Dinosaurs that roamed the earth millions of years ago became extinct due to a huge asteroid that hit the earth, right? Wrong. Dinosaurs had started dying long before the asteroid had hit earth about 65 million years ago, according to a new study by the University of Albany in the United States. They discovered that there were certain plants that were toxic to the huge reptiles. The dinosaurs were unable to associate the taste of those plants with their toxicity, which had already made their numbers decline rapidly.

‘Learned Taste Aversion’ is an evolutionary defense mechanism seen in a number of animals where the creatures learn to associate consumption of a certain material with negative observations like falling ill. For example, attempts to terminate rats are sometimes unsuccessful because they have evolved to recognize the taste of toxic plants, says Gordon Gallup, a professor at the University of Albany who led the study published in Ecology and Evolution. “When rats encounter a new food, they typically sample only a small amount; and if they get sick, they show a remarkable ability to avoid that food again because they associate the taste and smell of it with the negative reaction,” he said.

Fossils of the first flowering plants or angiosperms from before the asteroid impact and right before the dinosaurs began gradually disappearing have been an indication of this discovery. Researchers claim that some of these caused gastrointestinal distress in the dinosaurs, but they continued eating them.

Researchers also examined whether or not birds and crocodilians (both descendants of dinosaurs) could develop taste aversions. They found that birds formed aversions to the visual features of what made them sick instead of the taste, but they knew what to avoid to not get sick. In a previous study, 10 crocodilians were fed different kinds of meat, some slightly toxic, and like their ancestors, the crocodilians did not develop learned taste aversions.“Though the asteroid certainly played a factor, the psychological deficit which rendered dinosaurs incapable of learning to refrain from eating certain plants had already placed severe strain on the species,” said Gallup. If the asteroid impact had indeed been the cause of dinosaur extinction, their disappearance should have been sudden, but the evidence clearly shows the opposite. “Dinosaurs began to disappear long before the asteroid impact and continued to gradually disappear for millions of years afterward.”

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