Wooster’s Fossil of the Week: A most unlikely clam — rudists from the Upper Cretaceous of the Oman Mountains

This week’s fossil was collected on a memorable trip in 2000 to the United Arab Emirates and Oman with my friend Paul Taylor, an invertebrate paleontologist at the Natural History Museum in London. We were there to study hard substrate faunas (sclerobionts) in an Upper Cretaceous (Maastrichtian) unit known as the Qahlah (pronounced “coke-lah”) Formation. We traveled along the border between these two countries in an old Toyota Landrover plotting out the distribution and characteristics of the Qahlah and its fossils. If you want a pdf of the resulting paper (and I’m sure you do), just click here: Wilson & Taylor (2001).

One of the most interesting fossil types common in the Late Jurassic through the Cretaceous is the rudist clam. The image above is one of our Qahlah specimens known as Vaccinites vesiculosus. There are two conical rudists growing together here, with the one on the left still retaining most of its upper valve.

Rudist clams are an example of just how far evolution can go with a basic body plan. They are heterodont clams sharing a common ancestry with the typical modern Mercenaria we so love to eat (and dissect). Starting in the Jurassic, the left valve began to elongate into a cone and the right valve became a cap-like cover. They attached to each other and formed reef-like masses throughout the warm, shallow tropical seas of the Cretaceous. They were so successful that they appear to have competitively excluded most of the coral reefs. Corals had the last gurgly laugh, though, because the end-Cretaceous extinction completely wiped out the rudists, allowing the later rise of modern coral reefs.

A typical heterodont clam is in the upper left of this diagram; the rest are rudist clams. In the lower right is a drawing of the type of rudist photographed above. Diagram from Schumann & Steuber (1997; Kleine Senckenbergreihe 24: 117-122).

When I see our rudist clam specimen I’m reminded not only of its complex evolutionary heritage, but also of our own desert odyssey with grim musket-bearing Omani tribesmen, endless sand dunes stretching west, and delicious banquets of lamb and dates.

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The Very First Analysis Goes To…

WOOSTER, OH – The XRF and XRD are officially installed! We learned the basics about how to operate and maintain the XRF this afternoon. We even ran our first official sample using the EZScan. It was a difficult choice, but the honor of the first sample goes to an Icelandic basalt from Todd Spillman’s I.S. Congratulations, Todd! You’ve just made history at the College of Wooster.

I absolutely love the animation that shows the inner workings of the XRF! The cartoon shows how the x-ray tube (on the left) aims x-rays at the sample (in the middle). The resulting fluorescent x-rays (red line) travel through the slits to the crystal and finally to the detector.

Tomorrow, we’ll learn to operate the XRD. I wonder who will be the lucky owner of the first XRD sample?

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New Geology X-Ray Lab

WOOSTER, OH – Big news in the Geology Department: our new X-ray lab is being installed this week! Early last year, the Geology Department was awarded funding from the National Science Foundation to acquire X-ray instruments to enhance our robust undergraduate research program. Installation has been long awaited, highly anticipated, and wouldn’t have happened without the hard work of many people on campus. We have Ron, Patrice, Tracy, and the electricians and plumbers to thank for making it happen. The installation will probably take all week, but so far (knock on wood), things are going smoothly.

It's as if the space was designed especially for the X-ray fluorescence spectrometer (XRF).

The XRF will allow us to measure the compositions of Earth materials right here on campus. No longer will we need to send our samples (or our students) to other labs for major element analyses! Not pictured (and still wrapped in plastic) is the benchtop X-ray diffractometer (XRD), which will enable us to analyze the mineralogy of samples.

We hope our lab serves as a regional center for X-ray analyses and encourages collaborations with physicists, chemists, archeologists, and geologists. Stay tuned for updates!

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Wooster’s Fossil of the Week: A cystoid (Middle Ordovician of northeastern Estonia)

Fossils don’t get much more spherical than Echinosphaerites aurantium, an extinct creature common in the Early and Middle Ordovician of North America and Europe. These are cystoids, a somewhat informal category of filter-feeding, stalked echinoderms that are relatives of the better known crinoids. My students and I found bucketloads of them in the oil shales of the Baltic country Estonia three years ago. They are like stony golf balls.

