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

June 24th, 2016

1 pdt19598 D1253Deep 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 D7139Last week Paul 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.

Wooster’s Fossils of the Week: Symbiotic interactions in the Silurian of Baltica

June 17th, 2016

EcclimadictyonThis week’s fossils are from work Olev Vinn (University of Tartu, Estonia) and I did last summer that is soon to appear in the journal Lethaia. (An early electronic version of the manuscript has been available since November.) After numerous smaller studies describing symbiotic relationships recorded in Silurian fossils in the paleocontinent Baltica, we wrote a summary paper under Olev’s leadership. All the images are take by Olev and in the paper itself. I love this kind of study because it is about fossils as living, interacting organisms, not just static sets of characteristics.

For example, the top image is of the stromatoporoid Ecclimadictyon astrolaxum (a kind of hard sponge) with embedded rugosan corals (Palaeophyllum, with arrows) from the Jaagarahu Formation (Sheinwoodian) exposed at Abula cliff, Saaremaa Island, Estonia. The stromatoporoid and corals were growing together, each having their particular needs met and maybe even enhanced by the other.
syringoporidThe network of holes in this stromatoporoid from the Paadla Formation (Ludfordian) of Katri cliff, Saaremaa, represent the corallites of a syringoporid coral. Again, the coral and sponge formed an intergrown association.
ChaetosalpinxThis is a thin-section view of what was likely a soft-bodied worm (represented by Chaetosalpinx sibiriensis, noted by a white arrow) embedded in the tabulate coral Paleofavosites cf. collatatus from the Muksha Subformation (Homerian), Bagovitsa A, Podolia, Ukraine. Again, the worm was embedded in the living tissues of the host.

We found 13 such symbiotic associations in the Silurian of Baltica. Most of these interactions involved large skeletal organisms like stromatoporoids and corals, which provided stable hosts for smaller sessile filter-feeders and micro-predators. This work is part of a larger study looking at evolutionary trends in symbiotic associations during the Paleozoic.

References:

Tapanila, L. 2005. Palaeoecology and diversity of endosymbionts in Palaeozoic marine invertebrates: trace fossil evidence. Lethaia 38: 89–99.

Vinn, O. and Wilson, M.A. 2016. Symbiotic interactions in the Silurian of Baltica. Lethaia 49: 413–420.

Vinn, O., Wilson, M.A. and Motus, M.-A. 2014. Symbiotic endobiont biofacies in the Silurian of Baltica. Palaeogeography, Palaeoclimatology, Palaeoecology 404: 24–29.

Wooster’s Fossil of the Week: A 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.

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.

Wooster’s Fossil of the Week: A Recent Sponge Boring from South Carolina

May 13th, 2016

1 Coral on bored bivalveWe’re not actually looking at fossils here, but this bivalve-coral-sponge assemblage from the very modern Myrtle Beach in South Carolina is to cool not to share. Jacob Nowell (Wooster ’18) picked it up while on Spring Break this year and donated it to the collections. This is a bit of very worn bivalve shell punctured by clionaid sponge borings and encrusted by a columnar scleractinian coral.

2 Bored bivalve hingeHow do we know the shell remnant is from a bivalve? This is what’s left of the hinge region, the thickest part of the shell. We can tell this is a heterodont bivalve, probably of the common genus Mercenaria. The shell material is calcite.

3 Coral over EntobiaThe coral is aragonitic and exquisitely preserved. It did not make the long tumbling journey the bivalve shell did. At its encrusting base you can see that it partially covers some of the sponge borings, showing that it attached after the sponge was at least partly gone. The round structures on the coral are the corallites, each of which housed a coral polyp. The corallites have radiating vertical septa inside in the classic scleractinian manner.

4 Entobia gallery 041316 585The sponge boring is the star here. This is a side view showing the interconnected galleries and tunnels excavated by a clionaid sponge like Cliona. As a trace fossil this structure would be known as Entobia. It is very common in the fossil record, especially in the Cretaceous and later.

Bronn 041616Entobia was named and described by Heinrich Georg Bronn (1800-1862), a German geologist and paleontologist. He had a doctoral degree from the University of Heidelberg, where he then taught as a professor of natural history until his death. He was a visionary scientist who had some interesting pre-Darwinian ideas about life’s history. He didn’t fully accept “Darwinism” at the end of his life, but he made the first translation of On The Origin of Species into German.

References:

Bromley, R.G. 1970. Borings as trace fossils and Entobia cretacea Portlock, as an example. Geological Journal, Special Issue 3: 49–90.

Bronn, H.G. 1834-1838. Letkaea Geognostica (2 vols., Stuttgart).

Tapanila, L. 2006. Devonian Entobia borings from Nevada, with a revision of Topsentopsis. Journal of Paleontology 80: 760–767.

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

Wilson, M.A. 2007. Macroborings and the evolution of bioerosion, p. 356-367. In: Miller, W. III (ed.), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, 611 pages.

