Wooster Geology at AGU 2017

acrawford December 18, 2017 4:32 pm

The Mississippi River in New Orleans, Louisiana. Photo: Dr. Karen Alley

Three Wooster Geologists (Dr. Karen Alley, Dr. Alex Crawford, and senior Geology major Cole Jimerson) descended on New Orleans last week to attend the Fall Meeting of the American Geophysical Union. With 20 to 25 thousand attendees each year, this is the largest Earth and space science meeting in the world.

On Wednesday, Dr. Crawford gave a talk about his research in seasonal sea ice prediction. As the Arctic continues to warm, seasonal sea ice melt is occurring progressively earlier each year. Although almost unheard of 20 years ago, commercial shipping along the Russian coastline (the “Northern Sea Route”) is now a routine summer operation. However, the seasonal timing of when the sea ice melts enough for normal shipping is highly variable from year to year. Dr. Crawford and his collaborators are investigating various ways of improving our ability to predict that variability. Better predictions can aid shipping companies in planning their summer routes.

The Northern Sea Route through the Arctic Ocean and the “last retreat day” (LRD), which means the last day of the year on which sea ice concentration is above 50% (left) or 15% (right). Adapted from Stroeve, Crawford, & Stammerjohn (2016); 10.1002/(ISSN)1944-8007.

On Thursday, Dr. Alley gave an invited talk about a new data product she and her collaborators have developed for researchers studying the Antarctic ice sheet. Using ice velocity derived from satellites and sophisticated mathematics and computer coding, they calculated strain rates for Antarctica’s ice sheet and ice shelves. These strain rates are a measure of how fast the ice deforms by stretching and compressing as it moves. They are a fundamental parameter to know for anybody trying to understand how Antarctica’s ice is responding to climate change.

Strain rates on the Filchner Ice Shelf, Antarctica. From Dr. Karen Alley.

Finally, Cole Jimerson presented a poster on Friday overviewing some of the research he and other students performed through a Keck Geology project concerning erosion rates on the Caribbean Island of Dominica. Dominica is a volcanic island prone to explosive ash eruptions. Many of the rocks and sediments on the island are quickly eroded by rivers and chemical weathering in the hot, wet tropical climate. These and other factors lead to landslide risks, and better understanding erosion rates can improve hazard mitigation strategies.

Cole Jimerson presents his poster at the Fall Meeting of the American Geophysical Union.

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Wooster’s Fossil of the Week: Echinoid bite marks from the Upper Cretaceous of southwestern France

Mark Wilson November 30, 2017 12:01 am

Above is another beautiful image from Paul Taylor’s paleontological lab at the Natural History Museum, London. It is one of our fossil oysters (Pycnodonte vesicularis) from the French Type Campanian collected in the town of Archiac in southwestern France on our most enjoyable expedition this past summer. The fine crossing short grooves are bite marks produced by grazing regular echinoids (sea urchins). They form the trace fossil Gnathichnus pentax Bromley, 1975. You can learn more about this type of fossil in a previous blog entry describing Cretaceous Gnathichnus from southern Israel.

This is a good time to update our readers on the French Campanian sclerobiont project. Macy Conrad (’17) has done extraordinary work identifying the hundreds of encrusting bryozoans on our oysters. She is using a series of mugshots of Campanian bryozoans produced by our colleague Paul Taylor to name our specimens as accurately as possible. All the pink you see in these trays represents bryozoans that have been identified.

Here is a closer view. Very distinct patterns of diversification of bryozoans and trace fossils upward through the stratigraphic column are emerging. Macy will continue this work next semester as she finishes her Independent Study thesis. I will be doing my parts as well, but from a bit of a distance: I’ll be on a research leave next semester.

Which leads me to this announcement: Wooster’s Fossil of the Week will no longer be weekly. Since I’ll have other writing goals and travel plans over the next several months during my leave, I will contribute blog entries less frequently. The name “Fossil of the Week” has become a bit of a brand, so I’ll keep it, just no longer post every week (which I’ve been doing since January 2, 2011).

 

 

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Wooster’s Fossils of the Week: Barnacle borings from the Cretaceous of southwestern France

Mark Wilson November 24, 2017 12:01 am

Small comma-shaped trace fossils this week in a Cretaceous (Upper Campanian) oyster (Pycnodonte vesicularis) from the Aubeterre Formation of southwestern France. (Locality C/W-747, Plage des Nonnes, to be exact.) These are borings produced by barnacles, which are sedentary crustaceans more typically found in multi-plated shells of their own making. We’ve seen this fine type of boring before in this blog, so some of this information is repeated.

