Wooster’s Fossils of the Week: Intricate networks of tiny holes (clionaid sponge borings)

May 13th, 2012

The most effective agents of marine bioerosion today are among the simplest of animals: clionaid sponges. The traces they make in carbonate substrates are spherical chambers connected by short tunnels, as shown above in a modern example excavated in an oyster shell. The ichnogenus thus created is known as Entobia Bronn, 1838. I’ve become quite familiar with Entobia throughout its range from the Jurassic through the Recent (with an interesting early appearance in the Devonian; see Tapanila, 2006).
The holes in this Cretaceous oyster are the sponge boring Entobia; the cyclostome bryozoan is Voigtopora. This specimen is from the Coon Creek Beds of the Ripley Formation (Upper Cretaceous) near Blue Springs, Mississippi. (This specimen was collected during a 2010 Wooster/Natural History Museum expedition to the Cretaceous and Paleogene of the Deep South.)
This is a modern clam shell showing Entobia and several other hard substrate dwelling organisms (sclerobionts).
Entobia was named and first described by Heinrich Georg Bronn (1800-1862), a German geologist and paleontologist. He had a doctoral degree from the University of Heidelberg, where he then taught as a professor of natural history until his death. He was a visionary scientist who had some interesting pre-Darwinian ideas about life’s history.

References:

Bromley, R.G. 1970. Borings as trace fossils and Entobia cretacea Portlock, as an example. Geological Journal, Special Issue 3: 49–90.

Bronn, H.G. 1834-1838. Letkaea Geognostica (2 vols., Stuttgart).

Tapanila, L. 2006. Devonian Entobia borings from Nevada, with a revision of Topsentopsis. Journal of Paleontology 80: 760–767.

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. 2007. Macroborings and the evolution of bioerosion, p. 356-367. In: Miller, W. III (ed.), Trace Fossils: Concepts, Problems, Prospects. Elsevier, Amsterdam, 611 pages.

Wooster’s Fossil of the Week: the classic bioclaustration (Upper Ordovician of Ohio)

April 29th, 2012

We’re looking at two fossils above. One is the bryozoan Peronopora, the major skeletal structure. The second is the odd series of scalloped holes in its surface. These are a trace fossil called Catellocaula vallata Palmer and Wilson 1988. They at first appear to be borings cut into the bryozoan colony. Instead they are holes formed by the intergrowth of a soft-bodied parasite with the living bryozoan colony. This type of trace fossil is called a bioclaustration. We gave it the Latin name for “little chain of walled pits”.

My good friend Tim Palmer and I found this specimen and many others in 1987 as we explored the Upper Ordovician Kope Formation in the Cincinnati region. We were collecting bioeroded substrates like hardgrounds and shells, and these features were clearly different from the usual borings. They do not actually cut the bryozoan skeleton, for one thing. For another it is apparent that the bryozoan growth was deflected around whatever sat in those spaces. Tim and I called this kind of interaction “bioclaustration”, meaning “biologically walled -up”.
Catellocaula vallata on the Upper Ordovician bryozoan Amplexopora. Note that the scalloped holes have more lobes than those seen in the lead image. This may mean it was a different species of infesting soft-bodied organism.

The infesting parasite on the bryozoan colony was itself colonial, consisting of small clusters connected by extended stolons. The bryozoan grew around the parasite, roofing over the stolons and making walls on the margins of the clusters. We think the parasite was a soft-bodied ascidian tunicate like the modern Botryllus. If true, it is the earliest fossil tunicate known.

This closer view of C. vallata shows the scalloped margins of the pits and the horizontal connections between them.

Another specimen of C. vallata. This view shows the flat floors of the bioclaustration features.

Acetate peels cut longitudinally through the bryozoan and bioclaustrations. On the left you can see that the bryozoan zooecia (long tubes) were deflected sideways as they grew. On the right is a tunnel connecting two pits, with bryozoan zooids forming the roof. (From Palmer and Wilson, 1988.)

References:

Bromley, R.G., Beuck, L. and Taddei Ruggiero, E. 2008. Endolithic sponge versus terebratulid brachiopod, Pleistocene, Italy: accidental symbiosis, bioclaustration and deformity. Current Developments in Bioerosion, Erlangen Earth Conference Series, 2008, III, 361-368.

