At the time when Charles Darwin published his famous book, On the Origin of Species, in which evolution was intensively explored, there was no adequate tangible evidence to support his arguments. Charles hinted that fossil record could reveal species with intermediate or transitional features. He anticipated that lack of transitional fossil records could be the major loophole of his theory and most likely the major concern of his critics. However, today, there are many transitional fossils that provide the missing links in the evolutionary theory. A transitional fossil can be defined as any fossilized remnants of life that reveal similar characteristics between both the ancestral group and the descendant group. Due to inadequate fossil evidence, it is not easy to prove how the ancestral group transformed into its assumed descendant group.
The common transitional fossils are Archaeopteryx (which was discovered two year after publication of On the Origin of Species. It represents a transition between dinosaurs and birds.), Tiktaalik roseae among many others.
Among the transitional fossils, is the Tiktaalik roseae, which is no longer in existence. This was an aquatic animal which resembled fish and lived about 370 million years ago in Devonian era. Tiktaalik roseae was found in the year 2004, on the Ellesmere Island, in Nunavut, Canada.
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Tiktaalik roseae provides a missing link between fishes and amphibians. This fossil, is similar to fish in many ways. For instance, it possessed gills, fins and scales just like fish. On the other hand, the appearance of Tiktaalik roseae suggests that it could be an ancestor of vertebrates hence it represents a change of habitat of vertebrate from aquatic to terrestrial. It had tetrapod like features such as mobile neck and a ribcage which were used to support its body and help in breathing through poorly developed lungs. The bones inside this creature’s fins resemble those found in human hand hinting that it was able to support weight.
This animal had a flat head and eyes positioned on top of head akin to that of a crocodile; a feature that strongly suggests that the animal spent most of its life time looking up. Furthermore, Tiktaalik roseae had a well refined jaw for seizing its prey and a spiracle which later on developed into an ear.
Tiktaalik roseae was similar to ancient lungfish and coelacanth species that are still present today in many ways which is a concrete evidence that it represents emergence of vertebrates on to dry land.
In conclusion, it is clearly evident from the issues tackled above that Tiktaalik roseae is a transitional fossil between fish and tetrapods inhabiting in dry land. This is particularly the case because it is akin to fish and tetrapods in many respects. Among them is undistinguished skeletal configuration which is prevalent in fish. There have, however, been recent discoveries that have discredited Tiktaalik roseae as the real ancestor of tetrapods. A full tetrapod that lived nearly 20 million years before Tiktaalik roseae was discovered.
References
- Ahlberg, P. E., & Clack, J. A. (2006). Palaeontology: a firm step from water to land. Nature, 440(7085), 747.
- Lyson, T. R., Bever, G. S., Bhullar, B. A. S., Joyce, W. G., & Gauthier, J. A. (2010). Transitional fossils and the origin of turtles. Biology Letters, 6(6), 830-833.
- Shubin, N. H., Daeschler, E. B., & Jenkins Jr, F. A. (2006). The pectoral fin of Tiktaalik roseae and the origin of the tetrapod limb. Nature, 440(7085), 764.
- Shubin, N. H., Daeschler, E. B., & Jenkins, F. A. (2014). Pelvic girdle and fin of Tiktaalik roseae. Proceedings of the National Academy of Sciences, 111(3), 893-899.
