Info

Animal groups represented

Bone types limb elements vertebrae and ribs skull and jaw elements dermal armor

Bone types skull and jaw elements dermal armor

teeth fish scales fish scales

teeth

Taphonomic classes: bone shapes

| fishes H amphibians | turtles H lizards, etc.

□ crocodiles | pterosaurs 3 dinosaurs

□ mammal-like reptiles 0 mammals rounded subrounded

Taphonomic classes: bone shapes subrounded

subangular

Ratio L/W

Ratio L/W

Figure 1.11 Composition of a Middle Jurassic vertebrate fauna from England. The proportions of the major groups of vertebrates in the fauna are shown as a pie chart (a). The sample can be divided into categories also of bone types (b) and taphonomic classes (c), which reflect the amount of transport. Dimensions of theropod dinosaur teeth show two frequency polygons (d) that are statistically significantly different (i-test), and hence indicate two separate forms.

The graph suggests that there is in fact a single species, but that the population has an imbalance (is skewed) towards smaller size classes, and hence that there was a high rate of juvenile mortality. This is confirmed when the frequency of occurrence of size classes is summed to produce a cumulative frequency polygon (Fig. 1.10b). It is possible to test ways in which this population diverges from a normal distribution (i.e. a symmetric "bell" curve with a single peak corresponding to the mean, and a width indicated by the standard deviation about the mean).

It is also interesting to consider growth patterns of Dielasma: did the shell grow in a uniform fashion, or did it grow more rapidly in one dimension than the other? The hypothesis is that the shell grew uniformly in all directions, and when the two measurements are compared on logarithmic scales (Fig. 1.10c), the slope of the line equals one. Thus, both features grew at the same rate.

In a second study, a collection of thousands of microvertebrates (teeth, scales and small bones) was made by sieving sediment from a Middle Jurassic locality in England. A random sample of 500 of these specimens was taken, and the teeth and bones were sorted into taxonomic groups: the results are shown as a pie chart (Fig. 1.11a). It is also possible to sort these 500 specimens into other kinds of categories, such as types of bones and teeth or taphonomic classes (Fig. 1.11b, c). A further analysis was made of the relatively abundant theropod (carnivorous dinosaur) teeth, to test whether they represented a single population of young and old animals, or whether they came from several species. Tooth lengths and widths were measured, and frequency polygons (Fig. 1.11d) show that there are two populations within the sample, probably representing two species.

cooperation of many people. The spectacular Burgess Shale fauna (Gould 1989; Briggs et al. 1994) was found by the geologist Charles Walcott in 1909. The discovery was partly by chance: the story is told of how Walcott and his wife were riding through the Canadian Rockies, and her horse supposedly stumbled on a slab of shale bearing beautifully preserved examples of Marrella splendens, the "lace crab". During five subsequent field seasons, Walcott collected over 60,000 specimens, now housed in the National Museum of Natural History, Washington, DC. The extensive researches of Walcott, together with those of many workers since, have documented a previously unknown assemblage of remarkable soft-bodied animals. The success of the work depended on new technology in the form of high-resolution microscopes, scanning electron microscopes, X-ray photography and computers to enable three-dimensional reconstructions of flattened fossils. In addition, the work was only possible because of the input of thousands of hours of time in skilled preparation of the delicate fossils, and in the production of detailed drawings and descriptions. In total, a variety of government and private funding sources must have contributed hundreds of thousands of dollars to the continuing work of collecting, describing and interpreting the extraordinary Burgess Shale animals.

The Burgess Shale is a dramatic and unusual example. Most paleontological research is more mundane: researchers and students may spend endless hours splitting slabs, excavating trenches and picking over sediment from deep-sea cores under the microscope in order to recover the fossils of interest. Laboratory preparation may also be tedious and long-winded. Successful researchers in paleontology, as in any other discipline, need endless patience and stamina.

Modern paleontological expeditions go all over the world, and require careful negotiation, planning and fund-raising. A typical expedition might cost anything from US$20,000 to $100,000, and field paleontologists have to spend a great deal of time planning how to raise that funding from government science programs, private agencies such as the National Geographic Society and the Jurassic Foundation, or from alumni and other sponsors. A typical high-profile example has been

Box 1.4 Giant dinosaurs from Madagascar

How do you go about finding a new fossil species, and then telling the world about it? As an example, we choose a recent dinosaur discovery from the Late Cretaceous of Madagascar, and tell the story step by step. Isolated dinosaur fossils had been collected by British and French expeditions in the 1880s, but a major collecting effort was needed to see what was really there. Since 1993, a team, led by David Krause of SUNY-Stony Brook, has traveled to Madagascar for nine field seasons with funding from the US National Science Foundation and the National Geographic Society. Their work has brought to light some remarkable new finds of birds, mammals, crocodiles and dinosaurs from the Upper Cretaceous.

One of the major discoveries on the 1998 expedition was a nearly complete skeleton of a titanosau-rian sauropod. These giant plant-eating dinosaurs were known particularly from South America and India, though they have a global distribution, and isolated bones had been reported from Madagascar in 1896. The new fossil was found on a hillside in rocks of the Maevarano Formation, dated at about 70 million years old, in the Mahajanga Basin. The landscape is rough and exposed, and the bones were excavated under a burning sun. The first hint of discovery was a series of articulated tail vertebrae, but as the team reported, "The more we dug into the hillside, the more bones we found". Almost every bone in the skeleton was preserved, from the tip of the nose, to the tip of the tail. The bones were excavated and carefully wrapped in plaster jackets for transport back to the United States.

Back in the laboratory, the bones were cleaned up and laid out (Fig. 1.12). Kristi Curry Rogers worked on the giant bones for her PhD dissertation that she completed at SUNY-Stony Brook in 2001. Kristi, and her colleague Cathy Forster, named the new sauropod Rapetosaurus krausei in

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