Wooster’s Fossil of the Week: A bitten brachiopod (Upper Ordovician of southeastern Indiana)

February 5th, 2016

1 Best bitten Glyptorthis insculpta (Hall, 1847)This brachiopod, identified as Glyptorthis insculpta (Hall, 1847), was shared with me by its collector, Diane from New York State. She found it in a muddy horizon of the Bull Fork Formation (Upper Ordovician) in southeastern Indiana. She immediately noted the distorted plicae (radiating ribs) on the left side of this dorsal valve, along with the invagination along the corresponding margin. (Thanks for showing this to me, Diane, and allowing me to include it in this blog.)
2 Best closer Glyptorthis insculpta (Hall, 1847)Above  is a closer view of the unusual plicae. Note that they radiate from the top center of the brachiopod, extending as the shell grew outward along its margins. Something happened, though, when the brachiopod was growing. The shell was seriously damaged by a puncturing object. The brachiopod repaired the hole by closing it up with additional shell material coming from either side. The inwardly-curved plicae show the pattern of shell regrowth.
3 Reverse of best Glyptorthis insculpta (Hall, 1847)This is a view of the same brachiopod from the other side, showing that the ventral valve was damaged in the same event, but with slightly less destruction.

So how did such damage occur on that Ordovician seafloor? Some predator likely took a bite out of the brachiopod as it lay in its living position with the valves extended upwards into the seawater. Most brachiopods do not survive such events, but this one did.

Who was the probable predator? For that we turn to the work of the late Richard Alexander (1946-2006). He did the definitive study of pre mortem damage to brachiopods in the Cincinnatian Group in 1986, concluding that the most likely predators on these brachiopods were nautiloid cephalopods. Some of this figures show nearly identical healed scars on similar orthid brachiopods.
4. Richard AlexanderRichard Alexander was an accomplished paleontologist who lost his life in a swimming accident off the coast of St. Lucia just over nine years ago. He was born in Covington, Kentucky, right across the river from Cincinnati. As is so common with children in that part of the world, he developed a passion for fossils. He attended the University of Cincinnati, majoring in geology, He then went to Indiana University, completing a PhD dissertation titled: “Autecological Studies of the Brachiopod Rafinesquina (Upper Ordovician), the Bivalve Anadara (Pliocene), and the Echinoid Dendraster (Pliocene).” (We don’t see such diverse projects very much these days.) He taught at Utah State University from 1972 to 1980, and then at Rider University in New Jersey from 1981 until his death. He served as an administrator at several levels at Rider, and was known as an excellent teacher. His research interests changed when he moved to the East Coast, becoming increasingly focused on modern mollusks. No doubt he would still be contributing to paleontology but for the randomness of a freak wave in the Caribbean.

References:

Alexander, R.R. 1981. Predation scars preserved in Chesterian brachiopods: probable culprits and evolutionary consequences for the articulates. Journal of Paleontology 55: 192-203.

Alexander, R.R. 1986. Resistance to and repair of shell breakage induced by durophages in Late Ordovician brachiopods. Journal of Paleontology 60: 273-285.

Dodd, J.R. 2008. Memorial to Richard Alexander (1946-2006). Geological Society of America Memorials 37: 5-7.

Wooster’s Fossil of the Week: A brachiopod with a heavy burden (Upper Ordovician of southeastern Indiana)

January 29th, 2016

1 Trepostome on Hebertella richmondensisYes, the above image doesn’t look much like a brachiopod, but just wait. We see a trepostome bryozoan with extended knobs and a few borings. Flip it over, though …
2 Hebertella richmondensis ventral view 585… and we see that the bryozoan almost entirely covers a brachiopod. So far, so common among Ordovician fossils. However, look closely at the margin of the brachiopod valve and how clearly it is delineated from the bryozoan. It is apparent that the bryozoan had encrusted a living brachiopod, and the brachiopod stayed alive, keeping the essential commissure (the gap between the valves) open for feeding. We are looking at the valve that was in contact with the substrate (the underside of the living brachiopod). The bryozoan occupied the upper exposed surface, growing across that valve (which is invisible to us now), past its edge, but not closing the gap with the other valve. The same bryozoan species is found on the above visible valve, but only as two thin films unconnected to the colony on the upper side.
3 Hebertella richmondensis bryo close annotatedA closer view of the brachiopod hinge shows additional evidence that the bryozoan and brachiopod were living together. The red arrow on the left points to where the fleshy pedicle (attaching stalk) of the brachiopod extended from the shell to meet the substrate. The bryozoan here curves around the now-vanished pedicle. The yellow arrow on the right shows how the bryozoan growth surface folded to accommodate the opening valves at the hinge. Pretty cool.

