Fossil Friday: Insects Part 1

Insects and their fellow creepy crawlies have been around for a long, long, looong time. Long before dinosaurs ever showed up on stage. A common misconception is that creepy crawlies in prehistoric times were limited to just dragonflies, millipedes, and perhaps spiders, and they were all giant. I’m thinking about a certain eagle-size dragonfly and six-foot long millipede in particular. But there was only one period of history that insects and their other arthropod relatives (like spiders) were truly giant- the Carboniferous period. The Permian Period- the Age of Amphibians- is the span of time between the Carboniferous and Triassic period. The Triassic Period, of course, is when the first dinosaurs came on the scene.

The reason for the giant size of creepy-crawlies during the Carboniferous, and no other period, where the high levels of oxygen from the boom in forest and tree growth around the world. By the time the Jurassic Period rolls around, oxygen levels are a bit more like they are today, and bugs are about as big as they get today. The “bugs” in this series are only a tiny fraction of the diversity there was during the Jurassic. They are delicate creatures and do not fossilize easily, so who knows how many there really were? Most of these still have surviving species today that look very similar to how they looked so many years ago, and they provide a tiny glimpse to the many strange and wonderful insects that flew in the air and crawled in the leaf litter during the Jurassic.

For part one of this series I’ll explore beetles. The oldest known fossil insect that looks more like modern beetles is from the Permian Period, about 270 million years ago. At that time beetles were mostly limited to a few fungus and algae-feeding species, including a few that started to look a little like the weevils and rove beetles below. It wasn’t until the Jurassic period that beetles really started to diversify into the shapes we recognize today. Below are a few of the basic groups we could observe if we went back in time to the Jurassic Period.

Rove beetles have fossils dating back to the Triassic or possibly even earlier. They are known for the small wing cases that protect their wings, which fold up into two tiny, convenient packages of masterful origami. Modern rove beetles are found in almost every corner of the planet, and eat virtually everything, but their early relatives most likely fed on rotting leaves or fungus in the leaf litter.

Weevils appeared about the same time as Rove beetles. They are known for their long snouts, and are typically tiny insects (less than 6mm). Many lay their eggs inside plants. Inside the seeds of cycad cones would be a good Jurassic example, but you may have come across one of these delightful grubs when cracking pecans, or invading the flour stored in your cupboard.

Th Netwing, or Reticulated, Beetle appeared during the late Triassic period, and by the Jurassic period can be found across the globe. It is known for its thick, segmented antennae and the lacy or “net” texture of its wing cases. It prefers to eat fungus.

Water beetles appeared in the Late Triassic period and quickly diversified into groups that ate algae and groups that hunted other insects. The larvae are voracious hunters and entirely dependent on water, but many adults that live in ponds or streams at risk of drying out can fly to a new water source.

Click beetles first appeared late in the Triassic period, and then exploded in diversity during the Jurassic. They are most famous for their ability to catapult themselves by snapping their body segments with a loud clicking sound. Many larvae and even some of the adults have bio-luminescence. The larvae are burrowers that eat decaying plant matter and microscopic bits in the soil, while the adults usually graze on algae or other simple plants.

These colorful beetles are just starting to make an appearance in the early Jurassic period, so they are rare jewels hidden in the foliage. Their brilliant colors and patterns are not from color pigments, but from light reflecting off of the microscopic texture of the exoskeleton. The grubs typically bore under bark or through plant roots or stems,

You may recognize scarab beetles as those curious little insects rolling a ball of poop across the lawn, but the first scarab beetles appearing in the Jurassic where plant eaters, not poop eaters. Their strong legs and shovel-shaped heads would be useful for burrowing through leaf litter or shoving into rotting wood softened by fungus- their favorite snack.

There are so many different kinds of beetles that it can be difficult to name them all! Leaf beetles are an enormous group of hard-shelled beetles with many different families and genera. They are typically known as leaf beetles because of their herbivorous diet of leaves and other plant parts. There may also be beetle groups that I am missing here because they are extinct, or I couldn’t find information on them.

Resources:

Any sort of list for prehistoric insects was mostly unhelpful. Research for this series mostly involved painstaking unwinding of threads from modern groups, then tracing back on which ones are the oldest and most “primitive” groups. Luckily, Wikipedia has a handy little chart on the upper right-hand corner for almost every insect genus and family that says when in time it appeared. I would then trace those lineages and see if I could find fossil versions, or modern species that look nearly identical to their fossil ancestors.

Once I crawled into the rabbit hole I just had to keep going, even when I realized I’d bitten into quite a bit more than I could chew! I hope you enjoyed it as much as I did! 😀

I am eternally grateful that Wikipedia is such a great resource. From the sheer number of insects I discovered I’m afraid I did not have the time to cross reference with other resources, but you can always look into the many resources Wikipedia lists at the bottom of each article if you want to find out more!

“Dicondylia.” Wikipedia, https://en.wikipedia.org/wiki/Dicondylia#Taxonomy

“Beetle.” Wikipedia, https://en.wikipedia.org/wiki/Beetle#Evolution

“Hydrophylidae.” Wikipedia, https://en.wikipedia.org/wiki/Hydrophilidae

“Cupedidae.” Wikipedia, https://en.wikipedia.org/wiki/Cupedidae

“Weevil.” Wikipedia, https://en.wikipedia.org/wiki/Weevil

“Belidae.” Wikipedia, https://en.wikipedia.org/wiki/Belidae

Kundrata, Robin & Pačková, Gabriela & Hoffmannova, Johana. (2020). Fossil Genera in Elateridae (Insecta, Coleoptera): A Triassic Origin and Jurassic Diversification. Insects. 11. 394. 10.3390/insects11060394.

“Bubrestidae.” Wikipedia, https://en.wikipedia.org/wiki/Buprestidae

“Scarabaeidae.” Wikipedia, https://en.wikipedia.org/wiki/Scarabaeidae

“Leaf Beetle.” Wikipedia, https://en.wikipedia.org/wiki/Leaf_beetle