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The Advantages and Disadvantages of the Fossil Record in Comparison to Extant Species in Understanding Evolutionary Ecology

Ecological diversity comprises two components: the number of species present and their relative abundance within ecosystems (Raffaelli, 2007). The fossil record, however, is used to estimate the number of ancient species and their abundance in the distant past. It is, therefore, logical to study the behaviour, morphology, general biology and ecology of any present (extant) species, which are more closely related to ancient fossils. This can then help elucidate the ecological diversity of species from the past and their evolutionary ecology, i.e. how they interacted with each other and their evolutionary histories. This includes evolutionary life cycles, behaviour, inter-specific relations and the evolution of biodiversity (Fox et al., 2001; Mayhew 2006; Pianka 2000).

Fossils can also, therefore, provide insights on the ecology and behaviour of extant species, how they evolved and adapted to changing biotic and abiotic factors. Invertebrate fossils are far more numerous than vertebrate ones. This is partly due to their tough exoskeletons and decay-resistant shells (Taylor and Lewis, 2005), not just their size and reproductive capabilities. Fossilised arthropod species, especially those of arachnids, are often found beautifully preserved in amber. This form of fossil not only gives valuable information about the species but also ancient forest ecosystems. However, most arthropod species in amber are often described from singleton finds or are too few in number. This means species' numerical abundance data are very limited (Penny and Langan, 2006). Usually terrestrial invertebrates caught in amber correlate well with underlying species' distribution and diversity patterns of extant tropical insects at the family level (Labandeira 2005). Many Cenozoic spiders have been preserved this way and belong to extant species (Penny et al., 2003). These examples often reveal similar ecologies and behaviour to their present close relatives at the family level also (Penny and Langan, 2006).

The fossil record is, nevertheless, limited, often representing only one of a hundred or thousand related species and offers few characteristics (Gull 2007). For example, the amphibian and reptile fossil record in Mexico between 1869 and 2004 is poor. The fossils are often fragmentary, making their taxonomic identity difficult (Reynoso, 2006). It is not always possible to distinguish parts of fossilised bones from parts belonging to another species. Large gaps in evolutionary history become obvious when studying the proportion of extant families with a fossil record (Forey et al., 2004). The bias towards preservation of animals with tough skeletons or plants with woody bark leaves many of those soft-bodied and/or rapidly decaying species out of the record. It is only unusual environmental conditions that preserve these kinds of organisms. Recently, numerous well-preserved fossils were discovered in a Bahamian sink-hole which lacked oxygen, preventing microbial decomposition (ScienceDaily, 2007).

Morphological, taxonomic hierarchy and behavioural information from fossil species can be questioned. However, the combined study of extant species, molecular systematics and further fossil discoveries must enhance the facts about evolutionary and ecological diversity.

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