Palmer, T.J. and Wilson, M.A. 1988. Parasitism of Ordovician bryozoans and the origin of pseudoborings. Palaeontology 31: 939-949.

Tapanila, L. 2006. Macroborings and bioclaustrations in a Late Devonian reef above the Alamo Impact Breccia, Nevada, USA. Ichnos 13: 129-134.

Taylor, P.D. and Voigt, E. 2006. Symbiont bioclaustrations in Cretaceous cyclostome bryozoans. Courier Forschungsinstitut Senckenberg 257: 131-136.

Wooster’s Fossil of the Week: a nestling bivalve (Pleistocene of The Bahamas)

April 22nd, 2012

This weathered and encrusted shell was pulled from a round hole bored in a Pleistocene reef (about 125,000 years old) exposed on San Salvador Island, The Bahamas. It is Coralliophaga coralliophaga (Gmelin 1791), a derived venerid bivalve (a type of heterodont, meaning that it has cardinal and lateral articulating teeth inside its valves.) I collected it back in 1991 while studying an inter-reef unconformity that recorded a drop and rise of sea level (Wilson et al., 1998; Thompson et al., 2011).

Coralliophaga means “coral eater”, which is a bit of a bum rap for this clam. It is found inside borings in coral, true enough, but those holes were drilled by some other types of clams. C. coralliophaga only occupies the holes after the original dweller is dead and gone (Morton, 1980). We call this kind of behavior “nestling“, which seems a polite way of saying “squatting”. These bivalves grew to adulthood in these cavities protected from most predators as they filtered the seawater for food.
The trace fossil Gastrochaenolites torpedo (the elongate borings) with a nestling (and broken) C. coralliophaga in the lower right corner.

The posterior ends of these shells are encrusted by a variety of calcareous algae and other organisms during life, so they look a bit rough on their outsides. Often the encrustations are so thick that the shells are difficult to extract from the holes, so getting a nice complete shell like the one at the top of this entry is rare.
C. coralliophaga was named by Johann Friedrich Gmelin (1748–1804) in 1791. Gmelin was an accomplished naturalist from Tübingen, Germany. He received an MD degree in 1769, with his father (Philipp Gmelin) as his advisor. He taught at Tübingen and the University of Göttingen, writing many textbooks in fields from chemistry through botany. He published the 13th edition of Systema Naturae by Carolus Linnaeus, inserting his new taxa in the text, including our new friend Coralliophaga coralliophaga.

References:

Gmelin, J.F. 1791, in Linnaeus, C. Systema Naturae per Regna Tria Naturae, Secundum Classes, Ordines, Genera, Species, cum Characteribus, Differentiis, Synonymis, Locis. 13th Edition, Lyon : J.B. Delamolliere Tom.

Morton, B. 1980. Some aspects of the biology and functional morphology of Coralliophaga (Coralliophaga) coralliophaga (Gmelin, 1791) (Bivalvia: Arcticacea): a coral-associated nestler in Hong Kong. pp. 311-330, in: Morton, B., The Malacofauna of Hong Kong and southern China. Proceedings of the First International Workshop on the Malacofauna of Hong Kong and Southern China, Hong Kong, 1977. Hong Kong: Hong Kong University Press.

Thompson, W.G., Curran, H.A., Wilson, M.A. and White, B. 2011. Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas corals. Nature Geoscience 4: 684–687.

Wilson, M.A., Curran, H.A. and White, B. 1998. Paleontological evidence of a brief global sea-level event during the last interglacial. Lethaia 31: 241-250.

A Drool-Worthy College Museum

April 11th, 2012

AMHERST, MA – Last weekend, some Wooster Geologists attended the Keck Symposium at Amherst College and were awed by their geology museum. The Beneski Museum of Natural History  is housed in a modern building and covers three floors, displaying over 1,700 specimens. The museum hosts the Hitchcock Ichnology collection, the world’s largest collection of dinosaur footprints. Other highlights include the wall of mammals, an impressive mineral collection, and exquisite table tops of polished stone. Here are a few photos that might just make your jaw drop.

