Tracing Insect Evolution with Fossils

The first insects appeared on Earth roughly 480 million years ago. They are thought to have evolved from crustaceans. The most widely recognized oldest insect fossil is Rhyniognatha hirsti. This insect has large mandibles, suggesting that it may have been partially a hunter. In addition to perhaps eating other animals, insects of this time probably ate plants, as well, especially leaves.

Earliest Flying Insect
Meganeuropsis

However, these insects were not the same as those which we see today. It wouldn’t be until about 400 million years ago that there is first evidence of flight. These flying insects were probably the first animals on Earth to develop this ability. Of all the insect fossils preserved from the Carboniferous Period, many of them are the predecessors to today’s cockroaches and have wings. The largest ever winged insect was discovered from this time. Found in Oklahoma, this insect was named Meganeuropsis americana. In general, insects from this time were larger than those today, possibly for the same reasons that mammals grew to such great size later. The air was richer in oxygen, there were not yet predators to insects which could fly, and there was abundant food.

 

 

Insect in Cocoon on Branch280 million years ago would see the emergence of a new type of insect into the fossil record: those which undergo metamorphosis as part of their life cycle. Prior to these insects, they would emerge fully formed from their eggs. Fossils found from this time point to metamorphosis because distinctly different juvenile insects have been preserved. One possible theory about why some insects evolved this way is that they began to hatch early, in a way. Most insects would metamorphose in their egg, undergoing a larval stage before turning into their final form before hatching. These new insects didn’t have enough nutrients in their eggs to complete this process and so continued to feed after hatching in order to complete the change outside of the egg.

 

Bee Rests on LogThe families and species of insects that are alive today came into being in the Jurassic Period, about 200 million years ago. The wide variety of insects, such as bees and flies, flourished into being as recently as 70 million years ago, with the diversification of flowering plants. This type of connected evolution is known as co-evolution, where two species or groups evolve because of one another.

 

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