A typical cystoid has a sac-like theca forming the bulk of the body. This theca is made of dozens to hundreds of plates of the mineral calcite fitted together like tiles. On one end of the theca is a small stem to attach it to the substrate; the other end has short brachioles, which are filter-feeding arms surrounding a tiny mouth at their base. An anus is present on the side, distinguished by a circlet of special plates.

If you look carefully at the specimen on the left in the above illustration, you’ll see at least two sclerobionts (hard-substrate dwellers) attached to the theca.  The black branching form is a graptolite (like our last Fossil of the Week) called Thallograptus sphaericola (the species name means “sphere dweller”) and the raised disk is a bryozoan.

Every once in awhile the cystoids in Estonia were buried quickly and did not fill with sediment. The hollow space within became a kind of geode with crystals of calcite growing from the thecal plates inward. Each plate is a single crystal of calcite, so the crystals grew syntaxially (maintaining crystallographic continuity). These specimens are spectacular if broken open carefully so they don’t shatter into a thousand sparkles.

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Wooster’s Fossil of the Week: A three-branched graptolite (Lower Ordovician of southeastern Australia)


This week I’m correcting a mistake I’ve been making in my paleontology courses for nearly thirty years. Our subject is a graptolite from the teaching collections — a specimen that has been at least cursorily examined by all of my paleontology students. It is not a particularly pretty fossil, but an important one for biostratigraphy and evolution.

Graptolites were colonial marine organisms which thrived from the Late Cambrian (roughly 510 million years ago) into the Early Carboniferous (about 350 million years ago). Their colonies, termed rhabdosomes, were not mineralized, so they are most commonly preserved as thin carbon films like our featured specimen. The rhabdosome usually began with a single individual, known as a sicula, that budded branches called stipes. Each stipe is lined with cup-like thecae that held what we presume were filter-feeding individuals termed zooids (much like bryozoans). The number of stipes per rhabdosome varies considerably, from one to dozens. Some graptolites were sessile benthic epifaunal (attached to the seafloor on hard surfaces) while others were planktic (suspended or floating).

Our specimen above is the planktic graptolite Pendeograptus fruticosus from the Lower Ordovician (about 477-474 million years old) near Bendigo, Australia. There are actually two specimens overlapping here. I’ve labeled one sicula as “S1” and the other as “S2”.

This is where my mistake began. I identified these graptolites during my first professorial year as Tetragraptus fruticosus, believing that there were two specimens with, as you might guess from the name, four stipes each. When I counted the actual stipes present, though, I found only three each. I believed, though, that graptolites had either one, two, four or many stipes, so specimens with only three had to have one stipe missing or folded over as to be invisible. So for the curious student who counted three where there should have been four, I confidently explained the preservational oddity. That both specimens lacked the fourth stipe did not apparently shake my resolve.

It was only after photographing this specimen that I looked closely enough to see that, indeed, three stipes are present and there is no evidence of a fourth for either rhabdosome. (I added numbers and letters to the above image to delineate the stipes.) Maybe there really are three-stiped graptolites? This was easily enough confirmed by simply Googling “three-stiped graptolite”. Who knew? This version of “Tetragraptus” is actually the genus Pendeograptus. Oops.

Turns out that our Pendeograptus fruticosus is part of an evolutionary series proceeding from four to three to two stipes. The three-stiped version we have is an indicator for the Australian Bendigonian Stage and a global index fossil for this narrow time interval 477 to 474 million years ago.

You can now see this specimen (without the red labels) on the Wikipedia page for graptolites. I’m correcting my mistake and sharing a useful little fossil with the world.

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Wooster’s Fossil of the Week: The tabulate coral Aulopora (Devonian of northwestern Ohio)

We’re going to start 2011 with a new blog feature: Fossil of the Week! My colleagues, of course, are welcome to also start “Mineral of the Week”, “Structural Geologic Feature of the Week”, or “Climate Event of the Week”.  The more the better to keep our blog active through the winter!


