Wooster’s Fossil of the Week: A Biserial Graptolite (Middle Ordovician of Tennessee)

April 21st, 2017

This week’s fossils are graptolites (from the Greek for written rocks) I found many years ago in the Lebanon Limestone near the town of Caney Springs south of Nashville, Tennessee. They are of the genus Amplexograptus and probably belong to the species A. perexcavatus (Lapworth, 1876).

Graptolites were colonial organisms consisting of hundreds and sometimes thousands of tiny zooids (individuals) connected together in a flexible proteinaceous skeleton (the rhabdosome). They first appeared in the Late Cambrian (around 510 million years ago) and disappeared forever in the Early Carboniferous (around 350 million years ago). Amplexograptus colonies were probably attached to floats so they could drift through the ancient oceans filtering out organic particles; they would be officially “passively mobile planktonic suspension feeders”. They belong to the Phylum Hemichordata, although there have always been disputes about their actual evolutionary relationships. This matters because graptolites are important index fossils for sorting out the age relationships of Lower and Middle Paleozoic rocks.

Graptolites are usually preserved as thin carbonaceous films on dark shales, making them rather hard to see (as my paleontology students will readily agree). The great 18th Century naturalist Linnaeus even said that they were “pictures resembling fossils rather than true fossils”. Sometimes, though, they are found in lighter-colored rocks like limestones, as above. Goldman et al. (2002) found Amplexograptus in limestones preserved in three dimensions, possibly because the limestones were cemented early around them before they collapsed with decay. They even studied this same species from the Lebanon Limestone. The 3-D preservation allows for a much more detailed analysis of the tiny cups (thecae) which held the individual zooids. It is possible that I could dissolve the limestone shown above and retrieve some delicate three-dimensional graptolites — but I could also just as easily destroy them.

Amplexograptus perexcavatus was originally described in 1876 by the famous geologist Charles Lapworth (1842-1920), who referred it to the genus Diplograptus. Actually, he had two species in his D. perexcavatus group, so it took some taxonomic detective and legal work to fix the current naming system. Lapworth, who I’ve figured below with an inset of his not-very-helpful diagram of the original D. perexcavatus, is well known by paleontologists for his work with graptolites as index fossils. Scientists and historians of science know him as the man who invented the Ordovician Period in 1879 to solve a bitter dispute between Roderick Murchison and Adam Sedgwick who each claimed the same rock interval in Wales for the Silurian and Cambrian periods respectively. Lapworth’s primary biostratigraphic argument for the Ordovician as a separate period was the distribution of graptolites, including our friend Amplexograptus perexcavatus. (Murchison and Sedgwick were long gone by the time their dispute was settled.)

(Charles Lapworth. Image courtesy of The Lapworth Museum of Geology.)

References:

Goldman, D., Campbell, S.M. and Rahl, J.M. 2002. Three-dimensionally preserved specimens of Amplexograptus (Ordovician, Graptolithina) from the North American mid-continent: taxonomic and biostratigraphic significance. Journal of Paleontology 76: 921-927.

Lapworth, C. 1876. The Silurian System in the South of Scotland, p. 1–28. In: Armstrong, J. Young, J. and Robertson, D. (eds.), Catalogue of Western Scottish Fossils. Blackie and Son, Glasgow.

[Originally posted August 28, 2011]

Wooster’s Fossil of the Week: A Conulariid (Lower Carboniferous of Indiana)

April 14th, 2017

I have some affection for these odd fossils, the conulariids. When I was a student in the Invertebrate Paleontology course taught Dr. Richard Osgood, Jr., I did my research paper on them. I had recently found a specimen in the nearby Lodi City Park. It was so different from anything I had seen that I wanted to know much more. I championed the then controversial idea that they were extinct scyphozoans (a type of cnidarian including most of what we call today the jellyfish). That is now the most popular placement for these creatures today, although I arrived at the same place mostly by luck and naïveté. (I love the critical marks in that word! And yes, I always have to look them up.)

The specimen above is Paraconularia newberryi (Winchell) found somewhere in Indiana and added to the Wooster fossil collections before 1974. (The scale below it is in millimeters.) A close view (below) shows the characteristic ridges with a central seam on one of the sides.
Conulariids range from the Ediacaran (about 550 million years ago) to the Late Triassic (about 200 million years ago). They survived three major extinctions (end-Ordovician, Late Devonian, end-Permian), which is remarkable considering the company they kept in their shallow marine environments suffered greatly. Why they went extinct in the Triassic is a mystery.