 

Wooster’s Fossil of the Week: A craniid brachiopod from the Upper Cretaceous of The Netherlands

May 6th, 2016

1 Isocrania costata Sowerby 1823 double 2 smThese striking little brachiopods are gifts from Clive Champion, a generous Englishman with whom I occasionally exchange packets of fossils. In January I received a surprise box with lots of delicious little brachs, including the two shown above. I remember this type well from a field trip I had to the Upper Cretaceous of The Netherlands.
2 Isocrania costata Sowerby 1823 double 1 smHere we see the reverse sides of the shells at the top. These are most likely dorsal valves of Isocrania costata Sowerby, 1823, from the Lichtenberg Horizon, Upper Maastrichtian (Upper Cretaceous) of the ENCI Quarry near Maastricht, The Netherlands. It is possible they are the closely-related species Isocrania sendeni Simon, 2007, but we don’t have enough material to sort this out.
4 Surlyk 1973 fig 2 copyCraniid brachiopods usually live out their lives attached to hard substrates, as with this Ordovician example. This species of Isocrania, however, was only attached to shelly debris on the seafloor for a short time, outgrowing its substrate early and then living free in the chalky sediment. The above reconstruction image is Figure 2 from Surlyk (1973).

Christian Emig (2009) has a bit of folklore about Isocrania. In medieval Sweden these fossils were called “Brattingsborg pennies” for their size, shape and the face-like image on their interiors. Don’t see the face? Check this out from Emig (2009):
5 Ventral C craniolaris fig 6 SurlykThe “eyes” in this ventral valve are large adductor muscle scars, and the “mouth” and “nose” are a smaller set. Here is one of the “Brattingsborg pennies” legends Emig (2009) relates —

“… at the beginning of the 13th century the archbishop Anders Sunesen spent his last days on the island of Ivö, in his own castle of which the cellar was about 2 km southeast of the castle. In 1221, subjected to the terminal stages of leprosy, he spent his last days on the island. One day he was informed that warriors had stolen a large sum of money from the Brattingsborg castle. They spent that night gambling and carousing in the cellar. The archbishop cursed this money and the following morning the warriors were stunned to find that the coins had turned into stones with a laughing death’s-head on them.”

Thanks for starting us on this trip with your gift, Clive!
3 Isocrania costata Sowerby 1823 sm
References:

Emig, C. 2009. Nummulus brattenburgensis and Crania craniolaris (Brachiopoda, Craniidae). Carnets de Géologie/Notebooks on Geology, Brest, Article, 8.

Hansen, T., and Surlyk, F. 2014. Marine macrofossil communities in the uppermost Maastrichtian chalk of Stevns Klint, Denmark. Palaeogeography, Palaeoclimatology, Palaeoecology 399: 323-344.

Simon, E. 2007. A new Late Maastrichtian species of Isocrania (Brachiopoda, Craniidae) from The Netherlands and Belgium. Bulletin de l’Institut royal des Sciences naturelles de Belgique, Sciences de la Terre 77: 141-157.

Surlyk, F. 1973. Autecology and taxonomy of two Upper Cretaceous craniacean brachiopods. Bulletin of the Geological Society of Denmark 22: 219-242.

Wooster’s Fossil of the Week: A terebratulid brachiopod from the Middle Jurassic of northwestern France

April 29th, 2016

1 Cererithyris arkelli Almeras 1970 dorsal 585We have another beautiful brachiopod this week from our friend Mr. Clive Champion in England. He sent me a surprise package of fossils earlier this year. They are very much appreciated by me and my students!

The specimen above is Cererithyris arkelli Almeras, 1970, from the Bathonian (Middle Jurassic) of Ranville, Calvados, France. (Ranville, by the way, was the first village liberated in France on D-Day.) It is a terebratulid brachiopod, which we have seen before on this blog from the Miocene of Spain and the Triassic of Israel. They have the classic brachiopod form. The image above shows the dorsal valve with the posterior of the ventral valve housing the round hole for the fleshy stalk (pedicle) it had in life.
2 Cererithyris arkelli Almeras 1970 sideThis is a side view of C. arkelli. The dorsal valve is on the top; the ventral valve on the bottom. It is from this perspective that brachiopods were called “lamp shells” because they resemble Roman oil lamps.
3 Cererithyris arkelli Almeras 1970 ventralThis is the ventral view of the specimen. These brachiopods are remarkably smooth.
4 William_Joscelyn_ArkellCererithyris arkelli was named by Almeras (1970) in honor of William Joscelyn Arkell (1904–1958). Arkell was an English geologist who essentially became Dr. Jurassic during the middle part of the 20th Century. I’m shocked to see that with all his publications, awards and accomplishments, he died when he was only 54 years old.

W.J. Arkell grew up in Wiltshire, the seventh child of a wealthy father (a partner in the family-owned Arkell’s Brewery) and artist mother (Laura Jane Arkell). He enjoyed nature as a child, winning essay contests on his observations of natural history in his native county and south on the Dorset coast. Arkell was unusually tall for his age (6 feet 4.5 inches by age 17.5 years in an unusually detailed note) and was considered to have “outgrown his strength”. Nature and writing were escapes from athletic events. He also published poems.

