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Wooster’s Fossil of the Week: A twisted scleractinian coral from the Middle Jurassic of southern Israel

April 24th, 2015

1 Epistreptophyllum Matmor CW366 585Another exquisite little coral this week from the collection of Matmor Formation (Middle Jurassic, southern Israel) corals Annette Hilton (’17) and I are working through. We believe this is Epistreptophyllum Milaschewitsch, 1876. It is a solitary (although more on that in a moment) scleractinian coral found in marly sediments at our location C/W-366 in Hamakhtesh Hagadol. I’m always impressed at how well preserved these corals are considering their original aragonitic skeletons were replaced long ago.
2 Epistreptophyllum lateral bentOne cool thing about this specimen is the near 90° bend it took during growth. Apparently it was toppled over midway through its development but survived and grew a twist so it could keep its oral surface (where the polyp resided) upwards. Another interesting observation is the small bud visible near the base. Gill (1982) suggested that the solitary Epistreptophyllum in the Jurassic of Israel may have been able to branch into separate individuals. Pandey and Lathuilière (1997) doubted this and suggested that Gill had misidentified his Israeli specimens. Maybe so, but we’re pretty sure we have Epistreptophyllum here, and we definitely have budding. We’re always open to other ideas!
3 Epistreptophyllum orientedHere is another view of the specimen in its living position after the fall. I love the sweep of the vertical ribs as it made the bend.
4 Epistreptophyllum septaTo complete the tour of this specimen, here’s a view of the oral surface where the polyp lived. The radiating lines are the septa that extended vertically through the interior of the corallite.
5 Milaschewitsch plate 50Epistreptophyllum was named in 1876 by Constantin Milaschewitsch. Here is Plate 50 from that massive work. Epistreptophyllum is marked by the red rectangles. (Note the misspelling of the genus in the caption for figure 2.) I wish I knew more about Mr. Milaschewitsch, but his particulars are thus far not available. I can tell he worked in Moscow and St. Petersburg, Russia, but that’s all. If anyone knows more about this man, please add your information in the comments.

References:

Gill, G.A. 1982. Epistreptophyllum (Hexacorallaire Jurassique), genre colonialou solitaire? Examen d’un matériel nouveau d’Israel. Geobios 15: 217-223.

Milaschewitsch, C. 1876. Die Korallen der Nattheimer Schichten. Palaeontographica 21: 205-244.

Pandey, D.K. and Lathuilière, B. 1997. Variability in Epistreptophyllum from the Middle Jurassic of Kachchh, western India: an open question for the taxonomy of Mesozoic scleractinian corals. Journal of Paleontology 71: 564-577.

Flipping the Classroom with Meteorite Impacts

April 21st, 2015

Our introductory courses don’t have labs, but that doesn’t stop our students from having hands-on experiences. Today, students in the Geology of Natural Hazards investigated the relationship between impact craters and projectile properties (size, mass, velocity) by experimenting with a tray of sand and a variety of projectiles. Students had a marble, ping pong ball, golf ball, and tennis ball that they could use to run experiments that would help them understand the factors that control the size and appearance of impact craters.

Students made craters by dropping the projectiles from a known height into the sand trays.

Students made craters by dropping the projectiles from a known height into the sand trays.

They repeated the experiment for a range of heights above the sand.

They repeated the experiment for a range of heights above the sand.

They measured the depth and diameter of each crater formed, and used their data to come up with the relationship between the size of the crater, the size and mass of the projectile, and the velocity.

They measured the depth and diameter of each crater formed, and used their data to come up with the relationship between the size of the crater, the size and mass of the projectile, and the velocity.

One group managed to conduct their experiments outside, although the brisk spring breeze introduced some error into their ping pong ball measurements!

One group managed to conduct their experiments outside, although the brisk spring breeze introduced some error into their ping pong ball measurements!

To prepare for today’s class, the students completed an online reading quiz. We reviewed questions from the reading quiz at the start of class, then covered the experiment setup. Students had the remaining period to work on their experiments. Some groups completed the assignment in class while others will need some more time to finish plotting their data. We’ll go over their results in our next class meeting.

