A study by international researchers has challenged a popular theory that high oxygen levels allowed massive insects to grow so large, suggesting that the flight muscles of insects are not constrained by atmospheric oxygen levels. The study, published in Nature, found strong evidence that insects the size of griffinflies could not fly in today’s atmosphere. The researchers also found that the tracheal system, which delivers oxygen to insect flight muscles via a network of air-filled tubes, was more common in flying insects than a different organ with similar functions in birds and mammals. The findings suggest that larger animal species are more prone to extinction than smaller ones. If confirmed, there's no reason that the griffinfly could not survive in today's atmosphere.