Wooster’s Fossil of the Week: a siliquariid gastropod (Eocene of Alabama)

December 25th, 2011

It is hard to believe that this twisty tube is a snail, but it is. Tenagodus vitis (Conrad, 1835) is the scientific name for this worm-like gastropod from the Claiborne Sand (Eocene) of Alabama. It was originally named by Conrad as Siliquaria vitis, a name still commonly used even though it was made a junior synonym by CoBabe and Allmon (1994).

This kind of gastropod with its awkward shell clearly didn’t crawl around. It was a sessile benthic epifaunal filter-feeder, meaning that it lived stationary on the seafloor filtering organic material from the water. Some of these sessile snails twisted their tubes around each other and formed a kind of gastropod reef.
The twisty part of Tenagodus vitis shows its true snaily nature.
The related Siliquaria anguina. (From Cooke et al., 1895, Cambridge Natural History, volume 3, Fig. 153.)
The discoverer of Tenagodus vitis was Timothy Abbott Conrad (1803-1877). He was a conchologist (one who studies shells) and paleontologist in New York and New Jersey, and he was a paleontological consultant during the early days of the Smithsonian Institution.

References:

CoBabe E.A. and Allmon, W.D. 1994. Effects of sampling on paleoecologic and taphonomic analyses in high-diversity fossil accumulations: an example from the Eocene Gosport Sand, Alabama. Lethaia 27: 167-178.

Conrad, T.A. 1835. Fossil shells of the Tertiary formations of North America, illustrated by figures drawn on stone by T.A.Conrad. vol. 1, no. 3, p. 29-56, pl. 15-18 (pp. 77-110, pl. 15-18 in 1893 reprint by G.D. Harris [with pl. 19-20 not included in original by Conrad], reprinted 1963 by the Paleontological Research Institution, Ithaca, NY).

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.

From Alabama to Mississippi

May 24th, 2010

STARKVILLE, MISSISSIPPI — Early this morning we left Demopolis, Alabama, and drove to Livingston, home of the University of West Alabama.  Our first localities, in fact, were very close to campus as we again explored the Upper Cretaceous Prairie Bluff Formation.

Megan, Caroline and Paul doing the paleontology thing on an outcrop in Livingston, Alabama (N 32.59827°, W 88.19301°). The scene looks pretty quiet and usually is, except for the occasional utterance like, "Cool! More cyclostomes!". It is a culture all to itself.

In the early afternoon we crossed the border into Mississippi.  It may be our imagination and a limited sample size, but we swear the accents got thicker and the British among us especially had difficulty understanding it.  The fossils, though, know no boundaries and were just as good as their Alabama cousins.

A bored Cretaceous oyster waiting patiently to be picked up on a Mississippi outcrop of the Prairie Bluff Formation (N 33.48371°, W 88.85309°).  The fossils here are found on a dried mud so when you pick them up they give a satisfying sound as they detach from the ground.  It is like opening a sealed package knowing you're the first to find it.

A bored oyster waiting patiently to be collecting on a Mississippi outcrop of the Prairie Bluff Formation (N 33.48371°, W 88.85309°). The evenly-spaced holes were produced by an endolithic clionaid sponge. Note the splendid preservation of the shell and just the right kind of weathering. This is the kind of outcrop where you wonder why more people aren't here picking up this great stuff!

Her Majesty's Own Bryozoologist, Dr. Paul D Taylor, in action on a Mississippi outcrop. (Shout-out to Emma: This is the best I can do with your father. Always crouching close to the ground, he is. Bendiest man in paleontology.)

Sweet Home Alabama

May 23rd, 2010

Lonely highway near Jefferson, Alabama, at one of our roadside outcrops (N 32.39412°, W 87.92422°).

DEMOPOLIS, ALABAMA — We practically had the state to ourselves on this steamy Sunday as we drove around western Alabama looking for outcrops of the latest Cretaceous and earliest Paleogene.  As is often the case, localities described in the literature disappear because of housing developments, road expansions, new dams on rivers, and the luxuriant growth of vegetation (especially kudzu down here).  Still, we found that even a meter-thick strip of the Prairie Bluff Formation in a roadside ditch can be loaded with encrusted and bored fossil shells, so we collected enough specimens to make the driving worthwhile.  Now we settle down for our last night in Alabama before crossing over into Mississippi tomorrow.  (This gives me time to soothe the chigger bites on my ankles!)

