Wooster’s Fossils of the Week: Echinoderm holdfasts from the Upper Cambrian of Montana

May 27th, 2016

Pelmatozoans051216The white buttons above are echinoderm holdfasts from the Snowy Range Formation (Upper Cambrian) of Carbon County, southern Montana. They and their hardground substrate were well described back in the day by Brett et al. (1983). We have these specimens as part of Wooster’s hardground collection. (The largest collection of carbonate hardgrounds anywhere! A rather esoteric distinction.)

These holdfasts are the cementing end of stemmed echinoderms, conveniently called pelmatozoans when we don’t know if they were crinoids, blastoids, cystoids, or a variety of other stemmed forms. I suspect these are eocrinoid attachments, but we have no evidence of the rest of the organism to test this.
Snowy bedThe hard substrate for the echinoderms is a flat-pebble conglomerate, a distinctive kind of limestone found mostly in the Lower Paleozoic. They are in some places associated with limited bioturbation (sediment stirring by organisms) and early cementation, but there are other origins for these distinctive sediments (see Myrow et al., 2004).
Snowy crossThis particular flat-pebble conglomerate was itself cemented into a carbonate hardground, as seem in this cross section. The pelmatozoan holdfasts are just visible on the upper surface.

These pelmatozoans are among the earliest encrusters on carbonate hardgroounds and thus have an important position in the evolution of hard substrate communities.

References:

Brett, C.E., Liddell, W.D. and Derstler, K.L. 1983. Late Cambrian hard substrate communities from Montana/Wyoming: the oldest known hardground encrusters: Lethaia 16: 281-289.

Myrow, P. M., Tice, L., Archuleta, B., Clark, B., Taylor, J.F. and Ripperdan, R.L. 2004. Fat‐pebble conglomerate: its multiple origins and relationship to metre‐scale depositional cycles. Sedimentology 51: 973-996.

Sepkoski Jr, J.J. 1982. Flat-pebble conglomerates, storm deposits, and the Cambrian bottom fauna. In: Cyclic and event stratification (p. 371-385). Springer, Berlin Heidelberg.

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

Wooster’s Fossil of the Week: A phyllocarid crustacean from the Middle Cambrian Burgess Shale of British Columbia, Canada

May 20th, 2016

Canadaspis perfecta Burgess Shale 585We are fortunate at Wooster to have a few fossils from the Burgess Shale (Middle Cambrian) collected near Burgess Pass, British Columbia, Canada, including this delicate phyllocarid Canadaspis perfecta (Walcott, 1912). This species is one of the oldest crustaceans, a group that includes barnacles, crabs, lobsters and shrimp. Please note from the start that I did NOT collect it. The Burgess Shale is a UNESCO World Heritage Site, so collecting there is restricted to a very small group of paleontologists who have gone through probably the most strict permitting system anywhere. I had a wonderful visit to the Burgess Shale with my friend Matthew James in 2009, and we followed all the rules. (The photo below is of the Walcott Quarry outcrop.) Our Wooster specimen was in our teaching collection when I arrived. I suspect it was collected in the 1920s or 1930s and probably purchased from a scientific supply house.

walcottquarryMarrellaSuch a dramatic setting, which is perfect for the incredible fossils that have come from this site.

Canadaspis perfecta drawing

Canadaspis perfecta has been thoroughly studied by Derek Briggs, the most prominent of the paleontologists who have studied the Burgess Shale fauna. The above reconstruction of C. perfecta is from his classic 1978 monograph on the species. He had spectacular material to work with, including specimens with limbs and antennae well represented. Our specimen is a bit shabby in comparison! Nevertheless, we can still make out abdominal segments and a bit of the head shield.

Briggs (1978, p. 440) concluded that C. perfecta likely “fed on coarse particles, possibly with the aid of currents set up by the biramous appendages”. This is a similar feeding mode to many of the trilobites who lived alongside.

References:

Briggs, D.E. 1978. The morphology, mode of life, and affinities of Canadaspis perfecta (Crustacea: Phyllocarida), Middle Cambrian, Burgess Shale, British Columbia. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 281: 439-487.

