Monday, July 10, 2006

Teeth! Burnie, David. The Kingfisher Illustrated Dinosaur Encyclopedia. Edited by Illustrated by John Sibbick. London: Kingfisher, 2001.

Wish I had more time for this book.

What makes the book work particularly well is that explanations of process are offered to explain why "factual materia;" is evidence for the claim being made.

I've selected three pages which are worth considering in detail: "How Animals Evolve" (14-15); "How Fossils Form" (18-19) and "A Question of Size" (84-85).

1. : "How Animals Evolve" (14-15)

Here I was impressed by the way the process of evolution is described. "During his [Darwin's] lifetime, many people imagined that evolution followed a set path, steadily 'improving' living things in the same way that designers improve machines. But today, biologists take a rather different view. The reason for this is that, unlike a human designer, natural selection cannot plan ahead. Instead, it works like an impartial judge, testing every tiny variation, and rejecting any that do not have an immediate use. It cannot select anything that simply might prove useful in the future.

"This way of selecting features means that complicated structures, such as eyes... have to evolve through a succession of stages, and that each of these stages must bring benefits of its own. Primitive feathers, for example, would have been useless for flight, so they must have served some other function when they first arose. Paleontologists believe that they know what this function was--a discovery that has had a major impact on our understanding of dinosaurs as well as birds.

"Another feature of evolution is that it can never start from scratch. Instead, natural selection works from living thing as they currently exist, encouraging features that helo them to make the most of their way of life. But no matter how much living things change on the outside, their bodies still contain the evidence of their long-distant evolutionary past. For paleontologists, this evidence is a treasure-trove of information about how living things have evolved." (15)

2. "How Fossils Form" (18-19)

Here, two things attracted my attention, first simply that it succeeds in explaining why fossils are so rare, that there are many things that can go wrong in he process, and second that it explains how the relative frequency of trilobites (and their skin shedding) has enabled paleontologists to use them to construct a time line or fossil calender.

There is a very beautiful diagram at the bottom that shows the process of fossilsation.

3. "A Question of Size" (84-85).

The book explains gigantism as driven partially by predation (larger animals survive, but larger predators are also more successful) and the way in which the larger dinosaurs digestive system worked, which put a premium on the generation of heat from larger and larger stomachs. However, gigantism is stalled by "increasing difficulties mating and laying eggs" and the strain put on the heart.

"But from an engineering standpoint, a more fundamental problem concerned their weight: as they evolved larger and larger bodies, this climbed at a prodigious rate.

"To visualise how this happened, imagine three 'dinosaurs' shaped like cubes, with sides 1cm, 5cm and 10cm long. The second dinosaur is only five times as long as the first, but is weight is 125 times as great (the result of multiplying 5x5x5). The third dinosaur is 10 times as long, which means that it weighs a thousand times as much as the first. Once sauropods reached lengths of about 20m, each additional metre meant a jump in weight of over a tonne--a tremendous burden that still had to be supported by just four legs.

"The strength of a leg depends on its cross-sectional area, rather than its volume. This means that if an animal gets larger while keeping the same overall shape, its weight outstrips its strength, so its legs are put under greater and greater stress, Sauropods coped with this by modifying their leg bones, and by keeping bending to a minimum, but in the end it would have been weight, rather than anything else, that brought their growth to a halt."

Without any great efforts, the authors succeed in demonstrating the openness of science and the degree to which one element of knowledge rests on many others, that knowledge is an expanding jigsaw, not independent particles.


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