Wooster’s Fossil of the Week: An unusual scleractinian coral from the Upper Cretaceous of Israel

April 13th, 2014

Aspidiscus 041114aOriginally this was going to be a mystery fossil for a crowd-sourced identification while I’m here in Israel doing fieldwork, but through the wonders of the internet I finally found a match for the strange fossil above: it is the scleractinian coral Aspidiscus König, 1825 (Family Latomeandridae) Yoav Avni and I found several specimens in the lower third of the En Yorqe’am Formation (Upper Cretaceous, Cenomanian) in the Negev of southern Israel. I had never seen anything like it before.

The view above is of the upper surface of this discoidal fossil. There are several short and seemingly random ridges, which I learned later are called monticules in this genus. Each monticule has a series of septa, or thin vertical partitions. This was a compound coral, meaning it had multiple polyps on its surface, presumably each sitting on a monticule.
Aspidiscus 041114bThis is a reverse view of the En Yorqe’am variety of Aspidiscus. The pits appear to be molds of a gastropod on which the young coral must have recruited. It then grew centripetally, making a fine series of growth lines across a soft sediment.
Aspidiscus cristatus diagramThis diagram from Pandey et al. (2011) is a diagram of Aspidiscus cristatus found in the Cenomanian of Sinai, not too far from here. (This species is also found in Algeria, Tunisia, Spain, Greece, and Afghanistan — all in the Cenomanian.) Note that the center of A. cristatus has two large crossing monticules and the Israeli specimen does not. This is why I’m keeping it in open nomenclature — it doesn’t appear to be the same species. A. cristatus is found in the middle to early late Cenomanian; the En Yorqe’am specimen seems so far to be only in the early Cenomanian. This may mean the Israeli version is an older species. Both clearly liked living in marly shallow marine sediments.
Aspidiscus symbiontsHere’s the bonus: look at the round holes in the upper surfaces of these two specimens. These are caused by symbionts of some kind that lived within the growing coral. You can see best in the specimen on the right how the coral grew around the symbionts, producing a kind of tube. Nice.

Sorry for the lower quality of images this week. I’m photographing the fossils as best I can with a bedside lamp, a tiny tripod, and a shirt for background.

References:

Avnimelech, M. 1947. A new species of Aspidiscus from the Middle Cretaceous of Sinai and remarks on this genus in general. Eclogae geologicae Helvetiae 40: 294-298.

Gill, G.A. and Lafuste, J.G. 1987. Structure, repartition et signification paleogeographique d’Aspidiscus, hexacoralliaire cenomanien de la Tethys. Bulletin de la Societe Geologique de France 3: 921-934.

Pandey, D.K., Fürsich, F.T., Gameil, M. and Ayoub-Hannaa, W.S. 2011. Aspidiscus cristatus (Lamarck) from the Cenomanian sediments of Wadi Quseib, east Sinai, Egypt. Journal of the Paleontological Society of India 56: 29-37.

Field trip to the lesser known makhteshim at Har ‘Arif

April 10th, 2014

Har 'Arif 041014MITZPE RAMON, ISRAEL–We’ve talked a lot about makhteshim in this blog, with so much of our geological work located in Hamakhtesh Hagadol and Makhtesh Ramon. A makhtesh is essentially a breached anticline, usually with a single drainage running from it. There are two small makhteshim at Har ‘Arif that are rarely seen because it takes some effort to get to them (major dirt road challenges and a significant hike) and they are in a military area that has very limited access. The Geological Survey of Israel got permission to run a field trip up to the top of Har ‘Arif today, and I was privileged to go along. The image above is of Har ‘Arif (the peak in the middle) looking up through the axis of the larger of the two makhteshim here. Its elevation is 956 meters, and it is the ninth highest peak in Israel. It is noted for its craggy, angular top, which is unlike most other Negev mountains with their rounded or flattened outlines.