Briggs, D.E. 1992. Phylogenetic significance of the Burgess Shale crustacean Canadaspis. Acta Zoologica 73: 293-300.

Wooster’s Fossil of the Week: A tectonically-deformed Early Cambrian trilobite from southeastern California

April 10th, 2015

Olenellus terminatus whole 585This wonderful trilobite was found last month by Olivia Brown (’15), a student on the Wooster Geology Department’s glorious field trip to the Mojave Desert. Olivia collected it at Emigrant Pass in the Nopah Range of Inyo County, southeastern California. It comes from the Pyramid Shale Member of the Carrara Formation and is uppermost Lower Cambrian. It appears to be the species Olenellus terminatus Palmer, 1998. It is a great specimen because most of the body segments are still in place. At this locality we find mostly the semi-circular cephalon (the head) separated from the rest of the body. The species O. terminatus is so named because it represents the last of its famous lineage of Early Cambrian trilobites. The last time we found such a whole trilobite at this site was in 2011, with Nick Fedorchuk as the paleo star of the day.

This trilobite has been tectonically strained along its main axis, giving it a narrow look it did not possess in life. In fact, these trilobites with their semi-circular cephala make nice indicators of the strain their hosting rocks have experienced.
spines 032515 585This particular kind of trilobite has very distinctive spines, as shown in the close-up above. The long spine on the right comes from the trailing edge of the cephalon and is called a genal spine. The one in the center is a thoracic spine emerging from the third thoracic segment. The primary role of these spines was probably the obvious one: protection from predators. They may also have helped spread the weight of the animal across the substrate if they were walking across soupy mud (much like a snowshoe).

We’ve met this man before in this blog. James Hall (1811–1898) named the genus Olenellus in 1861. He was a legendary geologist, and the most prominent paleontologist of his time. He became the first state paleontologist of New York in 1841, and in 1893 he was appointed the New York state geologist. His most impressive legacy is the large number of fossil taxa he named and described, most in his Palaeontology of New York series. James Hall is in my academic heritage. His advisor was Amos Eaton (1776-1842), an American who learned his geology from Benjamin Silliman (1779-1864) at Yale. One of James Hall’s students was Charles Schuchert (1856-1942), a prominent invertebrate paleontologist. Schuchert had a student named Carl Owen Dunbar (1891-1979). Schuchert and Dunbar were coauthors of a famous geology textbook. Dunbar had a student at Yale named William B.N. Berry (1931-2011), my doctoral advisor. Thus my academic link to old man Hall above.

References:

Adams, R.D. 1995. Sequence-stratigraphy of Early-Middle Cambrian grand cycles in the Carrara Formation, southwest Basin and Range, California and Nevada, p. 277-328. In: Sequence Stratigraphy and Depositional Response to Eustatic, Tectonic and Climatic Forcing. Springer Netherlands.

Cooper, R.A. 1990. Interpretation of tectonically deformed fossils. New Zealand Journal of Geology and Geophysics 33: 321-332.

Hazzard, J.C. 1937. Paleozoic section in the Nopah and Resting Springs Mountains, Inyo County, California. California Journal of Mines and Geology 33: 273-339.

Palmer, A.R. 1998. Terminal Early Cambrian extinction of the Olenellina: Documentation from the Pioche Formation, Nevada. Journal of Paleontology 72: 650–672.

Palmer, A.R. and Halley, R.B. 1979. Physical stratigraphy and trilobite biostratigraphy of the Carrara Formation (Lower and middle Cambrian) in the southern Great Basin. U.S. Geological Survey Professional Paper 1047: 1-131.

Shah, J., Srivastava, D.C., Rastogi, V., Ghosh, R. and Pal, A. 2010. Strain estimation from single forms of distorted fossils—A computer graphics and MATLAB approach. Journal of the Geological Society of India 75: 89-97.