This week’s fossil was collected by Brian Bade of Sullivan, Ohio, and donated to Wooster as part of my hederelloid project.  It is a beautiful specimen of the tabulate coral Aulopora encrusting a brachiopod valve from the Silica Shale (Middle Devonian — about 390 million years old) of northwestern Ohio.  Auloporid corals are characterized by an encrusting habit, a bifurcating growth pattern, and horn-shaped corallites (individual skeletal containers for the polyps).

What is especially nice about this specimen is that we are looking at a well preserved colony origin.  The corallite marked with the yellow “P” is the protocorallite — the first corallite from which all the others are derived.  You can see that two corallites bud out from the protocorallite 180° from each other.  These two corallites in turn each bud two corallites, but at about 160°.  This pattern continues as the colony develops (a process called astogeny).  The angles of budding begin to vary depending on local obstacles; they never again go below 160°.

The polyps inside the corallites are presumed to have been like other colonial coral polyps.  Each would have had tentacles surrounding a central opening, and all were connecting by soft tissue within the skeleton.  They likely fed on zooplankton in the surrounding seawater.  This type of coral went extinct in the Permian, roughly 260 million years ago.

Again, we thank our amateur geologist friends for such useful donations to the research and educational collections in the Geology Department at Wooster.

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Wooster Geologists Pass Through Travel Hell

I think the lowest moment was this morning as I stood in one of those long, snaking security lines in the Delta portion of Terminal 3 at JFK International Airport. The high ceiling has pigeon nests in it, and the evil birds occasionally fly over the helpless travelers below and poop on their heads.

Following on our previous “Heathrow Diversion” post, this is our final report on a failed geological trip. Because of the snow and ice in England, our London flight was alternately canceled and reinstated (or at least that’s how it was communicated to us). We feared yet another mid-Atlantic diversion or, worse, getting to Heathrow and not being able to return home before the holidays. After many little adventures, we gave up on getting to London. I just arrived in Wooster and Megan is on a flight home to Detroit. My luggage, of course, is missing in action, but fortunately I did not keep in it the Permian type specimens or our Cretaceous collection. [Update: My luggage apparently never left Detroit!]

Throughout this journey we were accompanied by people who just want to get home to their families for the holidays. Here’s to their safe and successful travels.

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“The Heathrow Diversion”: Wooster Geologists unexpectedly in New York City

A street scene outside our hotel in New York.

FLUSHING, QUEENS, NEW YORK–It seemed like such a good plan months ago. My Senior Independent Study student Megan Innis and I worked this summer in the American South with Paul Taylor and Caroline Sogot, as documented in this blog. We collected hundreds of fossils from the Late Cretaceous and Early Paleogene, many of which are encrusted with nearly perfectly-preserved bryozoans, serpulids and foraminiferans. The best way to study them is with a Scanning Electron Microscope (SEM), and the world’s expert in such paleontological imaging AND bryozoans is Paul Taylor himself. Since Paul is at The Natural History Museum in London, we planned to take our best specimens to him after classes were over in the Fall and before Christmas. That was the plan — and it still may work out!

Somewhere over Halifax our flight was diverted from London Heathrow because an epic snow and ice storm closed the runways. Delta flew us into JFK International Airport and put us up in a hotel in the middle of Flushing, Queens, New York City. Our flight will be reconstituted this evening and we’ll try again to reach London (and get out on Thursday, we can only hope). We are persevering because this is an important part of Megan’s I.S. project (for which she received Copeland Funds from the college), the fossils we bring will be significant for Caroline and Paul (and they have some for us), and I’m also hand-delivering a set of type specimens from the Permian of Texas. So in the interest of science and education we will soldier through!

In the meantime we are staying in a fascinating neighborhood. It certainly is one of the most diverse places on Earth as it has a colonial understructure (going back to the 17th Century Dutch) and added layers of culture through the centuries. We would have never guessed we’d be wandering its streets today!

