Archive for February, 2017

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]

Coring the Bog – An 18,000 Year Record of Environmental Change

February 13th, 2017

Two class projects kick off the Climate Change 2017 course. The first deals with tree-ring dating (dendrochronology, blog post coming soon) of historical structures and then analyzing the tree-rings for their climate significance. The second is is shown below and it concerned with analyzing sediment cores from Browns Lake Bog that document climate variability since the last Ice Age. Below are some photos of the bog coring – great thanks to Dr. Tom Lowell and his Glacial Geology class from the University of Cincinnati – the folks who did most of the work.

Setting up the coring rig at Browns Lake – early in the day snow covered the ground by 4 pm it was gone (albedo feedback in play).

The core boss (Dr. Tom Lowell) oversees the extraction of another meter of mud from the bog.

The probing team sends down 7 rods through the mud until refusal. Mapping the mud thickness gives an idea of the geometry of the bog and allows for the construction of an isopach map.

Extracting peat – the upper 5 meters or so are peat (significant amount of sphagnum moss and carbon). Note the trees, it is not a sphagnum bog now here.

Setting up the production line and assigning teams and tasks.

Coring a tree to determine the recruitment time – the hypothesis is that these trees moved into the bog recently (past 200 years) – the first trees here since the Ice Age. This nutrient limited bog was fertilized by wind blown dust during European Settlement allowing these vascular plants to obtain a foothold in the previously sphagnum moss dominated bog.

Hey there is a Wooster student – good job Ben. This white oak is growing on the top of  a kame and it has witnessed the changes in the climate and land use for the last 300 years.


Nick samples the bog water for its isotopic composition. This is work done in collaboration with isotope geologists at the University of Cincinnati.

Wooster’s Fossil of the Week: A receptaculitid (Middle Ordovician of Missouri)

February 10th, 2017

This week’s fossil is a long-standing paleontological mystery. Above is a receptaculitid from the Kimmswick Limestone (Middle Ordovician) near Ozora, Missouri. I think I found it on a field trip with Frank Koucky in the distant mists of my student days at Wooster, but so many outcrops, so many fossils …

Below is a nineteenth century illustration of a typical receptaculitid fossil. They are sometimes called “sunflower corals” because they look a bit like the swirl of seeds in the center of a sunflower. They were certainly not corals, though, or probably any other kind of animal. Receptaculitids appeared in the Ordovician and went extinct in the Permian, so they were confined to the Paleozoic Era. Receptaculitids were bag-like in form with the outside made of mineralized pillars (meroms) with square or diamond-shaped heads. The fossils are usually flattened disks because they were compressed by burial. You may notice now that the fossil at the top of this post is a mold of the original with the dissolved pillars represented by open holes. (Paleontologists can argue if this is an external or internal mold.)So what were the receptaculitids? When I was a student we called them a kind of sponge, something like a successor of the Cambrian archaeocyathids. In the 1980s a convincing case was made that they were instead a kind of alga of the Dasycladales. Now the most popular answer is that they belong to that fascinating group “Problematica”, meaning we have no idea what they were! (Nitecki et al., 1999). It’s those odd meroms that are the problem — they appear in no other known group, fossil or recent.

I find it deeply comforting that we still have plenty of fossils in the Problematica. We will always have mysteries to puzzle over.
Another Wooster receptaculitid specimen, this time seen from the underside showing side-views of the meroms.
Diagram of a receptaculitid in roughly life position showing its inflated nature and pillar-like meroms. From Dawson (1880, fig. 25): a, Aperture (probably imaginary here). b, Inner wall. c, Outer wall. n, Nucleus, or primary chamber. v, Internal cavity.

Finally, this is what a typical receptaculitid looks like in the field (Ordovician of Estonia). Note that nice sunflower spiral of the merom ends.

References:

Dawson, J.W. 1880. The chain of life in geological time: A sketch of the origin and succession of animals and plants. The Religious Tract Society, 272 pages.

Nitecki, M.H., Mutvei, H. and Nitecki, D.V. 1999. Receptaculitids: A Phylogenetic Debate on a Problematic Fossil Taxon. Kluwer Academic/Plenum, 241 pages.

[Originally published on September 18, 2011]

Wooster’s Fossils of the Week: Peanut worms from the Silurian of Illinois

February 3rd, 2017

1-lecthaylus-gregarius-5-copyThis week’s fossils are a set of cool sipunculan worms from the Lockport Shale Member of the Racine Formation (Wenlockian, Silurian) of Blue Island, Illinois (which, it turns out, is not an island.). This is Lecthaylus gregarius Weller, 1925. (There is a common misspelling of the genus name as “Lecathylus”, which is how it is labeled in our collection.) They are masses of partially-carbonized bodies and external molds in a very fine-grained matrix. They are well known from this particular fossil-lagerstätte (a fossil fauna of remarkable preservation) in northern Illinois.

The Phylum Sipuncula did not often make it into the fossil record because of their entirely soft bodies, but a few are preserved way back in the Cambrian Chengjiang and Burgess Shale faunas. They show virtually no evolutionary changes in their long run to today, at least not in their outer form. They are commonly known as “peanut worms”.

2-lecthaylus-gregarius-2This is an example of the preservation modes: a black carbon film that has mostly flaked away, leaving behind a detailed external mold of the squashed peanut worms.

3-lecthaylus-gregarius-1Sipunculan bodies are divided into a main thick posterior trunk and a narrow, retractable anterior “introvert”. We’re looking here at the anterior introvert of Lecthaylus gregarius.

4-lecthaylus-gregarius-3-copyThis is the squat trunk of Lecthaylus gregarius.

5-themiste_petricola_evertedHere is the modern sipunculan Themiste petricola with introvert extended. It is the same basic plan as the Silurian Lecthaylus gregarius. Image from Wikipedia courtesy of Tomás Lombardo and Guillermo A. Blanco.

6-themiste_petricola_invertedThe modern sipunculan Themiste petricola with its introvert retracted. Image from Wikipedia courtesy of Tomás Lombardo and Guillermo A. Blanco.

stuart-weller-1870-1927Lecthaylus gregarius was described and named by Stuart Weller (1870-1927), an American paleontologist and geologist. He was born in the small town of Maine, New York. He earned a Bachelor’s degree in geology at Cornell University in 1894 followed by a PhD at Yale in 1901. Shortly after his Cornell degree, though, Weller traveled to the University of Chicago, where he worked his way through the ranks from a research associate to a full professor of Paleontology and Geology in 1915. He was also the director of the Walker Museum at the University of Chicago, and in 1926 he was president of the Paleontological Society. One of his sons, J. Marvin Weller (1899-1976) had a remarkably similar career as a stratigrapher and paleontologist.

References:

Kluessendorf, J. 1994. Predictability of Silurian Fossil‐Konservat‐Lagerstatten in North America. Lethaia 27: 337-344.

Roy, S.K. and Croneis, C. 1931. A Silurian worm and associated fauna. Field Museum of Natural History, Geological Series IV(7): 229-247.

Weller, S. 1925. A new type of Silurian worm. Journal of Geology 33: 540-544.