These boring barnacles (yes, I know the joke) are still around today, so we know quite a bit about their biology. (More on how in a minute.) These acrothoracican barnacles drill into shells head-down and then kick their legs up through the opening to filter seawater for food. They’ve been doing it since the Devonian (Seilacher, 1969; Lambers and Boekschoten, 1986).

This particular trace fossil is Rogerella elliptica Codez & Saint-Seine, 1958. It is part of a diverse set of borings collected on our wonderful field trip this past summer to the Bordeaux region with Paul Taylor.

We know so much about boring barnacles because Charles Darwin himself took an almost obsessive interest in them early in his scientific career. While on his famous voyage on the HMS Beagle, Darwin noticed small holes in a conch shell, and he dug out from one of them a curious little animal shown in the diagram below.


Cryptophialus Darwin, 1854

He called it “Mr. Arthrobalanus” in his zoological notes. He figured out early that it was a barnacle, but he was astonished at how different it was from others of its kind. He later gave it a scientific name (Cryptophialus Darwin, 1854) and took on the problem of barnacle systematics and ecology. Eight years and four volumes later his young son would ask one of his friends, “Where does your father do his barnacles?” The diversity of barnacles played a large role in Darwin’s intellectual development and, consequently, his revolutionary ideas about evolution (Deutsch, 2009).

Burrowing barnacle diagram from an 1876 issue of Popular Science Monthly.

References:

Codez, J. and Saint-Seine, R. de. 1958. Révision des cirripedes acrothoracique fossiles. Bull. Soc. géol. France 7: 699-719.

Darwin, C.R. 1854. Living Cirripedia, The Balanidae, (or sessile cirripedes); the Verrucidae. Vol. 2. London: The Ray Society.

Deutsch, J.S. 2009. Darwin and the cirripedes: Insights and dreadful blunders. Integrative Zoology 4: 316–322.

Lambers, P. and Boekschoten, G.J. 1986. On fossil and recent borings produced by acrothoracic cirripeds. Geologie en Mijnbouw 65: 257–268.

Seilacher, A. 1969. Paleoecology of boring barnacles. American Zoologist 9: 705–719

 

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Wooster’s Fossils of the Week: Encrusting cyanobacteria from the Upper Ordovician of the Cincinnati region — now published

Mark Wilson November 17, 2017 12:01 am

1 pdt19598 D1253[This week’s post is a repeat from last year, with some modifications. The paper Paul Taylor and I wrote on these microbial beauties has just appeared this week in the latest issue of the journal Palaios. A pdf is yours if you send me an email message.] Update: The paper is now a cover story.

Deep in the basement of the Natural History Museum in London, Paul Taylor and I were examining cyclostome bryozoans encrusting an Upper Ordovician brachiopod with a Scanning Electron Microscope (SEM). This is one of our favorite activities, as the SEM always reveals tiny surprises about our specimens. That day the surprises were the smallest yet – fossils we had never seen before.

2 Infected brachWe were studying the dorsal exterior surface of this beat-up brachiopod from a 19th Century collection labelled “Cincinnati Group”. (Image by Harry Taylor.) We knew it was the strophomenid Rafinesquina ponderosa, and that the tiny chains of bryozoans encrusting it were of the species Corynotrypa inflata. We’ve seen this scene a thousand times. But when we positioned the SEM beam near the center of the shell where there was a brown film …

3 pdt16920 D1253… we saw that the bryozoans were themselves encrusted with little pyritic squiggles. These were new to us.

4 pdt19580 D7139In some places there were thick, intertwining mats of these squiggles. We later found these fossils on two other brachiopod specimens, both also Rafinesquina ponderosa and from 19th Century collections with no further locality or stratigraphic information.

5 pdt19578 D7139Paul and I scanned these specimens again and began to put together an analysis. We believe these are fossil cyanobacteria. They are uniserial, unbranching strands of cells that range from 5 to 9 microns in length and width. Some of individual strands are up to 700 microns long and many are sinuous. The cells are uniform in size and shape along the strands; there are no apparent heterocysts. They appear very similar in form to members of the Order Oscillatoriales.

