Archive for January, 2019

Conulariid and trepostome bryozoan symbiosis in the Upper Ordovician of Estonia

January 22nd, 2019

A new paper is just out in which all the characters have been covered previously in this blog, but not as parts of a single story. It describes an interprets the relationship between the mysterious conulariids and trepostome bryozoans in the Katian and Sandbian (Upper Ordovician) of northern Estonia. The authors have all made appearance here, including lead author Olev Vinn (Institute of Ecology and Earth Sciences, University of Tartu, Estonia). Andrej Ernst (Institut für Geologie, Universität Hamburg, Germany), myself, and Ursula Toom (Institute of Geology, Tallinn University of Technology, Estonia). It was a fun team to work on, and Olev led it masterfully.

There are numerous trepostome bryozoans in the Upper Ordovician of Estonia that grew up and around the bases of conulariids, which are extinct cnidarians. This is, in fact, an example of bryoimmuration as covered in my last post. The puzzle is what was the relationship between these two groups. Were the conulariids parasites on the bryozoans? Did they gain protection from predators by embedment in the bryozoan calcitic skeleton? Were the bryozoans prime real estate for the conulariids because they were hard substrate islands on a muddy seafloor? We think the answers are probably yes to all these questions.

The top composite of images is Figure 3 in the paper. The caption: A, Two conulariids Climacoconus bottnicus (Holm, 1893) in Diplotrypa bicornis (Eichwald, 1829) from Haljala Regional Stage, northern Estonia, note the slightly elevated apertures of conulariids (GIT 720-4). B, Longitudinal section of Diplotrypa abnormis (Modzalevskaya, 1953) with conulariid Climacoconus bottnicus (Holm, 1893) (GIT 537-1822) from Haljala Regional Stage, northern Estonia. C, Longitudinal section of completely embedded Climacoconus bottnicus (Holm, 1893) in Esthoniopora communis (GIT 537-1656) from Haljala Regional Stage, northern Estonia. D, Conulariid in Mesotrypa expressa Bassler, 1911 from Oandu Regional Stage, northern Estonia; note the depression around the conulariid’s aperture (GIT 770-7). E, Conulariid in Mesotrypa expressa Bassler, 1911 from Oandu regional Stage, northern Estonia; note the malformation of a zooid near the aperture of the conulariid (GIT 770-92). F, Conulariid in Esthoniopora subsphaerica from Rakvere Regional Stage, northern Estonia; note the strongly elevated aperture of the conulariid (GIT 537-1760).

This work is another product of Wooster’s generous research leaves program that has supported many trips to Estonia.


Vinn, O., Ernst, A., Wilson, M.A., and Toom, U. 2019. Symbiosis of conulariids with trepostome bryozoans in the Upper Ordovician of Estonia (Baltica). Palaeogeography, Palaeoclimatology, Palaeoecology 518: 89-96.

The Everglades Are All About Geology

January 16th, 2019

If you’ve ever been to the Everglades or even heard of them, you probably are picturing something like this:

Taylor Slough

Or maybe this:

American alligator

In other words, Everglades National Park exists because it is “important habitat for numerous rare and endangered species”  (from the Everglades NP homepage).  I visited the Everglades recently, and thankfully all four major National Park Service sites in South Florida are still open despite the government shutdown thanks to non-profit partners like the Florida National Parks Association. (Seriously, South Florida’s private groups have done an admirable job preventing the sort of issues experienced at other National Parks.) One thing I learned, starting with a diagram in the Big Cypress National Preserve welcome center, then while driving and walking around the Everglades, was that the great diversity of habitats found in the Everglades is strongly dependent on the geology.  More specifically, the habitats you in the Everglades are dependent on two things: 1) the seasonal rise and fall of the water table between the rainy and dry seasons and 2) minute changes in elevation.

Ignoring for a moment the low-lying areas along the coast that are impacted by seawater, even the freshwater ecosystems of the Everglades are sensitive to very small changes in elevation.  The sensitivity comes from an interaction between precipitation cycles and elevation.  During the rainy season, so rain water enters the Everglades that the water table (the level below which the ground is saturated) rises, and water seeps out of the ground to flood low-lying areas.  Lower areas get flooded for a longer period of the year.

In the heart of Big Cypress National Preserve, for example, the high points are about 13 ft in elevation.  This high ground is dominated by “hardwood hammocks”, evergreen broadleaf trees live gumbo limbo, live oak, and mahogany.  It looks almost like a tropical rainforest, but with fewer vines and ferns.  These hammocks are the only reliably dry ground in the wet season.