A beautiful day for Wooster Geologists in the Silurian of Ohio

April 18th, 2015

aDSC_5072FAIRBORN, OHIO–It’s field trip season at last for the Wooster Geologists. Several geology classes have now been out in Ohio, taking advantage of windows of spectacular weather. Today was one of those days for 25 students in the Sedimentology & Stratigraphy class. We returned to the Oakes Quarry Park exposures in southwestern Ohio (N 39.81472°, W 83.99471°). Three years ago here in April it was 37°F and raining. This year the conditions were perfect. We studied outcrops of the Brassfield Formation (Early Silurian, Llandovery) in the old quarry walls. The students measured stratigraphic columns of these fossiliferous biosparites as part of an exercise, and then explored the glacially-truncated top of the unit.

bDSC_5079The Brassfield is intensely fossiliferous. Large portions of it are virtually made of crinoid fragments. In the random view above you can see columnals, as well as a few calyx plates. This is why this unit is very popular among my echinodermologist friends at Ohio State.

DSC_5056Kevin Komara, Brian Merritt and Dan Misinay (Team Football) are here contemplating the quarry wall, planning how to measure their sections.

DSC_5063One of our Teaching Assistants, Sarah Bender, is here pointing out one of the many thin intercalated clay units in the Brassfield biosparites.

DSC_5065Fellow Californian Michael Williams directed the action. No, actually he’s doing the time-honored technique of following a measured unit with his finger as he finds a place he can safely climb to it and the units above. He is holding one of our measuring tools, a Jacob’s Staff. Why do we call them “Jacob’s Staffs”? Read Genesis 30:25-43. (Yes, today’s students are mystified by Biblical references.)

DSC_5066Here’s Rachel Wetzel, giving me a heart attack. Don’t worry, insurance companies and parents, she’s fine.

DSC_5068Rachel is again on the left. Team Ultimate Frisbee (Meredith Mann and Mae Kemsley) are in the front, and Sharron Ostermann is above. This is the recommended way to get to the top of the exposure!

DSC_5070We carried our lunches in “to go” boxes from the dining hall. Our Teaching Assistants Sarah Bender and Kaitlin Starr enjoyed a sunny picnic on the rocks.

yDSC_5077The top level of the quarry was cleared of soil and brush many years ago to expose a glacially truncated and polished surface of the Brassfield. Looking for glacial grooves and fossils here are (from the left) Tom Dickinson, Jeff Gunderson (another Californian!), Andrew Conaway, and Luke Kosowatz (who seems to also be making a little pile of rocks as a memorial to a great day).

zDSC_5074One of the many corals we found in the top of the Brassfield was this halysitid (“chain coral”), an indicator fossil for the Late Ordovician and Silurian.

Everyone returned safely to Wooster with their completed stratigraphic columns, lithological descriptions, and a few fossils. Thank you to Mark Livengood, our bus driver. Good luck to the other field trip groups later this month!

Wooster’s Fossil of the Week: A Middle Jurassic trace fossil from southwestern Utah

April 17th, 2015

1 Gyrochorte 2 CarmelTime for a trace fossil! This is one of my favorite ichnogenera (the trace fossil equivalent of a biological genus). It is Gyrochorte Heer, 1865, from the Middle Jurassic (Bathonian) Carmel Formation of southwestern Utah (near Gunlock; locality C/W-142). It was collected on an Independent Study field trip a long, long time ago with Steve Smail. We are looking at a convex epirelief, meaning the trace is convex to our view (positive) on the top bedding plane. This is how Gyrochorte is usually recognized.
2 Gyroxhorte hyporelief 585A quick confirmation that we are looking at Gyrochorte is provided by turning the specimen over and looking at the bottom of the bed, the hyporelief. We see above a simple double track in concave (negative) hyporelief. Gyrochorte typically penetrates deep in the sediment, generating a trace that penetrates through several layers.
3 Gyrochorte Carmel 040515Gyrochorte is bilobed (two rows of impressions). When the burrowing animal took a hard turn, as above, the impressions separate and show feathery distal ends.
4 Gyrochorte 585Gyrochorte traces can become complex intertwined, and their detailed features can change along the same trace.
5 Gibert Benner fig 1This is a model of Gyrochorte presented by Gibert and Benner (2002, fig. 1). A is a three-dimensional view of the trace, with the top of the bed at the top; B is the morphology of an individual layer; C is the typical preservation of Gyrochorte.