6 CyanobacteriaCyanobacteria are among the oldest forms of life, dating back at least 2.1 billion years, and they are still abundant today. The fossils are nearly identical to extant forms, as seen above (image from: http://www.hfmagazineonline.com/cyanobacteria-worlds-smallest-oldest-eyeball/).

7 pdt19599 D1253Paul made this remarkable image, at 9000x his personal record for high magnification, showing the reticulate structure preserved on some of the fossil surfaces. Note that the scale bar is just 2 microns long. These are beautiful fossils in their tiny, tiny ways.

We have not seen these cyanobacteria fossils before on shell surfaces, so we submitted an abstract describing them for the Geological Society of America annual meeting in Denver this September. We are, of course, not experts on bacteria, so we are offering our observations to the scientific community for further discussion. Here is the conclusion of our abstract —

“We suggest the cyanobacterial mats developed shortly before final burial of the brachiopod shells. Since the cyanobacteria were photosynthetic, the shells are inferred to have rested with their dorsal valve exteriors upwards in the photic zone. That Cincinnatian brachiopod shells were occupied by cyanobacteria has been previously well demonstrated by their microborings but this is the first direct evidence of surface microbial mats on the shells. The mats no doubt played a role in the paleoecology of the sclerobiont communities on the brachiopods, and they may have influenced preservation of the shell surfaces by the “death mask” effect. The pyritized cyanobacteria can be detected with a handlens by dark squiggles on the brachiopod shells, but must be confirmed with SEM. We encourage researchers to examine the surfaces of shells from the Cincinnatian and elsewhere to find additional evidence of fossilized bacterial mats.”

References:

Noffke, N., Decho, A.W. and Stoodle, P. 2013. Slime through time: the fossil record of prokaryote evolution. Palaios 28: 1-5.

Tomescu, A. M., Klymiuk, A.A., Matsunaga, K.K., Bippus, A.C. and Shelton, G.W. 2016. Microbes and the Fossil Record: Selected Topics in Paleomicrobiology. In: Their World: A Diversity of Microbial Environments (pp. 69-169). Springer International Publishing.

Vogel, K. and Brett, C.E. 2009. Record of microendoliths in different facies of the Upper Ordovician in the Cincinnati Arch region USA: the early history of light-related microendolithic zonation. Palaeogeography, Palaeoclimatology, Palaeoecology 281: 1-24.

Wilson, M.A. and Taylor, P.D. 2017. Exceptional pyritized cyanobacterial mats encrusting brachiopod shells from the Upper Ordovician (Katian) of the Cincinnati, Ohio, region. Palaios 32: 673-677.

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How to Combat a Drought

acrawford November 14, 2017 10:57 am

About a month ago, I wrote on this blog about an exceptionally dry late summer for Wooster.  It was dry enough to put much of northeast Ohio in a moderate drought.  But of course the moment I published that blog post, it started to rain… and historically so.  Using the Wooster Experimental Station data going back to 1900, Wooster has gone from one of the driest August-September periods to one of the wettest October-early Novembers.  The average precipitation in Wooster for Oct 3 through Nov 7 is 2.99″.  This year, we had 6.91″, more than double the average and ranking third highest ever (0.46″ lower than the record from 1954).*

So this brings us to two important questions: 1) Did this kick the drought? and 2) Why did this happen?

Figure 1. Change in drought levels for Ohio from October 3 to November 7. Data from US Drought Monitor. Wayne County is all still abnormally dry or in moderate drought, but the dryness has waned considerably.

To answer the first question: almost, but not quite.  Figure 1 shows the change in drought levels from October 3 to November 7.  The area of Ohio experiencing drought shrunk from 11% to 6% of the state, although half of Wayne County is still “in the beige”. Areas experiencing either “dryness” or “drought” shrunk from 40% to 22% of the state. The rate of evapotranspiration is also at play here, but the change in rain fortunes has likely been the main driver in alleviating the dry spell.