Geologist camp 041014We began the day with an early departure from Mitzpe Ramon to meet most of the team camped out near Har ‘Arif. Note as the sun rises the crew has jackets on. It was an unseasonably cool start.

Hike begins 041014The hike begins. The goal is the very tippy-top of the mountain, so lots of work ahead in this beautiful setting.

Group outcrop 041014As with any geology field trip, we stopped occasionally for lectures on the outcrops. These lectures were in Hebrew so I was a spectator. It’s funny that after awhile I could pick out what the major arguments were from the tone of voice and various hand gestures. Several participants (especially Yoav) kindly interpreted for me afterwards. We are here examining an outcrop of the Middle Triassic Raaf Formation. This is a unit low in the Triassic that is not seen elsewhere in Israel.

Ripples Gyrochorte 041014These are ripplemarks in a fine sandstone of the Gevanim Formation (Middle Triassic, Anisian). Note the trace fossils that are convex epirelief, meaning they are positive relief on the surface of the bed. They are of the ichnogenus Gyrochorte, an old friend of mine from the Jurassic of Utah.

View west Har 'Arif 041014We reached the top of the mountain after an arduous climb. The coordinates are N 30.42591°, E 34.734°. (Really, google map these numbers. I worked hard for them!) This is the view to the east looking over the Negev all the way to the mountains of Jordan. One limb of the smaller makhtesh is below.

Har 'Arif Makhtesh 041014Here is the larger of the two makhteshim, looking west from the top of Har ‘Arif. It is gorgeous. All the rocks making the floor and walls are Triassic. The ridge line in the far distance is the border with Egypt.

I’ll have more later on the abundant flowers of the Har ‘Arif area. Right now it is a much-anticipated bedtime for me!

A mission in the Cretaceous of southern Israel

April 9th, 2014

Wadi Mishar viewMITZPE RAMON, ISRAEL–Today Yoav and I set out to solve a mapping dilemma concerning the boundaries of the Upper Cretaceous (Cenomanian) En Yorqe’am Formation in the Negev and, eventually, the Judean Desert to the north. It involved a bumpy ride deep into some of the most beautiful areas of the country, and it produced all sorts of delicious paleontological and sedimentological mysteries. I’ll talk more about this trip in later entires. Since it was 12 hours and I get up at 4:00 a.m. tomorrow, this is a truncated entry!

The setting is the stratigraphy of the En Yorqe’am and its bounding units: the Hevyon Formation below and the Zafit Formation above. Our job was to examine the contacts between these units and help come up with consistent definitions that can be used throughout the region. Right now there is considerable fuzziness as to where each formation begins and ends. Above is a labeled image showing the magnificent outcrop in Wadi Mishar (taken from our studied section at N 30.54899°, E 34.98843°).

Oysters En Yorqeam 040914In the process of sharpening the definition of the En Yorqe’am, we found some magnificent fossils. There are many paleontological and sedimentological projects possible in this unit. Oysters dominate the En Yorqe’am in mot places we visited. Above is a close view of one outcrop (at N 30.65788°, E 35.08764°; Nahal Neqarot) showing that the sediment is almost entirely oyster. The shells are often beautifully bored, but strangely there are virtually no encrusters.

Stromatoporoid En Yorqeam 040914To our surprise, we found these large roundish objects that look very much like stromatoporoids (at N 30.65788°, E 35.08764°). The lack visible mamelons (or corallites, for that matter), but internally they appear to show the typical laminations and pillars of these calcareous sponges. I’ve never seen them in the Cretaceous before, which is at the end of their range. I could be wrong and these fossils are odd altered corals. Only cutting and polishing will tell.

Terebratulids En Yorqeam 040914Also unexpected was the prevalence of brachiopods in parts of the En Yorqe’am (at N 30.65788°, E 35.08764°). These are articulated terebratulid brachiopods. They look very Jurassic in their appearance, but here they are in the Upper Cretaceous.

