Fossils are the preserved bodies or traces of animals or plants that have lived in the past. Commonly the fossil records that have been found were the fossilized hard parts such as bones of the animals or woody tissues from the plants. Scientists have been using fossils as a medium to obtain biological data. These data are important as it provides us a better understanding of evolutionary processes in the past (Jablonski & Shublin 2015). In other words, to understand diversification and evolution patterns of life, fossil records seem to be an important ‘ingredient’ as majority of life has gone extinct (Puttick & Thomas 2015). However, there is some debate on whether fossils should be used in phylogenetic studies to determine the relationship of organisms. How have they been used? Should they be used as a ‘tool’ to study evolutionary relationships among organisms? In this essay, the method that could fossils be used to inspect the past, how fossils are advantageous and disadvantageous in studying evolutionary relationships will be discussed.
One of the ways of using fossils to study evolution was to obtain ancient DNA encoded in the fossils. By analyzing and comparing genetic changes in the fossils to living organisms, systematic relationships between genera sharing a common ancestors that have become extinct can be solved (Yang et al. 1995). It was suggested by Yang (1997) that DNA molecules will be degraded over a period of time. However, by using molecular biology technology such as application of PCR, damaged DNA was able to be repaired and cloned (Yang 1997). Although it was difficult to reproduce DNA from pre-Quaternary fossils but Ancient DNA studies works better on Quaternary fossils as it is relatively young and stored in shallower underground. Therefore, Quaternary fossil DNA experiences less damaged and preserves better (Yang 1997). In phylogenetic studies, fossil DNA might be used as ancestral sister taxa within orders, known as ‘outgroup’ to show characters in a phylogenetic tree with a clearly picture (Yang et al. 1995). In Yang, Goldenberg and Shoshani’s work has demonstrated how fossil DNA was used to resolve systematic relationship within Elephantidae family with American mastodon as the outgroup. DNA was extracted from extinct American mastodon, extinct woolly mammoth and living Asian and African elephants. The outgroup American mastodon has effectively reduced the branch length to more distant outgroups and helped to recognize common traits in cladistical terms (Yang et al. 1995).
There is a debate on whether fossils should be used for phylogenetic DNA studies. It was argued that fossils should be discounted for understanding evolutionary patterns and living form should be used instead. This is due to the incomplete fossil records that have been discovered. One of the factors that have caused to the incompleteness of fossil records was that soft bodies organisms are rarely preserved (Benton 2005). That could lead to no trace of these soft-bodies animals even if they had dominated the habitat in the past. As a consequences of this, paleontologists would not to be able to prove in Jurassic seas a group of animals with purple body that feeds on dinosaurs were not existed (Benton 2005). With incomplete fossils, inconsistent readings from both the fossil record and molecular dating will be resulted due to underestimation of node ages in phylogenetic tree (Forest 2009). Rate of evolution across the taxa will not be comparable (Springer 1994). Again, fossils are incomplete due to different organisms have different preservation potential (Forest 2009). Insufficient fossil record will lead to confusing and inconsistent phylogenetic tree with large number of taxonomic groups. For example, fossil records have suggested decrease in diversity of cetaceans due to extinction while on the other hand, analysis of this group based on phylogeny indicates that the diversity has been increasing (Morlon et al. 2011).
It is true that the fossil quality reduces as it gets older, and also newer fossils are always studied better than older fossil records. There has been a debate on when major groups of animals were originated, it was suggested by molecular studies that the time of origination of animals, mammalian animal and modern Aves was much earlier than what had fossil evidence recorded. Further debate on this might be due to mistake from new results or it indicates there is a long period of missing fossil records that have not be found. In Benton and his fellow scientists research in 2000, it was aimed to assess the efficiency of stratigraphy comparing to phylogeny. The result after comparing 1000 published phylogeny samples have shown that the quality of fossils did not diminish (Benton et al. 2000). Benton et al. (2000) state that it seems impossible for the fossil quality to stay the same as it is very commonly destructed by geological event. However, by looking at both the stratigraphy and taxonomy, orders and families are relatively the same while definition of genera and species of fossils were often changed by new discoveries. Quental and Marshall (2010) believe with fossil records 1it review our ways of looking at the diversification rates and patterns. They stated “if we cannot access to extinct lineages, we are blind to their extinction and the origination dynamics” (Quental & Marshall 2010). One example presented in Quental & Marshall (2010) would be the differences in diversity trajectory in Cetacea period, different stories were told by analyzing fossil records from the Cetacea and molecular phylogeny. Molecular phylogeny had suggested that in Cetacean period there was an exponential growth of diversity. However, no evidence was able to support this hypothesis. On the other hand, with the assumption that there was around similar average number of species in fossil genera and living genera, the fossils have indicated that the rate of diversification was relatively stable instead of what was proposed by using molecular phylogeny (Quental & Marshall 2010).
