovician. By plotting the occurrences of Arachnostega over time, we conclude that the makers of Arachnostega likely preferred cool climates and bivalve shells over gastropods. The tracemakers may have also been negatively influenced by the many biotic changes associated with the Great Ordovician Biodiversification Event.

Please check out the article itself. As with all papers in Palaeontologia Electronica, it is open access.

References:

Bertling, M. 1992. Arachnostega n. ichnog. – burrowing traces in internal moulds of boring bivalves (late Jurassic, northern Germany). Paläontologische Zeitschrift 66: 177-185.

Vinn, O., Wilson, M.A., Zatoń, M. and Toom, U. 2014. The trace fossil Arachnostega in the Ordovician of Estonia (Baltica). Palaeontologia Electronica 17, Issue 3; 41A; 9 p.

Wooster’s Fossils of the Week: Embedded cornulitids from the Lower Silurian of Estonia

May 12th, 2013

Cornulitids_Strom_051113At first specimen this looks like a series of holes drilled into a small, smooth substrate (like Trypanites), but then you notice that the substrate has grown up around the holes, and on the far left you can make out two cones. These are cornulitid tubes that lived on and then inside a living stromatoporoid sponge. Jonah Novek (’13), a Wooster geologist graduating tomorrow, found these in the Hilliste Formation (Rhuddanian, Llandovery) during his Independent Study work on Hiiumaa Island in Estonia.

My Estonian paleontologist friend Olev Vinn is the expert in bioclaustrated (embedded in a living substrate) cornulitids, as you can see from the papers listed below. These fossils are an excellent example of endosymbiosis, or the living relationship of one organism embedded within the skeleton of another (see Tapanila and Holmer, 2006). We can’t tell yet without a thin-section, but the cornulitid here is probably very similar to the Sheinwoodian (Wenlock) Cornulites stromatoporoides Vinn and Wilson, 2010. The specimen shown above is already in the mail to Estonia for further analysis. This specimen is the earliest example of cornulitid endosymbiosis in the Silurian.
Closer_Cornulitids_Strom_051113A closer view of the embedded cornulitid tubes. The tubes in these holes appear to have dissolved away, at least in their distal parts. Some of the details of the stromatoporoid substrate are just visible.

Jonah_MW_Richa_071213Fond memories of the 2012 Wooster-Ohio State University expedition to Estonia. Jonah Novek (’13), me, and Richa Ekka (’13) on the top of the Kõpu Lighthouse, Hiiumaa Island, Estonia. Photo by our friend Bill Ausich (OSU).

Congratulations to Jonah on his find, and best wishes to all the senior Wooster Geologists on this graduation weekend.

References:

Tapanila, L. and Holmer, L.E. 2006. Endosymbiosis in Ordovician-Silurian corals and stromatoporoids: A new lingulid and its trace from eastern Canada. Journal of Paleontology 80: 750-759.

Vinn, O. and Wilson, M.A. 2010. Abundant endosymbiotic Cornulites in the Sheinwoodian (Early Silurian) stromatoporoids of Saaremaa, Estonia. Neues Jahrbuch für Geologie und Paläontologie 257:13-22.

Vinn, O. and Wilson, M.A. 2012a. Encrustation and bioerosion on late Sheinwoodian (Wenlock, Silurian) stromatoporoids from Saaremaa, Estonia. Carnets de Géologie [Notebooks on Geology], Brest, Article 2012/07 (CG2012_A07).

Vinn, O. and Wilson, M.A. 2012b. Epi- and endobionts on the Late Silurian (early Pridoli) stromatoporoids from Saaremaa Island, Estonia. Annales Societatis Geologorum Poloniae 82: 195-200.

Stratigraphy and paleoenvironments of the Soeginina Beds (Paadla Formation, Lower Ludlow, Upper Silurian) on Saaremaa Island, Estonia (Senior Independent Study Thesis by Richa Ekka)

January 28th, 2013

DSC_0387

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We post abstracts of each study as they become available.  The following was written by Richa Ekka, a senior geology major from Jamshedpur, India. She finished her thesis and graduated in December, so her work is the first of her class to be posted. You can see earlier blog posts from Richa’s study by clicking the Estonia tag to the right.

In July 2012, I travelled to Estonia with my advisor, Dr. Mark Wilson, a fellow Wooster geology major Jonah Novek, Dr. Bill Ausich and three geology students of The Ohio State University. It was quite an adventure with a few unexpected changes in our travel plans. Dr. Wilson and I had to spend a day in Tallinn, waiting for Jonah as his flight was delayed. Upon Jonah’s arrival we headed for the island of Saaremaa, where I carried out my research. We stayed in Kuressaare, on the southern shore of the island. I did my field research on the Soeginina Beds at Kübassaare in eastern Saaremaa.

