Archive for April, 2011

Wooster’s Fossil of the Week: Reef-forming brachiopods (Middle Permian of southwestern Texas)

April 10th, 2011

In my early days of teaching paleontology I had an enthusiastic trading program with colleagues around the country. I would supply fine fossils from the Upper Ordovician of southern Ohio for what I considered exotic specimens from elsewhere. In one of the trades I received a block of limestone from the Road Canyon Formation found in the Glass Mountains of southwestern Texas. It was from the Roadian Stage of the Guadalupian Series of the Permian System, so about 270 million years old.

This limestone is famous for its silicified fossils. The original calcite shells of the fossils were replaced by silica (similar to the mineral quartz), yet the matrix of the limestone remained mostly calcite. This meant that my students and I could immerse the limestone block in hydrochloric acid and watch the calcite matrix dissolve and the silicified shells remain as an insoluble residue. What emerged from the acid were beautiful fossils where even the finest spines are preserved.

Cluster of Hercosestria cribrosa brachiopods with the conical ventral valve (VV) and lid-like dorsal valve (DV) labelled.

Our particular block was part of a reef complex in which the primary framework was made by conical brachiopods attached to each other by long spines. These brachiopods are unlike any that came before or since. Each shell consists of two valves: the ventral valve is an open cone and the dorsal valve attaches to it as a hinged lid. The spines come from the ventral valve and wrap around other shells to make a wave-resistant structure — a reef. These brachiopod reefs were unique to the Permian.

The species we have, Hercosestria cribrosa Cooper & Grant 1969, belongs to the Superfamily Richthofenioidea in the Order Productida, so they are often called richthofenids and productids. Hercosestria had its moment of paleontological fame in the mid-1970s. Two prominent paleontologists, Richard Cowen and Richard Grant, debated the role of models in assessing the functional morphology of extinct species.  Richthofenid brachiopods were used as an example: did they flap their dorsal valves to create a current (Cowen’s suggestion), or did they crack the valves open and pump the water in and out with their fleshy lophophores? Grant showed a specimen of Hercosestria cribrosa with another brachiopod living on its dorsal valve, convincingly demonstrating that the valves did not likely flap.

On the left is a figure from Grant (1975) showing Hercosestria cribrosa with a small brachiopod living on its dorsal valve; on the right is a side view of two H. cribrosa ventral valves with attaching spines.

To make it even more interesting, by the 1980s there was considerable support for the idea that richthofenid brachiopods like Hercosestria had algal symbionts in their tissues and thus were effectively photosynthetic!

Reconstruction of a Permian reef from the University of Michigan Exhibit Museum of Natural History.

To see the other Wooster’s Fossil of the Week posts, please click on this link or the appropriate tag to the right.

References –

Cooper, G.A. and Grant, R.E. 1969. New Permian brachiopods from west Texas. Smithsonian Contributions to Paleobiology 1: 1-20.

Cowen, R. 1975. ‘Flapping valves’ in brachiopods. Lethaia 8: 23-29.

Cowen, R. 1983, Algal symbiosis and its recognition in the fossil record: in Tevesz, M.J.S. and McCall, P.L., eds., Biotic Interactions in Recent and Fossil Benthic Communities: Plenum Press, New York, p. 431-478.

Grant, R.E. 1975. Methods and conclusions in functional analysis: a reply. Lethaia 8: 31–33.

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.

When Volcanoes Erupt

April 6th, 2011

WOOSTER, OH – Students in the Geology of Natural Hazards course spent a day studying the products of volcanic eruptions. Here are some of the outstanding samples in our volcanic collection:

Reticulite is a delicate network of basaltic glass that forms during Hawaiian fire fountaining. Volatiles expand easily in the low-viscosity magma, creating a dense network of interconnected vesicles separated by thin strands of quenched lava (sideromelane).

Accretionary lapilli are rounded pea-sized pieces of tephra that consist of volcanic ash. Ash aggregates into balls because of electrostatic forces in the eruption column.

Volcanic bombs are formed when lava is ejected and becomes airborne. The fusiform bomb has a rounded aerodynamic shape with an elongated tail, which tells us that the material was molten when it was ejected and was shaped as it traveled through the air.

The glassy surface of this basalt shows the classic ropy texture of pahoehoe. Ropy pahoehoe develops when the surface of a lava flow becomes partially solidified and wrinkles as the underlying lava continues to flow.

Wooster’s Fossil of the Week: A little brachiopod gets a name (Middle Jurassic of southern Israel)

April 3rd, 2011

Moorellina negevensis Krawczyński & Wilson 2011; 1a – general view of the dorsal valve interior; 1b – oblique view showing brachial cavities and cardinalia.

This week our fossil star is a new brachiopod species a Polish colleague (Cezary Krawczyński — a brachiopod expert) and I described in this March 2011 paper:

The first Jurassic thecideide brachiopods from the Middle East: A new species of Moorellina from the Upper Callovian of Hamakhtesh Hagadol, southern Israel. Acta Geologica Polonica, Vol. 61, No. 1, p. 71-77. [Free pdf available on that site.]

These tiny shells of Moorellina negevensis encrust corals and sponges in the Matmor Formation (Lamberti Zone, Upper Callovian, Middle Jurassic) in the Negev Desert of southern Israel.  (Our species name means “from the Negev”.) They are prominent members of a diverse sclerobiont assemblage including tubeworms, oysters, bryozoans and various borings. Several specimens were collected over the past few years of our Wooster work in Israel. Wooster student Will Cary and I will return to these outcrops in Israel this summer for further Jurassic work.

Moorellina negevensis is among the smallest of adult brachiopods, averaging only about two millimeters in width. It is the first species of the Order Thecideida found in the Jurassic of the Middle East. No doubt it escaped previous notice because it is so tiny!

One of our specimens has a gall-like structure that we believe was likely made by a ascothoracid parasite in the shell. The ascothoracids are tiny crustaceans usually found as parasites in echinoderms and cnidarians.

Parasitic (ascothoracid?) infestation in the dorsal valve interior of Moorellina negevensis; A – interior of the dorsal valve of Moorellina negevensis with parasitic (ascothoracid?) infestation marked in red; B – enlargement of parasitic infestation, posterior-lateral view; C – Synagoga paucisetosa Grygier, 1990, a recent ascothoracid parasite (redrawn from Grygier 1990, slightly modified); D – recent ophiuroid Ophiocten sericeum (Forbes, 1852) with the genital bursae infested by Ascothorax ophioctenis Djakonov, 1914 (redrawn from Wagin 1946, slightly modified).

So a little fossil with the surprise of an even smaller fossil inside!

Matmor Formation exposed in the Matmor Hills, Hamakhtesh Hagadol, Negev Desert, southern Israel. Type locality for Moorellina negevensis. This kind of outcrop is heaven for paleontologists and sedimentary geologists. It is a beautiful desert setting.

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