I can’t identify the bryozoan beyond Order Trepostomata without cutting it open. The brachiopod, though, appears to be Hebertella richmondensis Foerste, 1909. This specimen is from the Whitewater Formation (Upper Ordovician, upper Katian) exposed near Richmond, Indiana. It was collected on one of my field trips in 2003.
4 Hebertella richmondensis ventral view 585 annotatedWhat do we learn from this little assemblage? We first see a relatively uncommon example of a clear living relationship between a sclerobiont and its host. We also learn that the brachiopod could continue to open its valves for feeding despite the heavy calcitic bryozoan weighing it down. We even can see that this brachiopod was not living on a soft muddy substrate because only a small triangular-shaped area (see above) in the center was clear of encrusters; the thin bryozoan (and maybe a bit of the stromatoporid sponge Dermatostroma) had enough space between the valve and the substrate to feed and respire. None of this is surprising, but it is nice to see our models of how these organisms lived are congruent with the evidence.

References:

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

Foerste, A.F. 1909. Preliminary notes on Cincinnati fossils. Bulletin of the Scientific Laboratory of Denison University 14: 208–232.

Walker, L.G. 1982. The brachiopod genera Hebertella, Dalmanella, and Heterorthina from the Ordovician of Kentucky. USGS Professional Paper 1066-M.

Wright, D.F. and Stigall, A.L. 2013. Phylogenetic revision of the Late Ordovician orthid brachiopod genera Plaesiomys and Hebertella from Laurentia. Journal of Paleontology 87: 1107-1128.

Wooster’s Fossils of the Week: Atrypid brachiopods attached to a trepostome bryozoan from the Upper Ordovician of southern Indiana

January 8th, 2016

Zygospira Attached 585This is a follow-up post to our entry on Christmas Day two weeks ago. Above is a trepostome bryozoan (the long porous piece) with specimens of the atrypid brachiopod Zygospira modesta clustered around it. They are positioned with their ventral valves outward because in life they were attached to this bryozoan with tiny fleshy stalks called pedicles. They were buried quickly enough that this spatial relationship was preserved. Cool. This assemblage was found in the Liberty Formation (Upper Ordovician) exposed in a roadcut in southern Indiana.
Zygospira modesta dorsal annotatedThis is a view of the dorsal side of Zygospira modesta showing the pedicle opening in the ventral valve at the apex of the shell.

References:

Copper, P. 1977. Zygospira and some related Ordovician and Silurian atrypoid brachiopods. Palaeontology 20: 295-335.

Sandy, M.R. 1996. Oldest record of peduncular attachment of brachiopods to crinoid stems, Upper Ordovician, Ohio, USA (Brachiopoda; Atrypida: Echinodermata; Crinoidea). Journal of Paleontology 70: 532-534.

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

July 31st, 2015

Conulariid03 585

This summer I’ve been updating some of the photos I placed in the Wikipedia system (check them out here, if you like; free to use for any purpose). I was especially anxious to replace a low-resolution image I had made of an impressive conulariid (Paraconularia newberryi) from the Lower Carboniferous of Indiana. The new version is above. Since I used the same specimen as a Fossil of the Week exactly four years ago to the day, I thought I’d take advantage of a slow summer and update that earlier text for this week:

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 that 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.

The specimen above is Paraconularia newberryi (Winchell) found somewhere in Indiana and added to the Wooster fossil collections before 1974. A close view (below) shows the characteristic ridges with a central seam on each side.

Conulariid01 585Conulariids 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.

ConulataThe 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!

References:

Driscoll, E.G. 1963. Paraconularia newberryi (Winchell) and other Lower Mississippian conulariids from Michigan, Ohio, Indiana, and Iowa. Contributions from the Museum of Palaeontology, The University of Michigan 18: 33-46.

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

Sendino, C., Zagorsek, K. and Taylor, P.D. 2012. Asymmetry in an Ordovician conulariid cnidarian. Lethaia, 45: 423-431.

Van Iten, H.T., Simoes, M.G., Marques, A.C. and Collins, A.G. 2006. Reassessment of the phylogenetic position of conulariids (?Vendian–Triassic) within the subphylum Medusozoa (Phylum Cnidaria). Journal of Systematic Palaeontology 4, 109–118.

 

Wooster’s Fossils of the Week: An encrusted bivalve external mold from the Upper Ordovician of Indiana

June 26th, 2015

1 Anomalodonta gigantea Waynesville Franklin Co IN 585I love this kind of fossil, which explains why you’ve seen so many examples on this blog. We are looking at an encrusted external mold of the bivalve Anomalodonta gigantea found in the Waynesville Formation exposed in Franklin County, Indiana. I collected it many years ago as part of an ongoing study of this kind of preservation and encrustation.
2 Anomalodonta gigantea Waynesville Franklin Co IN 585 annotatedTo tell this story, I’ve lettered the primary interest areas on image above. First, an external mold is an impression of the exterior of an organism. In this case we have a triangular clam with radiating ribs in its shell. The exterior of the shell with its ribs was buried in sediment and the shell dissolved, leaving the basic impression above. It is a negative relief. Please now refer to the letters for the close-up images below.

3 Bryo Anomalodonta gigantea Waynesville Franklin Co INA. At the distal end of the bivalve mold is what looks at first to be the original shell. It is calcitic, though, and we know this bivalve had an aragonitic shell. A closer look shows that this is actually the attaching surface of an encrusting bryozoan that bioimmured the original bivalve shell, which has since dissolved away. This smooth surface is the bryozoan underside; we see the characteristic zooecia (tubes holding the individual zooids) only when this surface is weathered away.

