Climate Change Once Made Ancient Creatures Shrink, and As Global Temperatures Rise, It Might Happen Again

The fossil record suggests climate change could cause animals to shrink as they appear to have done in the past.

A pilot study recently published in Royal Society Open Science adds to a growing body of evidence suggesting historic shifts in temperature have caused species to downgrade in terms of size—a trend that may very well repeat in response to anthropomorphic climate change.

Paleontologists at University of Erlangen-Nuremberg (FAU) in Germany focused their research on a prehistoric squid-like animal called a belemnite. These ancient cephalopods were a key feature of the Jurassic period ecosystem (circa 199-145 million years ago) and regularly pop up on the fossil record.

"Belemnites are particularly interesting, as they were very widespread for a long time and are closely related to the squid of today," Dr. Patricia Rita, a paleontologist at FAU and study co-author, said in a statement.

"Their fossilised remains, for example the rostrum, can be used to make reliable observations."

The scientists based a lot of their observations on the belemnites' rostrum—or beak—which they explain represents a sizable portion of the animal and can be used as a proxy for body-size.

Samples collected near Peniche, Portugal, show a 40 percent decrease in the volume of the rostrum approximately 183 million years ago, which appears to have been triggered by a period of volcanically-driven warming. This preceded the Toarcian Oceanic Anoxic Event, which saw extreme ocean warming and the local extinction of belemnites.

This size-change was almost entirely caused by the two most dominant species: Pseudohastites longiformis and Passaloteuthis bisulcata.

The researchers say the "most significant and largest reduction" was seen in P. longiformis, the most abundant species, which saw a reduction in body size of 17 percent and a reduction in rostrum volume of 51 percent. While P. bisulcata saw a 7 percent decline in body size and a 21 percent decline in rostrum volume. Bucking the trend was a species named Hastitidae, which appears to have grown 8 percent over a similar timeframe.

The team suspect the tendency towards a smaller body size is down to an increase in sea temperature and a decrease in oxygen—but stress more research is needed to confirm that this is the case. Neither is it clear the changes occurred due to differences in the organisms' metabolism or thanks to more indirect factors, such as a shortage in food.

The study's authors hope to continue their research by examining hundreds of belemnites from across Europe and put together a more comprehensive picture of their response to temperature change all those millions of years ago.

Squid swimming near Komodo Island
A stock image of a squid swimming near Komodo Island. A study suggests an ancient squid-like creature became smaller as temperatures rose and oxygen levels decreased. iStock/atese

Decreases in body size, called the the Lilliput effect, is not a one-off phenomenon. Several studies have investigated the ways in which climate change affects body size across different species and warming events, including the end-Permian extinction event.

Scientists writing in Nature described smaller body size as "the third universal response to global warming"—the first and second being changes in phenology (related to seasons and climate) and distribution of species.

A second study published in Nature found that animals already "exhibit smaller sizes" thanks to human-caused climate change and many more are likely to in the future.