The edge of a hardwood hammock; the light at the far end of the photo is from the adjacent pinelands.

About two feet lower (11 ft elevation), you’ll transition into the pinelands.  Having lived out West, I’d call this “parkland” — lots of grass, with tall slash pines dispersed throughout. It’s the only habitat in the Everglades that looks appealing for a stroll, and it only floods about 2-3 months during the year. The pinelands have regular fires, just like the ponderosa pine forests of the Rockies.

Pinelands; this photo is taken a few horizontal feet from the hammock photo above!

Go another two feet lower (9 ft elevation), and there is “open” prairie.  “Open” is deceptive here because 4-6 months of the year it’s basically a giant pond.  This is the habitat that wading birds like egrets, storks, and spoonbills love. Still, they also burn regularly enough to prevent trees from growing.

Sawgrass Prairie (hardwood hammock in the background)

Another foot lower (8 ft) elevation, and you’re into the cypress swamps. These swamps are flooded more than half the year, so it’s too wet for hardwoods or pine trees.  They’re even too wet for prairie because they rarely burn. Bald cypress trees, though, are well-suited for this life. They thrive in freshwater — so much so, in fact, that they shed their leaves in the dry season (boreal winter).  That’s right, in South Florida, the broadleaf trees are evergreen and the needle-leaf trees are deciduous! The madness!

A bald cypress “strand” in Big Cypress National Preserve

The lowest inland elevations are the “gator holes” and “sloughs”; permanent pools of water that are wet all year round.  This is where all of the fish, the turtles, and the water birds congregate (with the alligators) in the dry season. (That’s also why the dry season is the best time to see wildlife — it’s confined!)

Closer to the coast, the entire system is shifted down and compressed to an even tighter elevation range.  The water table slopes toward the coast, so the top of the system (hardwood hammock) is 7 feet elevation, the cypress are down at about 3.5 feet, and anything lower is probably brackish water. Depending on salinity of the water and soil, you might see mangroves, grasses, pickleweed, or even cactus. But suffice it to say, the interplay of the wet and dry seasons and subtle changes in elevation dictate the balance of four distinct freshwater habitats and several brackish habitats, as well.  This is a very sensitive system, and even slight changes to elevation (or sea level) can make a world of difference.

Red mangroves in Biscayne National Park

New paper on bryoimmuration and taphonomic engineering

January 12th, 2019

I’m pleased to link to a new paper that has just appeared in the journal Lethaia. My wonderful coauthors are Caroline Buttler (National Museum Wales) and Paul Taylor (Natural History Museum, London). The paper explores the role calcitic bryozoans play in preserving molds of aragonitic shells, a process we call bryoimmuration. In the image above we have two views of a single specimen from the Cincinnatian (Upper Ordovician) of the Cincinnati, Ohio, region. It is a trepostome bryozoan that encrusted the exterior of a bivalve shell. The bivalve shell was aragonitic and thus dissolved away during diagenesis. The bryozoan skeleton is calcite, a mineral that does not dissolve as easily as its cousin aragonite. The surviving bryozoan skeleton thus preserved our only record of the now-dissolved bivalve shell. The larger concept of one group of organisms affecting the preservation of another we call taphonomic engineering. Below are cross-sections of these bryoimmuring bryozoans, with the original caption.

Fig. 3. Acetate peels of bryoimmuring bryozoans cut perpendicular to basal growth surface (longitudinal); all from the Upper Whitewater Formation (Katian) near Richmond, Indiana (locality as in Fig. 2). A, heterotrypid bryozoan that grew across the ribs of an ambonychid bivalve. Note the thin zooecial walls in the early fast-growing stage, later thickening upwards (CW‐148‐92). B, very thin sheet of a trepostome bryozoan that encrusted an ambonychid bivalve (CW‐148‐93). This bryozoan did not develop an exozone and is thus impossible to identify. C, heterotrypid bryozoan that developed a thick exozone while growing on an ambonychid bivalve shell (CW‐148‐94). The shell later dissolved and sediment took its place. D, multilaminar growth of a heterotrypid bryozoan on an ambonychid bivalve (CW‐148‐95). The bryozoan colony overgrew itself.

This research was supported by an award from the Henry Luce III Fund for Distinguished Scholarship at The College of Wooster. Nick Wiesenberg helped with the fieldwork. It was a fun project.