Life Finds a Way: Research on Ancient Clams, Snails Reveals Climate Change Had Little Effect on Long-Term Migration Patterns

From the shells of ancient snails, UC researchers have found clues that provide insight into how modern species might adapt to future climatic shifts and environmental changes. While prehistoric marine migration changed very little from one era to another, scientists hope these data can help connect the dots to predict species' future adaptability to climatic events yet to come.

Andrew Zaffos, a UC graduate who completed his PhD in December 2014, and Arnold Miller, professor of geology and paleobiology, mapped and analyzed marine fossils to understand how the distribution of ancient marine organisms has changed along latitude over the course of the Cenozoic era (from 65 million years ago until the present day).

They looked specifically at different groups of bivalves (e.g., clams, scallops, oysters) and gastropods (snails) to see how each group moved north, south or stayed put over time. Shelly marine animals like clams and snails are commonly used in paleobiology studies because they are more frequently preserved as fossils than land animals, and are easily identified by their hard shells, even after millions of years.

Zaffos and Miller recently published the results of their study, titled “Cenozoic latitudinal response curves: individualistic changes in the latitudinal distributions of marine bivalves and gastropods,” in the February issue of the prestigious journal

Paleobiology,

(Volume 41, February 2015).

Looking at how bivalves and gastropods are distributed across the globe, Zaffos and Miller used a comprehensive

Paleobiology Database

–– a 17-year-old, nonprofit initiative dedicated to the collection and storage of fossil information. Researchers and fossil enthusiasts around the world can access and use the critical online data input by other scientists.

After organizing the PaleoDB information into various sub-units of the Cenezoic era –– known as geologic epochs (varying in size from 2 to 15 million years) –– Zaffos studied the Earth’s climatic changes in relation to the migration of marine animals during those epochs.

During the first two epochs of the Cenozoic period (Paleocene and Eocene)

• there was a prolonged warming phase, eventually peaking at the hottest temperatures in Earth’s history since the extinction of the dinosaurs.
• this warming period was followed by a steady period of gradual cooling over the subsequent 55 million years.
  

Zaffos explains that

many geologists consider the thermal peak of 55 million years ago as an analogue to the current trend of renewed global warming.

Beyond this broad, long-term pattern of warming followed by cooling, research shows there have been many smaller, irregular swings in climate –– which, it is traditionally hypothesized –– might change the way species are distributed along latitude. For example, during brief ice ages, species might move from temperate regions toward the tropics to compensate for the colder temperatures.

Ancient Climate Shifts Caused Little Change in Migration Patterns

Zaffos and Miller found that the

basic rate of change in the latitudinal distribution of marine animals remains relatively consistent across geologic epochs, and, on average, is impervious to those swings.

In other words,

marine animals did not typically migrate further or more frequently in one epoch compared to another, despite the climate conditions unique to each block of time.

Furthermore, they found that there was less migration than would be predicted by pure chance, suggesting that marine animals are relatively conservative in their choice of latitudes.

“We have seen all kinds of environmental change throughout the history of the past 65 million years, but when you look at the problem in aggregate, meaning to step back and look at the overall pattern, it appears that big climatic swings have not really shaken things up terribly much,” says Zaffos. “There is a relatively consistent pattern of change, at least in how organisms are distributed in terms of latitude. And so, at a scale of tens of millions of years, the things that we are most worried about (mass migration and extinction of species) really tends to fade into the noise.”

An important implication of their work is how ancient migration patterns affect global biodiversity. As new species migrate into an area, then the total number of species in that area increases, raising regional biodiversity. Despite over 100 years of work in this area, Zaffos notes that people still have a poor understanding of why some areas are more or less diverse than others. In particular, the tropics have historically been the richest in terms of biodiversity, so why this is the case and how biodiversity has changed is a recurring theme in Zaffos’ work.

Zaffos says the greatest outcome of this research is to help put the hot topic of biodiversity into perspective:

based on their findings, recent climate changes, in the very long run, are likely not as strong a threat to the global biodiversity of marine organisms as other anthropogenic (man-made) factors.

How Will Man’s Industrial Footprint Change Future Biodiversity Patterns?

The researchers' study indicates that natural climate change might not have had a significant impact on these animals' migration, but man-made climate change could have different effects, according to Miller.

“Given that the rate of temperature change happening now may fall outside the bounds of anything we have observed in the past 65 million then all bets may be off in a way,” says Miller. “As paleontologists, we study the past and hope that what we look at is relevant to what is happening today, and more importantly we hope to shed light on what will happen in the future.  But it’s possible that, in the end, there is no ancient analogue for what we are witnessing at present.”

Funding for this project was provided by a NASA exobiology grant (NNX10AQ44G) to Arnold I. Miller and a Paleontological Society Stephen J. Gould grant to Andrew Zaffos. This is Paleobiology Database Publication No. 203.

About the PaleoDB

The

PaleoDB

contains more than 1,227,967 unique fossil occurrences catalogued by location and age, constituting approximately 78,230 continuous man-hours of effort by contributing scientists.