Reading down through the article kindly submitted here after first reading the previous comments, I see, "Certain key events, also highlighted by the study's au

Reading down through the article kindly submitted here after first reading the previous comments, I see, "Certain key events, also highlighted by the study's authors, deliver an extra boost. Most obviously, at the stages when land animals like reptiles and, later, mammals returned to the water, the size graph lurched upward. "It was the return of mammals, after all, that eventually produced the modern giants of the sea: whales. "'You can see in the data, there is this trend to increasing size - but a real kick comes when you have these air-breathers re-entering the water,' Dr Berenbrink told the BBC. "'Then you have a sort of a step change in size.' "Breathing air delivers extra oxygen to an animal's tissues, he explained, allowing them to sustain bigger bodies beneath the waves." Oxygen-delivery systems indeed have to be crucial for animal life on land or in the sea. Fish and their gills simply can't bring in as much oxygen for an energetic large-mass lifestyle as whales and their lungs can. It would be interesting to find out how much whale blood deoxygenates as it flows through the tissues of the largest whales. The duration of movement on one breath for whales is already quite impressive compared to what most land mammals can achieve, so whales probably have some good adaptations for efficient use of oxygen from each breath.