4 Borings Anomalodonta gigantea Waynesville Franklin Co INB. These tubular objects are infillings of borings (maybe Trypanites)that were cut into the original aragonitic shell of the bivalve. The tunnels of the borings were filled with fine sediment, and then the shell dissolved away, leaving these casts of the borings.

5 Inarticulate scar Anomalodonta gigantea Waynesville Franklin Co INC and D. In the middle of the external mold is this curious circular feature (C) mostly surrounded by a bryozoan (D). There was at one time a circular encruster, likely an inarticulate brachiopod like Petrocrania, that sat directly on the external mold surface. The bryozoan colony grew around but not over it because it was alive and still opening and closing its valves for feeding. The bryozoan built a vertical sheet of skeleton around it as a kind of sanitary wall. You may be able to see the other three or four structures in the top image showing brachiopod encrusters that left the building. This is an example of fossils showing us a living relationship, even if one is not longer preserved.

This fossil and its sclerobionts (hard substrate dwellers) show us that soon after the bivalve died its aragonitic shell dissolved away, leaving as evidence the external mold in the sediment, the bioimmuring bryozoan, and the boring casts. Very soon thereafter bryozoans and brachiopods encrusted the available hard substrate. This is a typical example of early aragonite dissolution on the sea floor during a Calcite Sea interval.

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.

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

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

Wilson, M.A., 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: 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.

 

Wooster’s Fossil of the Week: Upper Ordovician bivalve bioimmured by a bryozoan

November 7th, 2014

DSC_4503This week’s fossil is a simple and common form in the Cincinnatian Series (Upper Ordovician) of the Ohio, Indiana and Kentucky tri-state area. We are looking above at the base of a trepostome bryozoan that encrusted the outside of an aragonite bivalve shell. The bivalve shell (probably a species of Ambonychia) dissolved away, leaving its impression in the base of the calcitic bryozoan. This fossil is from the Upper Whitewater Formation (Richmondian) in eastern Indiana near Richmond itself.
DSC_4516In this closer view you can see the plications (“ribs”) of the bivalve preserved in negative relief on the attachment surface of the bryozoan. Close examination shows the individual zooecia of the bryozoan exquisitely molding the bivalve topography.

This is a kind of substrate bioimmuration, a preservational mode in which a skeletal organism (the bryozoan here) overgrows another organism (with a soft body or hard skeleton), making an impression of it in its base. The overgrown organisms is rots or dissolves away, leaving the exposed mold. You can also think of it as a kind of external mold produced by a living organism (the encruster). Such “vital immuration” was first described by Vialov (1961), and it is thoroughly covered by Paul Taylor in his 1990 paper cited below.

Again, these fossils are common in the Cincinnatian, and this one is far from being the fanciest. It is the Fossil of the Week because of its very ordinary nature, yet it provides extraordinary information. The aragonitic shell the bryozoan encrusted would have been lost forever after it dissolved if this bryozoan hadn’t occupied it and built a calcitic memorial. I’ve collected now hundreds of these substrate bioimmurations, and they have been critical in many studies, from the preservation of soft-bodied sclerobionts (see Wilson et al., 1994) to the revelation of boring interiors (and thus the behavior of the borers) and skeletal sclerobiont paleoecology. I’m also convinced there are many aragonitic mollusk taxa in the Cincinnatian that are known only through this bioimmuration process. These are fascinating fossils my students and I will continue to collect and study.

References:

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

Vialov, O.S. 1961. Phenomena of vital immuration in nature. Dopovidi Akademi Nauk Ukrayin’ skoi RSR 11: 1510-1512.

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: 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: 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.

Ordovician bioerosion and encrustation project begins

March 9th, 2014

Coleman 030914RICHMOND, INDIANA–Meet Coleman Fitch (’15) standing on the iconic outcrop of the Whitewater Formation (Upper Ordovician) on Route 27 about a mile south of Richmond (C/W-148; N 39.78722°, W 84.90166° — which has a nice Google Maps street view). This was his first day of fieldwork for his study of the complex relationship between borings and encrusters on brachiopods and mollusks. Note that Coleman has manfully taken off one glove for fossil collection. Despite the sun, we were freezing for science. Later in the day we collected from a warmer exposure of the Liberty Formation (Locality C/W-149) on IN-101 (N 39.48134°, W84.94843°).

Our collecting was very successful today. We found numerous examples of “half-borings” on trepostome bryozoan attachment surfaces, and many other curious fossils showing an interplay of early diagenesis (especially aragonite dissolution and calcite precipitation) and biotic processes.

Richmond specimen 030914Above is an example of the fun and complex fossils at the Whitewater locality. What processes do you think this specimen represents?

Tomorrow I meet William Harrison (’15) in northern Kentucky to search for bored bryozoans and bioclaustrations. It promises to be much warmer down there!

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