I’m looking forward to working with Wooster students on these outcrops next year! More on the En Yorqe’am later this week.

Cretaceous echinoderms are today’s stars

April 8th, 2014

Zichor 040814MITZPE RAMON, ISRAEL–There’s a joke in the title, in case you didn’t notice! I was on my own for my second day of fieldwork in southern Israel. I revisited yesterday’s outcrops of the Upper Cretaceous (Coniacian) Zichor Formation, taking more time to plot out future section-measuring and fossil-collecting sites for students. I was also able to spend a lot of classic nose-on-the-ground time sorting out the fossils.

The outcrop above is about the top half of the Zichor Formation in this area (N 30.30587°, E 34.96543°). Note the cemented limestones near the top and the soft marls in the foreground. Both have plenty of fossils, but you can imagine which is easier to collect from.

Filograna? 040814One mystery of this unit is at the very top of the section in one of the last bedding planes. There are extensive amounts of a twisty worm-tube called Filograna (or at least something close to it). You can see it in the above image. I was told earlier it was a “mat”, but it appears to be instead broken fragments of tube accumulations scattered about. Strange critter, this worm.Echinoid tests 040814The marls of the Zichor have an impressive echinoderm content. Since they have calcitic tests, they are very well preserved. Above are five heart urchins showing their classic pentameral symmetry.

Echinoid test plates 040814Here are fragments of a cidaroid echinoid test. In the middle of each plate is a circle with a boss extending outwards. Spines were attached to these, one of which is included in the image. I hope on our later expedition we can find whole specimens. Students are always up for these discovery challenges.

Asteroid ray oral 040814This was a first find for me: an asteroid (sea star) ray fragment. I don’t think I’ve ever found a sea star fossil before. We are looking above at the oral side where tube feet would have extended.

Asteroid ray aboral 040814This is the other side of the fragment — the aboral side. Beyond being cool, I’m afraid there is not a lot of significance for this fossil unless I can identify it further. Sea stars are famous for living in all sorts of marine environments, from the intertidal to deep trenches.

Some future Wooster students are going to have a good time with this unit sorting out the paleontological, sedimentological and stratigraphic contexts and then comparing this tropical fauna to the better known assemblages in the temperate north.

A Triassic afternoon in southern Israel

April 8th, 2014

Mitzpe Ramon distant view 040814MITZPE RAMON, ISRAEL–This afternoon I walked through the spectacular Middle Triassic sections in Wadi Gevanim on the southern side of the Makhtesh Ramon structure. I will be on a fantastic trip this Thursday to a little-visited Triassic section farther south, so I wanted to refresh my memory of these units. The above image is looking north from Wadi Gevanim to Mitzpe Ramon just visible on the cliff edge of the makhtesh. (What a setting, eh?)

Nautiloids Ammonites 040814I found myself almost completely repeating an entry from last year on Wadi Gevanim (which had the added bonus of students in it). Today I gathered some impressive fossil cephalopods from the Saharonim Formation (Middle Triassic, Anisian-Ladinian) for a group photograph. I note only now that one of the nautiloids above appears last year as well! From the upper left going clockwise: nautiloid, ammonite, nautiloid, ammonite. All are internal molds (the outer shell has been removed).

Nautiloid 040814That upper left nautiloid is worth a closer look. The mold has been split down the middle showing the septa (internal walls dividing the chambers) and an impressive “beaded” siphuncle (connecting tube) running the length of the conch (shell).

Terebratulids 040814Finally, here is a handful of the common terebratulid brachiopods from the Saharonim. Speaking of which, have I mentioned the species Menathyris wilsoni from the Saharonim? You certainly must meet Menathyris wilsoni!

