Wooster Geologists in Bristol, England

June 11th, 2016

1 Bristol Museum and UniversityBristol, England — Cassidy Jester (’17) and I are spending the weekend in Bristol after finishing our fieldwork in Dorset this week. Our travel and lodging arrangements required a couple of days here before we go to London on Monday and then our separate ways. We’ll continue to sort out our specimens, work on a GSA abstract, and explore the city. This afternoon, while waiting for our hotel rooms to open, we walked through the central part of the city to the Bristol City Museum and Art Gallery. It is the building with the pillars on the left. The magnificent tall building on the right is part of the University of Bristol — the part that houses the Earth Sciences Department.

2 Bristol City Museum and Art GalleryThis museum is a wonderful combination of art, history and science, with considerable space devoted to geology and paleontology.

3 Bristol pregnant ichthyosaurAmong the many exhibits, I picked one to share: a pregnant ichthyosaur from the local Jurassic. Note the tiny arrow in the lower left of the skeleton.

4 Bristol ichthyosaur fetusAt the arrow, among the bones of this female ichthyosaur is this hand-sized skeleton of a fetus, direct evidence that ichthyosaurs, though reptiles, gave live birth. Paleontology is so cool.

Team Dorset finishes its fieldwork

June 10th, 2016

1 Snuffbox serpulidssSherborne, England — Cassidy Jester (’17), Tim Palmer and I today finished our fieldwork. Cassidy is now set for her Senior Independent Study project with plenty of specimens, observations, photographs and ideas to last the next 10 months. This morning we visited the Burton Bradstock beach exposure of the snuffboxes, meeting our great colleague Caroline Buttler (Department of Natural Sciences, Amgueddfa Cymru – National Museum Wales, Cardiff) and her husband Simon for lunch on the outcrop. It was great fun, and Caroline had additional discoveries for us, including the exfoliated snuffbox layer shown above with serpulid worm tubes.

2 Ammonite gastropod snuffboxesWe had time to look for more fossils associated with the snuffboxes. Above you see a gastropod on the left and an ammonite on the right, with snuffbox bits scattered about.

3 Burton Bradstock pendentWe also found many examples of burrow systems with cryptic pendent iron-rich layers, including those shown above. (I rotated the image 180° because the block we studied on the beach is upside-down.)

4 Maiden Castle rampartsOn the way back to our lodgings near Sherborne we stopped by the Iron Age hill fort Maiden Castle, a portion of the massive earthen ramparts of which are shown above.

Our collecting, measuring and describing is done. Most of the work for this project, of course, will be in the Wooster geology labs. We will have delightful memories of our sunny days in Dorset, and the invaluable assistance of our colleagues Bob Chandler and John Whicher. I am personally most grateful for the geological and navigational skills of Tim Palmer, our wonderful companion and astute advisor. Without him none of this could be done.

Crew in Whicher MuseumThe Dorset crew in the Whicher Museum. From the left, Bob Chandler, Mark Wilson, Tim Palmer, John Whicher, nd Cassidy Jester (’17).

Wooster’s Fossil of the Week: A fracture-shaped bioerosion trace from the Pliocene of Cyprus

June 10th, 2016

Caedichnus_01_scale_Mark 500This past semester I worked with three colleagues on a massive trace fossil review paper, which we hope meets success in the next month or so. My primary job on the team was to sort out bioerosion traces, especially those that are macroscopic. As always with such studies, I learned a great deal when forced to do a systematic literature review. One of the ichnogenera new to me was Caedichnus, a wedge-shaped excision found primarily in gastropod shells. It was only described last year by Stafford et al. (2015). Above is an example we happened to have in our collections. Note the fractured margins in this Fusinus shell aperture from the Pliocene of Cyprus. It was likely made by a predatory crustacean (such as a crab or lobster) bashing away at the shell to get to the living snail inside. The predator may have been successful in this case since there is no sign of healing in the snail shell.
Fusinus Cyprus Pliocene 500Above is an undamaged Fusinus showing a complete aperture. This snail also had its travails, though. Note the round, incomplete borehole just above the aperture. This was made by some kind of drilling predator, likely a naticid snail.