Wooster Geologist at Valley Forge, Pennsylvania

March 20th, 2013

ValleyForgeHuts032013BRYN MAWR, PENNSYLVANIA–While visiting my friends and colleagues Katherine and Pedro Marenco at Bryn Mawr College, I visited the nearby Valley Forge National Historical Park. Everyone will remember, of course that this is the place outside Philadelphia that the Continental Army made its rough winter quarters in 1777-1778. The huts above are reconstructions of the soldiers’ quarters on the windy and cold fields. Commander-in-Chief George Washington chose this place because it was easily defensible, had plenty of timber for construction and fuel, and was close enough to British-occupied Philadelphia to keep an eye on the enemy — yet not so close to be likely attacked.

LedgerOutcrop032013

As a geologist, of course, I also looked for the rocky bones beneath the landscape. They were easily found in the above cliff near the main parking area. This is the Ledger Dolomite, a Cambrian unit found throughout this part of eastern Pennsylvania.

LedgerDolomite032013The Ledger Dolomite here is distinguished by these fine laminations visible on its weathered cross-sections. These are apparently stromatolites: laminar structures built by bacterial mats. We’ve met Cambrian stromatolites before in this blog.

Smilodon_gracilisI was surprised to learn that there is also a significant middle Pleistocene fossil deposit in Valley Forge called the Port Kennedy Bone Cave. This is a sinkhole deposit within the Ledger Dolomite. A particularly large sinkhole apparently trapped a variety of animals, including the gracile sabre-tooth Smilodon gracilis, the skull of which is on display in the Valley Forge Historical Park visitor center. S. gracilis was the smallest and earliest member of its genus. The Port Kennedy Bone Cave was one of the first fossil assemblages that the famous paleontologist Edward Drinker Cope studied. The location was lost to science until its rediscovery in 2005.

ValleyForgeCannon032013This is the requisite cannon image, even though no battle was fought here. It is nevertheless a dramatic place for the privations the soldiers suffered during the darkest days of the Revolutionary War. It is hard to imagine the conditions in 1777-1778 now since highways and casinos surround the old encampment.

Cambrian bryozoans? Not yet!

December 17th, 2012

Screen shot 2012-12-17 at 6.01.54 PMDUBLIN, IRELAND — It was a great day of talks at the 56th Palaeontological Association Annual Meeting being held at University College Dublin. I learned many things, from new ideas about the Burgess Shale and its characteristic fauna to why there is no demonstrated sexual dimorphism among Mesozoic vertebrates. (I also learned that the students in this university must sit in very cramped spaces in chilly rooms. Wooster students: note your classroom comforts!) My favorite talk of the day was one on which I was a co-author: “Is the world’s oldest bryozoan actually the world’s oldest pennatulacean?” Our senior author and genius of the project, Paul Taylor, gave the lecture. I’m presenting here two slides from the PowerPoint presentation. We’ll have much more about this topic when we have our paper on it in press. In the top image you see on the left Pywackia baileyi, a putative Cambrian bryozoan recently described in a high-profile journal. This is a big deal because bryozoans are known as one of the very few phyla not found in the Cambrian. We looked at the evidence and the specimens and quickly concluded this Pywackia baileyi is not a bryozoan. (Tell your friends!). Instead it appears to be pennatulacean-like octocoral. The image in the top right is of Lituaria, a modern pennatulacean. Note how similar these structures are, except for almost an order of magnitude size difference (which is reduced when looking at the range of sizes in other pennatulaceans).

Screen shot 2012-12-17 at 6.03.34 PMIn the above slide from Paul’s presentation you see Pywackia and Lituaria again on the left, and then a variety of living pennatulacean octocorals on the right. We have strong evidence, from the morphology to the possible original phosphatic composition, that Pywackia baileyi is not the earliest bryozoan. We have thus far a good case that it instead represents the earliest pennatulacean octocoral. Again, this story will be developed further later in this blog after our paper is accepted for publication.

Jameson121712The day ended with the traditional, raucous annual Palaeontological Association dinner at the Jameson Distillery in downtown Dublin. In the above image you can see in the foreground on the right Wooster alumna Lisa Park Boush and her husband Carlton. We are among just a scattering of Americans at this European meeting. It was a very pleasant (if very loud) evening!