A Wooster Geologist is finally warm enough

April 7th, 2014

Yoav Zichor 040714MITZPE RAMON, ISRAEL–When I left Wooster on Saturday morning it was 34°F and overcast. It was sunny and an astonishing 84°F when I arrived in Tel Aviv on Sunday afternoon. That additional 50 degrees felt very good indeed after a winter of polar vortices and late-March snowstorms. I’m now based in the Ramon Suites Hotel in Mitzpe Ramon near the lip of the spectacular Makhtesh Ramon (N 30.60638°, E 34.80128°).

I’m back in Israel as part of my research leave from the College. This is my chance to explore new outcrops and ideas with my Israeli colleagues to prepare for the next generation of Independent Study students — and, of course, to do plenty of science for its own sake. I miss my students, though, for their companionship, sharp eyes, challenging questions, and navigation abilities (i.e., telling me when I’ve taken a wrong turn). This is how the leave system works so that we always have fresh projects with interesting and testable hypotheses. This is my 11th field season in Israel.

Today I met my long-time friend Yoav Avni of the Geological Survey of Israel, along with Zeev Lewy, a paleontologist retired from the Survey, to look at a fossiliferous unit Zeev discovered over two decades ago south of Mitzpe Ramon. We looked at the thickest section of the Zichor Formation (Late Cretaceous, Coniacian) to sort out a remarkably diverse set of silicified (silica-replaced) fossils associated with a mat of worm tubes (possibly of the genus Filograna). The top image shows the upper portion of the Zichor, with Yoav for scale (location: N 30.30587°, E 34.96543°). The image below is a view of the bedding plane with most (but not all) of the silicified fossils colored dark brown.

Zichor silcified fossils 040714One of the cool things about this layer is that the fossils are silicified, which is rare in this part of the Cretaceous section. Another is that aragonitic mollusks are preserved in this way (especially gastropods and bivalves), along with their calcitic cousins (like oysters and pectenids). The Filograna-like worm tube layer itself is fascinating since no one knows much about the paleoecology of this group, and we suspect it may have some significant evidence about the paleoenvironment encoded in its spaghetti-like appearance.

Zichor Menuha contact 040714The top of the Zichor meets the bottom of the Menuha Formation chalks (Late Cretaceous, Santonian). In this view, the yellow and brown Zichor is in the foreground and middle ground, with the whitish Menuha in the background.

Zichor Menuha close 040714Yoav and I visited the boundary between the Zichor (darker unit on the left) and Menuha (lighter on the right) to assess their relationship (N 30.30212°, E 34.95909°). At outcrops 30 km to the north this boundary is marked by a deep unconformity (eroded interval) and a layer of encrusted and bored cobbles. Here the boundary is flat and nearly continuous. The layer of silicified shells is just a few centimeters below the unconformity. This may not be by chance — units immediately below unconformities often have silicified zones.

Some of you may remember these unit names from previous expeditions. Micah Risacher (’11) worked on the Zichor Formation and its fossils in the Makhtesh Ramon area, and Andrew Retzler (’11) did his Independent Study research on the Menuha. We can now build on their excellent work as we develop additional outcrops and new questions.

Ordnance 040714Finally, it wouldn’t be the Negev if there wasn’t some ordnance on the outcrop. Can you tell what kind of bomb is shown above? The clues are in its current condition!

Wooster’s Fossil of the Week: A brontothere jaw fragment (Miocene of South Dakota)