These shells come from the 1996 Wooster-Keck expedition to Cyprus with Steve Dornbos (’97) and me. Like the rest of the Cypriot specimens on this blog, it is from the Nicosia Formation (Pliocene) exposed on the Mesaoria Plain in the center of the island. This specimen comes from the “Exploration” locality described in Dornbos and Wilson (1999).

References:

Dornbos, S.Q. and Wilson, M.A. 1999. Paleoecology of a Pliocene coral reef in Cyprus: Recovery of a marine community from the Messinian Salinity Crisis. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 213: 103-118.

Molinaro, D.J., Stafford, E.S., Collins, B.M., Barclay, K.M., Tyler, C.L. and Leighton, L.R. 2014. Peeling out predation intensity in the fossil record: A test of repair scar frequency as a suitable proxy for predation pressure along a modern predation gradient. Palaeogeography, Palaeoclimatology, Palaeoecology 412: 141-147.

Stafford, E.S., Dietl, G.P., Gingras, M.P. and Leighton, L.R. 2015. Caedichnus, a new ichnogenus representing predatory attack on the gastropod shell aperture. Ichnos 22: 87-102.

Stafford, E.S., Tyler, C.L. and Leighton, L.R. 2015. Gastropod shell repair tracks predator abundance. Marine Ecology 36: 1176-1184.

Team Dorset makes a cryptic discovery

June 9th, 2016

1 Cassidy Mapperton 060916Sherborne, England — It was a good day for Team Dorset. Cassidy Jester (’17) is shown above in Coombe Quarry near Mapperton, Dorset. She is standing on an erosion surface between the Comptocostosum Bed (Aalenian) below and Horn Park Ironshot (Bajocian) above. These are beds 2d and 3a in the local stratigraphic system, and ammonite zones Scissum and Discites. There is a considerable disconformity here, meaning a significant hiatus of unrecorded time, several ammonite zones worth. The snuffboxes we’re interested in are found jut above this boundary.

2 Pendent layers 060916Tim Palmer picked up the above rock as we started our measurements and descriptions. He deduced right away that he was looking at a cross-section of a burrow now filled with light brown sediment. The darker layers above are ferruginous (iron-rich), serpulid-bearing laminae like those that make up the snuffbox cortices, and they are hanging pendently from the roof of this burrow into the original cavity beneath. At one time this burrow was an open tunnel with cemented walls and the iron-rich layers grew from the ceiling like stalactites. Tim demonstrated with this single specimen that the iron-rich layers grew in dark, cryptic spaces, strongly supporting the hypothesis of Palmer and Wilson (1990) that the equivalent snuffbox layers accumulated on the undersides in gloomy darkness

3 Infilled Thalassinoides MappertonCassidy and I then recognized that the iron-rich “stromatolites” we had seen on our earlier visit to the quarry were actually these iron-rich layers filling Thalassinoides burrow systems that are truncated by the erosion surface. In the above image you are looking down on the erosion surface at a branching burrow filled with iron-rich layers. These are not stromatolites but cryptic burrow fills.

5 Sherborne Thalassinoides 2 585Later in the afternoon we returned to the Sherborne Stone quarry yard and looked at Thalassinoides burrow systems in the Sherborne Building Stone cut by giant saws. We see here a view parallel to bedding showing a box work of tunnels filled with a darker sediment. This matches the pattern seen in the Coombe Quarry erosion surface.

6 Sherborne Thalassinoides section 585This is a cross-section of the same kind of Thalassinoides burrow in the Sherborne Building Stone. We see the vertical connections to the surface and the lateral tubes. These burrows formed the cryptic spaces for iron-rich layer deposition as seen at Coombe Quarry. Or at least that is our hypothesis! Tomorrow we will test it by examining the burrow systems associated with the snuffboxes at Burton Bradstock.