References:

Landing, E., English, A. and Keppie, J.D. 2010. Cambrian origin of all skeletalized metazoan phyla—Discovery of Earth’s oldest bryozoans (Upper Cambrian, southern Mexico). Geology 38: 547-550.

Taylor, P.D., Berning, B. and Wilson, M.A. 2012. Is the world’s oldest bryozoan actually the world’s oldest pennatulacean? Palaeontological Association 56th Annual Meeting, Dublin, Ireland, Programme and Abstracts, p. 52.

Grand Canyon Expedition 2012

August 9th, 2012

This summer (26 July through 2 August) I had the pleasure to serve as a guest geologist on a rafting trip to the Grand Canyon. The trip logistics were engineered by Doug Drushal under the auspices of Environmental Experiences, Inc. These trips were begun by former Wooster Geology Professor, Dr. Frederick W. Cropp III in 1980. Doug and Fred’s son Tom Cropp have continued to provide the organization and logistics for these exciting and geologically enlightening rafting trips. Special thanks to JP, our boatman, and Phil (swamper) of Hatch River Expeditions for sharing their knowledge and extensive experience of the history and geology of the Canyon.

The group poses in front of the Great Angular Unconformity. Note the tilted Precambrian Supergroup underlying the Cambrian section consisting of Tapeats Sandstone and Bright Angel Shale (see the stratigraphic section here to remind yourself of the stratigraphy). On the boat is the boatman JP and swamper Phil.

Some of the geological highlights are explained in the captions below. Not only were we treated to classic geology, but we also were able to experience and view some of the power of water in the canyon – flash floods and debris flows.

The reverse exfoliation in the Permian Esplanade Sandstone is one the the best examples of its kind. Usually when we discuss exfoliation we think of domes. The homogeneous nature of the stone along with the local stresses and erosion by the stream combine to give this unnamed side valley of the Grand Canyon such a unique (and highly photographed) look.

Springs emanating from the fractures and karst in the Redwall-Muav Limestone Aquifer provide an oasis in the Canyon and a needed water source for travelers.

Some of the group reclines on chairs in the Throne Room at Dutton Spring in the Redwall Limestone. Clarence Dutton (born in Wallingford, CT) published one of the earliest geologic studies of the canyon in 1882.

An inside-out waterfall (JP’s term). Note the encased waterfall of travertine.  Three physical effects can lead to travertine deposition at waterfall sites: aeration, jet-flow, and low-pressure effects. The three physical effects are induced by two basic changes in the water: an accelerated flow velocity, and enlargement of the air-water interface area. These two changes increase the rate of CO2 outgassing so that a high degree of supersaturation of calcite (travertine) is reached, which then induces travertine precipitation. Note also the four intrepid  explorers who facilitated the older folks into getting more involved with the water holes and falls.

 

 

Robbie reacts strongly to the Great Unconformity (aka Powell Unconformity). This gap in the geologic record is between the lower Vishnu Schist, Precambrian in age and the upper Cambrian Tapeats Sandstone. About 1 billion years is missing at the boundary where Robbie points. Think also about the burial and exhumation stages that must occur to form this, it is quite profound.

Anasazi petroglyphs – this site is dated to AD 1000-1300 and perhaps was abandoned when the Medievel Anasazi droughts descended on the region.

Anasazi ruins – perhaps this outlook spot was occupied by the higher-ups in the society with others practiced dryland farming the floodplain of the Colorado River below.

The group on the overlook point – farther up-valley another settlement is located within sight of this point.

Deer Creek falls – one of the great falls in the Canyon. This stream was rerouted when a landslide dammed the Colorado and displaced the stream. The slide occurred shortly after the damming of the Colorado River by lava flows downstream. This new lake then saturated the Bright Angel Shale, which formed the slip surface of the massive landslide.

The team scopes out lava falls a class ten rapids. Most rapids exist where side canyons bring in large boulders in debris flows that accumulate at the confluence of the tributaries and the Colorado.

A side canyon that experienced a debris flow a few weeks before our trip. In the distance is the Colorado River – it is easy to see how these rapids are evolving as flash flooding and debris flows swept boulders and debris to the river. The tributary was dry the day of our visit.

