Some experts have long believed that a massive asteroid was a primary cause of dinosaurs’ extinction some 65 million years ago, but now a new study indicates that the dinosaurs were in trouble long before the asteroid hit.

A new research from a University at Albany led by Professor Gordon Gallup and Michael Frederick suggests the emergence of toxic plants combined with dinosaurs’ inability to associate the taste of certain dangerous foods had their population significantly decreased.

‘Learned taste aversion’ is an evolutional defence seen in many species, in which the animal learns to associate the consumption of a plant or other food with negative consequences, such as feeling ill,” the evolutionary psychologist said. “A reason why most attempts to eliminate rats have not been successful is because they, like many other species, have evolved to cope with plant toxicity.”

The first flowering plants, called angiosperms, appear in the fossil record well before the asteroid impact and right before the dinosaurs began to gradually disappear. Gallup and his team claim that as plants were evolving and developing toxic defences, the terrestrial vertebrates continued eating them despite gastrointestinal distress. Albeit there is uncertainty about exactly when flowering plants developed toxicity and exactly how long it took them to proliferate, the team observed that their appearance coincides with the gradual disappearance of dinosaurs.

Further, the team examined whether or not birds (descendants of dinosaurs) and crocodilians (also descendants of dinosaurs) could develop taste aversions. They found that the birds, rather than forming aversions to taste, developed aversions to the visual features of whatever made them sick. Still, they knew what they should not eat in order to survive. In a previous study in which 10 crocodilians were fed different types of meat, some slightly toxic, Gallup discovered that like dinosaurs, 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. He said the prevailing view of dinosaur extinction based on the asteroid impact implies that the disappearance of dinosaurs should have been sudden and the effects should have been widespread, but the evidence clearly shows just the opposite. “Dinosaurs began to disappear long before the asteroid impact and continued to gradually disappear for millions of years afterwards,” said Gallup.

The full paper, published in the peer-reviewed journal Ideas in Ecology and Evolution, can be read here.