April 6th, 2014

Titanotherium proutiiThis fossil has been sitting in a glass case outside my office door for nearly three decades. Only this year — in the desire to find more Fossils of the Week — did I bother to open the cabinet and take it out for a looksie. On the reverse was a 19th century label: “Titanotherium proutii, Badlands, SD”. That started me on a complicated journey through the literature to see just what sort of creature bore these magnificent molars, as well as the history of its discovery.
Titanotherium proutii occlusalIn this occlusal (meaning the biting surface) view you can see in the beautiful flowing lines of the hard (dark) and softer (light) enamel that there are some serious cracks repaired with a dodgy yellowish glue. The specimen is very fragile — that glue has probably been holding it together for well over a century. These are classic plant-eating teeth for both cutting and grinding leaves, roots and small branches.
TitanotheriumThe animal represented here is a titanothere, a large extinct mammal common in what would become the Badlands of South Dakota during the Paleogene. Above is a recreation of a relative of our species: Megacerops (Titanotherium) robustum. (The artist who drew this illustration in 1912 was Robert Bruce Horsfall, 1869-1948.) The titanotheres, now better known as brontotheres, were roughly the size and shape of rhinoceroses, but were actually more closely related to horses. They had elephant-like feet, inwardly-curved skull caps, and impressive horns on the nose.

I usually delight in tracking down taxonomic histories (the technical history of scientific names), but Titanotherium proutii has defeated me. The history of this taxon is convoluted beyond recovery — a sad tale of mistakes, misplaced fossils, specimens given multiple names, and over-zealous “splitting” of taxa. In other words, typical middle 19th century vertebrate paleontology. Mader (1998) says that Titanotherium Leidy 1853 (or 1852?) is a nomen dubium or “doubtful name”. Even the species, which later became Palaeotherium proutii, is nomen dubium. The names are simply worthless to science. I have been unable to figure out what the accepted name for our fossil now is.
Joseph_LeidyJoseph Leidy (1823-1891) named Titanotherium and (maybe) T. proutii (there is dispute as to who named it first). Leidy was a well known American biologist and paleontologist who taught first at the University of Pennsylvania and then Swarthmore College. He described and named the first nearly-complete dinosaur skeleton, Hadrosaurus foulkii. (It was found in the Cretaceous of New Jersey and he named it in 1858.) Leidy was also an early supporter of Charles Darwin and his the new theory of evolution, early enough for this to be an unpopular position. Edward Drinker Cope was one of his students, which forever places him at the beginning of the famous “Bone Wars” between Cope and Othniel Charles Marsh, which raged from 1877 to 1892. That epic conflict actually began in the New Jersey marl pits where Leidy’s hadrosaur was found. Leidy thus leaves us with a mixed legacy of discoveries, innovations and insights mixed with errors and folly. Just the sort of character we would expect on the frontier of a new science in a new country.
Leidy1Leidy’s 1853 (Plate XVI) figure of a jaw fragment of “Titanotherium proutii“.

References:

Leidy, J. 1853. The ancient fauna of Nebraska: or, a description of remains of extinct Mammalia and Chelonia, from the Mauvaises Terres of Nebraska. Smithsonian contributions to knowledge, vol. 6. Washington, Smithsonian Institution.

Mader, B.J. 1998. Brontotheriidae. In: C.M. Janis, K.M. Scott, and L.L. Jacobs (eds.), Evolution of Tertiary Mammals of North America 1: 525-536.

Mihlbachler, M.C., Lucas, S.G. and Emry, R.J. 2004. The holotype specimen of Menodus giganteus, and the “insoluble” problem of Chadronian brontothere taxonomy. Paleogene Mammals. New Mexico Museum of Natural History and Science Bulletin 26: 129-135.

Warren, L. 1998. Joseph Leidy: the last man who knew everything. Yale University Press, New Haven; 303 pages.

Wooster’s Fossil of the Week: Thoroughly encrusted brachiopod from the Upper Ordovician of Indiana