During our stay in the Canyon there was a massive storm event in the Havasu basin on 1 August. Above is the hydrograph showing the flash flood. We were unable to visit the Havisu Creek the next day because of the high flow. Below one can see the sediment and debris rich water in the Colorado River. Note also on the hydrograph that we had more than one rain event during our days in the Canyon. JP and Phil almost had to evacuate our camp as the Colorado was rising feet per hour.

The flash flood on 1 August flushed out an amazing amount of debris that included more logs and tree debris than seemed to be growing in the canyon. This beach and eddy in the distance is full of wood and debris.

Flying out of the Grand Canyon to Bar Ten Ranch by helicopter. We then took a fixed wing flight out to the Flagstaff Airport.

 

Wooster’s Fossil of the Week: Marrella splendens (Burgess Shale, Middle Cambrian, British Columbia)

January 15th, 2012

The first story about this iconic fossil is the trouble I went through to get the photograph above. Our specimen of Marrella splendens is preserved in the common Burgess Shale fashion as a thin dark film on a black piece of shale. A normal photograph would show just a black rock with a grayish smudge. To increase the contrast, I coated the fossil with mineral oil and used very bright lights to capture the image. I then tweaked the contrast further with Photoshop. Curiously, a black envelope appeared around the specimen that resembles the famous dark stain found with some Burgess Shale fossils. It may be remnants of body fluids.

Before I go further, I must clarify the origins of this fossil from the Burgess Shale (Middle Cambrian) near Burgess Pass, British Columbia, Canada. I did NOT collect it. The Burgess Shale is a UNESCO World Heritage Site, so collecting there is restricted to a very small group of paleontologists who have gone through probably the most strict permitting system anywhere. I had a wonderful visit to the Burgess Shale with my friend Matthew James in 2009, and we followed all the rules. (The above is a photo of the Burgess Shale outcrop and its extraordinary setting.) Our Wooster specimen was in our teaching collection when I arrived. I suspect it was collected in the 1920s or 1930s. Marrella splendens is one of the most common Burgess Shale fossils, so no doubt there are many out there in older collections.

(Reconstruction from Stephen Jay Gould's famous Burgess Shale book titled "Wonderful Life".)

Marrella splendens is supposedly the first fossil Charles Doolittle Walcott discovered in the Burgess Shale in 1909. He called it a “lace crab”, and then later as a strange trilobite. Later work by Harry Whittington demonstrated that it was neither a crab nor a trilobite. It is likely a stem-group arthropod (near the base of arthropod phylogeny).

Marrella splendens was probably a bottom-dwelling deposit-feeder living on organic material in the seafloor sediment. There are thousands and thousands of specimens known in the Burgess Shale. They are preserved in many different angles, providing the first evidence that some sort of sedimentary mass movement was involved in the formation of this famous unit.

Walcott invented the name Marrella in honor of John Edward Marr (1857-1933). Marr was a paleontologist at Cambridge University in England. By the end of his career he was a Fellow of the Geological Society and the Royal Society, hence FGS and FRS follow his name.

Reference:

García-Bellido, D.C. and Collins, D.H. 2006. A new study of Marrella splendens (Arthropoda, Marrellomorpha) from the Middle Cambrian Burgess Shale, British Columbia, Canada. Canadian Journal of Earth Sciences 43: 721-742.

Wooster’s Fossil of the Week: A trilobite (Middle Cambrian of Utah)

August 14th, 2011

I’ve avoided having a trilobite as Fossil of the Week because it seems like such a cliché. Everyone knows trilobites, and they are the most common “favorite fossil” (invertebrate, anyway). Plus our best trilobite (seen above) is the most familiar trilobite of all: Elrathia kingii (Meek, 1870). One professional collector — just one guy — said that in 20 years he sold 1.5 million of these.

Still, trilobites are cool. They virtually define the Paleozoic Era, appearing in the Early Cambrian and leaving the stage (with so many others) in the latest Permian. They were arthropods, sharing this very large phylum with insects, spiders, crabs and centipedes. The name “trilobite” means “three lobes” referring to the axial lobe (running down the center along the length of the animal) and the two pleural lobes, one on each side. They  also have three parts the other way: a head, thorax and pygidium (the tail end).

