Paleontology Today

Dinosaurs and fossil humans

Much of 19th century paleontology was dominated by remarkable new discoveries. Collectors fanned out all over the world, and knowledge of ancient life on Earth increased enormously. The public was keenly interested then, as now, in spectacular new discoveries of dinosaurs. The first isolated dinosaur bones were described from England and Germany in the 1820s and 1830s, and tentative reconstructions were made (Fig. 1.9). However, it was only with the discovery of complete skeletons in Europe and North America in the 1870s that a true picture of these astonishing beasts could be presented. The first specimen of Archaeopteryx, the oldest bird, came to light in 1861: here was a true "missing link", predicted by Darwin only 2 years before.

Darwin hoped that paleontology would provide key evidence for evolution; he expected that, as more finds were made, the fossils would line up in long sequences showing the precise pattern of common descent. Archaeopteryx was a spectacular

Figure 1.9 The first dinosaur craze in England in the 1850s was fueled by new discoveries and dramatic new reconstructions of the ancient inhabitants of that country. This picture, inspired by Sir Richard Owen, is based on his view that dinosaurs were almost mammal-like. (Courtesy of Eric Buffetaut.)

Figure 1.9 The first dinosaur craze in England in the 1850s was fueled by new discoveries and dramatic new reconstructions of the ancient inhabitants of that country. This picture, inspired by Sir Richard Owen, is based on his view that dinosaurs were almost mammal-like. (Courtesy of Eric Buffetaut.)

start. Rich finds of fossil mammals in the North American Tertiary were further evidence. Othniel Marsh (1831-1899) and Edward Cope (1840-1897), arch-rivals in the search for new dinosaurs, also found vast numbers of mammals, including numerous horse skeletons, leading from the small four-toed Hyracotherium of 50 million years ago to modern, large, one-toed forms. Their work laid the basis for one of the classic examples of a long-term evolutionary trend (see pp. 541-3).

Human fossils began to come to light around this time: incomplete remains of Neandertal man in 1856, and fossils of Homo erectus in 1895. The revolution in our understanding of human evolution began in 1924, with the announcement of the first specimen of the "southern ape" Australopithecus from Africa, an early human ancestor (see pp. 473-5).

Evidence of earliest life_

At the other end of the evolutionary scale, paleontologists have made extraordinary progress in understanding the earliest stages in the evolution of life. Cambrian fossils had been known since the 1830s, but the spectacular discovery of the Burgess Shale in Canada in 1909 showed the extraordinary diversity of soft-bodied animals that had otherwise been unknown (see p. 249). Similar but slightly older faunas from Sirius Passett in north Greenland and Chengjiang in south China have confirmed that the Cambrian was truly a remarkable time in the history of life.

Even older fossils from the Precambrian had been avidly sought for years, but the breakthroughs only happened around 1950. In 1947, the first soft-bodied Ediacaran fossils were found in Australia, and have since been identified in many parts of the world. Older, simpler, forms of life were recognized after 1960 by the use of advanced microscopic techniques, and some aspects of the first 3000 million years of the history of life are now understood (see Chapter 8).

Macroevolution_

Collecting fossils is still a key aspect of modern paleontology, and remarkable new discoveries are announced all the time. In addition, paleontologists have made dramatic contributions to our understanding of large-scale evolution, macroevolution, a field that includes studies of rates of evolution, the nature of speciation, the timing and extent of mass extinctions, the diversification of life, and other topics that involve long time scales (see Chapters 6 and 7).

Studies of macroevolution demand excellent knowledge of time scales and excellent knowledge of the fossil species (see pp. 70-7). These two key aspects of the fossil record, our knowledge of ancient life, are rarely perfect: in any study area, the fossils may not be dated more accurately than to the nearest 10,000 or 100,000 years. Further, our knowledge of the fossil species may be uncertain because the fossils are not complete. Paleontologists would love to determine whether we know 1%, 50% or 90% of the species of fossil plants and animals; the eminent American paleontologist Arthur J. Boucot considered, based on his wide experience, that 15% was a reasonable figure. Even that is a gener alization of course - knowledge probably varies group by group: some are probably much better known than others.

All fields of paleontological research, but especially studies of macroevolution, require quantitative approaches. It is not enough to look at one or two examples, and leap to a conclusion, or to try to guess how some fossil species changed through time. There are many quantitative approaches in analyzing paleon-tological data (see Hammer and Harper (2006) for a good cross-section of these). At the very least, all paleontologists must learn simple statistics so they can describe a sample of fossils in a reasonable way (Box 1.3) and start to test, statistically, some simple hypotheses.

Paleontological research

Most paleontological research today is done by paid professionals in scientific institutions, such as universities and museums, equipped with powerful computers, scanning electron microscopes, geochemical analytic equipment, and well-stocked libraries, and, ideally, staffed by lab technicians, photographers and artists. However, important work is done by amateurs, enthusiasts who are not paid to work as paleontologists, but frequently discover new sites and specimens, and many of whom develop expertise in a chosen group of fossils.

A classic example of a paleontological research project shows how a mixture of luck and hard work is crucial, as well as the

Box 1.3 Paleobiostatistics

Modern paleobiology relies on quantitative approaches. With the wide availability of microcomputers, a large battery of statistical and graphic techniques is now available (Hammer & Harper 2006). Two simple examples demonstrate some of the techniques widely used in taxonomic studies, firstly to summarize and communicate precise data, and secondly to test hypotheses.

The smooth terebratulide brachiopod Dielasma is common in dolomites and limestones associated with Permian reef deposits in the north of England. Do the samples approximate to living populations, and do they all belong to one or several species? Two measurements (Fig. 1.10a) were made on specimens from a single site, and these were plotted as a frequency polygon (Fig. 1.10a) to show the population structure. This plot can test the hypothesis that there is in fact only one species and that the specimens approximate to a typical single population. If there are two species, there should be two separate, but similar, peaks that illustrate the growth cycles of the two species.

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