March 30th, 2014

1 Rafinesquina ponderosa (Hall) ventralLast week was an intensely bored Upper Ordovician bryozoan, so it seems only fair to have a thoroughly encrusted Upper Ordovician brachiopod next. The above is, although you would hardly know it, the ventral valve exterior of a common strophomenid Rafinesquina ponderosa from the Whitewater Formation exposed just south of Richmond, Indiana (locality C/W-148). I collected it earlier this month on a trip with Coleman Fitch (’15).
2 Rafinesquina ponderosa (Hall) dorsalThis is the other side of the specimen. We are looking at the dorsal valve exterior. Enough of the brachiopod shows through the encrusters that we can identify it. Note that both valves are in place, so we say this brachiopod is articulated. Usually after death brachiopod valves become disarticulated, so the articulation here may indicate that the organism had been quickly buried. This brachiopod is concavo-convex, meaning that the exterior of the dorsal valve is concave and the exterior of the ventral valve is convex.
3 Protaraea 032314Returning to the ventral valve, this is a close-up of the encruster that takes up its entire exterior surface. It is the colonial heliolitid coral Protaraea richmondensis Foerste, 1909. (Note the species name and that it was collected just outside Richmond, Indiana.) This thin coral is a common encruster in the Upper Ordovician. Usually it is a smaller patch on a shell. This is the most developed I’ve seen the species. The holes, called corallites, held the individual polyps.
4 Bryo on Protaraea 032314The encrusting coral has an encruster on top of it. This is a trepostome bryozoan, which you can identify by the tiny little holes (zooecia) that held the individuals (zooids). The patch of coral it is occupying must have been dead when the bryozoan larva landed and began to bud.
5 Trepostome 032314Now we’re returning to the concave dorsal valve with its very different set of encrusters. This is a close-up of another kind of trepostome bryozoan, this one with protruding bumps called monticules. They may have functioned as “exhalant current chimneys”, meaning that they may have helped channel feeding currents away from the surface after they passed through the tentacular lophophores of the bryozoan zooids. For our purposes, this is a feature that distinguishes this bryozoan species from the one on the ventral valve.
6 Cuffeyella 032314There is a third, very different bryozoan on the dorsal valve. This blobby, ramifying form is a well-developed specimen of Cuffeyella arachnoidea (Hall, 1847). It is again a common encruster in the Upper Ordovician, but not usually so thick.
7 Cuffeyella on hinge 032314If we look closely at the hinge of the brachiopod on the dorsal side, we can see a much smaller C. arachnoidea spreading on the ventral valve.
8 Encrusted edge 032314Finally, this is a side view of the brachiopod with the ventral valve above and the dorsal valve below. We’re looking at the junction of the articulated valves, the commissure. For the entire extent of the commissure, the encrusting coral grows to the edge of the ventral valve and no further. This is a strong indication that the brachiopod was alive when the coral was growing on it. The brachiopod needed to keep that margin clear for its own feeding.

The paleoecological implications here are that the coral was alive at the same time as the brachiopod. This means that the convex exterior surface of the ventral valve was upwards for the living brachiopod. The concave exterior surface of the dorsal valve faced downwards. The coral and bryozoan encrusting the top of the living brachiopod were exposed to the open sea; the bryozoans encrusting the undersurface of the living brachiopod were encrusting a cryptic space. We are thus likely seeing the living relationships between the encrusters and the brachiopod — this encrustation took place during the life of the brachiopod.

Further, this demonstrates that this concavo-convex strophomenid brachiopod was living with the convex side up. This has been a controversy for decades in the rarefied world of brachiopod paleoecology. This tiny bit of evidence, combined with some thorough recent studies (see Dattilo et al., 2009; Plotnick et al., 2013), strengthens the case for a convex-up orientation. Back when I was a student these would be fighting words!

References:

Alexander, R.R. and Scharpf, C.D. 1990. Epizoans on Late Ordovician brachiopods from southeastern Indiana. Historical Biology 4: 179-202.

Dattilo, B.F., Meyer, D.L., Dewing, K. and Gaynor, M.R. 2009. Escape traces associated with Rafinesquina alternata, an Upper Ordovician strophomenid brachiopod from the Cincinnati Arch Region. Palaios 24: 578-590.

Foerste, A.F. 1909. Preliminary notes on Cincinnatian fossils. Denison University, Scientific Laboratories, Bulletin 14: 208-231.