7 Sherborne Castle 585As usual, we ended our day with more historical architecture and stonework, this time at nearby Sherborne Castle, a 16th century Tudor mansion sitting on magnificent estate grounds. Much of our work is on land owned by this estate.

The format below is a bit messy, but here is a download of our GPS data for the localities on this expedition:

GPS# Latitude Longitude Location
138 50.96268903 -2.503268039 Frogden Quarry
139 50.96319797 -2.501848983 Frogden Quarry older
140 50.93710503 -2.601833018 Babylon Hill
141 50.94292902 -2.556813983 Louse Hill
142 50.79496597 -2.71623401 Coombe Quarry, Mapperton
143 50.70015801 -2.734380998 Hive Beach, Burton Bradstock
145 50.81626003 -2.771674013 Horn Park
146 50.70154396 -2.737065973 Burton Bradstock snuffboxes

Snuffboxes! Team Dorset has a project

June 8th, 2016

1 Snuffbox colection BBSherborne, England — Cassidy Jester (’17) now has a Senior Independent Study project: Origin and paleoecology of ferruginous oncoids (“snuffboxes”) from the Middle Jurassic (Bajocian) of southern England and northern France. (We’re not going to France; I have specimens I collected 20 years ago there.) Pictured above is a nice collection of these snuffboxes on the Dorset coast near Burton Bradstock. More on them below. Today Tim Palmer, Cassidy and I had a great time starting our data collection.

2 Whicher museumThe first thing we did this morning, though, was visit the astounding fossil collection of John Whicher, one of our new citizen scientist friends. He has a spectacular collection of exquisite fossils, most from the Inferior Oolite and all meticulously curated. His preparations are amazing, especially when you know what a fossil looks like when first collected.

3 Tim Cassidy Whicher museumTim and Cassidy are here admiring some of the Inferior Oolite ammonites in John’s display cases. Each specimen is numbered and has full locality and stratigraphic context.

4 Whicher workshopJohn has a workshop that would be the envy of any university, along with storage for those specimens awaiting his patient preservation. Here we see our other new friend Bob Chandler cutting a rock for us. Bob has his own equal collection. These indefatigable amateurs are making extraordinary contributions to science.

5 Burton cliff fallAt noon we started our own work along the coast at Burton Bradstock, Dorset. We depended upon cliff falls like this one where the rocks of the Inferior Oolite at the top of the cliff crashed to the beach below.

6 Burton Bradstock large block 060816This gorgeous block is an example of the snuffbox bed fallen into our hands on the Burton Bradstock beach. The long part of the measuring stick is one meter. We are looking at the base of the snuffbox-bearing unit, so the block is upside-down.

7 Cassidy working 060816Cassidy is here studying that above block, with the English Channel in the background and brilliant sunlight.

8 Snuffbox bored shell nucleusThis is one of the snuffboxes with a shell fragment as a nucleus. The shell has many borings that were excavated before it started accumulating the layers of iron oxides.

9 snuffboxes horns ooidsThe snuffboxes have all sorts of details, from the compositions of the nuclei, the structure of the cortices, the fossils found encrusting them, and their overall shapes. Many have “horns” in cross-section like the two above. Note also the iron ooids (rusty red dots) between the snuffboxes. Their origin is another mystery.

10 Cerne Abbey 585We ended the day with a visit to the ruins of Cerne Abbey in Cerne Abbas, which was founded in 987. The remaining buildings are considerably later but still incorporate remnants of the old. This is now a romantic ruin on a small estate.

11 Cerne Abbey signTomorrow we continue to study the snuffboxes in other localities. We hope again to avoid the rains that have affected much of the country this week.

Reference:

Palmer, T.J. & Wilson, M.A. 1990. Growth of ferruginous oncoliths in the Bajocian (Middle Jurassic) of Europe. Terra Nova 2: 142-147.

