Investigating Fossils. Wilson J. Wall. Читать онлайн. Newlib. NEWLIB.NET

Автор: Wilson J. Wall
Издательство: John Wiley & Sons Limited
Серия:
Жанр произведения: Биология
Год издания: 0
isbn: 9781119698487
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that the calf would be preserved at all, as while the original discoverers went to report the find to their local museum, the corpse was lifted and removed for display outside a shop. It was retrieved, with a little damage due to local dogs, and has been widely exhibited since. The permanent display is at the Shimanovsky Museum and Exhibition Centre in Salekhard, Russia. Salekhard is reputedly the only town where the Arctic Circle actually runs through the town.

      Completely submerging an organism in what is in effect a preservative is another way in which plant remains or animal corpses can survive for very long periods. One of the ways this can happen is found in tar pits. These are rare sites, but can be quite extensive, for example, Pitch Lake in Trinidad is the largest natural deposit of asphalt in the world, covering about 44 ha. Other such deposits include Binagadi asphalt lake in urban Baka, Azerbaijan, and the second largest lake, Lake Guanoco in Venezuela.

      Probably the most investigated and well known of all the asphalt deposits are the Tar Pits of La Brea in Los Angeles. This is the most well studied of the rare tar pits, and it is also unique in having been an asphalt mine during the nineteenth and early‐twentieth century. The position of the tar pits, in what is now an extensive suburban area of Los Angeles, has added to the development of interest in this particular site. The current pits are mostly man‐made, a leftover from asphalt mining during 1913 and 1915, and partially created by deliberate digging for bones. It had been realised for a long time prior to the twentieth century that there were bones in considerable numbers present in the tar pits, but they had been assumed to be those of stray cattle that had wandered in to the tar and become stuck. It is true that animals wandered onto the unsupportive and sticky surface, making the mistake of thinking it was a watering hole, what had not been realised was that these wandering animals were not generally domesticated cattle. It would have been an easy mistake to make for wildlife to imagine the surface was solid as it would accumulate twigs and leaves and form pools on the surface when it rains. This would also attract night flying aquatic insects, such as water beetles that would similarly become trapped in the sticky tar. This is a well‐known phenomenon, where newly made roads with an apparently wet surface will attract night flying aquatic insects when there is a bright moon.

      The lack of preserved soft parts in the tar pits has allowed speculation regarding the coat colour of species of Smilodon. They have been represented as plain‐coated or spotted, either of which would be possible. The coat colour of modern felids seems to be broadly dependent on the preferred terrain in which they live, but since there are exceptions to this, it becomes impossible to be sure of the coat in these species.

Photo depicts smilodon fatalis (californicus) skull from La Brea Asphalt, Upper Pleistocene Rancho La Brea tar pits, Los Angeles, California, USA.

      Source: Photo. James St John, Creative Commons, generic.

      Although preservation of ancient material, plant or animal, by encapsulation can result in very high resolution remains, the most usual way of thinking about preserved remains is as inclusions within rock. This process requires considerable changes in chemical structure and composition, a process described as taphonomy. The final outcome of taphonomy in the most frequently considered situations of fossilisation may appear to be the same, that is leaving a permanent record set in stone, but it takes little time investigating various fossils to see that the mineral nature of fossils can be radically different. This is most notably so when comparing fossils from different areas, as the colours vary quite widely. These colour variations reflect different mineral compositions within the final product of fossilisation, which of course is a reflection of the mineral composition of the rock in which the fossil was formed.

      In broad terms and very simple terms, fossilisation resulting in a stone product requires rapid sedimentation of material which will eventually bind in a cement‐like fashion to become rock. The details can, of course, vary enormously from site to site, but in broad terms it always starts with sedimentation. This is one of the reasons that it is generally considered that fossilisation only takes place in shallow seas, lakes or shallow slow rivers and very wet swamp land.

      Slow rivers and swamp land are often associated with floodplains, which also accumulate remains washed down stream and silt to cover them. The converse conditions are not so conducive, that is, fossilisation would not normally take place in dry, arid, conditions. This inevitably has some implication for the types of fossils which are most frequently found. Aquatic species will naturally form the bulk of fossilised material, but all species need water to drink and watering holes that attract grazing livestock also attract carnivores, both to drink and as an easy way to gain access to prey species.

      It has been suggested that by comparing modern ecosystems with the fossil record, it may be possible to determine the biodiversity and species numbers in extinct ecosystems. By making a