The primary oddity about conulariids is their four-fold symmetry. They had four flat sides that came together something like an inverted and extended pyramid. The wide end was opened like an aperture, although sometimes closed by four flaps. Preservation of some soft tissues shows that tentacles extended from this opening. Their exoskeleton was made of a leathery periderm with phosphatic strengthening rods rather than the typical calcite or aragonite. (Some even preserve a kind of pearl in their interiors.) Conulariids may have spent at least part of their life cycle attached to a substrate as shown below, and maybe also later as free-swimming jellyfish-like forms.

It is the four-fold symmetry and preservation of tentacles that most paleontologists see as supporting the case for a scyphozoan placement of the conulariids. Debates continue, though, with some seeing them as belonging to a separate phylum unrelated to any cnidarians. This is what’s fun about extinct and unusual animals — so much room for speculative conversations!

[Thanks to Consuelo Sendino of The Natural History Museum (London) for correcting the age range of these fascinating organisms.]

References:

Hughes, N.C., Gunderson, G.D. and Weedon, M.J. 2000. Late Cambrian conulariids from Wisconsin and Minnesota. Journal of Paleontology 74: 828-838.

Van Iten, H. 1991. Evolutionary affinities of conulariids, p. 145-155; in Simonetta, A.M. and Conway Morris, S. (eds.). The Early Evolution of Metazoa and the Significance of Problematic Taxa. Cambridge University Press, Cambridge.

[Modified from an original post on July 31, 2011]

Wooster’s Fossils of the Week: Bivalve escape trace fossils (Devonian and Cretaceous)

April 7th, 2017

It is time again to dip into the wonderful world of trace fossils. These are tracks, trails, burrows and other evidence of organism behavior. The specimen above is an example. It is Lockeia James, 1879, from the Dakota Formation (Upper Cretaceous). These are traces attributed to infaunal (living within the sediment) bivalves trying to escape deeper burial by storm-deposited sediment. If you look closely, you can see thin horizontal lines made by the clams as they pushed upwards. These structures belong to a behavioral category called Fugichnia (from the Latin fug for “flee”). They are excellent evidence for … you guessed it … ancient storms.
The specimens above are also Lockeia, but from much older rocks (the Chagrin Shale, Upper Devonian of northeastern Ohio). Both slabs show the fossil traces preserved in reverse as sediment that filled the holes rather than the holes themselves. These are the bottoms of the sedimentary beds. We call this preservation, in our most excellent paleontological terminology, convex hyporelief. (Convex for sticking out; hyporelief for being on the underside of the bed.)

The traces we know as Lockeia are sometimes incorrectly referred to as Pelecypodichnus, but Lockeia has ichnotaxonomic priority (it was the earliest name). Maples and West (1989) sort that out for us.
Uriah Pierson James (1811-1889) named Lockeia. He was one of the great amateur Cincinnatian fossil collectors and chroniclers. In 1845, he guided the premier geologist of the time, Charles Lyell, through the Cincinnati hills examining the spectacular Ordovician fossils there. He was the father of Joseph Francis James (1857-1897), one of the early systematic ichnologists.

References:

James, U.P. 1879. The Paleontologist, No. 3. Privately published, Cincinnati, Ohio. p. 17-24.

Maples, C.G. and Ronald R. West, R.R. 1989. Lockeia, not Pelecypodichnus. Journal of Paleontology 63: 694-696.

Radley, J.D., Barker, M.J. and Munt, M.C. 1998. Bivalve trace fossils (Lockeia) from the Barnes High Sandstone (Wealden Group, Lower Cretaceous) of the Wessex Sub-basin, southern England. Cretaceous Research 19: 505-509.

[Originally published January 29, 2012]

Wooster’s Fossils of the Week: A slab of Upper Ordovician bivalves from northern Kentucky

March 31st, 2017

Earlier this month, Luke Kosowatz, Matt Shearer and I went on a field trip through the Cincinnati region collecting Upper Ordovician (Katian) bryozoans and examples of bioerosion for their Independent Study projects and other investigations. I picked up the above slab and put it in our vehicle for future study not because of its beauty, but the preservational modes it displays. The black, rounded objects are bivalves, probably of the Order Modiomorphida. They are miserable fossils to identify because they originally had shells made of the mineral aragonite, which dissolved quickly after the animals died. What is left are a few scrappy molds and that black film. This is a common preservation of bivalves in the Cincinnatian.