 

 

Team Dorset closes in on a project

June 7th, 2016

1 Burton Radstock cliffSherborne, England — Another gorgeous day of exploring in the Middle Jurassic of southern England. The weather and the companions could not be better. Today was our last day of reconnaissance and tomorrow Cassidy Jester (’17) begins her Independent Study project fieldwork. Exactly what that project will be will be decided in the morning. So many possibilities. No doubt Tim Palmer and Cassidy are thinking about them as they walk the beach at Burton Bradstock (above).

2 Cassidy on Maperton surfaceWe began the day at Coombe Quarry near Maperton, Dorset. There we saw an interesting combination of snuffboxes (essentially iron-rich, fossiliferous oncoids), a carbonate hardground, and microbially-generated layers of iron oxides. Cassidy is standing above on the top of the most interesting unit.

3 Maperton surfaceAbove is a close view of the Maperton carbonate hardground surface (light-colored) perforated by Gastrochaenolites borings with the microbial iron oxides (darker and brownish) filling in the low spaces. The snuffboxes are just below. These are complex units that are highly condensed, so a few centimeters of section represents multiple depositional events.

4 Hive Beach snuffboxesWe next traveled to Hive Beach at Burton Bradstock along the English Channel (see the topmost image). Here we found blocks of the Inferior Oolite that had fallen down to the beach, enabling us to see the stratigraphy in separate bits. In this limestone cross-section, Cassidy’s hand is at the snuffbox level. The snuffboxes are the elliptical, layered brown objects.

7 Snuffbox in dikeThe layered object above is a snuffbox in cross-section. The center is a bit of limestone that served as the nucleus on which the brown microbial layers grew. The snuffbox occasionally was overturned by currents, allowing the layers to grow completely around the nucleus. These have been called snuffboxes since the 19th century because the inner limestone bit often weathered out, leaving the iron-rich parts looking a bit like a flat box to carry snuff.

5 Cassidy on neptunian dikeAt Burton Bradstock we also saw this very unusual rock along the beach. It has a limestone matrix and very diverse clasts in seemingly random orientations. The clasts include large red blocks (Cassidy has her hand on one), ammonites, and snuffboxes (including the one shown earlier).

6 Dike rubble 060716In this closer view of what is thought to be a neptunian dike rock, Cassidy’s finger is on an ammonite in cross-section. There are many iron-rich layers and calcite-filled veins. This rock appears to have been formed from sediment collecting in a large fissure that cut across rock layers.

8 Stromatactis debrisThese odd flat-bottomed clasts were quite mysterious to us until Tim nailed them as fragments of a stromatactis layer. Still a mystery, though, where these clasts came from.

9 Horn Park surfaceOur last stop of the day was at Horn Park Quarry, a gated natural reserve, reputed to be the smallest in the United Kingdom. The whole of the Inferior Oolite is exposed here, including this remarkable flat surface that we’re told extends for miles.

10 Horn Park ammonite 1The surface is almost perfectly flat, and it truncates thousands of fossils, including this ammonite.

11 Horn Park belemnitesAnd these belemnites with no preferred orientation.

12 caged ammonitesThe site was at one time heavily exploited for its ammonites, some of which are now preserved under this locked cage.

13 Tim Puzzled 060716Tim seems despondent because we have no strong explanation for the origin of this remarkable surface. We think it was likely formed by abrasion processes, but how is unclear. There are numerous such surfaces in this small section, compounding the mystery.

Now Cassidy decides what to do!

 

 

Jurassic cephalopod heaven in southwestern England

June 6th, 2016

1 Trail to old FrogdenSherborne, England — Cassidy Jester (’17) and I are now at our main base in a bed and breakfast in northern Dorset. Our lodgings are a converted milking house on an estate with a beautiful view of the surrounding rolling hills and fields around Sherborne. We met our first partner Tim Palmer yesterday in Bristol, and today we met our guide to the local stratigraphy and fossils, Bob Chandler. We were also joined by retired physician John Whicher for part of the day. Bob and John are amateur paleontologists, but that hardly seems the right label considering how long they’ve been studying the fossils in the region, and the number of papers they’ve published. They are “citizen scientists” of the highest order. We are grateful for their enthusiasm and essential assistance.

