Fossil butterfliesPosted on 15-06-2017 by Hilde Pracht; Rienk de Jong
Cover photo: fossil of the oldest known butterfly: Protocoeliades kristenseni
Fossil butterflies are extremely rare. Only 49 species are known, against approximately 17.000 living species. Therefore, these few fossils are very important to get more insight in the time of origin of the characteristics that are preserved and with that, insight in the origin of species, genera and families which are recognized on the basis of these characteristics.
This is done by making use of the ‘molecular clock’: DNA evolves with a certain speed, which is called the speed of the molecular clock. By comparing the DNA of two species, researchers can determine the amount of difference between their DNA. When we know when these two species diverged, we can calculate how fast the DNA changes: the speed of the clock (or: the number of changes per unit of time) of the lineage the two species belong to.
Photo: Locations where the fossil butterflies have been found
So first, it has to be decided when two species split. This is done by using fossils. They mark a point on the phylogenetic tree with a certain age: a so-called calibration point for estimating the speed of the molecular clock. When the clock speed is calculated by means of the fossils, researchers can use this speed to estimate the divergence time of other couples of taxa of the same lineage, for which DNA data is known. To optimize this estimates, it is important to have as many calibration points as possible.
Photo: fossil of the oldest known butterfly: Protocoeliades kristenseni
For this reason, Naturalis researcher Rienk de Jong wrote an article in which all known butterfly fossils and their applicability as calibration points are discussed. The currently known butterfly fossils span a period of 55 million years. This means that butterflies in any case have originated earlier than that. Moreover, the characteristics of the oldest butterfly fossil indicate that it does not belong to the root of the butterfly tree, but that already several divergences have taken place. This is evidence for the fact that butterflies are even older and that the oldest fossils are yet to be found. According to modern estimates, the butterflies originated between 80 and 100 million years ago. In a current international project, the DNA of members of almost 1000 butterfly genera is being analyzed. The results of the present paper are used to estimate the times of divergence events as good as possible.
Apart from this, much more information can be derived from fossils. They can, for example, tell us more about the former distribution. The oldest known butterfly fossil was found in Denmark. However, it belongs to a species of butterflies that nowadays is only distributed in tropical Africa and Asia. This illustrates that 55 million years ago the area which now forms the Northern Hemisphere, used to have a subtropical to tropical climate.
The whole article of Rienk de Jong, is available online (open access) via this link: http://www.biotaxa.org/Zootaxa/article/view/zootaxa.4270.1.1/27620
Photo: Scheme of the known fossils (red dots) and their place in the family tree of the butterflies.