That second question — why did we oscillate from very dry to very wet? — has a coy answer and a serious answer.  Coy answer: The weather is fickle. Serious answer: It’s all about the polar jet stream.  The polar jet stream is a narrow band of strong westerly winds that sits up roughly 10 km (6 mi) above sea level.  Especially in winter, this jet stream is main conveyor belt of storms that affect Ohio. In a typical August and September, it usually sits a bit north of us, just north of the US-Canada border (Figure 2, upper-left), occasionally giving Ohio rain.  This year (lower left), the main jet stream path was much farther north than normal, just grazing the Canadian Arctic Archipelago.  It was a non-factor this summer for Ohio.  This abnormal ridge was also associated with a large high pressure area over most of North America.  High pressure typically means calmer, warmer summer weather — and that is precisely what we had in the Midwest. These two features — the ridge in the jet stream and the high pressure at the surface — reinforced each other to create the dry conditions in late summer.

Figure 2. Comparing jet stream patterns and “blocking highs” from August to mid-November 2017 to normal. The star (roughly) indicates Wooster Ohio. Stylized from NCEP-NCAR Reanalysis.

But since about October 3, the jet stream pattern has shifted.  A normal October has the jet stream shift southward a little anyway (Figure 2, upper right), but this year it pushed much farther south than normal over the western half of the country (lower right).  This put Ohio in a prime position to receive more storms than normal — just downwind of a big trough in the jet stream. Related to this, a smaller blocking high set up off the coast of New England and Nova Scotia, which helped direct warm, wet Atlantic air over the Appalachians and toward Wooster. The best example of the results came from the November 5 storm, when nearly 2″ of rain was accompanied by tornado warnings across several Ohio counties.

*Footnote: The start and end dates of October 3 and November 7 are rather arbitrary, but 2017 still ranks in the top ten rainiest years out of 117 even if you add or subtract a few days — so long as you include the big rain storm from November 5.

References:

Mason, John (2013 May 20). “A Rough Guide to the Jet Stream”. Skeptical Science. Retrieved 13 Nov 2017. https://skepticalscience.com/jetstream-guide.html

Kalnay, E. and Coauthors (1996). The NCEP/NCAR Reanalysis 40-year Project. Bull. Amer. Meteor. Soc., 77, 437-471.  https://www.esrl.noaa.gov/psd/data/composites/day/

United States Drought Monitor. The National Drought Mitigation Center. Retrieved 13 Nov 2017. http://droughtmonitor.unl.edu/Maps/CompareTwoWeeks.aspx

Wooster Experimental Station at Climate Data Online (1900 – 2017). NOAA. Retrieved 13 Nov 2017. https://www.ncdc.noaa.gov/cdo-web/datasets/GHCND/stations/GHCND:USC00339312/detail

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Wooster’s Fossil of the Week: A Middle Jurassic trace fossil from southwestern Utah

Mark Wilson November 10, 2017 12:01 am

1 Gyrochorte 2 CarmelTime for a trace fossil! This is one of my favorite ichnogenera (the trace fossil equivalent of a biological genus). It is Gyrochorte Heer, 1865, from the Middle Jurassic (Bajocian) Carmel Formation of southwestern Utah (near Gunlock; locality C/W-142). It was collected on an Independent Study field trip a long, long time ago with Steve Smail. We are looking at a convex epirelief, meaning the trace is convex to our view (positive) on the top bedding plane. This is how Gyrochorte is usually recognized.
2 Gyroxhorte hyporelief 585A quick confirmation that we are looking at Gyrochorte is provided by turning the specimen over and looking at the bottom of the bed, the hyporelief. We see above a simple double track in concave (negative) hyporelief. Gyrochorte typically penetrates deep in the sediment, generating a trace that penetrates through several layers.
3 Gyrochorte Carmel 040515Gyrochorte is bilobed (two rows of impressions). When the burrowing animal took a hard turn, as above, the impressions separate and show feathery distal ends.
4 Gyrochorte 585Gyrochorte traces can become complex intertwined, and their detailed features can change along the same trace.
5 Gibert Benner fig 1This is a model of Gyrochorte presented by Gibert and Benner (2002, fig. 1). A is a three-dimensional view of the trace, with the top of the bed at the top; B is the morphology of an individual layer; C is the typical preservation of Gyrochorte.

Our Gyrochorte is common in the oobiosparites and grainstones of the Carmel Formation (mostly in Member D). The paleoenvironment here appears to have been shallow ramp shoal and lagoonal. Other trace fossils in these units include Nereites, Asteriacites, Chondrites, Palaeophycus, Monocraterion and Teichichnus. (I also ran into Gyrochorte in the beautiful Triassic of southern Israel.)