2 Sherborne Stone signOur first stop of the day was to a quarry yard on the estate of Sherborne Castle. As always, the local quarry offices are fantastic places to start exploring the rocks of a region. The quarry operators are always keen on fossils, and usually save the best ones they find to share with visiting geologists. This particular quarry specializes in Sherborne Building Stone, part of the Middle Jurassic Inferior Oolite we are studying.

3 Sherborne Stone yardThe quarry yard has many cut and polished blocks and slabs of the Sherborne stone, providing useful views of the rock interiors and cross-sections of the fossils.

5 Cut nautiloid FrogdenThe Sherborne Building Stone and associated rocks above and below also have huge nautiloids. They make fine polished sections showing interior chambers filled with combinations of sediment and calcite cement. We found the range of infillings to be surprisingly diverse, even within a single conch.

4 Sherborne Stone ammonites yardHere is a collection of ammonites the workers saved from the saws and splitters.

6 Macro micro conchs FrogdenAmmonites are very common in the Sherborne quarries. On the left is the macroconch Stephanoceras with its long body chamber (the lighter-colored part) and on the right is its microconch Normannites. (Thanks to Bob Chandler for all the names.) The macroconch is most likely the female of the species, and the microconch the male, despite the different names. The ammonites are so numerous in this unit that whole breeding populations appear to be preserved.

7 Frogden nautiloid yardThis is a polished section through one of the large nautiloids we saw in the quarry yard. Not the complex infillings of the chambers, including geopetal structures indicating the orientation of the conch when filled.

8 Frogden QuarryThis is Frogden Quarry itself, which we visited this morning. The lower parts here contain the Sherborne Building Stone.

9 Frogden woodThere are many other fossils in the Sherborne units, including wood that is apparently from gingko trees.

10 Babylon Hill Road LiasIn the afternoon we visited other exposures of the Inferior Oolite and associated units, including this odd exposure on Babylon Hill. This excavation in the soft rocks of the lower Inferior Oolite and upper Lias was made by horses and carriages when this was a main road in the 19th century and earlier. A lesson in the erosion of unpaved roads without even gravel as a cover.

11 Cassidy Lias Babylon HillCassidy Jester (’17) in the Babylon Hill road exposure. A poorly-cemented sand of the Upper Lias is behind her.

12 Louse Hill quarryOur last stop of the day was an old abandoned quarry on Louse Hill. (It is pronounced “lows” and apparently has nothing to do with the parasite!). Bob Chandler is on the left, with Tim Palmer in the middle, and Cassidy on the right searching through the many fossils in the top of the Inferior Oolite. Not the best exposure, but a historically-important one.

We ended our day of exploration with a fine meal in downtown Sherborne, followed by a walk around the local medieval abbey with its rich history and, of course, diverse building stones!

Sherborne Stone crewThank you to the staff at Sherborne Stone for such fine hospitality and excellent geological observations!

Wooster’s Fossils of the Week: A bored Ordovician hardground from Ohio, and an introduction to a new paper on trace fossils and evolution

June 3rd, 2016

Bull Fork hdgdAbove is an image of a carbonate hardground (cemented seafloor) from the Upper Ordovician of Adams County, Ohio. It comes from the Bull Fork Formation and was recovered along State Route 136 north of Manchester, Ohio (Locality C/W-20). It is distinctive for two reasons: (1) the many external molds (impressions, more or less) of mollusk shells, including bivalves and long, narrow, straight nautiloids, and (2) its many small borings called Trypanites, a type of trace fossil we’ve seen on this blog before.
Bull Fork boringsIn this closer view we can see the shallow external molds of small bivalve shells, especially on the left side, and the many round perforations of the Trypanites borings.