A large mastodon and other mammals greet visitors as they enter the museum.

The Hitchcock Ichnology Collection is the largest collection of dinosaur footprints in the world.

Casts of dinosaur footprints featured on the Hitchcock Collection webpage.

Was the dinosaur running or walking to make these tracks?

A large mold.

The cast that fits into the mold above.

Fossilized mudcracks, viewed from below.

Fossilized raindrops.

The petrified trunk of an ancient tree.

Want to keep a geologist busy for hours? Give her a countertop that looks like this.

 

 

Wooster’s Fossil of the Week: An asteroid trace fossil from the Devonian of northeastern Ohio

February 12th, 2012

It is pretty obvious what made this excellent trace fossil: an asteroid echinoderm. (The term “asteroid” sounds odd here, but it is the technical term for a typical sea star.) The above is Asteriacites stelliformis Osgood, 1970, from the Chagrin Shale (Upper Devonian) of northeastern Ohio.

We can tell that it was made by a sea star burrowing straight down into the sediment because it has faint chevron-shaped marks in the rays made by tube feet as they moved sediment aside. The mounds of excavated sediment can be seen between the rays at their bases. This tells us that we are not looking at an external mold of a dead sea star, but instead its living activity. This is what a trace fossil is all about.

A living asteroid from the shallow sea off Long Island, The Bahamas. (The hand belongs to my son, Ted Wilson.)

The ichnogenus Asteriacites was named by von Schlotheim in 1820. We profiled him earlier with the genus Cornulites. The author of Asteriacites stelliformis was Richard G. Osgood, Jr., my undergraduate advisor and predecessor paleontologist at The College of Wooster.
Richard Osgood, Jr., was born in Evanston, Illinois, in 1936. He went to Princeton for his undergraduate degree (I still remember his huge Princeton ring) and received his Ph.D. from the University of Cincinnati. He worked for Shell Oil Company in Houston just prior to joining the Wooster faculty in 1967. He was one of the pioneers of modern ichnology (the study of trace fossils), naming numerous new ichnotaxa and providing ingenious interpretations of them. At least one trace fossil was named after him: Rusophycus osgoodii Christopher, Stanley and Pickerill, 1998. Dr. Osgood died in 1981 in Wooster. He was an inspiration to me and many other Wooster geology students during his productive career, which was all too short.

References:

Osgood, R.G., Jr. 1970. Trace fossils of the Cincinnati area. Palaeontographica Americana 6: 281-444.

Schlotheim, E.F. von. 1820. Die Petrfactendunde auf ihrem jetzigen Standpunkte durch die Beshreibung seiner Sammlung versteinerter und fossiler Überreste des Thier- und Pflanzernreichs der Vorwelt erläutert 1-457.

Stanley, D.C.A. and Pickerill, R.K. 1998. Systematic ichnology of the Late Ordovician Georgian Bay Formation of southern Ontario, eastern Canada. Royal Ontario Museum Life Sciences Contribution 162, 56 pp., 13 pl. Toronto.

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

January 29th, 2012

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

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

References:

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

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

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

Wooster’s Fossils of the Week: Sponge and clam borings that revealed an ancient climate event (Upper Pleistocene of The Bahamas)

September 11th, 2011

This week’s fossils celebrate the publication today of a paper in Nature Geoscience that has been 20 years in the making. The title is: “Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas coral”, and the senior author is the geochronological wizard Bill Thompson (Woods Hole Oceanographic Institution). The junior authors are my Smith College geologist friends Al Curran and Brian White and me.

The paper’s thesis is best told with an explanation of this 2006 image:
This photograph was taken on the island of Great Inagua along the coast. The flat dark surface in the foreground is the top of a fossil coral reef (“Reef I”) formed during the Last Interglacial (LIG) about 123,000 years ago. It was eroded down to this flat surface when sea-level dropped, exposing the reef to waves and eventually terrestrial weathering. The student sitting on this surface is Emily Ann Griffin (’07), one of three I.S. students who helped with parts of this project. (The others were Allison Cornett (’00) and Ann Steward (’07).) Behind Emily Ann is a coral accumulation of a reef (“Reef II”) that grew on the eroded surface after sea-level rose again about 119,000 years ago. These two reefs show, then, that sea-level dropped for about 4000 years, eroding the first reef, and then rose again to its previous level, allowing the second reef to grow. (You can see an unlabeled version of the photograph here.) The photograph at the top of this post is a small version of the same surface.

