It Pays to Be the Small Fish in Case of a Mass Extinction

It pays to be the small fish in case of a mass extinction according to recent findings stemming from a University of Pennsylvania study.

359 million years back, a mass extinction occurred. Scientifically termed the Hangenberg event, this strange occurrence was the lasting trigger of a transformation suffered by all vertebrates inhabiting our home planet. Specifically, shifts in size were the norm. While ecosystem were ruled by the largest and meanest, 40 millions after the Hangenberg event, small vertebrates were the norm.

According to Lauren Sallan, the lead researcher on the study and assistant professor with the Department of Earth and Environmental Sciences at the University of Pennsylvania:

“Rather than having this thriving ecosystem of large things, you may have one gigantic relict, but otherwise everything is the size of a sardine”.

Sallan referred to the ocean’s ecosystem, the focal point of her team’s study. The main finding of the study seems to suggest that it pays to be the small fish in case of a mass extinction. While it may seem counter-intuitive, the idea is that smaller fish have an evolutionary advantage in the case of such catastrophes. Mainly, their reproduction is a fast process that enables the survival of the species and its perpetuation in larger numbers.

Part of the evolutionary puzzle scientists are trying to figure out refers to understanding the factors that influence the size of animals. Several scales and theories have been set in place. One of the theories, dubbed Cope’s rule posits that animals increase in size to gain an evolutionary advantage. Larger sizes translate in better protection in the face of predation threats. At the same time, they translate in having the opportunity to pick from a larger prey choice.

Another theory posits that due to higher oxygen levels or colder climates, animals tend to get bigger. Yet another, dubbed the Lilliput Effect accounts for the decrease in size following a mass extinction.

For this study, Lauren Sallan and her team focused on fish fossils dating from 419 to 323 million years ago. 1,120 fossils were examined for body size. All resources at hand were perused, including photographs, modern renditions, museum specimens and previous studies.

What the researchers found is that indeed, during the Devonian period, which is in line with the dating of the fish fossils, ocean vertebrates did increase in size as Cope’s rule posits. Following the Hangenberg event, 97 percent of the species disappeared. At this point, the Lilliput effect came into force. For the following 40 million years, the species surviving the mass extinction declined in size considerably.

The research, published in the Science journal brings one piece of the evolutionary puzzle to the table. 
Photo Credits: Pixabay