This is the Corryville Formation outcrop from which the slab came. It is just west of Maysville, Kentucky, along the AA Highway (N 38.60750°, W 83.76775°; C/W-740).

Here is the slab along the roadside before we cleaned it up. Not much to see, really, except the low-relief black blobs that are remains of bivalves.

As you see, not much detail in the bivalves other than an outline matching somewhat the modiomorphids. Those of you with sharp paleontological eyes will note a round gray patch with radiating lines. This is a bryozoan that was attached to the bivalve shell. When the shell dissolved, the bryozoan attachment surface became visible. In other words, this is an upside-down encrusting bryozoan, a condition we’ve seen several times in this blog.

Here’s another bivalve with an upside-down encrusting bryozoan. This time you can see that the black film was underneath the bryozoan and on the outside of the bivalve shell. In a 2004 paper, Tim Palmer and I wrote: “We have also long been curious about why some of the epifaunal aragonitic Ordovician genera in the Cincinnatian such as Modiolopsis are preserved with a thick black outer shell covering (e.g. Pojeta 1971, pl. 15, fig. 6). It now seems likely that this was a hypertrophied periostracum that conferred some protection against dissolution during life, similar to the situation seen in Recent unionids that are susceptible to dissolution in their fresh-water habitats” (p. 425). Maybe it’s time we followed up on these speculations? I’m sure other paleontologists have had similar ideas.

Among the indistinct modiomorphid bivalves is this old friend: Ambonychia with its characteristic radiating ridges.

References:

Palmer, T.J. and Wilson, M.A. 2004. Calcite precipitation and dissolution of biogenic aragonite in shallow Ordovician calcite seas. Lethaia 37: 417-427.
Pojeta, J. 1971. Review of Ordovician pelecypods. United States Geological Survey, Professional Paper 695, 1-46.

Wooster’s Fossils of the Week: Strophomenid brachiopods from the Upper Ordovician of southern Ohio

March 24th, 2017

Usually I find fossils in the field or lab and then craft a Fossil of the Week entry around them. This time, though, I started with a paper and then searched for fossils to illustrate it. I found this recent paper very well done:

Bauer, J.E. and Stigall, A.L. 2016. A combined morphometric and phylogenetic revision of the Late Ordovician brachiopod genera Eochonetes and Thaerodonta. Journal of Paleontology 90: 888-909.

It does classic systematics on a group of brachiopods with the modern tools of morphometric and phylogenetic analyses. Its conclusions are direct and convincing: The genus Thaerodonta is synonymous with Eochonetes, and a variety of species are shifted around, solving problems that have lingered for over a century, Plus as a bonus, who can’t love a new species named Eochonetes voldemortus? So I set out to find specimens of this brachiopod group in our collections. Above are internal valve views of the brachiopod Eochonetes clarksvillensis (Foerste, 1912), showing characteristic denticles (little teeth) along the hinge line. Below are external valve views. Jen Bauer herself kindly confirmed the identifications!

These specimens come from the Waynesville Formation (Katian) exposed at Caesar Creek in southern Ohio, a place we have had many paleontology field trips. E. clarksvillensis is common in the Waynesville and overlying Liberty formations. Read much more about it in Bauer and Stigall (2016).

The genus Eochonetes was named by Frederick Richard Cowper Reed in 1917 from the Ordovician of Scotland. (The British Isles were not too far away from Ohio in the Late Ordovician.) Reed was born in London in 1869 and died in Cambridge, England, in 1946. I tried mightily but could find no images of him to enter into the digital archives of the web. He was a smart and diverse geologist, attending Trinity College, Cambridge, and winning important awards and scholarships. He was appointed assistant to the Woodwardian Professor of Geology at Cambridge in 1892, a position he kept until retirement. In 1901 he earned the Sedgwick Prize for his work on the rivers of East Yorkshire, wrote a book on the geology of the British Empire (much easier to do today!), and yet still found time to describe fossils in numerous papers.