The Kübessaare coastal area is an outcrop of the Soeginina Beds in the Paadla Formation (lowermost Ludlow) that represents a sequence of dolostones, marls, and stromatolites (see figure above). The Soeginina Beds represent rocks just above the Wenlock/Ludlow boundary, which is distinguished by a major disconformity that can be correlated to a regional regression on the paleocontinent of Baltica. The occurrence of these sedimentary structures and fauna in the Soeginina Beds provide us with evidence that there was a change in paleoenvironmental conditions from a shelfal marine environment to a restricted shallow marine setting followed by a hypersaline supratidal setting.

The base of the section has Chondrites trace fossils and marly shale that represent a shelfal marine environment. The next section on top has dolostones with Herrmannina ostracods, oncoids, and eurypterid fragments that indicate a shallow marine setting (lagoonal). The next section above has stromatolites (see figure below) that form in exposed intertidal mud flats. The topmost section has halite crystal molds that represent a hypersaline supratidal setting. Thus, we see a change from shelfal marine environment to a restricted shallow marine setting and finally to a hypersaline supratidal setting.

DSC_0367

The first Wooster Geology student posters at GSA 2012

November 4th, 2012

CHARLOTTE, NORTH CAROLINA–The brave souls Jonah Novek (’13) above and Kit Price (’13) below were the first Wooster students to present their posters at the 2012 Geological Society of America meeting. Jonah worked in Estonia this past summer on Early Silurian recovery faunas in the Hilliste Formation on Hiiumaa Island. You can read his abstract directly here, and you can recall his field adventures by searching for “Jonah” in this blog. Kit collected Upper Ordovician cryptic sclerobiont fossils in Indiana in the late summer. Her abstract is here, and you can see her work in this blog by searching for “Kit“. Jonah and Kit started off our GSA presentation experience with confidence and joy.

Wooster’s Fossils of the Week: Giant ostracods (Silurian of Estonia)

October 7th, 2012

During our Estonian expedition this summer, Richa Ekka (’13) chose as her Independent Study project focus the Soeginina Beds (lowermost Ludlow, Upper Silurian) of the Paadla Formation exposed in southeastern Saaremaa Island. These carbonate sediments, mostly dolomitized, were deposited in very shallow conditions — so shallow that in some places we have syneresis cracks and halite crystal molds. I expected the fossils to be mostly stromatolites and rare traces. We were pleasantly surprised to also find, though, a bed with numerous valves of the giant ostracod Herrmannina Kegel 1933 (shown above). I should have guessed that the hardy and extraordinarily successful ostracods would have been present.

At first we thought that these slightly-recrystallized shells must be bivalves (clams) because of their relatively large size (up to 25 mm long). But we didn’t see the typical bivalve muscle scars or hinging teeth and sockets. They had to be ostracods — but so big? The typical ostracod valve, shown below, is two mm or less in length. These Silurian examples are over 10 times that size. It would be like me meeting my 60-foot equivalent. Turns out that Herrmannina is known for its gigantism in the ostracod world — and it is not even the largest.

Cyamocytheridea sp. from the Eocene of Nederokkerzeel, Belgium. (Public Domain, Wikimedia.) This is the typical small size for an ostracod.
Today the ostracods, members of the Phylum Arthropoda, have over 8000 living species in both fresh and marine waters. Most crawl or burrow into sediments (that is, most are vagrant benthic epifaunal and infaunal), and a few are suspended in the water column (planktic). They have a wide range of feeding habits, from filter-feeding and deposit-feeding to herbivory and carnivory. (This is a key to their survival from the Early Paleozoic to today.) The living ostracod above shows that they are essentially a large head with several pairs of appendages inside two hinged valves. (The image is public domain from Anna33 at Wikipedia.) Their sex life is astonishing: ostracods have the largest sperm of any animals in both relative and absolute measures. Ostracod sperm are often ten times the length of the male body. (No, I don’t know how that works!)

Herrmannina is in the Order Leperditicopida of the Class Ostracoda. This genus was named in 1933 by Wilhelm Kegel (1890-1971), a geologist in the Preussische Geologische Landesanstalt of Berlin, Germany, who specialized in the Devonian and Carboniferous systems. I couldn’t find out much more about Dr. Kegel, but did stumble across an uncredited, undated low-resolution photo of him above. A fuzzy face from our paleontological past!

References:

Abushik, A. 2000. Silurian-earliest Devonian ostracode biostratigraphy of the Timan-Northern Ural Region. Proceedings of the Estonian Academy of Sciences, Geology 49: 112-125.

Belak, R. 1977. Ontogeny of the Devonian Leperditiid ostracode Herrmannina alta. Journal of Paleontology 51: 943-952.

Kegel, W. 1933. Zur Kenntnis palaozoischer Ostrakoden 3, Leperditiidae aus dem Mitteldevon des Rheinischen Schiefergebirges. Preussischen Geologischen Landesanstalt, Jahrbuch fur das Jahr 1932, Bd. 53, p. 907-935.

Kesling, R.V. 1958. A new and unusual species of the ostracod genus Herrmannina from the Middle Silurian Hendricks Dolomite of Michigan. Contributions, Museum of Paleontology, The University of Michigan 14, No. 9: 143-148.

Putzer, H. 1971. Wilhelm Kegel. Geologisches Jahrbuch 89: xiii-xxii.

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