So what kind of animal produced Gyrochorte? There is no simple answer. The animal burrowed obliquely in a series of small steps. Most researchers attribute this to a deposit-feeder searching through sediments rather poor in organic material. It may have been some kind of annelid worm (always the easiest answer!) or an amphipod-like arthropod. There is no trace like it being produced today.

We have renewed interest in Gyrochorte because a team of Wooster Geologists is going to southern Utah this summer to work in these wonderful Jurassic sections.
6 Heer from ScienceOswald Heer (1809-1883) named Gyrochorte in 1865. He was a Swiss naturalist with very diverse interests, from insects to plants to the developing science of trace fossils. Heer was a very productive professor of botany at the University of Zürich. In paleobotany alone he described over 1600 new species. One of his contributions was the observation that the Arctic was not always as cold as it is now and was likely an evolutionary center for the radiation of many European organisms.

References:

Gibert, J.M. de and Benner, J.S. 2002. The trace fossil Gyrochorte: ethology and paleoecology. Revista Espanola de paleontologia 17: 1-12.

Heer, O. 1864-1865. Die Urwelt der Schweiz. 1st edition, Zurich. 622 pp.

Heinberg, C. 1973. The internal structure of the trace fossils Gyrochorte and Curvolithus. Lethaia 6: 227-238.

Karaszewski, W. 1974. Rhizocorallium, Gyrochorte and other trace fossils from the Middle Jurassic of the Inowlódz Region, Middle Poland. Bulletin of the Polish Academy of Sciences 21: 199-204.

Sprinkel, D.A., Doelling, H.H., Kowallis, B.J., Waanders, G., and Kuehne, P.A., 2011, Early results of a study of Middle Jurassic strata in the Sevier fold and thrust belt, Utah, in Sprinkel, D.A., Yonkee, W.A., and Chidsey, T.C., Jr. eds., Sevier thrust belt: Northern and central Utah and adjacent areas, Utah Geological Association 40: 151–172.

Tang, C.M., and Bottjer, D.J., 1996, Long-term faunal stasis without evolutionary coordination: Jurassic benthic marine paleocommunities, Western Interior, United States: Geology 24: 815–818.

Wilson. M.A. 1997. Trace fossils, hardgrounds and ostreoliths in the Carmel Formation (Middle Jurassic) of southwestern Utah. In: Link, P.K. and Kowallis, B.J. (eds.), Mesozoic to Recent Geology of Utah. Brigham Young University Geology Studies 42, part II, p. 6-9.

[An earlier version of this article was posted on April 17, 2015.]

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West Antarctic mantle plumes: A lesson in ice flow and science communication

kalley November 9, 2017 4:01 pm

Newsweek published a scary-looking headline yesterday: “NASA DISCOVERS MANTLE PLUME ALMOST AS HOT AS YELLOWSTONE SUPERVOLCANO THAT’S MELTING ANTARCTICA FROM BELOW.” It’s a scary idea, right? That heat that drives Yellowstone’s steam vents, boiling hot springs, and explosive geysers is sitting under Antarctica, and scientists didn’t even know about it?? It has certainly generated some discussion in our department. But don’t panic yet – scientists have been aware for decades of volcanic activity under West Antarctica, and it’s not nearly as hot as the article would like you to think.

The Newsweek article goes on to explain some of the details of a study that was published last month in the Journal of Geophysical Research: Solid Earth (Seroussi et al., 2017). The study used an ice flow model to try to capture the ice dynamics of West Antarctica as accurately as possible, and then used that model to glean some details about how much heat is being released through the ground (that’s called the “geothermal heat flux”) under the West Antarctic Ice Sheet.

What they found is both unsurprising and important. West Antarctica has a much higher heat flux than surrounding areas, because there is hot mantle rock near the surface driving volcanic activity. That’s hardly a secret in glaciology – for example, it was an important consideration in this study by J. Weertman from 1982. Ice flow models of the area have always had to take into account this warming of the base of the ice to accurately model how easily the ice slides and deforms. What this new paper brings us is some more accuracy to use in our models. It gives us more reliable numbers for just how much heating there is and where it is concentrated, so we can make our ice flow models more accurate. Specifically, the authors calculate that the mantle plume is bringing up to 150 milliwatts of heat per square meter to the base of the West Antarctic Ice Sheet, with isolated areas perhaps getting to 180 milliwatts of heat per square meter.

