After the dinosaurs died out, why didn’t the remaining animals grow as big as dinosaurs again?
• Most dinosaurs weren’t particularly large, especially if we count birds. Also, the largest animal we know of is alive today: the blue whale. Still, dinosaurs were the giants on land.
Mammals became dominant only in the past 65 million years or so, after dinosaurs had lasted more than 180 million years, almost three times as long. Generally, the giants evolved nearer the end, after millions of years of competition in which the largest tended to win. But when things went wrong, the biggest species also died out fastest.
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It then took the mammals perhaps 20 to 40 million years to produce land giants, and theirs were smaller than the biggest dinosaurs. That might be because there was less oxygen in the air at the time. In another 120 million years, mammals might beat the dinosaurs – except that extreme size is no advantage against guns and other human technology. We may be what stops land animals from ever rivalling the dinosaurs.
Jon Richfield
Somerset West, South Africa
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