We promised Megan and Caroline that if they crossed the muddy creek to see what was on the other side, we would immortalize their heroics in the blog.

We all had our photographs taken under this most appropriate ranch sign. (For the non-geologists, "KT" is our code for "Cretaceous-Tertiary".)

Mud, Sun and Fossils

May 22nd, 2010

GREENVILLE, ALABAMA — Reconnaissance is over for this part of the state, and our work commenced this morning.  We want to find good sclerobiont communities above and below the Cretaceous-Tertiary boundary, so here that means we want specimens from the Upper Cretaceous (Maastrichtian) Prairie Bluff Formation and the Paleocene (Danian) Clayton Formation.  That means plenty of muddy creekbeds and sun-smacked roadcuts.

Megan Innis (below) and Caroline Sogot (above) collecting bored and encrusted fossil oysters from the Prairie Bluff Formation in Mussel Creek (N 31.97259°, W 86.70387°).

Megan (in the fashionable yellow wellies) and Caroline collecting oysters from the Prairie Bluff Formation along Alabama 263 (N 32.04082°, W 86.79367°).

This would be a good time to mention that Caroline’s father is a famous magician in England with the stage name Jack Stephens.  We think this is very cool.  And I quickly add, Megan’s father Jeffrey is a famous pediatric geneticist at the University of Michigan.  We like that too!

This is the kind of fossil we like. It is a bivalve shell from the Clayton Formation (Tertiary, Danian) thoroughly bored by sponges. Unfortunately it is also well locked into this silicified rock matrix!

Post-Cretaceous Weirdness

May 22nd, 2010

GREENVILLE, ALABAMA — The Cretaceous-Tertiary boundary at Mussel Creek, Lowndes County, Alabama, has some unusual complexity.   At the southern end of the section it is simple enough, as shown in a previous blog post.  Just a few meters north, though, the boundary section looks like this:

Cretaceous-Tertiary boundary section at Mussel Creek, Lowndes County, Alabama (N 31.97176°, W 086.70414°). The "K" indicates Cretaceous rock; the "T' marks Tertiary sediments; the rounded black object is charcoalized wood.

This strange stratigraphy appears to be a stream channel filled with carbonaceous (carbon-bearing) laminated sediments which were incised into the Cretaceous Prairie Bluff Formation below.  Is this channel Cretaceous or Tertiary?  What sort of environmental conditions does it represent?  We discussed and tested many hypotheses on the outcrop this morning, which is always great fun.  We finally decided that these channel-filling sediments are Tertiary, following the conclusions of some (but not all) previous authors.  Still, the beds are unlike any channel-fills I’ve seen before, especially with all the carbon.  My favorite idea (which has no support in the literature, I quickly add) is that this channel represents erosion of a continent devastated by the impact blast in Yucatan just across the Gulf of Mexico.  The local forests were burned off in the massive wildfires (and maybe further devastated by a tsunami), leading to rapid erosion and the cutting and filling of channels on the shallow marine shelf here.  All the carbon is from the enormous amounts of burned wood.

This is what we would call a romantic view of stratigraphy.  It would mean that the big piece of charcoal in the section above is from a tree burned in the end-Cretaceous cataclysm.  I like that idea!

Another beautiful fossil hard substrate

May 21st, 2010

Megan Innis studying the Ripley Formation rockground near Greenville, Alabama.

GREENVILLE, ALABAMA — I have a soft spot for hard places.  (Always wanted to say that!)  Much of my career has been spent studying marine hard substrates and the communities that have evolved on and in them.  These include rocks, hardgrounds and shells on seafloors which have been encrusted and bored by diverse organisms for hundreds of millions of years.  In all the many marine environments where these substrates occur, we know the organisms faced one common problem: how to occupy and defend space in an essentially two-dimensional world.  This provides a thread to follow through the long evolution of sclerobionts (hard-substrate dwellers, to use one of my favorite words.)

