Mollusks chronicle the climate

Down in the basement of the Institute of Geosciences is a canyon running between rows of metal cabinets that house the Paleontology Collection of Johannes Gutenberg University Mainz. It's cold. A window has been left open, allowing the outside winter air into the room. "Now who forgot to shut that?," Professor Dr. Bernd Schöne asks. He shakes his head and stretches out to close the high window. The institute's director can now get down to the business that has brought us here. Together with PD Dr. habil. Kirsten Grimm, he plans on showing off a few of the treasures hidden in this cellar.

Grimm unlocks a tall, gray cabinet. A cardboard sign indicates the contents: Mammalia XVIII, Quatenary, Pleistocene, Mainz Basin. This drawer contains the remains of long-extinct animals.

Wolves and water buffaloes in the Rhine area

"Here we've got a lovely mammoth tooth," explains paleontologist Kirsten Grimm, lifting out a ridged, gray-brown mass. It is roughly the size of a brick, but heavier. There are a few of these teeth in the collection. "We can see quite well here just how worn down the tooth is. And we can examine how the ridges on it compare to those on the teeth of modern elephants."

Over the course of the last hundred throusands of years, there were not only mammoths living in the region of the Mainz Basin. In the interglacial periods, the warm periods between the ice ages, water buffaloes and hippos also roamed the area. "If we go back 125,000 years, it would have been two degrees Celsius warmer on annual average," Schöne notes. There were also horses at that time. Grimm points to a skull to demonstrate the point. Near them are a set of more diminuitive bone – two skulls from wolves with a well-preserved jaw.

"All of these objects were acquired in order to build up a research and teaching collection," Schöne says. When the collection was established in the 1950s, its goals were ambitious. "The intention was to have all taxonomic groups together." The range of the collection is correspondingly broad. "It carves a path through all fossil groups." A focus was put on regional speciments, such as the finds from the Mainz Basin, for example.

500 million years of Earth history

"The problem is that we don't have a curator for the collection," laments the Director of the JGU Institute of Geosciences. For the present, Kirsten Grimm is taking care of it. She also works for the Natural History Museum in Mainz. The networking of the two institutions is certainly a beneficial side effect, but it's no replacement for a full-time custodian.

Specimens ready to bear witness to 500 million years of the Earth's history lay waiting in the drawers. Neither Grimm nor Schöne know precisely how many they are. "If we also include our microfossils, it's certainly over a million," Grimm estimates. The microfossils include, for example, the remains of the single-cell organisms that produced limestone. However, the section of tusk that Grimm is pulling out right now seems a little bit more spectacular.

"With specimens like this one we can certainly add a bit of pep to our courses," claims Schöne. "It's one thing to see a picture of a fossil and another thing entirely to hold it in your own hands," Grimm adds. "We regularly have our students sketch pieces like this one." There is no modern medium capable of replacing that experience.

Mussels as a diary of the climate

The Paleontology Collection at Mainz University has always been shaped by the respective research focus of the holder of the relevant teaching chair. Heinz Tobien, for example, was a paleontologist specializing in vertebrates, and so in the 1950s the focus was on mammoths and water buffaloes and the like. Schöne, by contrast, is mainly interested in much smaller animals. He opens up another cabinet.

Mussels. Hundreds, if not thousands of them. They point back 30 million years into the past, to the Oligocene period. At that time a sea covered Rhenish Hesse. "Here we have an outstandingly well-preserved example of the genus Glycymeris." These mussels were not rare at all back then. Even today many representatives of this species still live in the seas.

Some of the mollusks were found in Bodenheim near Mainz and have been dated as roughly 29 million years old. Others come from Weinheim in Baden-Wuerttemberg and their furrowed humps are even some two million years older. "What you see here is the original shell material. And we even have some specimens where both the upper and lower portions are preserved," Schöne explains. This is no given, because once a mollusk dies there is nothing to hold the two parts of the shell together anymore. In these cases both pieces survived in all likelihood because they were quickly covered by sediment. In other words, the mussels were not lying around all too long unprotected on the ocean bed.

Growth rings attest to high pressure over the Azores

Schöne uses the mollusks to gain information about climatic conditions some 30 million years ago. The animals could live for up to 100 years, meaning each specimen opens up a relatively broad time window. The growth rings on the shells give a lot of information to paleontologists. "We can determine the temperatures at the time to within one degree Celsius."

What Schöne also finds truly interesting are the fluctuations in temperature in the past and the information provided on circulation currents in the atmosphere and the ocean. "We can prove that the North Atlantic Oscillation existed even back then." This interplay between high-pressure systems in the Azores and low-pressure over Iceland still has a major influenece on our weather today.

Schöne closes the cabinet. This was just a small selection of the Paleontology Collection at Mainz University. There are also insects to be admired, together with corals and fish – and there is also the Labyrinthodontia, the first amphibian.

But this has been a fine start. The light of the winter sun penetrates weakly though the window. It's still cold. High time to retreat back to the warmth of the office.