Our Gyrochorte is common in the oobiosparites and grainstones of the Carmel Formation (mostly in Member D). The paleoenvironment here appears to have been shallow ramp shoal and lagoonal. Other trace fossils in these units include Nereites, Asteriacites, Chondrites, Palaeophycus, Monocraterion and Teichichnus.

So what kind of animal produced Gyrochorte? There is no simple answer. The animal burrowed obliquely in a series of small steps. Most researchers attribute this to a deposit-feeder searching through sediments rather poor in organic material. It may have been some kind of annelid worm (always the easiest answer!) or an amphipod-like arthropod. There is no trace like it being produced today.

We have renewed interest in Gyrochorte because a team of Wooster Geologists is going to Scarborough, England, this summer to work in Jurassic sections. One well-known trace fossil there is Gyrochorte (see Powell, 1992).
6 Heer from ScienceOswald Heer (1809-1883) named Gyrochorte in 1865. He was a Swiss naturalist with very diverse interests, from insects to plants to the developing science of trace fossils. Heer was a very productive professor of botany at the University of Zürich. In paleobotany alone he described over 1600 new species. One of his contributions was the observation that the Arctic was not always as cold as it is now and was likely an evolutionary center for the radiation of many European organisms.

References:

Gibert, J.M. de and Benner, J.S. 2002. The trace fossil Gyrochorte: ethology and paleoecology. Revista Espanola de paleontologia 17: 1-12.

Heer, O. 1864-1865. Die Urwelt der Schweiz. 1st edition, Zurich. 622 pp.

Heinberg, C. 1973. The internal structure of the trace fossils Gyrochorte and Curvolithus. Lethaia 6: 227-238.

Karaszewski, W. 1974. Rhizocorallium, Gyrochorte and other trace fossils from the Middle Jurassic of the Inowlódz Region, Middle Poland. Bulletin of the Polish Academy of Sciences 21: 199-204.

Powell, J.H. 1992. Gyrochorte burrows from the Scarborough Formation (Middle Jurassic) of the Cleveland Basin, and their sedimentological setting. Proceedings of the Yorkshire Geological Society 49: 41-47.

Wilson. M.A. 1997. Trace fossils, hardgrounds and ostreoliths in the Carmel Formation (Middle Jurassic) of southwestern Utah. In: Link, P.K. and Kowallis, B.J. (eds.), Mesozoic to Recent Geology of Utah. Brigham Young University Geology Studies 42, part II, p. 6-9.

Geomorphology at Fern Valley and along the Little Killbuck

April 12th, 2015

group_fernThe group at Fern Valley. Gaging Wilkin Run and measuring water levels in wells. We are fortunate to be able to monitor the streamflow, climate and geomorphic changes along Wilkin Run. Thanks again to Betty and David Wilkin for donating Fern Valley to the College.

leo_icsdLeo examining the Ice Contact stratified drift of the terminal moraine that in part lies across Fern Valley. This deposit records the Laurentide’s ice sheet advance into the proglacial Odell Lake (note the gray lacustrine clays and silts to Leo’s left). The exposure is capped with loess – the parent material of the soils here.

wellA well installed in the middle of the Run indicates whether the stream is gaining or losing. It is confusing at first.

gagingThe Archaeology team measures the velocity profile at Fern Valley. Note the terrace in the background, most of this sediment is eroded soils – likely introduced over the past few hundred years – so-called Legacy sediments.

deltaDescribing the stratigraphy along the Little Killbuck Valley – this is a delta – topsets (note the channel fills at the top) and foresets (The students are standing on the foreset beds, the foresets are muddy and weathered because the local bedrock is weathered shale and there was some rain falling that day) – the bottomsets are shown below.

lacustrineThe bottomset beds – gray silts to the right.  Jim navigates a modern mudflow fan on his way to the colluvium that  lies above the bedrock contact.