Mõtus, M.-A. and Zaika, Y. 2012. The oldest heliolitids from the early Katian of the East Baltic region. GFF 134: 225-234.

Ospanova, N.K. 2010. Remarks on the classification system of the Heliolitida. Palaeoworld 19: 268–277.

Plotnick, R.E., Dattilo, B.F., Piquard, D., Bauer, J. and Corrie, J. 2013. The orientation of strophomenid brachiopods on soft substrates. Journal of Paleontology 87: 818-825.

Wooster’s Fossil of the Week: Intensely bored bryozoan from the Upper Ordovician of Kentucky

March 23rd, 2014

Bored Bryo 1 585Yes, yes, I’ve heard ALL the jokes about being bored, and even intensely bored. I learn to deal with it. This week we continue to highlight fossils collected during our productive expedition to the Upper Ordovician (Cincinnatian) of Indiana (with Coleman Fitch ’15) and Kentucky (with William Harrison ’15). Last week was Coleman’s turn; this week it is William’s.

The beautiful fan-like bifoliate (two-sided) trepostome bryozoan above was collected from the lower part of the Grant Lake Formation (“Bellevue Limestone”) at our locality C/W-152 along the Idlewild Bypass (KY-8) in Boone County, Kentucky (N 39.081120°, W 84.792434°). It is in the Maysvillian Stage and so below the Richmondian where Coleman is getting most of his specimens. I’ve labeled it to show: A, additional bryozoans encrusting this bryozoan; B, a very bored section; C, a less bored surface showing the original tiny zooecia, monticules, and a few larger borings.
Bored Bryo 2 585The other side of this bryozoan is more uniform. It has an even distribution of small borings and no encrusters. This likely means that at some point after the death of the bryozoan and subsequent bioerosion this side was placed down in the mud while the exposed opposite side was encrusted.
Encruster Bored Bryo 031314_585A closer view of the upwards-facing side (with the encrusting bryozoan at the top) shows just how intense the boring was prior to encrustation. Some of the borings are close to overlapping. The encrusting bryozoan has its own borings, but far fewer and significantly larger.
Close borings 031314_585In this close view of the downwards-facing side we see lots of the small borings. Some are star-shaped if they punched through the junction of multiple zooecia. Note that these borings are rather evenly spread and seem to have about the same external morphology and and erosion. Likely they were all produced about the same time. It must have been a crowded neighborhood when all those boring creatures were home.

The questions that are provoked by this specimen are: (1) Were there any borings produced while the host bryozoan was still alive? (We may find elements of bioclaustration with some holes); (2) Why are zones B and C in the top image so different in the amount of bioerosion? Could zone C have still been alive at the time and resisted most bioeroders? Maybe zone C was covered by sediment? (But the margin is very irregular); (3) Why are the later encrusting bryozoans (zone A) so much less bioeroded?; (4) How do we classify such tiny pits that are between microborings and macroborings in size? (Trypanites is becoming a very large category) (5) What kind of organism made so many small pits? Were they filter-feeders as we always say, or was something else going on? (Sectioning specimens like this may reveal some internal connections between the pits.)

William has plenty of fun work ahead of him!

References:

Boardman, R.S. and Utgaard, J. 1966. A revision of the Ordovician bryozoan genera Monticulipora, Peronopora, Heterotrypa, and Dekayia. Journal of Paleontology 40: 1082-1108

Bromley, R.G. 1972. On some ichnotaxa in hard substrates, with a redefinition of Trypanites Mägdefrau. Paläontologische Zeitschrift 46: 93–98.

Erickson, J.M. and Waugh, D.A. 2002. Colony morphologies and missed opportunities during the Cincinnatian (Late Ordovician) bryozoan radiation: examples from Heterotrypa frondosa and Monticulipora mammulata. Proceedings of the 12th International Conference of the International Bryozoology Association. Swets and Zeitlinger, Lisse; pp. 101-107..