At the top of the Maastrichtian (Upper Cretaceous) Ripley Formation is a rockground which was bored and encrusted on the seafloor in the classic way.  It was ably described in a paper by Jon Bryan, and we were pleased to see that the surface is still exposed and accessible today.  There were some tasty encrusting bryozoans on some of the cobbles here!

Spondylid bivalve encrusting the Ripley Formation rockground.

Geological fieldwork in the Deep South

May 21st, 2010

An Alabama Creek where, oddly enough, we found superb Paleocene nautiloids in the McBryde Member of the Clayton Formation (N 31.91739°, W 086.68906°).

GREENVILLE, ALABAMA — This is the first time I’ve done fieldwork in the southern USA.  The outcrops are of course very different from my favorite desert locations and oddly similar to those I visited in western Russia last summer.  I’m learning once again not to pass by the muddy creek or grass-covered hillside assuming that no useful rocks or fossils will be present.  Southern geologists Jon Bryan and Peter Harries have been excellent guides here because they know what treasures lurk under the vegetation and on the river banks.

A grassy hillside with beautiful Cretaceous oysters just underneath. We collected the lot by feeling for the fossils with our feet! (N 32.02580°, W 086.76788°)

An intimate visit to the Cretaceous-Tertiary boundary

May 21st, 2010

Cretaceous-Tertiary boundary at Mussel Creek, Lowndes County, Alabama (N 31.97176°, W 086.70414°). Megan's hand marks the level with the Cretaceous below and the Tertiary above.

A closer view of the same boundary. My finger is thrilled to be in such a place.

GREENVILLE, ALABAMA — It is one of the most famous geological horizons.  It marks the end of the Mesozoic Era and the beginning of the Cenozoic.  The “K/T boundary” is dated at 65.5 million years ago (±0.3 my) and is found around the world.  It is the primary datum for our work on this expedition, and we were led right to it by our friend Jon Bryan.  We want to just pause a moment and enjoy the historical and stratigraphic significance of these sediments.  (And yes, I know I should be calling this the more modern “Cretaceous-Paleogene Boundary” as Megan insists, but I grew up with “K/T” since my Berkeley graduate school days and it is hard to give up!)

More later from our hot and muggy day in southern Alabama!

Wooster Geologists in Alabama!

May 20th, 2010

Mark Wilson (Wooster), Caroline Sogot (University of Cambridge), Megan Innis (Wooster) and Paul Taylor (Natural History Museum, London) on our first evening in Alabama. This is our "before" photograph. Let's see what we look like in 10 days of mud, sun and mosquitoes.

GREENVILLE, ALABAMA–We were told many times before this trip that we will find the people in the Deep South to be friendly.  This has been very much the case from the employees at the Atlanta airport to the young man in Greenville who insisted on carrying our few small bags of groceries out to the car.  We also knew it would be hot, muggy, and that at the store we could buy (if we ever wanted to) loads of pig’s ears and feet!  It is a delight to experience such cultural gradients in our own country.

Megan Innis, a senior geology major at The College of Wooster, is here with me to pursue her Independent Study project on changes in bioerosion patterns across the boundary between the Mesozoic and Cenozoic Eras (the “K/T” boundary marking the end-Cretaceous extinctions).  This event 65 million years ago was the result of an asteroid impact which triggered a global ecological catastrophe, most famously taking out the dinosaurs.  Megan and I want to see what happened to the community of organisms which bore and drill shells and other hard substrates.  Some of the best exposures of rocks associated with this extinction are found here in southern Alabama and neighboring Mississippi.

My friend and colleague Paul Taylor of the Natural History Museum in London is here with his PhD student Caroline Sogot (University of Cambridge) to investigate similar patterns in the other hard substrate faunas across the boundary, especially bryozoans.  We have joined forces so that we can most efficiently measure sections and collect specimens, many of which we will be sharing in later laboratory analyses.

Tomorrow is our initial orientation in the field.  We have been joined by Peter Harries of the University of South Florida and two of his graduate students, and in the morning we will meet Jon Bryan of Northwest Florida State College.  Peter and Jon are Cretaceous experts who know the local outcrops and are enthusiastic about the chance to talk paleontology for days on end!