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

April 10th, 2015

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

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

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

References:

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

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

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

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

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

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

Wooster’s Fossil of the Week: A disturbingly familiar coral from the Middle Jurassic of southern Israel

April 3rd, 2015

Single Axosmilia side 585Our fossil this week is one I don’t share with my Invertebrate Paleontology classes until they’re ready for it. Those of us who grew up with Paleozoic fossils think we recognize it right away. Surely this is a solitary rugose coral? It has the right shape and the fine growth lines we call rugae (think “wrinkles”). This view below of the oral surface is not surprising either, unless you’re an enthusiast of septal arrangements.
Axosmilia oral view 585Instead of a rugose coral, though, this is a scleractinian coral from the Matmor Formation (Middle Jurassic, Callovian) of Hamakhtesh Hagadol, Israel. It is part of the collection of Matmor corals Annette Hilton (’17) and I are working through. This coral belongs to the genus Axosmilia Milne Edwards, 1848.
Axosmilia group 031815 585These corals are excellent examples of evolutionary convergence. The scleractinians are only very distantly related to the rugosans. They do not share a common ancestor with a calcareous skeleton, let alone a cone-shaped one like this. Instead the scleractinians like Axosmilia developed a skeleton very similar to that of the solitary rugosans, probably because they had similar life modes in similar environments, and thus similar selective forces. The rugosans, though, built their skeletons out of the mineral calcite, whereas the scleractinians use aragonite. (This specimens are calcite-replaced, like our specimen last week.) The vertical septa inside the cone are also arranged in different manners. Rugosans insert them in cycles of four (more or less), giving them a common name “tetracorals”; scleractinians have septal insertions in cycles of six, hence they are “hexacorals”. Rugose corals went extinct in the Permian; scleractinians are still with us today. Our friend Axosmillia appeared in the Jurassic and went extinct in the Cretaceous.

Rugose coral skeletons in the Paleozoic are commonly encrusted with a variety of skeletal organisms, and many are bored to some degree. I expected to see the same sclerobionts with these Jurassic equivalents, but they are clean and unbored. I suspect this means they lived semi-infaunally (meaning partially buried in the sediment).
Henri Milne-Edwards (1800–1885)Axosmilia was named by the English-French zoologist Henri Milne-Edwards (1800-1885) in the politically complex year of 1848. Henri was the twenty-seventh (!) child of an English planter from Jamaica and a Frenchwoman. He was born in Bruges, which is now part of Belgium but was then under the control of revolutionary France. Like many early 19th century scientists, Milne Edwards earned an MD degree but was seduced away from medicine by the wonders of natural history. He was a student of the most accomplished scientist of his time, Georges Cuvier, and quickly became a published expert on an amazing range of organisms, from crustaceans to lizards. The bulk of his career was spent at the Muséum National d’Histoire Naturelle in Paris. When he was 42 he was elected a foreign member of the Royal Society, receiving from them the prestigious Copley Medal in 1856. He died in Paris at the age of 85.

References:

Fürsich, F.T. and Werner, W. 1991. Palaeoecology of coralline sponge-coral meadows from the Upper Jurassic of Portugal. Paläontologische Zeitschrift 65: 35-69.

Martin-Garin, B., Lathuilière, B. and Geister, J. 2012. The shifting biogeography of reef corals during the Oxfordian (Late Jurassic). A climatic control?. Palaeogeography, Palaeoclimatology, Palaeoecology 365: 136-153.

Pandey, D.K., Ahmad, F. and Fürsich, F.T. 2000. Middle Jurassic scleractinian corals from northwestern Jordan. Beringeria 27: 3-29.

Pandey, D.K. and Fürsich, F.T. 2005. Jurassic corals from southern Tunisia. Zitteliana 45: 3-34.

Wooster’s Fossil of the Week: An encrusted scleractinian coral from the Middle Jurassic of southern Israel

March 27th, 2015

Amphiastrea Etallon 1859 Matmor Formation 585This week’s fossil is in honor of Annette Hilton (’17), who is my Sophomore Research Assistant this year. She has been diligently working through a large and difficult collection of scleractinian corals from the Matmor Formation (Middle Jurassic, Callovian) of Hamakhtesh Hagadol, Israel. These specimens were collected as parts of many paleoecological studies in our Wooster paleontology lab, so I thought it was time they received some systematic attention on their own. I knew it would be difficult, but Annette was up to the task and has done a splendid job.

