Ecology of the Dinos

kw: book reviews, nonfiction, palaeontology, dinosaurs, ecology

I began reading this book before the one I reviewed two days ago, but got bogged down and set it aside while finishing that one. Dinosaur Odyssey: Fossil Threads in the Web of Life by Scott D. Sampson is a big book with a lot to say. Though there are copious illustrations, there is still a ton of text.

There are also a number of good ideas. Dr. Sampson dwells on the relationships among dinosaurs and with the plants and animals about them for about half the book. Some of his writing got me thinking along the lines I explored in yesterday's post.

I happened across the online article by Mike Taylor, Sauropods Held Their Necks Erect, which included this screen shot from Walking With Dinosaurs by the BBC. While the sauropods are shown here walking "horizontally", Taylor reasons that they used a posture more like a giraffe. With trees blocking one's view, it is likely one would see at most one or two small herds of sauropods at a time.

The first part of Dinosaur Odyssey goes over earth history, the geologic time scale, and other obligatory material for a book on the Mesozoic animals. I've read so many such treatments that I wound up skipping a lot. But I don't begrudge its presence; if this book is the first dinosaur book a precocious middle-schooler reads, the discussion will be helpful and necessary.

More than any other book I've read, though, this one details the ecological relationships of dinosaurs and their place in our history…and in our present: birds are dinosaurs, taxonomically. They continue the ecological success of creatures that dominated terrestrial landscapes for 160 million years—until the K-T extinction—and bring it forward another 65 million years to the present. Bird species outnumber mammal species two-to-one, and it was only after humans got into South America some 13,000 years ago that the reign of flightless "terror birds" as dominant large vertebrates came to an end.

The author makes an interesting case in favor of dinosaurs, at least some of them, being "mesothermic", not ectotherms like modern lizards, but not quite wholly endothermic like modern birds and mammals. Indeed, many bird species can regulate their body temperature downward to save energy when they can't feed. Hummingbirds do so at night, for example. Many birds do this, but very few mammals, and not as completely. There appear to me to be two styles of endothermy, which probably evolved separately.

Now, if dinosaurs were mesothermic, particularly the predatory ones, a given landscape could support more of them. A fully endothermic tyrannosaur, weighing as much as a large bull elephant, would need between twenty and fifty times the area to feed in as an elephant needs, because its energy supply is one step removed from the herbivory the elephant employs. It takes ten to twenty pounds of good-quality feed to produce one pound of cow or elephant; herbivorous dinosaurs were probably similar.

Also, it takes five to ten pounds of the herbivore's meat to yield one pound of predator. But day-to-day energy use depends on metabolism. Comparing two modern, similar-sized beasts: a well-fed lion can go two or three days until the next kill. A well-fed Komodo dragon can last a month. Thermal strategy dictates efficiency.

Bringing us the scenarios of dinosaur ecology requires weaving together, not just biological strands, but also palaeogeography and plate tectonics, the rise and fall of oceans, and even cosmology, for it was a cosmic event that killed all the dinosaur lineages except the birds.

The author closes the book with an epilogue, musing about using dinosaurs as a vehicle to better teach biology, ecology, evolution, and scientific principles in general. He also proposes them as the "poster children" for a grand story that teaches us better stewardship of the planet. He repeats what is well known in some circles, that we are in the midst of a human-driven great extinction that could be as severe as the one that ended the "age of Dinosaurs" and ushered in this mammal-dominated one (though remember there are twice as many birds). It doesn't have to be this way, but we seem to be like someone riding in a taxicab whose driver is drunk or insane, and the door won't open. Those of us who care haven't been able to do much about it. I hope a book like this can be a positive influence.