June 8. Brachiopods

Just a short one today, to mention the brachiopods again. 

Two of the major groups of brachiopods, the productids or spiny brachiopods, and the sprifers, with elongate, wing-like shells, continued to thrive during the Mississippian.

Productus longispinus (left); Spirifer glaber (right)

In 2008 a report by Chinese and Polish paleontologists described an unusual assemblage of silicified brachiopods, including 4 new species, from the Muhua area of southern China. LINK

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Laki Eruption

Beginning on June 8, 1783, and continuing for eight months, a fissure – a crack in the earth – and 130 eruptive vents began to pour basaltic lava over southern Iceland at Lakagigar, often called Laki. By most estimates the volume of erupted material, more than 14 cubic kilometers, is the greatest on record during historic times. The lava was accompanied by poisonous fumes composed of hydrofluoric acid and sulfur dioxide which killed half of all the livestock in Iceland and devastated the countryside well beyond the lava flows themselves. The resulting famine killed an estimated 25% of Iceland’s human population. Worldwide, the ash and acid aerosols in the atmosphere caused dramatic climatic effects – crop failures in Europe, droughts in India, extremely low flows in the river Nile, and a North American winter cold enough for the Mississippi River to freeze over at New Orleans. The sulfurous fumes were strong enough in France to kill a few dozen people, and the U.S. ambassador to France, Benjamin Franklin, speculated on the connections between the poisonous fogs in Europe and the Icelandic eruption – correctly, as it turned out. The total death toll worldwide from this eruption may have been as high as 6 million when all the impacts of the famines are included.

There’s a new book out on the Laki eruption, just published in March 2014. Island on Fire is by Alexandra Witze, an award-winning science journalist. I haven’t finished it yet, what I have read is an excellent report on the eruption and its worldwide consequences.

—Richard I. Gibson

Brachiopod drawing from an old textbook (public domain)

May 5. Devonian brachiopods

Brachiopods reached their peak of diversity during the Devonian. Brachiopods, you recall, are shelled animals that superficially resemble clams, but they are their own phylum. Pretty much the first fossil collecting field trips I went on as a college geology student turned up lots of Devonian brachiopods.

At some places, brachiopods were so abundant that their shells made up small reefs. One of the most famous exposures of a Devonian reef is the Falls of the Ohio River, at Clarksville, Indiana. Brachiopods are common there, but it’s fundamentally a coral reef, possibly the most diverse mass of Devonian corals in the world. It also contains the usual suspects in a reef – crinoids, bryozoans, trilobites, mollusks, and more, as well as fish bones. The limestone containing the reef dates to Middle Devonian time, about 385 million years ago, a time when North America was near the equator but south of it. Today, the Falls of the Ohio is an Indiana State Park. 

Some of the most common Devonian brachiopods belong to the genus Spirifer. They actually range from the Ordovician to the Jurassic Period, but I can tell you from personal experience that they’re really common in Devonian rocks in the Michigan-Indiana-Ohio-Ontario region. Spirifers have a long hinge line, the place where the two shells join together. Often, the hinge line is the widest part of the shell, and this gives them a characteristic wing-like shape. Their name, spirifer, means spiral-bearing, and it comes from a tiny coil within the animal that was the support structure for the lophophores, the fleshy, tentacle-like things that brachiopods used to feed. The spiral structure is often preserved even though it’s tiny, because it was probably made of calcite just as the shell was.

There were at least 40 families of spirifers and dozens of species, but they are all extinct today.

Another group of brachs that was common during the Devonian was the productids. These brachiopods are sometimes called spiny brachiopods for the long projections that grew on their shells. In some species, the spines were as long as or longer than the shells themselves. It seems that they might have used the spines for stability, but a 2013 paper on the subject does not rule out the possibility that they might have used the spines as some kind of sensory organ.

—Richard I. Gibson

Links:
Falls of the Ohio
Falls of the Ohio - brachiopods
Mucrospirifer
Spines
Photo by Richard Gibson

February 17. What's a Brachiopod?

Today, let’s talk about brachiopods. Possibly you’ve never heard about brachiopods – they are not widely distributed today, and when you do see their shells you might dismiss them as just another odd bivalve, or two-shelled mollusk like a clam. But brachiopods are not clams. They are their own phylum, not closely related to mollusks at all.

The main visible difference may seem subtle – brachiopods are symmetrical through a plane that divides the two shells vertically, while mollusks, if they have any symmetry at all, are symmetrical between the shells. There are other differences as well, especially in internal organs. Brachiopods have things called lophophores, tentacles that they extend and wave around to create a current from which they can filter food particles out of the ocean water where they live.


Brachiopods first appeared in the early Cambrian, part of the Cambrian explosion. They were incredibly prolific and successful during much of the Paleozoic Era, and in fact there are 12,000 fossil species known, in 5,000 genera, that is, groups of related species, in contrast to only 100 genera known today. Brachiopods suffered a lot in the Permian-Triassic extinction, at the end of the Paleozoic Era 250 million years ago, and their decreasing diversity after that time may also reflect the growing success and diversity of the bivalves that occupy some of the same ecological niches as brachs.

Although a few species reached nearly eight inches across, most brachiopods are an inch or two across, a perfect size for preservation and easy for collectors to find. There are two main types, articulate and inarticulate. Articulated brachs have two shells that are attached to each other along a hinge line, so the critter opens in a way similar to a clam. Inarticulate varieties have two shells that were not attached, but were held together by the animal’s muscular system. One of the most famous inarticulate brachs is one called Lingula – also called a living fossil, because the types that exist today are hardly changed from Lingulas that lived in the Cambrian period. They are also interesting because their shells are not made of calcium carbonate, like most clams, scallops, snails, and other shelly creatures, but they’re made of calcium phosphate, the mineral apatite, the same mineral that makes your bones and teeth.

I’ve never seen a modern brachiopod, alive or dead. But they were so prolific in Paleozoic seas that most any fossil collector will have some in his or her collection. We’ll talk about some of them later in the Paleozoic.

—Richard I. Gibson

Images from USGS.