What this article really gives us is a lesson in science communication and how a story can be easily hyped into something much scarier than it is. The Newsweek article uses two images – the first is of part of West Antarctica (Mari Byrd Land, by NASA/Michael Studinger), and the second of the Grand Prismatic Hot Spring in Yellowstone (by Mark Ralston/AFP/Getty Images):

                  

Putting these two images next to each other evokes some strong reactions. If you put ice on top of that hot spring, it’s going to melt – FAST!! The problem is, the heat flux numbers in Seroussi et al. (2017) don’t come anywhere near the heat flux you’d get at Grand Prismatic Spring. According to the USGS, some of Yellowstone’s thermal areas have heat fluxes of over 100 watts per square meter. Seroussi et al. (2017) measured heat flux under West Antarctica in milliwatts – 1000x smaller than a watt. So that picture of Grand Prismatic Spring probably represents a heat flux of something like 100,000 milliwatts per square meter, while the ice in the other picture is sitting on top of 150 milliwatts per square meter.

Now, you could argue averages with me – even if 150 milliwatts per square meter is the average, there could be some areas that are much hotter, just like in Yellowstone. The evidence really isn’t there for that, however. If a region under the ice did have a heat flux of 100,000 milliwatts per square meter, it would be hard to miss. I haven’t built the models, but we would expect obvious aberrations in ice flow and water discharge in the area, which isn’t consistent with our observations. It’s more likely that it’s a bit warmer in some areas and a bit cooler in others, but we aren’t going to find Grand Prismatic Spring under Antarctica.

Furthermore, while this is a new study that uses an impressive set of models to show that a mantle plume is likely causing the heat flux, it is hardly a new discovery that the ground is relatively warm under West Antarctica. Heat flux is already included in the models, and scientists are always working to refine their estimates and increase model accuracy. But regardless of the discovery, it’s always important to read scientific news articles critically, to understand if their main points are scientifically reasonable, or if there’s a spin to get you to click on the article. In this case, it’s the latter.

 

 

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#GSA2017 Wrap Up

mpollock November 4, 2017 9:00 am

It’s hard to believe that we were at the 2017 GSA Annual Meeting in Seattle, Washington just last week. Once again, the Wooster Geologists had a strong showing.

Macy Conrad (’18) kicked off our student presentations on Sunday with a poster on the paleoecology of encrusting sclerobionts in the Type Campanian of southwestern France. You can read more about Macy’s work in this Fossil of the Week blog post.

Brandon Bell (’18) followed Macy on Monday with his poster on the American scientific and cultural interaction with Japan and Europe after the 1906 earthquake. Brandon learned how historical methods can be used to study geologic phenomena like earthquakes and landslides.

You may remember Keck Geology Team Utah from their summer research exploits. They are Addison Thompson (’20, Pitzer), Madison Rosen (’19, Mt. Holyoke), Emily Randall (’20, Wooster), and Sam Patzkowsky (’20, Franklin and Marshall). At GSA, they presented the results of their research on dating young lava flows in the Black Rock Desert in Utah.

The intrepid Keck Geology Team Alaska, who also blogged about their summer research experiences, presented their dendrochronology research on declining yellow cedar and correlations with climate. They are Chris Messerich (’20, Washington and Lee), Malisse Lummus (’20, Trinity), Alora Cruz (’20, Macalester), and Josh Charlton (’19, Wooster).

Even our own Dr. Wilson had a poster presentation. His research on the bioerosion of oysters in the Type Campanian of southwestern France was the counterpart to Macy’s presentation.

As always, we had a fantastic alumni gathering where we caught up with recent graduates and former Wooster Geologists who have done wonderful things in their careers. Our students had an opportunity to interact with current graduate students, new geology department chairs, and emeritus faculty who specialize in paleontology, sedimentology, geochemistry, oceanography, and a vast range of Earth sciences. Once a Wooster Geologist, always a Wooster Geologist.

 

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Wooster’s Fossils of the Week: The tiniest of brachiopods (Middle Jurassic of Utah)

Mark Wilson November 3, 2017 12:01 am

While preparing for this summer’s expedition to the Middle Jurassic of southwestern Utah, I found this specimen in our collection from the 1990s. You may be able to just make out the wedge-shaped outline of a mytilid-like bivalve with several cup-like oysters (Liostrea strigilecula of oyster reef and oyster ball fame) encrusting the shell exterior. This specimen, labeled EM-1, is from our Eagle Mountain exposure of Member D, Carmel Formation, near Gunlock, Utah.