The significance of this set of reefs is that the erosion surface separating them can be seen throughout the world as evidence of a rapid global sea-level event during the Last Interglacial. Because the LIG had warm climatic conditions similar to what we will likely experience in the near future, it is crucial to know how something as important as sea-level may respond. The only way sea-level can fluctuate like this is if glacial ice volume changes, meaning there must have been an interval of global cooling (producing greater glacial ice volume) that lowered sea-level about 123,000 years ago, and then global warming (melting the ice) that raised it again within 4000 years. As we write in the paper, “This is of great scientific and societal interest because the LIG has often been cited as an analogue for future sea-level change. Estimates of LIG sea-level change, which took place in a world warmer than that of today, are crucial for estimates of future rates of rise under IPCC warming scenarios.” With our evidence we can show a magnitude and timing of an ancient sea-level fluctuation due to climate change.

Much of the paper concerns the dating techniques and issues (which is why Bill Thompson, the essential geochronologist, is the primary author). It is the dating of the corals that makes the story globally useful and significant. Here, though, I want to tell how the surface was discovered in the first place. It is a paleontological tale.

In the summer of 1991 I worked with Al Curran and Brian White on San Salvador Island in The Bahamas. They were concentrating on watery tasks that involved scuba diving, boats and the like, while I stayed on dry land (my preferred environment by far). I explored a famous fossil coral exposure called the Cockburntown Reef (Upper Pleistocene, Eemian) that Brian and Al had carefully mapped out over the past decade. The Bahamian government had recently authorized a new harbor on that part of the coastline and a large section of the fossil reef was dynamited away. The Cockburntown Reef now had a very fresh exposure in the new excavation quite different from the blackened part of the old reef we were used to. Immediately visible was a horizontal surface running through the reef marked by large clam borings called Gastrochaenolites (see below) and small borings (Entobia) made by clionaid sponges (see the image at the top of this post).
Inside the borings were long narrow bivalve shells belonging to the species Coralliophaga coralliophaga (which means “coral eater”; see below) and remnants of an ancient terrestrial soil (a paleosol). This surface was clearly a wave-cut platform later buried under a tropical soil.


My colleagues and I could trace this surface into the old, undynamited part of the Cockburntown Reef, then to other Eemian reefs on San Salvador, and then to other Bahamian islands like Great Inagua in the far south. Eventually this proved to be a global erosion surface described or at least mentioned in many papers, but its significance as an indicator of rapid eustatic sea-level fall and rise was heretofore unrecognized. Finally getting uranium-thorium radioactive dates on the corals above and below the erosion surface placed this surface in a time framework and ultimately as part of the history of global climate change.

This project began 20 years ago with the discovery of small holes left in an eroded surface by humble sponges and clams. Another example of the practical value of paleontology.

References:

Thompson, W.G., Curran, H.A., Wilson, M.A. and White, B. 2011. Sea-level oscillations during the Last Interglacial highstand recorded by Bahamas coral. Nature Geoscience (DOI: 10.1038/NGEO1253).

White, B.H., Curran, H.A. and Wilson, M.A. 1998. Bahamian coral reefs yield evidence of a brief sea-level lowstand during the last interglacial. Carbonates and Evaporites 13: 10-22.

Wilson, M.A., Curran, H.A. and White, B. 1998. Paleontological evidence of a brief global sea-level event during the last interglacial. Lethaia 31: 241-250.

Wooster’s Fossils of the Week: barnacle borings (Middle Jurassic of Israel)

August 7th, 2011

Tiny little trace fossils this week in a Jurassic crinoid stem from the Matmor Formation of the Negev Desert. They are borings produced by barnacles, which are sedentary crustaceans more typically found in conical shells of their own making. These barnacles are still around today, so we know quite a bit about their biology. (More on how in a minute.) These acrothoracican barnacles drill into shells head-down and then kick their legs up through the opening to filter seawater for food. They’ve been doing it since the Devonian Period (Seilacher, 1969; Lambers and Boekschoten, 1986).