The above specimen is a scleractinian coral of the genus Amphiastrea Étallon, 1859. It was collected from locality C/W-227 in the makhtesh. Considering the original was aragonite, it is remarkably preserved in a calcitized version. The large disks stuck to it are encrusting bivalves, probably of the genus Atreta.
Amphiastrea reverseHere we see the reverse with more encrusters. It is apparent that this cylindrical specimen was encrusted on all sides while it was in its erect living position, or this piece rolled around loose on the seafloor for an extended interval.
Amphiastrea serpulidOne of the encrusting bivalves was itself encrusted by a serpulid worm, which left part of its twisty calcitic tube behind.
Amphiastrea plicatulidThis thin, ghostly encruster is probably the bivalve Plicatula.
Amphiastrea close viewA close view of the corallites shows how well preserved they are on the surface of the coral. Each of these pits shows the vertical septa (walls of a sort) that were underneath the coral polyps in life. Despite this beautiful outer preservation, the interior of the specimen is mostly occupied by blocky calcite crystals.

This coral was found in a marly sediment, which explains why it is not locked into a solid piece of limestone as many Jurassic corals are. Amphiastrea apparently preferred environments with a significant amount of siliciclastic sediment (see Pandey and Fürsich, 2001, and other references below). I hope my students and I can further study this diverse and abundant coral fauna in the Matmor Formation. Annette Hilton has prepared the way.

Claude Auguste Étallon (1826-1862) named the genus Amphiastrea in 1859. He was a prominent paleontologist and geologist in his time. He was only 35 years old when he died, though, and has almost completely dropped out of the literature in English, except for the numerous invertebrate taxa he named. (There is a kind of immortality in our system of adding author’s names to taxa.) Using my Google Translator skills, I can read in the French literature that he was born to “an honest merchant family” in Luxeuil, France. He was a mathematics teacher first at collège Paul Féval à Dol-de-Bretagne and then later several other institutions. He developed a specialty in the rocks and fossils of the local Jurassic. Étallon created and published a geological map (“Carte géologique des Environs de St. Claude”), which was quite advanced for the time. The Late Jurassic turtle Plesiochelys etalloni was named after him in 1857. Auguste Étallon died suddenly of “the rupture of an aneurysm after two days of a slight indisposition” in February 1862.

Here’s to the memory of the energetic, productive and too short-lived Auguste Étallon.

References:

d’Amat, R. 1975. Étallon, Claude Auguste. Dictionnaire de Biographie Française 13: 163-164.

Löser, H. 2012. Revision of the Amphiastraeidae from the Monti D’Ocre area (Scleractinia; Early Cretaceous). Rivista Italiana di Paleontologia e Stratigrafia 118: 461-469.

Pandey, D.K., Ahmad, F. and Fürsich, F.T. 2000. Middle Jurassic scleractinian corals from northwestern Jordan. Beringeria 27: 3-29.

Pandey, D.K. and Fürsich, F.T. 2001. Environmental distribution of scleractinian corals in the Jurassic of Kachchh, western India. Journal Geological Society of India 57: 479-495.

Pandey, D.K. and Fürsich, F.T. 2005. Jurassic corals from southern Tunisia. Zitteliana 45: 3-34.

Vinn, O. and Wilson, M.A. 2010. Sabellid-dominated shallow water calcareous polychaete tubeworm association from the equatorial Tethys Ocean (Matmor Formation, Middle Jurassic, Israel). Neues Jahrbuch für Geologie und Paläontologie 258: 31-38.

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.

Wilson, M.A., Feldman, H.R. and Krivicich, E.B. 2010. Bioerosion in an equatorial Middle Jurassic coral-sponge reef community (Callovian, Matmor Formation, southern Israel). Palaeogeography, Palaeoclimatology, Palaeoecology 289: 93-101.

Wooster’s Fossil of the Week: A bored and formerly encrusting trepostome bryozoan from the Upper Ordovician of Indiana

March 20th, 2015

1 Trep Upper 030115The lump above looks like your average trepostome bryozoan from the Upper Ordovician. I collected it from the Whitewater Formation of the Cincinnatian Group at one of my favorite collecting sites near Richmond, Indiana. In this view you can just barely make out the tiny, regular holes that are the zooecia (calcitic tubes that held the bryozoan individuals — the zooids). There are bits of other fossils stuck to the outside, so it’s not particularly attractive as fossils go. (Except that all fossils are fascinating messengers in time.)