Elrathia kingii is a ptychopariid trilobite found in extraordinary numbers in Middle Cambrian dark shales and limestones. There is a geological story here, two of them, in fact. One reason they are so common is that their populations were commonly buried by sediment stirred up in massive storms (Brett et al., 2009). They are among the only fossils found in organic-rich dark sediments because they lived in the harsh “exaerobic zone” at the very minimum of oxygen needed for animal life (Gaines and Droser, 2003). They apparently were the first large invertebrates to exploit this marginal environment.
Elrathia kingii gives us the opportunity to meet a pioneering American paleontologist: Fielding Bradford Meek (1817-1876). He originally described this species in 1870, calling it Conocoryphe kingii (see above). Paleontologists are quite familiar with the name “Meek” following a fossil species because he described hundreds of them. Meek was a native of Madison, Indiana, a place where Ordovician fossils are abundant and easily collected. He was apparently an unsuccessful businessman so he jumped at a chance in 1848 to work for the U.S. government surveying the geology of Iowa. Meek was good at this job and soon was working with James Hall in New York, the country’s premier paleontologist. Meek was eventually based in Washington, D.C., with the United States geological and geographical surveys. After many accomplishments in government service, he died of tuberculosis in 1876 (White, 1896).

Fielding Bradford Meek

References:

Brett C.E., Allison P.A., DeSantis M.K., Liddell W.D. and Kramer A. 2009. Sequence stratigraphy, cyclic facies, and lagerstätten in the Middle Cambrian Wheeler and Marjum Formations, Great Basin, Utah. Palaeogeography, Palaeoclimatology, Palaeoecology 277: 9-33.

Gaines, R.R. and Droser, M.L. 2003. Paleoecology of the familiar trilobite Elrathia kingii: An early exaerobic zone inhabitant. Geology 31: 941–944.

White, C.A. 1896. Memoir of Fielding Bradford Meek, 1817-1876. Biographical Memoirs, National Academy of Sciences, p. 75-91.

Trilobites! Now it’s a field trip.

March 18th, 2011

Just kidding about the trilobite requirement for a true field trip, but we must acknowledge a certain charm that comes only from these spiny little beasts. Thanks to my buddy Matthew James, we were directed to an especially fossiliferous set of outcrops of the Carrara Formation in the Nopah Range. The trilobites we collected there are Early Cambrian, roughly 540 million years old. Nick Fedorchuk found the whole specimen photographed above. Everyone collected cephala (“heads”) and the occasional brachiopod and hyolith. It was a very good afternoon for paleontologists!

Wooster students at work in what we now call "Trilobite Valley".

Travis Louvain finding good specimens.

The trilobites here are strained by tectonism, so they look "stretched" in one direction. Shelley Judge collected a set to use in her structural geology labs.

Anomalocaris now not so scary

November 1st, 2010

Whitey Hagadorn beginning his GSA talk on the feeding abilities of Anomalocaris. The large room was packed.

DENVER, COLORADO — I very much enjoyed a talk this afternoon by Whitey Hagadorn (a Wooster favorite since his Osgood lecture last year) entitled: “Putting Anomalocaris on a soft-food diet?” Even though Whitey says Anomalocaris “may still have been a fearsome predator”, slurping up worms from the mud is not the same as crunching trilobites. Spaghetti vs. steak.

Whitey’s presentation was an excellent example of testing a hypothesis with fossil evidence. If Anomalocaris really did bite through trilobite cuticle, surely it should have been able to at least close its mouth more than halfway and be able to apply the necessary forces? Whitey and his colleagues modeled the mouthparts of Anomalocaris and the exoskeletons of trilobites and subjected them to various engineering analyses. Turns out that the story of these nektic predators grabbing and killing trilobites just can’t be true. Their mouths could exert significant sucking forces, though, so maybe they were predators on soft-bodied worms they pulled from the sediment. Their “teeth” then may have served mainly to keep the worms from sliding out once in the mouth. Not nearly so dramatic, but a much more sensible take on the fossil evidence.

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