Washington, March 27 (ANI): A new study has unraveled why certain fishes went extinct 65 million years ago, attributing the reason of their decline to a large size and a fast bite.
Today, those same features characterize large predatory bony fishes, such as tuna and billfishes, that are currently in decline and at risk of extinction themselves, according to Matt Friedman, author of the study and a graduate student in evolutionary biology at the University of Chicago.
"The same thing is happening today to ecologically similar fishes," he said. "The hardest hit species are consistently big predators," he added.
Studies of modern fishes demonstrate that large body size is linked to large prey size and low rates of population growth, while fast-closing jaws appear to be adaptations for capturing agile, evasive prey-in other words, other fishes.
The fossil record provides some remarkable evidence supporting these estimates of function: fossil fishes with preserved stomach contents that record their last meals.
When an asteroid struck the earth at the end of the Cretaceous about 65 million years ago, the resultant impact clouded the earth in soot and smoke.
This blocked photosynthesis on land and in the sea, undermined food chains at a rudimentary level, and led to the extinction of thousands of species of flora and fauna, including dinosaurs.
Scientists had speculated that during that interval large predatory fishes might have been more likely than other fishes to go extinct because they tended to have slowly increasing populations, live more spread out, take longer to mature, and occupy precarious positions at the tops of food chains.
Today, ecologically similar fishes appear to be the least able to rebound from declining numbers due to overfishing.
To build the database he needed to test this prediction, Friedman traveled around the world measuring the body size and jaw bones of 249 genera of fossil fishes that lived during the late Cretaceous.
These kinds of direct measurements are possible in fossil fishes because many are represented by complete, articulated individuals.
This is unlike the fossil record of most other vertebrates, where bones, teeth and other parts of the skeleton are often scattered and found in isolation.
This study is the first to test this theory with hard data and to quantify the relationship between body size, jaw function and vulnerability of fishes during the Cretaceous extinction, according to Friedman.
"Anyway you sliced it, the data showed that if you were a big fish with a fast bite you were toast," he said. (ANI)