If you look very closely near the middle of the clam, you will see some super-small encrusting shells the size of sand grains. Two are shown above, photographed with all the extension tubes on my camera. Believe it or not, these are shells of thecideide brachiopods, among the smallest known. They are, as far as I can tell, the only brachiopods thus far recorded from the Carmel Formation. They are abundant in this unit, encrusting carbonate hardgrounds as well as shells.

We know who these minuscule critters are from the careful analysis of their interiors by my colleague Peter Baker at the University of Derby. They are, in fact, the first thecideide brachiopods to be described from the Jurassic of North America. We published a description of them in 1999, naming them as the new genus and species Stentorina sagittata. The etymology of the genus name: “From the Greek Stentor (herald, of the Trojan War) in recognition of the first discovery of thecideoid brachiopods in the Jurassic of North America.” How’s that for classical drama about an itty-bitty brachiopod? We said of the new species name: “From the way the edges of the hemispondylium converge on the median ridge to form a characteristic arrowhead-shaped structure on the floor of the ventral valve.” Sagittate means arrowhead-shaped.

I’m looking forward to more paleontological treasures from the Carmel Formation of southern Utah.

References:

Baker, P G. and Wilson, M A. 1999. The first thecideide brachiopod from the Jurassic of North America. Palaeontology 42: 887-895.

Carlson, S.J. 2016. The evolution of Brachiopoda. Annual Review of Earth and Planetary Sciences 44: 409-438.
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Wooster’s Fossils of the Week: Bryozoan encrusting a bryozoan (Campanian of southwestern France)

Mark Wilson October 27, 2017 12:01 am

Today’s post is in honor of Macy Conrad’s (Wooster ’18) poster at the annual meeting of the Geological Society of America, which was held earlier this week. It is also to recognize again the Scanning Electron Microscopy (SEM) genius of our friend Paul Taylor (Natural History Museum, London). The scene is the curving bryozoan ?Oncousoecia sp. encrusting the bifoliate erect bryozoan known as Onychocella aglaia (d’Orbigny, 1851). The specimen is from the Biron Formation (Upper Campanian,Upper Cretaceous), at Cailleau on the north side beneath fishing carrelets near Talmont-sur-Gironde, Charente Maritime, France. We collected from this location this past summer on our wonderful French paleontological expedition. This image comes from a fantastic library of Type Campanian encrusting bryozoan SEM photographs Paul gave us for our identifications in the Wooster lab. I especially like encrusters on encrusters.

This encrusting ?Oncousoecia is, as you can tell from the question mark, not placed for certain in this cyclostome genus, but it is similar to other known examples. This is a closer view of its ancestrula, the first zooid. You can also see pseudopores in the skeleton. The underlying Onychocella aglaia (d’Orbigny, 1851) is a cheilostome bryozoan. This is another reason I find this view interesting: Our larger project examines the dynamics of cyclostome and cheilostome distribution in the Campanian.

This image of Macy’s GSA poster is only symbolic because it is way too small to read. It at least conveys Macy’s neat organization and colorful images. You can read her published abstract on the GSA site. Nice work, Macy, and a major milestone on your way to completing your Independent Study thesis.

References:

Agostini, V., Ritter, M., Macedo, A., Muxagata, E., and Erthal, F., 2017, What determines sclerobiont colonization on marine mollusk shells? PLOS ONE, v. 12, doi.org/10.1371/journal.pone.0184745.

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Platel, J.-P., Célerier, G., Duchadeau-Kervazo, C., Chevillot, C., and Charnet, F., 1999, Notice explicative, Carte géologie France (1/50 000), feuille Ribérac, Orléans, BRGM, 103 p.

Taylor, P.D. and Wilson, M.A. 2003, Palaeoecology and evolution of marine hard substrate communities: Earth-Science Reviews, v. 62, p. 1-103.

Taylor, P.D. and Zatoń, M. 2008. Taxonomy of the bryozoan genera Oncousoecia, Microeciella and Eurystrotos (Cyclostomata: Oncousoeciidae). Journal of Natural History, v. 42, p. 2557-2574.

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