The dissolved mollusk shells (from bivalves and nautiloids) were originally composed of the calcium carbonate mineral aragonite. This aragonite dissolved early on the seafloor, liberating calcium carbonate that quickly precipitated as the mineral calcite in the sediment, cementing it into a rocky seafloor (hardground) that was then bored by the animal that made Trypanites. This all happened because of the distinctive geochemistry of the ocean water at that time. High levels of carbon dioxide and a decreased Mg/Ca ratio dissolved aragonite yet enabled calcite (the more stable polymorph of calcium carbonate) to rapidly precipitate. This geochemical condition is known as a Calcite Sea, which was common in the early to middle Paleozoic, especially in the Ordovician. This is not the case in today’s marine waters in which aragonite is the primary calcium carbonate precipitate (“Aragonite Sea“). See Palmer et al. (1988) for more details on this process and the evidence for it.

I’m using this Ordovician carbonate hardground to introduce a new paper that just appeared this week in the Proceedings of the National Academy of Sciences (PNAS): “Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Ordovician Biodiversification Event“. The authors are the renowned trace fossil experts Luis Buatois and Gabriela Mángano, the ace geostatistician Ricardo Olea, and me. I’m excited about this paper because it adds to the literature new information and ideas about two major evolutionary radiations: the “explosion” of diversity in the Cambrian (which established basic body plans for most animals) and the diversification in the Ordovician (which filled in those body plans with abundant lower taxa). This is one of the few studies to look in detail at the trace fossil record of these events. Trace fossils (records of organism behavior in and on the sediment substrate) give us information about soft-bodied taxa otherwise rare in a fossil record dominated by shells, teeth and skeletons. It is also the first systematic attempt to compare the diversification of trace fossils in soft sediments and on hard substrates (like the hardground pictured above).

As for the paper itself, I hope you can read it. Here is the abstract —

Contrasts between the Cambrian Explosion (CE) and the Great Ordovician Biodiversification Event (GOBE) have long been recognized. Whereas the vast majority of body plans were established as a result of the CE, taxonomic increases during the GOBE were manifested at lower taxonomic levels. Assessing changes of ichnodiversity and ichnodisparity as a result of these two evolutionary events may shed light on the dynamics of both radiations. The early Cambrian (Series 1 and 2) displayed a dramatic increase in ichnodiversity and ichnodisparity in softground communities. In contrast to this evolutionary explosion in bioturbation structures, only a few Cambrian bioerosion structures are known. After the middle to late Cambrian diversity plateau, ichnodiversity in softground communities shows a continuous increase during the Ordovician in both shallow- and deep-marine environments. This Ordovician increase in bioturbation diversity was not paralleled by an equally significant increase in ichnodisparity as it was during the CE. However, hard substrate communities were significantly different during the GOBE, with an increase in ichnodiversity and ichnodisparity. Innovations in macrobioerosion clearly lagged behind animal–substrate interactions in unconsolidated sediment. The underlying causes of this evolutionary decoupling are unclear but may have involved three interrelated factors: (i) a Middle to Late Ordovician increase in available hard substrates for bioerosion, (ii) increased predation, and (iii) higher energetic requirements for bioerosion compared with bioturbation.

Thank you to Luis Buatois for his leadership on this challenging project. I very much appreciate the way this work has placed the study of trace fossils into a critical evolutionary context.
Fig1_PNASFigure 1 from Buatois et al. (2016): “Ichnodiversity changes during the Ediacaran-Ordovician. Ichnogenera were plotted as range-through data (i.e., recording for each ichnogenus its lower and upper appearances and then extrapolating the ichnogenus presence through any intervening gap in the continuity of its record).”

References:

Buatois, L.A., Mángano, M.G., Olea, R.A. and Wilson, M.A. 2016. Decoupled evolution of soft and hard substrate communities during the Cambrian Explosion and Ordovician Biodiversification Event. Proceedings of the National Academy of Sciences (in press).

Palmer, T.J., Hudson, J.D. and Wilson, M.A. 1988. Palaeoecological evidence for early aragonite dissolution in ancient calcite seas. Nature 335: 809-810.

Wilson, M.A. and Palmer, T.J. 2006. Patterns and processes in the Ordovician Bioerosion Revolution. Ichnos 13: 109-112.

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.

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