Arkell attended New College, Oxford University, intending to become an entomologist, but Julian Huxley was his tutor and he quickly adopted geology and paleontology. Eventually he earned a PhD at Oxford in 1928, concentrating his research on Corallian (Upper Jurassic) bivalves of England. As a side project, he published work on Paleolithic human skeletons from northern Egypt.

Oxford suited Arkell, so he stayed there as a research fellow, expanding his research to the entire Jurassic System of Great Britain, then Europe, and then the world. His work became the standard for understanding Jurassic geology and paleontology for decades.

After World War II (in which he served in the Ministry of Transport), Arkell took a senior research position at Trinity College and the Sedgwick Museum, Cambridge University, continuing his work on the Jurassic. He travelled often, including long stints in the Middle East. His health was never good, though, and he had a stroke in 1956, and died after a second stroke in 1958.

During his career Arkell received the Mary Clark Thompson Medal from the National Academy of Sciences in the USA, a Fellowship in the Royal Society, the Lyell Medal from the Geological Society of London, and the Leopold von Buch medal from the German Geological Society.

References:

Almeras, Y. 1970. Les Terebratulidae du Dogger dans le Mâconnais, le Mont dʼOr lyonnais et le Jura méridional. Étude systématique et biostratigraphique. Rapports avec la paléoécologie. Documents des Laboratoires de Géologie Lyon, 39, 3 vol.: 1-690.

Arkell, W.J. 1956. Jurassic Geology of the World. New York; Edinburgh: Hafner Publishing Co; Oliver & Boyd; 806 pp.

Cox, L.R. 1958. William Joscelyn Arkell 1904-1958. Biographical Memoirs of Fellows of the Royal Society 4: 1.

Rousselle, L. and Chavanon, S. 1981. Le genre Cererithyris (Brachiopodes, Terebratulidae) dans le Bajocien supérieur et le Bathonien des Hauts-Plateaux du Maroc oriental. CR somm. Soc. Géol France, 1981: 89-92.

Wooster’s Fossil of the Week: A thoroughly encrusted rugose coral from the Upper Ordovician of southeastern Indiana

April 22nd, 2016

1 Rugosan Exterior 123015It doesn’t look like much, this long lump of gray stone. With a close view you might pick up a hint of a bryozoan or two, but mostly we see rather shabby shades of grey. One of the coolest perks of being a geologist, though, is that you get to use a saw to cut rocks in half to see what’s inside. So that’s what I did with this specimen from the Whitewater Formation (Upper Ordovician) of southeastern Indiana at a site we’ve visited often.

2 Rugosan interior 123015In this cross-section we see first a long, cone-shaped fossil made of white calcite. It is the rugose coral Grewingkia canadensis, one of the most common fossils in the upper part of the Upper Ordovician. This coral in life would have stood upright like an ice cream cone, spreading the tentacles of its polyp to catch very small swimming prey (and maybe to do a bit of symbiotic photosynthesis). The polyp sat in the cup-like cavity on the expanded end of the cone. The coral evidently died on the Ordovician seafloor and toppled over to be encrusted on one side, presumably the one that faced upwards.

3 Coral Bryo Sed BryoThis is a closer view of the cross-section showing the encrustations on the rugose coral skeleton. The image is annotated below.

4 Coral Bryo Sed Bryo annotatedThe coral skeleton in the lower right was first encrusted by a trepostome bryozoan, which you can recognize by the tubes (zooecia) extending perpendicular from the substrate. This bryozoan is thickest on the upwards-facing surface of the coral, and it thins as it wraps around and then colonizes the cryptic space beneath (but not too far). This bryozoan is covered with a layer of sediment which appears to have rapidly cemented in place (a function of Calcite Sea geochemistry). The sediment then is encrusted by a another trepostome bryozoan with long zooecia and several layers.

5 Bryo Sed 123015In this closer view of the second bryozoan you can see that its base is irregular as it grew across the rough cemented sediment surface. In the middle of this view some of the bryozoan zooecia are occupied by dark spots known as brown bodies. These are likely the remains of bryozoan polypides (main parts of the individual zooids) that were sealed into their zooecia by some disturbance. In this case the whitish bit of sediment above the cluster may represent something that settled on the colony, stopping the growth of the zooecia below, and forcing those nearby to grow around it.

6 Borings 123015Moving down the coral skeleton away from its opening we come across borings drilled down through the coral skeleton (the white mass at the bottom of the image). The conical, large boring is filled with golden crystals of the mineral dolomite, which were formed long after burial. The shape of this boring is unusual. Typical borings in these corals have straight parallel sides, but this boring is cone-shaped. We’ll see if we can find more like it to get a better idea of its shape and distribution.

This week’s fossil, then, is a demonstration of the hidden wonders sometimes found in even the dullest of grey rocks!

 

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