The author of Eochonetes clarksvillensis is much better known to paleontologists of the Cincinnati region. It is August F. Foerste (1862-1936), who named Thaerodonta clarksvillensis in 1912. Foerste grew up and worked in the Dayton, Ohio, area, graduating from Denison University after publishing many papers as a student. He returned to Dayton after earning a PhD from Harvard, teaching high school for 38 years. When he retired he turned down a teaching position at the University of Chicago and instead worked at the Smithsonian Institution until the end of his life. He is one of the giants of the Cincinnati School of paleontology.

References:

Bauer, J.E. and Stigall, A.L. 2016. A combined morphometric and phylogenetic revision of the Late Ordovician brachiopod genera Eochonetes and Thaerodonta. Journal of Paleontology 90: 888-909.

Reed, F.R.C. 1917. The Ordovician and Silurian Brachiopoda of the Girvan District: Transactions of the Royal Society of Edinburgh 51: 795–998.

Wooster’s Fossil of the Week: A large trepostome bryozoan on a nautiloid conch (Upper Ordovician of northern Kentucky)

March 17th, 2017

This massive trepostome bryozoan, a solid lump of biogenic calcite, was collected earlier this week on the latest Team Cincinnati field expedition into the treasure-filled Upper Ordovician underlying and surrounding that city. Wooster students Matt Shearer, Luke Kosowatz and I are pursuing projects related to trepostome bryozoans and bioerosion (the biological destruction of hard substrates). The above specimen combines both these worlds, and more. Note the concavity at the base of the specimen. It comes from the Bellevue Formation (Katian) exposed on Bullitsville Road near the infamous Creation Museum (C/W-152).

Underneath the bryozoan colony (its zoarium) is this conical impression. It is an external mold of a straight nautiloid conch, the shell of a common squid-like cephalopod during the Ordovician. After the death of the nautiloid its empty tubular conch rested on the seafloor. This hard surface attracted the larvae of a variety of bryozoans that spread their calcitic zoaria (colonial skeletons) across the surface. Eventually one trepostome bryozoan species gained dominance over the space and occupied it all, growing into the large colony we see today. It even wrapped around the aperture of the conch (on the left) and grew a bit into the tube. Since the nautiloid conch was made of unstable aragonite, it long ago dissolved away, leaving an impression (external mold) in the stable calcite of the bryozoan.

How do we know there were earlier generations of bryozoans on this conch? We see them exposed upside-down on the surface of the external mold. Above we see the thin, branching cyclostome bryozoan Cuffeyella in the foreground, with a sheet of an encrusting trepostome bryozoan in the background. There are several other earlier bryozoans visible on this surface, revealing an ecological succession. There may be soft-bodied organisms preserved on this surface as well. This locality yielded the first described specimens of bioimmuration in the Ordovician (see Wilson et al., 1994).

There were other large trepostome bryozoans found in this same locality. I couldn’t resist cutting one in half to see what the inside looked like.

In this close view of the cross-section through the calcitic trepostome bryozoan we see numerous round holes drilled by some sort of worm seeking protective space so it could filter-feed. (In other words, it was not preying on the bryozoan.) The most intense boring of the specimen appears to have taken place just before and after the death of the colony. We know some borings were excavated into living bryozoan skeleton because the bryozoan formed reactive tissue around the intruder. The very tiny reddish-brown dots scattered in layers are “brown bodies“, the organic remnants of bryozoan polypides in their skeletal tubes (zooecia).

It has been a pleasure to return to the extraordinary Cincinnati fossils!

References:

Taylor, P.D. 1990. Preservation of soft-bodied and other organisms by bioimmuration—a review. Palaeontology 33: 1-17.

Wilson, M.A. 1985. Disturbance and ecologic succession in an Upper Ordovician cobble-dwelling hardground fauna. Science 228: 575-577.

Wilson, M.A., Palmer, T.J. and Taylor, P.D. 1994. Earliest preservation of soft-bodied fossils by epibiont bioimmuration: Upper Ordovician of Kentucky. Lethaia 27: 269-270.

Wooster’s Fossil of the Week: Encrusting craniid brachiopods (Upper Ordovician of southeastern Indiana)

March 10th, 2017

The two irregular patches above are brachiopods known as Petrocrania scabiosa encrusting the ventral valve of yet another brachiopod (Rafinesquina). That species name “scabiosa” is evocative if not a little unpleasant — it is also the root of the English “scab”.