This particular trace fossil is Rogerella elliptica Codez & Saint-Seine, 1958. It is part of a diverse set of borings in the Matmor Formation (Callovian) of Hamakhtesh Hagadol, Israel, recently described in Wilson et al. (2010).

We know so much about boring barnacles because Charles Darwin himself took an almost obsessive interest in them early in his scientific career. While on his famous voyage in the HMS Beagle, Darwin noticed small holes in a conch shell, and he dug out from one of them a curious little animal shown in the diagram below.


Cryptophialus Darwin, 1854

He called it “Mr. Arthrobalanus” in his zoological notes. He figured out early that it was a barnacle, but he was astonished at how different it was from others of its kind. He later gave it a scientific name (Cryptophialus Darwin, 1854) and took on the problem of barnacle systematics and ecology. Eight years and four volumes later his young son would ask one of his friends, “Where does your father do his barnacles?” The diversity of barnacles played a large role in Darwin’s intellectual development and, consequently, his revolutionary ideas about evolution (Deutsch, 2009).

Burrowing barnacle diagram from an 1876 issue of Popular Science Monthly.

References:

Codez, J. and Saint-Seine, R. de. 1958. Révision des cirripedes acrothoracique fossiles. Bull. Soc. géol. France 7: 699-719.

Darwin, C.R. 1854. Living Cirripedia, The Balanidae, (or sessile cirripedes); the Verrucidae. Vol. 2. London: The Ray Society.

Deutsch, J.S. 2009. Darwin and the cirripedes: Insights and dreadful blunders. Integrative Zoology 4: 316–322.

Lambers, P. and Boekschoten, G.J. 1986. On fossil and recent borings produced by acrothoracic cirripeds. Geologie en Mijnbouw 65: 257–268.

Seilacher, A. 1969. Paleoecology of boring barnacles. American Zoologist 9: 705–719.

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: Ancient shrimp burrows (Middle Jurassic of Israel)

July 10th, 2011

This week we have a trace fossil, the burrow Thalassinoides. It is represented by one of my favorite images, reproduced above, showing a very large Thalassinoides suevicus in the Zohar Formation (Middle Jurassic, Callovian) of Makhtesh Qatan in the Negev of southern Israel. Holding the scale is Wooster geologist and Independent Study student Allison Mione (’05) during our 2004 Israel expedition. These burrows were originally described as giant desiccation cracks, but I.S. student Kevin Wolfe (’05), Israeli geologist Yoav Avni and I reinterpreted them as burrows in a rocky shore complex (see Wilson et al., 2005).

Thalassinoides is a complex trace fossil that is today made primarily by thalassinidean crustaceans (a type of shrimp; see below). We know a lot about how the burrows are made today by shrimp, and our knowledge is growing about how the ancient systems were excavated, at least in the Mesozoic and later. We have fossil shrimp preserved in Thalassinoides from the Jurassic (Sellwood, 1971) and the Cretaceous (Carvalho et al., 2007).

Pestarella tyrrhena, a modern thalassinidean shrimp. Image from Wikipedia.

Reconstruction of Mecochirus rapax in a Cretaceous Thalassinoides. A) In its burrowing life mode; B) Predominantly horizontal Thalassinoides suevicus burrow systems showing two successive event levels, with Mecochirus in life position. From Carvalho et al. (2007, fig. 3).

The burrow systems in the Zohar Formation of Israel were critical in working out the depositional environment of these carbonate sediments. We could see that first the water was comparatively deep (below wavebase) with worm burrows (Planolites). Then relative sea level dropped and the Thalassinoides burrows cut through the Planolites fabric, showing that the sediment was become stiffer. Finally bivalve borings (Gastrochaenolites) in the same rock indicated that the sediment had cemented into a shallow water hardground. This hardground showed tidal channels cut into its top surface (Wilson et al., 2005).

