Land of giants

89.4 – 84.6 million years ago

The sauropods of the Jurassic and Cretaceous are the largest land animals ever, more than an order of magnitude larger (in estimated body mass) than the largest terrestrial mammals.

And sauropods evolved enormous body size multiple times.

How did they get to be so big? Paleobiologist Martin Sanders recruited a multidisciplinary team of more than twenty researchers in fields ranging from engineering and materials science to animal nutrition and paleontology. They present their results in a review article (whence the figures above) and a book. It doesn’t look like Mesozoic ecology was unusual enough to favor sauropod gigantism on its own. Instead, the long neck of the sauropods was a key innovation, allowing a much greater food intake. The long neck in turn was allowed by a small head with limited chewing capacity and a lightly built pneumatized skeleton going along with avian-style lungs. Other features, including reproduction via many small fast maturing offspring, and a high metabolic rate, also contributed to the complex. The argument is summarized in this chart.

Compare: cold-blooded reptiles don’t command enough energy to grow large quickly. And mammals have taken another path, committed to more thorough mastication rather than sheer volume of food, and to bearing and caring for live young.

No other animal group before or since has had the suite of characters that favored gigantism in sauropods. Their like will not be there again.