May 18th – Volcano day for those of us here in the Pacific Northwest – the 32nd anniversary of the eruption o Mt. St. Helens. (OK – at least some of us in the NW celebrate.) For Darwin, it was more exploring, but no diary entry. So we continue with:
Today, I thought I take a brief look at the history of beetles with some help from the Virtual Fossil Museum. Check them out – it is a great resource for fossil images.
First off, it is worth mentioning that insects do not fossilize all that well. So although they outnumber mammals, fish, reptiles, and other vertebrates, there is limited geologic evidence of their history. However, a lot of work has been done in recent years to better understand the history of this amazing Class on the Tree of Life. Beetles are no exception – for the size of their order, they are very underrepresented.
Jewel Beetle Fossil from Germany (Eocene Epoch – about 40 million years old) (from Wikipedia Commons):
Poor preservation has to do with their exoskeletons, which, unlike bone and shell, breaks down more quickly after they die. What fossils we do find tend to come from very low energy environments (e.g., quite water) that preserve the insects in shale. (This is the same type of environment that preserves delicate fossil leaves.)
Amber, however, is the best way to preserve insect fossils. In this case, tree resin encases the insect’s entire body and completely isolates it from the destructive powers of oxygen. Once the resin hardens into amber the insect is preserved in a near-perfect form.
Firefly and click beetle preserved in amber from Columbia (from the Pliocene/Pleistocene Epoch – a few million years ago) (from the Virtual Fossil Museum):
Insects first show up in the fossil record back in the Devonian time period (roughly about 400 million years ago). Interestingly, the first insects correspond with the first vascular plants on land. Coincidence? I doubt it.
Insects take to the air in the Carboniferous time period (about 325 million years ago), paving the way for wings to be modified into elytra and the appearance of Coleoptera. The first beetle fossil shows up in the Permian time period (roughly about 275 million years ago). About 25 million years later the greatest mass extinction of all time wiped out 90% of marine (and a similarly high number for terrestrial) species. Beetles survived and may have even taken advantage of all the new food sources after the extinction. Then, about 150 million years ago in the Cretaceous, flowing plants evolved and beetles diversity exploded.
Hydrophilus sp. From the La Brea Tar Pits in California (about 35,000 years old) (from Wikipedia Commons):
Some claim that the incredible diversity of beetles is a direct result of flowering plants. Essentially, this hypothesis states that the beetles quickly adapted to take advantage of the many new types of food these plants provided (and never looked back). However, recent studies suggest that many beetle lineages go back further than the Cretaceous – even back to the Permian, long before flowering plants. This hypothesis suggests that what gives us so many beetles species today is the mere fact that they are survivors. Once a new species shows up, it sticks around – continually adding to the total number of species.
One of the classic insect fossil sites is actually in Brazil – the Santana Formation and underlying Crato Formation (deposited during the Cretaceous when beetles were diversifying.). Below are a couple of beetles (a Dystiscidae and Noteridae) from these formations (images from the Virtual Fossil Museum).
More on insect evolution in the future, but for now, a little something to allow you to evolve your own beetle species. – If you are interested in becoming a virtual “beetle breeder” I came across this free online game called Beetle Evolution. To be fair, I only played for a little while so I can’t tell much about it, but the goal is to feed and take care of little beetles, and breed them to try to create the ultimate beetle. For the true beetle nerd…I mean aficionado. You know Darwin would have played…(RJV)