A recent study has revealed that following a mass extinction, survival of the smallest creatures, which aren’t necessarily the fittest, is the most likely scenario.
Research was published on Thursday, November 12, in the Science journal, by a team of experts led by Lauren Sallan, paleontologist at the University of Pennsylvania.
Scientists conducted an analysis on 1,120 fish fossils pertaining to species which inhabited our planet between 419 and 323 million years ago.
It was determined that prehistoric fish had been increasing in size, but after the Hangenberg bioevent which occurred 359 million years ago, around 97% of the marine population of brachiopods, trilobites and coral reefs was depleted, as part of the Late Devonian extinction.
At the beginning of the Mississippian period, it was the smallest creatures that fared the best, whereas larger ones such as rhizodontids (the size of a killer whale) were the most vulnerable, and eventually died off.
According to Lauren Sallan, that was because tiny fish such as sardines were capable of breeding at much higher rates, and at earlier periods in their life cycle, in contrast to their larger counterparts. Moreover, they also required smaller quantities of nourishment, and this also gave them an evolutionary advantage.
As a result, the ocean came to be dominated by sharks with lengths of less than 3 feet, and by tetrapods and fish as little as 4 inches.
After a while, new large species of vertebrates began to emerge, but it took around 36 millions of years for that to happen, and throughout that period creatures which had remained at more diminutive proportions were the ones which thrived and ruled the Earth.
This fact is also supported by the Lilliput Effect, which claims that sudden mass extinctions are followed by the prevalence of smaller sized biota, and that this is a normal pattern, encountered as the ecosystem undergoes a process of recovery.
There are various theories as to why species eventually evolved to larger sizes. For instance, some researchers believe that this is achieved mostly in periods characterized by colder climates, or when oxygen is at higher levels.
In contrast, Cope’s rule states that animals develop more massive proportions as a means to hunt for prey more effectively, and to defend themselves against potential predators.
Based on their findings, researchers say that in the event of another mass extinction caused by natural cataclysms and other factors, several million years would have to pass until larger animals appear again.
According to some scientists, the sixth mass extinction is fast approaching, or has already started. In fact, the largest part of the blame for this phenomenon has been placed on man-made activities such as the burning of fossil fuels and overexploitation, which have triggered habitat loss and destruction.
On the other hand, it’s humans that also hold the key for salvaging endangered and threatened species, by undertaking conservation measures. For example, humpback whale populations have finally been restored, after prolonged efforts at a national and international level ever since the 1970’s.
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