Taiwanese researcher rebuilds ancient ecology through fish fossils

Minuscule organs in fish heads tell great stories about ancient environments

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Some of Lin Chien-hsiang's specimens and fossils

Some of Lin Chien-hsiang's specimens and fossils (Taiwan News photo)

TAIPEI (Taiwan News) — For modern researchers, fossils are gateways to the ancient world. They provide direct evidence of animal traits and serve as powerful indicators of changes in the global environment, especially after human beings began dominating the planet.

When talking about fish fossils, fish skeletons immediately come to mind. But finding these fossils, especially the intact ones, is not easy. One Taiwanese researcher is offering an alternative to the study of ancient oceanic ecology when prominent fossil records are lacking — the answers are hidden in the ears of fish.

Lin Chien-hsiang (林千翔), a research fellow at Academia Sinica's Biodiversity Research Center in Taiwan, is a paleontologist who devotes most of his research to studying fish otoliths, a tiny calcium carbonate structure in the inner ears of fish.

At first glance, otoliths resemble tiny stones commonly found on the seashore, but they actually offer tons of information to scientists. Similar to tree rings, the otoliths grow larger as fish age and leave circular marks that are distinctive under a microscope.

By studying these marks, the age of a fish becomes apparent, and scientists can then match the age and the size of different individuals to chart the growth rate of specific species.

Once the growth rate is confirmed, scientists can compare a species current and previous growth rates, to determine the change in their body size. As more evidence indicates wild fish are shrinking in size, owing to warming sea temperatures and overfishing, such a study provides a benchmark for the future conservation of fish populations.


Otoliths come with various sizes, shapes.

Interestingly, as the fish grow faster, the gap between the rings on the otoliths also widens. Scientists can even use the current growth rate to estimate the size of fish dating back millions of years.

More than that, the otolith fossil provides reliable environmental records. This tiny organ is mainly made of elements fish collect from the surrounding environment.

Different from bones, which have a density that might fluctuate over time in the bodies of fish, the otoliths remain unchanged after forming. The composition of each part of the otoliths also reflects specific time periods.

Through isotope analysis on otoliths, the migration patterns of fish are no longer a mystery. Scientists can build the profile of one particular fish, including when it changes habitats throughout its life.

"Each aquatic area contains different environmental information, and the messages that otoliths carry allow us to establish the life history of each individual, which is a remarkable thing," Lin said.

Working with otoliths requires solid knowledge in taxonomy — one has to know what otoliths look like and which fish they belong to before entering any research. From his first fish dissection in Taiwan to the excavation in Caribbean Panama, Lin has proven this small organ is a powerful tool in the field of paleontology.

"Doing otolith research is not a shot in the dark," Lin explained. "We have to know where the sedimentary rocks come from first to systematically analyze the fossils within."


Identifying otoliths is the first step for any further research.

The study of fish fossils does have its limits. For example, only bony fish form otoliths, and large fish like tuna usually have otoliths that are too small to be fossilized. In addition, otoliths from ancient times, say the Jurassic period, might remain unidentifiable, as the owner has been extinct for too long.

The use of otoliths is meant to supplement rather than replace other fossil records in the environment, Lin emphasizes.

"The diversity of Taiwanese fish communities is made of fish coming from tropical and temperate regions in East Asia. Our next goal is to find out when this phenomenon started, using these tiny fossils in our hands," Lin said.


Each fossil has a story