Petrocrania scabiosa is in a group of brachiopods we used to call “inarticulates” because their two valves are not articulated by a hinge as they are in most brachiopods. Instead they are held together by a complex set of muscles. Now we place these brachiopods in the Class Craniforma, an ancient group which originated in the Cambrian and is still alive today.

Petrocrania scabiosa was a filter-feeder like all other brachiopods, extracting nutrients from the seawater with a fleshy lophophore. The Wooster specimens are part of our large set of encrusting fossils (a type of sclerobiont) in our hard substrate collection. They have irregular shells that are circular in outline when they grew alone, and angular when they grew against each other.

Some craniid brachiopods were so thin that their shells repeated the features of the substrate underneath them, a phenomenon known as xenomorphism (“foreign-form”).

Petrocrania scabiosa brachiopods (circular) on a Rafinesquina brachiopod, along with a trepostome bryozoan that encrusted some brachiopods and grew around others. The P. scabiosa on the far left shows xenomorphic features. Specimen borrowed from the University of Cincinnati paleontology collections.

A 2007 College of Wooster paleontology field trip to the Upper Ordovician locality near Richmond, Indiana, where these specimens were found. Students are in the traditional paleontological poses.

[Originally published May 22, 2011.]

Wooster’s Fossil of the Week: Mysterious tentaculitids (Devonian of Maryland)

March 3rd, 2017

The sharp little conical fossils above are common Paleozoic fossils, especially in the Devonian. They are tentaculitids now most commonly placed in the Class Tentaculitoidea Ljashenko 1957. Tentaculitids appeared in the Ordovician and disappeared sometime around the end of the Carboniferous and beginning of the Permian. These specimens are from the Devonian of Maryland.

The systematic placement of the tentaculitids has been controversial. Their straight, narrow shells are usually ornamented by concentric rings, and many had septa (thin shelly partitions) inside the cones. The microstructure of the shells is most interesting — it looks very much like that of brachiopods and bryozoans. For this reason and several others, several of my colleagues and I believe the tentaculitids were lophophorates (animals that filter-feed with a tentacular device called a lophophore). They may thus be related to other problematic tubeworms like microconchids and cornulitids (Taylor et al., 2010).

Tentaculitids from the New Creek Limestone (Lochkovian, Early Devonian) of New Creek, West Virginia.

Knowing how the tentaculitids fit into an evolutionary scheme, though, has not helped us figure out what they did for a living. The figure below, from Cornell et al. (2003), shows these funny cones in just about every lifestyle imaginable!

References:

Cornell, S.R., Brett, C.E. and Sumrall, C.D. 2003. Paleoecology and taphonomy of an edrioasteroid-dominated hardground association from tentaculitid limestones in the Early Devonian of New York: A Paleozoic rocky peritidal community. Palaios 18: 212-224.

Taylor, P.D., Vinn, O. and Wilson, M.A. 2010. Evolution of biomineralization in ‘lophophorates’. Special Papers in Palaeontology 84: 317-333.

[Originally published May 29, 2011.]

Wooster’s Fossil of the Week: A scaphitid ammonite (Late Cretaceous of Mississippi)

February 24th, 2017

The beauty above is Discoscaphites iris (Conrad, 1858) from the Owl Creek Formation of Ripley, Mississippi. Megan Innis and I collected it during our expedition to the Cretaceous-Paleogene boundary in the southern United States last summer. It is a significant index fossil in biostratigraphy: the Discoscaphites iris Zone is the latest in the Cretaceous (the late Maastrichtian Stage). This animal lived in the final days of the Mesozoic Era just before the mass extinction 65.5 million years ago.

Discoscaphites iris is an ammonite, a type of extinct cephalopod mollusk related to the modern octopus, squid and nautilus. It had a planispirally-coiled shell with chambers divided from each other by complexly-folded walls. If you look closely near the top of the fossil above, you will see where the shell has flaked away revealing an internal mold of sediment and a peek at the folded walls inside. “Ammonite”, by the way, is a very old term for these fossils. Pliny the Elder himself used a variant of the name, which comes from the Egyptian god Amun with his occasional coiled ram’s horn headgear.

Reconstruction of an ammonite by Arthur Weasley (via Wikipedia).