Megan examining dried mushrooms and other unknown items outside a Korean-American grocery store in New York.

We even found a bit of geology to discuss in a World War I memorial. Geology is everywhere.

A 1920s marble memorial to World War I soldiers in Flushing, Queens, New York City.

This marble is odd because it has layers rich in muscovite mica. When Megan pointed these out I didn't believe her, but she was right.

There are also inclusions in the marble that look like hornblende. Our petrologist Dr. Pollock will have to figure this one out for us!

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The paleontology of hiatus concretions: fossils without sediment

Bryozoans (the thin branching structures) and an edrioasteroid (with the "star") encrusting a hiatus concretion from the Kope Formation (Upper Ordovician) of northern Kentucky.

Way back in 1984, when I was just a green Assistant Professor of Geology, my wife Gloria and I explored a series of Upper Ordovician (about 445 million years old) outcrops in northern Kentucky to plan a paleontology course field trip. It was a rainy day were, as is too often the case, slippery with mud. On our last roadcut exposure of the day I stepped out of the car and found at my feet the cobble pictured above. It had edrioasteroid echinoderms and bryozoans encrusting it on all sides — and we knew we had found something special. We collected dozens of the cobbles in a few minutes. It changed my research trajectory by introducing me to the splendors of hard substrate communities and hiatus concretions.

This post is a celebration of another chapter of that work published next month in the journal Facies (volume 57, pp. 275-300). This time I’m a member of a large team led by my young friend and colleague Michal Zaton of the University of Silesia in Sosnowiec. We thoroughly examined a set of bored and encrusted cobbles from the Middle Jurassic (about 170 million years old) of south-central Poland. It was a pleasure to use some of the same research techniques I employed 26 years ago to help reconstruct an ancient ecosystem and environment.

Hiatus concretions from the Middle Jurassic of Poland.

These cobbles are known as “hiatus concretions” because they collect in an environment when sediment has stopped (gone on “hiatus”, I suppose) and a lag of hard debris accumulates when fine sediment is washed away by currents. Organisms which require a hard substrate (“sclerobionts”) encrust the cobble surfaces (bryozoans, echinoderms, oysters and serpulid worms are most common) or bore into the matrix (sponges, bivalves, barnacles and worms commonly do this). A fossil record thus is formed in the absence of sedimentation, which is a bit different from the usual paradigm.

Various encrusters and borings on hiatus concretions from the Middle Jurassic of Poland.

Encrusting bryozoans on hiatus concretions from the Middle Jurassic of Poland.

I enjoy studying marine hard substrate organisms through time because they show a type of community evolution over hundreds of millions of years. These diverse fossils have also provided countless research opportunities for my Wooster students, and tracking them down has taken us all over the world and throughout the geological column. (The Cretaceous of Israel is another recent example of this work.) It is very satisfying to see a young geologist like Michal Zaton finding pleasure and research success in the same pursuit.

Bryozoans and crinoid holdfasts encrusting a cobble from the Upper Ordovician Kope Formation of northern Kentucky.

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Memories of warmer days…

Now that the semester is winding down and the cold weather has set in, I find my mind wandering back to the beginning of the academic year. It seems like it was years ago, not months, that our Mineralogy class visited Zollinger’s quarry.

2010 Mineralogy class at Zollinger's Quarry in late September.

It didn’t take long for students to discover the beautifully formed gypsum crystals that littered the ground.

From left to right, Will Cary, Matt Peppers, and Kevin Silver caught in the act of discovering the gypsum.

Truly, these are beautiful gypsum crystals.

In fact, next week  we’re using some of the crystals that we collected in our discussion of the thermodynamics of crystal nucleation and growth.

Of course, the minerals weren’t the only stars of the show. The students were excited to find these incredible mud cracks with preserved rain drops –  comparable to these mud cracks that a fellow geologist at Mountain Beltway observed in Turkey.

Mud cracks and preserved rain drops in Zollinger's Quarry.

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