Large species of fish, particularly the predatory kind, may have an advantage in the sea but in the aftermath of a catastrophic event, smaller could mean better.

Findings of a new study that looked at fossil records indicate that small and fast-reproducing fish has evolutionary advantage over their bigger counterparts in a post extinction event.

Study researcher and paleontologist Lauren Sallan, from University Of Pennsylvania, noticed that the fish that thrived 350 million to 323 million years ago during the Mississippian Period were smaller compared with their ancestors.

Other paleontologists have earlier noticed that certain species appeared to shrink in size overtime, a phenomenon they called the Lilliput effect, which researchers noticed tend to occur after abrupt and massive extinctions.

Sallan said that the Hangenberg mass extinction event that occurred 359 million years ago drastically transformed the Earth's vertebrates. Large creature dominated beforehand but for at least 40 million years after the die off, substantially smaller fish became the norm in the oceans.

Sallan and Andrew Galimberti, of the University of Maine, investigated the body size trends around the Hangenberg Event by looking at a dataset of over 1,000 fish fossils from between 419 to 323 million years ago.

The researchers also looked at museum specimens, published papers and photographs to gather information on fish body sizes and found that the size of the vertebrates has increased during the Devonian period 419 to 359 million years ago.

Some species were as large as school buses during this period. Sallan said that while there were small vertebrates, majority of the species were at least a meter long.

Following the mass extinction event that wiped out more than 97 percent of the vertebrate species, Sallan and Galimberti found that the body size of the marine animals declined and continued downward for millions of years.

The researchers said that the findings published in the journal Science on Thursday suggest that mass extinction events set off a lasting Lilliput Effect that favored smaller organisms.

Small vertebrates may possess an evolutionary edge that increased their odds for survival at the end of the Devonian. They likely grew fast and reproduced early in life making them less vulnerable to ecological disruptions.

"Before the extinction, the ecosystem is stable and thriving so that organisms can spend the time to grow to large sizes before they reproduce" Sallan said. "In the aftermath of the extinction, that ends up being a bad strategy in the long term. So tiny, fast-reproducing fish take over the entire world."