Ammonite shells were made of the carbonate mineral aragonite. This is the mineral that makes many modern mollusk shells have prismatic colors, which we call nacreous. You may know it best as “mother of pearl” or as pearls themselves. Aragonite has an unstable crystal structure and so is not common in rocks older than a few million years. The original aragonite in our ammonite fossil is thus a bonus.

In an oddly topical note, Discoscaphites iris was recently found in the Upper Cretaceous of Libya, giving it a disjunct range from the US Gulf and Atlantic coasts to the Mediterranean coast of northern Africa (Machalski et al., 2009).

Reference:

Machalski, M., Jagt, J.W.M., Landman, N.H. and Uberna, J., 2009. First record of the North American scaphitid ammonite Discoscaphites iris from the upper Maastrichtian of Libya. N. Jb. Geol. Paläont. Abh. 254: 373-378.

[Originally published April 24, 2011]

Wooster’s Fossil of the Week: A stromatoporoid (Middle Devonian of central Ohio)

February 17th, 2017

Stromatoporoids are very common fossils in the Silurian and Devonian of Ohio and Indiana, especially in carbonate rocks like the Columbus Limestone (from which the above specimen was collected). Wooster geologists encountered them frequently on our Estonia expeditions in the last few years, and we worked with at least their functional equivalents in the Jurassic of Israel (Wilson et al., 2008).

For their abundance, though, stromatoporoids still are a bit mysterious. We know for sure that they were marine animals of some kind, and they formed reefs in clear, warm seas rich in calcium carbonate (DaSilva et al., 2011). Because of this tropical habit, early workers believed they were some kind of coral, but now most paleontologists believe they were sponges. Stromatoporoids appear in the Ordovician and are abundant into the Early Carboniferous. The group seems to disappear until the Mesozoic, when they again become common with the same form and life habits lasting until extinction in the Late Cretaceous (Stearn et al., 1999).

The typical stromatoporoid has a thick skeleton of calcite with horizontal laminae, vertical pillars, mounds on the upper surface called mamelons, and dendritic canals called astrorhizae shallowly inscribed on the mamelons. These astrorhizae are the key to deciphering what the stromatoproids. They are very similar to those on modern hard sponges called sclerosponges. Stromatoporoids appear to be a kind of sclerosponge with a few significant differences (like a calcitic instead of an aragonitic skeleton).

Stromatoporoid anatomy from Boardman et al. (1987).

Top surface of a stromatoporoid from the Columbus Limestone showing the mamelons.

There is considerable debate about whether the Paleozoic stromatoporoids are really ancestral to the Mesozoic versions. There may instead be some kind of evolutionary convergence between two groups of hard sponges. The arguments are usually at the microscopic level!

The stromatoporoids were originally named by Nicholson and Murie in 1878. This gives us a chance to introduce another 19th Century paleontologist whose name we often see on common fossil taxa: Henry Alleyne Nicholson (1844-1899). Nicholson was a biologist and geologist born in England and educated in Germany and Scotland. He was an accomplished writer, authoring several popular textbooks, and a spectacular artist of the natural world. Nicholson taught in many universities in Canada and Great Britain, finally ending his career as Regius Professor of Natural History at the University of Aberdeen.

Henry Alleyne Nicholson (1844-1899) from the University of Aberdeen museum website.

References:

Boardman, R.S., Cheetham, A.H. and Rowell, A.J. 1987. Fossil Invertebrates. Wiley Publishers. 728 pages.

DaSilva, A., Kershaw, S. and Boulvain, F. 2011. Stromatoporoid palaeoecology in the Frasnian (Upper Devonian) Belgian platform, and its applications in interpretation of carbonate platform environments. Palaeontology 54: 883–905.

Nicholson, H.A. and Murie, J. 1878. On the minute structure of Stromatopora and its allies. Linnean Society, Journal of Zoology 14: 187-246.

Stearn, C.W., Webby, B.D., Nestor, H. and Stock, C.W. 1999. Revised classification and terminology of Palaeozoic stromatoporoids. Acta Palaeontologica Polonica 44: 1-70.

Wilson, M.A., Feldman, H.R., Bowen, J.C. and Avni, Y. 2008. A new equatorial, very shallow marine sclerozoan fauna from the Middle Jurassic (late Callovian) of southern Israel. Palaeogeography, Palaeoclimatology, Palaeoecology 263: 24-29.

[Originally published on October 30, 2011]

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