This work was done with virtually no “body fossils”, meaning evidence of the actual bodies of the organisms living in and on the sediment. Trace fossils, evidence of organism activity, were the only indications of this significant environmental change. This is why the study of trace fossils (ichnology) should be a part of the education of every paleontologist and sedimentologist.

References:

Carvalho, C.N., Viegas, P.A. and Cachao, M. 2007. Thalassinoides and its producer: Populations of Mecochirus buried within their burrow systems, Boca Do Chapim Formation (Lower Cretaceous), Portugal. Palaios 22: 104-109.

Sellwood, B.W. 1971. A Thalassinoides burrow containing the crustacean Glyphaea undressieri (Meyer) from the Bathonian of Oxfordshire. Palaeontology 14: 589-591.

Wilson, M.A., Wolfe, K.R., and Avni, Y. 2005. Development of a Jurassic rocky shore complex (Zohar Formation, Makhtesh Qatan, southern Israel). Isr. J. Earth Sci. 54: 171–178.

Bioerosion on oysters across the Cretaceous-Paleogene Boundary in Alabama and Mississippi (USA) (Senior Independent Study Thesis by Megan Innis)

April 8th, 2011

This is my research team at a road-cut locality in Mississippi. (Photo courtesy of George Phillips.)

Editor’s note: Senior Independent Study (I.S.) is a year-long program at The College of Wooster in which each student completes a research project and thesis with a faculty mentor.  We particularly enjoy I.S. in the Geology Department because there are so many cool things to do for both the faculty advisor and the student.  We are now posting abstracts of each study as they become available.  The following was written by Megan Innis, a senior geology major from Whitmore Lake, Michigan. Here is a link to Megan’s final PowerPoint presentation as a movie file (which can be paused at any point). You can see earlier blog posts from Megan’s field work by clicking the Alabama and Mississippi tags to the right.

During the summer of 2010, I traveled to Alabama and Mississippi with my research team including Dr. Mark Wilson, Dr. Paul Taylor, and Caroline Sogot.  Our trip was about ten days and included fieldwork and research. The purpose of our research was to collect fossils from below and above the Cretaceous-Paleogene (K/Pg) boundary to try and understand the Cretaceous mass extinction from a microfaunal level.

I chose to focus my thesis on oysters and the sclerobionts associated with these calcareous hard substrates.  Although my study was focused on oysters, I also collected a wide variety of other specimens including nautiloids, ammonites, belemnites, corals, sharks teeth, and bryozoans.

The oyster species present in each system.

When I got back to school in August, I identified all of my oyster species (three total) and began to identify and collect data for the sclerobionts. The oysters from the Cretaceous included Exogyra costata and Pycnodonte convexa and the oysters from the Paleogene included Exogyra costata, Pycnodonte convexa, and Pycnodonte pulaskiensis.

Sample specimens that I collected in Alabama and Mississippi. The oysters in yellow boxes and circles are the oyster species that were used in my study.

I identified nine sclerobionts including Entobia borings; Gastrochaenolites borings; Oichnus borings; Talpina borings; serpulids; encrusting oysters; encrusting foraminiferans; Stomatopora bryozoans; and “Berenicia” bryozoans.  My research showed:

1) Bioerosion of oyster hard substrates was common in the Late Cretaceous and Paleogene and sclerobionts were abundant before and after the extinction.

2) Entobia sponge borings appear to increase in abundance across the K/Pg boundary and become more common in the Paleogene.

3) Gastrochaenolites borings, made by bivalves, and serpulids were more prevalent in the Late Cretaceous, suggesting boring bivalves and serpulids were significantly reduced after the extinction.

4) Encrusting oysters and foraminiferans were more common in the Late Cretaceous, but also relatively abundant on Pycnodonte pulaskiensis in the Paleogene.

5) Encrusting bryozoans were more common in the Late Cretaceous and absent in the Paleogene, suggesting bryozoans were severely affected by the extinction.

6) Talpina borings were only found on Pycnodonte pulaskiensis in the Paleogene, but no significant data was collected elsewhere.

To my knowledge, this is the first study of bioerosion on oysters across the K/Pg boundary.

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