Kobluk, D.R. and Nemcsok, S. 1982. The macroboring ichnofossil Trypanites in colonies of the Middle Ordovician bryozoan Prasopora: Population behaviour and reaction to environmental influences. Canadian Journal of Earth Sciences 19: 679-688.

Taylor, P.D. and Wilson. M.A. 2003. Palaeoecology and evolution of marine hard substrate communities. Earth-Science Reviews 62 (1-2): 1–103.

Vogel, K. 1993. Bioeroders in fossil reefs. Facies 28: 109-113.

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

Wooster’s Fossil of the Week: Bryozoan bored and bryozoan boring in the Upper Ordovician of Indiana

March 16th, 2014

Bored Bryo on Brach top 585This week and next we will highlight fossils collected during our brief and successful expedition to the Upper Ordovician (Cincinnatian) of Indiana (with Coleman Fitch ’15) and Kentucky (with William Harrison ’15). We found what we needed to pursue some very specific topics.

Above is a trepostome bryozoan collected from the Liberty Formation (we should be calling it the Dillsboro Formation in Indiana; our locality C/W-149) on IN-101 in southeastern Indiana (N 39.48134°, W84.94843°). You can see the regular network of tiny little holes representing the zooecia (zooid-bearing tubes) of the calcitic zoarium (colony) of the bryozoan. The larger, irregular holes (still pretty small!) are borings cut by worm-like organisms into the bryozoan skeleton shortly after the death of the colony.
Bored Bryo on Brach bottom 585Flipping the specimen over we see the most interesting parts. On the left is a remnant of the original calcitic strophomenid brachiopod shell that was encrusted by the trepostome bryozoan. On the right the shell has broken away, exposing the encrusting surface of the trepostome. We are thus looking here at the inside of a brachiopod valve and the underside of the bryozoan that encrusted it.

This is just what we hoped to find for Coleman’s project on interpreting half-borings in brachiopod shell exteriors. This specimen demonstrates two crucial events after encrustation: First, the borings in the bryozoan extended down to the brachiopod shell and turned sideways to mine along the shell/bryozoan junction (note half-borings in the bryozoan base on the right), and second, the bryozoan broke mostly free of the brachiopod shell, with only a bit remaining on the left. Somewhere there is or was a fragment of that brachiopod with an exterior showing half-borings and no bryozoan encrustation. Thus a brachiopod without bryozoan encrusters may have actually been encrusted at some point, but the bryozoans were later detached. We’ve added a bit to the uncertainty of the encrusting fossil record — even calcitic skeletal evidence on this small scale can go missing. We’ve also started on a good story about the behavior of the tiny critters that bored into this shelly complex.
Ctenostome closer 031314_585A bonus in this specimen can be seen in this closer view of that brachiopod shell interior above. That branching network is a complex ctenostome bryozoan boring called Ropalonaria. This is a particularly well developed specimen with thicker, shorter zooids than I’ve seen before. This kind of boring is the subject of a previous Fossil of the Week entry.

Coleman has a great start on his Independent Study project with specimens like these. He has a lot of sectioning and adequate peeling ahead of him!

References:

Brett, C.E., Smrecak, T., Parsons-Hubbard, K. and Walker, S. 2012. Marine sclerobiofacies: Encrusting and endolithic communities on shells through time and space. In: Talent, J.A. (ed.) Earth and Life, International Year of Planet Earth, p. 129-157. Springer.

Pohowsky, R.A. 1978. The boring ctenostomate Bryozoa: taxonomy and paleobiology based on cavities in calcareous substrata. Bulletins of American Paleontology 73(301): 192 p.

Smrecak, T.A. and Brett, C.E. 2008. Discerning patterns in epibiont distribution across a Late Ordovician (Cincinnatian) depth gradient. Geological Society of America Abstracts with Programs 40:18.

Wilson, M.A., Dennison-Budak, C.W. 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 38:514.

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