There are gaps between fossils records. Some gaps between certain fossils were said to be the intermediate form which have characteristics from both organisms (Fischer & Steel 2008). For example the origination of fish is still a mystery, there is no transitional forms between spineless invertebrates and fishes with backbone. It was believed that modern fishes were evolved from lancelet-like fish, and therefore intermediate fossils were expected, however no evidence of lancelet-like-precursor-animal has yet to be found. Therefore, evolutionary relationships still remain unsolved (Bergman 2011). The improbability of fossilization which was discussed previously have been used as an explanation on why there are so many ‘missing links’ in the fossil records (Fischer & Steel 2008). This might not be the case in fish evolution because majority of known fish type has been found in the fossil record, and those new discoveries on new species often create new gaps. The evidence provided from the huge amount of fossil record is not significant to show the evolution of fish (Bergman 2011). Another example will be the way of how fossils of Archaeopteryx, the once-lived animal with reptile-like body and bird-like wings and feathers had misled our world of understanding towards the evolution of birds. It was believed that Archaeopteryx is the transitional form from reptile to birds. By comparing the structures of 6 fossil skeletons of Archaeopteryx such as sternum, furcula, bone, tail and foot with modern birds, the structures were recognized for the flight to be evolved (Wellnhofer 1990). This had placed Archaeopteryx to be the missing link between reptiles and flying bird. However, new discovery of Archaeopteryx-like theropod, Xiaotingia has led to conclusion that Archaeopteryx is not a bird at all, it is belong to the base Deinonychosauria. Those features which were thought to be avialan features turned out to be more related to Paraves (Xing Xu et al. 2011). For example Paraves might have longer and thicker forelimbs for other function but with similar appearance for flying purposes. This discovery has resulted the Archaeopteryx to be placed at the bottom of Deinonychosauria and removed from the Acialae (Xing Xu et al 2011). This shows how our understanding of evolution can be misled by the appearance of the fossil records.
Is fossil good enough to portrait what evolution looks like? In my opinion, digging the past have a significant impact on our understanding of evolution. It allows us to observe the evolutionary patterns and process of ancient organisms that have once-lived in the past. Archaeopteryx had been known as the intermediate of reptiles and birds for around 150 years and the truth has been revealed by the discovery of Xiaotingia, but all of the studies that have led to this conclusion were still based on fossil records. Although fossil records are misleading sometimes, however continuous investigation with data incorporated from fossil record will allow us to expand our insight of biological evolution. Besides, transitional fossils have been discovered over time. In China, couple of new fossil earwigs with both primitive and derived characteristic were discovered and claimed to be the missing link that bridges between the suborders Archidermaptera and Eodermaptera (Zhao et al. 2010). With the newly discovered earwigs, Zhao and his fellow scientists were able to look back in time and conduct phylogenetic studies and reassessing fossil Dermaptera relationships. Finally, this has allowed them to suggest when did the division of Dermaptera into Archidermaptera, Eodermaptera and Neodermaptera happened in the past (Zhap et al.2010). Continuous discovery of fossils will eventually prove that they are the evidence the life in the past (Benton 2005).
As what have been discussed above, how fossils have successfully contributed to the studies intended to investigate evolutionary relationships, as well as some debate on the how fossil might not be available for understanding of evolution were discussed. On overall, we cannot deny that it is impossible to ‘see’ the history of life, how life have evolved and the process of diversification without looking at fossils (Jablonski & Shubin 2015). Also, paleontological and molecular data together can result a clearer image on temporal framework of lineages (Magallón 2018). Last but not least, young fossil records ranging from 10 years to thousands of years can inform how domination of human population to the major natural processes on earth can impact and shape the biota we see today. Noteworthy to mention that, evolutionary dynamic of the biotas interact with climate change from the past until present day can be also assessed through fossils, which it might be useful when it comes to conservation biology (Jablonski & Shubin 2015).