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Dinosaurs may have been smart among reptiles but definitely not as intelligent as monkeys capable of wielding tools, according to a new study. Research published last year claimed dinosaurs like the mighty T rex had an exceptionally high number of nerve cells in the brain, suggesting they were substantially more intelligent than previously assumed. It went on to claim that high neuron counts could be indicative of high intelligence and metabolism and that T rex may have been monkey-like in some of its habits. The research even speculated that some dinosaurs may have used tools and transmitted knowledge culturally. However, a new review of studies published in The Anatomical Record found that assumptions about brain size in dinosaurs and the number of neurons their brains contained could be unreliable. Currently, information on dinosaur brains comes from mineral infillings of the brain cavity, termed endocasts, as well as shapes of the cavities themselves. The new study found that previous research overestimated brain size, especially of the forebrain, and thus neuron counts as well. "Moreover, neuron count estimates were not a reliable proxy for inferring intelligence," said Hady George, one of the researchers from Bristol University, UK. "Determining the intelligence of dinosaurs and other extinct animals is best done using many lines of evidence ranging from gross anatomy to fossil footprints instead of relying on neuron number estimates alone," he said. For reconstructing such biological traits of extinct species, the study argued, multiple lines of evidence should be assessed including skeletal anatomy, bone histology, the behaviour of living relatives, and trace fossils. "We argue that it's not good practice to predict intelligence in extinct species when neuron counts reconstructed from endocasts are all we have to go on," Kai Caspar, one of the authors of the study, said. "The possibility that T rex might have been as intelligent as a baboon is fascinating and terrifying but our study shows how all the data we have is against this idea. They were more like smart giant crocodiles, and that is just as fascinating," Darren Naish, another author of the study, added.