2 Trep Upper CloseWith this closer view you can see my initial interest in this particular bryozoan. Again, the regular, tiny holes are the zooecia. The larger pits are borings by worm-like, filter-feeding organisms. These borings are either in the ichnogenus Trypanites (if they are cylindrical) or Palaeosabella (if they are clavate, meaning clubbed at their distal ends). Such borings are common in all types of skeletal fossils in the Upper Ordovician — so common that they are part of the evidence for the Ordovician Bioerosion Revolution. So, let’s flip this ordinary, bored bryozoan over and see what’s underneath:

3 Trep Under 030115Here’s the main scientific beauty! We’re looking at the underside of the bryozoan. Ordinarily we’d expect to see a shell here that the bryozoan was encrusting, but the shell is gone. We’re gazing directly at the attachment surface of the bryozoan. It’s as if the colony had encrusted a sheet of glass and we’re looking right through it. The shell it was originally attached to has been removed either through dissolution (it might have been an aragonitic bivalve) or physical removal (it may have been a calcitic brachiopod). The borings are now much more prominent. They penetrated through the bryozoan into the mysterious missing shelly substrate. Some are small pits that just intersected the shell, others are horizontal as the boring organism turned at a right angle when it reached the shell and drilled along the bryozoan-shell interface. Removing the shell exposed the distal parts of these borings — parts that ordinarily would have been hidden by the encrusted shell.

4 Trep Under labeledHere is a closer, labeled view of this bryozoan basal surface. A is the earliest encruster recorded in this scenario; it is a small encrusting bryozoan that was first on the shelly substrate and then completely overgrown (or bioimmured) by the large trepostome. B shows that the trepostome was growing on a shell that already had borings from a previous encruster-borings combination that must have fallen off; these are grooves in the substrate that the trepostome filled in as it covered the shell. C is one of the many later borings that cut perpendicularly through the bryozoan and worked along the shell-bryozoan interface; as described above, only when that shelly substrate was removed would these be visible. In this surprisingly complex story, B represents an earlier version of C. We thus know that the shell was encrusted by one bryozoan, bored, and then that bryozoan was freed at its attachment (and not found in our collection). The same shell was then encrusted by this second bryozoan, which recorded the groove (or “half-borings”) made during the first encrustation.

These half-borings were first described in 2006 when my students Cordy Dennison-Budak and Jeff Bowen worked with me on them and we had a GSA abstract. Coleman Fitch is presently completing his Senior Independent Study enlarging the database for these features and developing detailed interpretations. The main implication from this work is that thick trepostome bryozoan encrusters often “popped off” shells, leaving no signs of their presence unless there were these half-borings in the shell surfaces and bryozoan undersides. Paleoecology and taphonomy on a very small scale!

References:

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

Wilson, M.A., Dennison-Budak, W.C., and Bowen, J.C. 2006. Half-borings and missing encrusters on brachiopods in the Upper Ordovician: Implications for the paleoecological analysis of sclerobionts. Geological Society of America Abstracts with Programs, Vol. 38, No. 7, p. 514.

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

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.

 

Days Five and Six – Mojave 2015

March 13th, 2015

Day five began at Kelso Dunes - sand, ripples, and Wooster Geologist footprints.

Day five began at Kelso Dunes – sand, ripples, and Wooster Geologist footprints.

Michael for scale.

Michael for scale.

Petroglyphs at Hole in the Wall.

Petroglyphs at Hole in the Wall.

Eric for scale, showing the size of tafoni at Hole in the Wall.

Eric for scale, showing the size of tafoni at Hole in the Wall.

Proof that the Wooster Geologists were at Hole in the Wall.

Proof that the Wooster Geologists were at Hole in the Wall.

And we made a friend at Hole in the Wall.

And we made a friend at Hole in the Wall.

Day five ended with a visit to a lava tube.

Day five ended with a visit to a lava tube.

Day six started with a visit to the Resting Springs Welded Tuff.

Day six started with a visit to the Resting Springs Welded Tuff.

Check out the fault at Resting Springs Pass.

Check out the fault at Resting Springs Pass.

We channeled our inner Dr. Mark Wilson and searched for fossils in the afternoon.

We channeled our inner Dr. Mark Wilson and searched for fossils in the afternoon.

Olivia found this trilobite! Wow!

Olivia found this trilobite! Wow!

We ended the day with date shakes at the China Ranch. Yum!

We ended the day with date shakes at the China Ranch. Yum!

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