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What the Fossil Record Tells Us About Insect Extinctions in Deep Time

Brodioptera sinensis

Brodioptera sinensis Pecharová, Ren, and Prokop 2015 lived during the Early Pennsylvanian, approximately 320 million years ago. This species belongs to Megasecoptera, one of the paleopterous insect orders that went extinct around the time of the “mother of all mass extinctions” at the Permian/Triassic boundary, 252 million years ago. (Image was redrawn by Labandeira (2019) from Prokop et al. (2016).)

By Sandra R. Schachat and Conrad C. Labandeira, Ph.D.

Sandra R. Schachat

Sandra R. Schachat

Lately, we’ve all been seeing more and more scientific articles—and newspaper headlines—about insects going extinct. And when we’re wondering about how and why extinctions happen, we typically look to the geologic record. Fossils provide us with the only direct evidence of how mass extinctions unfold.

But the fossil record of insects is very different from the fossil records of other groups, such as clams and sharks. That’s why we recently published a review article in the Annals of the Entomological Society of America to explain what the fossil record tells us about insect extinctions in deep time. In this blog post, we’ll outline some of the main points of our review.

The insect fossil record is overwhelmingly dominated by a few dozen “jackpot” fossil deposits.

Conrad C. Labandeira, Ph.D.

Conrad C. Labandeira, Ph.D.

The vast majority of insects in museum collections are not yet described in the scientific literature and probably have not even been identified—at any taxonomic level. But the hundreds of thousands of fossil insects that humans have dug out of the ground come from a few dozen fossil deposits. These deposits are called konzentrat Lagerstätten, which basically means “a deposit where a whole bunch of fossils were preserved.” Perhaps you’ve heard of Baltic amber or the Green River Formation. Those are konzentrat Lagerstätten.

Here is the distribution of insect konzentrat Lagerstätten in space and time.

Konzentrat Lagerstätten distribution

The hundreds of thousands of fossil insects that humans have dug out of the ground come from a few dozen fossil deposits. These deposits are called konzentrat Lagerstätten. Well-known examples include Baltic amber or the Green River Formation. This chart shows the distribution of insect konzentrat Lagerstätten in space and time. All data are from the Paleobiology Database and were compiled primarily by Matthew Clapham. (Image originally published in Schachat and Labandeira 2021, Annals of the Entomological Society of America)

As you can see, we have very few konzentrat Lagerstätten close to the three mass extinctions that occurred after winged insects originated (the end-Permian event, the end-Triassic event, and the end-Cretaceous event). We also don’t have many konzentrat Lagerstätten at tropical latitudes, where insect diversity and biomass are concentrated. For this reason, it’s impossible to say how many insect taxa disappeared during past mass extinction events.

Only one large group of insects has ever gone extinct.

Trilobites, ammonites, and non-avian dinosaurs are iconic animal groups that were abundant for millions of years but disappeared in mass extinction events. Only one group of insects fits this description, and you might not have heard of them: the strange and wondrous Palaeodictyopteroidea. This group contains multiple paleopterous orders (the tongue-twister Palaeodictyoptera, Megasecoptera, Diaphanopterodea, and Permothemistida) that were a huge part of Pennsylvanian communities such as those preserved at Commentry—one of the oldest konzentrat Lagerstätten for insects, as you can see in the graph above.

Stenodictya minima

An example of a paleodictyopteran insect: Stenodictya minima Brongniart. Several of the features of this insect have been corrected with the study of additional material, but this iconic historical image shows how strange these creatures were. (Image via Flickr/internetarchivebookimages)

But Palaeodictyopteroidea were already in decline when the Permian Period began 299 million years ago:

Paleoptera

This image shows the proportion of described insect occurrences that belong to Palaeodictyopteroidea and other paleopterous groups (i.e., those more closely related to Ephemeroptera and Odonata) at each of the konzentrat Lagerstätten that are over 200 million years old. The konzentrat Lagerstätten are arranged from oldest to youngest. All data are from the Paleobiology Database and were compiled primarily by Matthew Clapham. (Image originally published in Schachat and Labandeira 2021, Annals of the Entomological Society of America)

This image shows the proportion of described insect occurrences that belong to Palaeodictyopteroidea and other paleopterous groups (i.e., those more closely related to Ephemeroptera and Odonata) at each of the konzentrat Lagerstätten that are over 200 million years old. The konzentrat Lagerstätten are arranged from oldest to youngest.

The Palaeodictyopteroidea disappeared around the time of the end-Permian event, which was undoubtedly the worst extinction event in the history of animal life and is known as the “mother of mass extinctions.” But, as you can see in this graph, the Palaeodictyopteroidea were already on their way out long before the end-Permian event happened. For this reason, it seems that insects may not have suffered taxonomic losses during mass extinctions in the same way that corals and dinosaurs did.

That certainly is not to say that the end-Permian event wasn’t massively important for insects. Indeed, the end-Permian falls squarely within the biggest evolutionary shakeup in insect history: the transition between the Paleozoic Insect Fauna and the Modern Insect Fauna. The thing to remember is that each of these Faunas is a polyphyletic assemblage of dominant insect lineages, and the transition between the two Faunas took tens of millions of years. For insects, you can think of the end-Permian as a gradual “eclipse” rather than a sudden mass extinction.

Paleozoic and modern insect faunas

The end-Permian event can be thought of as a gradual “eclipse” for insects rather than a sudden mass extinction. The transition between the Paleozoic Insect Fauna and the Modern Insect Fauna was the biggest evolutionary shakeup in insect history, but it occurred over the course of tens of millions of years. (Image originally published in Schachat and Labandeira 2021, Annals of the Entomological Society of America. All icons are from PhyloPic.org. Mantoida nitida Newman, public domain. Petrobius brevistylis Carpenter by Birgit Lang; Somatochlora tenebrosa Say by Gareth Monger; Palomena prasina (L.) by Dave Angelini; and Trachypachus gibbsii Leconte by T. Michael Keesey and Yves Bousquet, CC BY 3.0.)

We don’t have abundance data for fossil insects.

Many studies of insect decline in modern ecosystems focus on abundance or biomass. We just don’t have the resources right now to evaluate extinction risk for each insect species in an ecosystem.

Unfortunately, we can’t measure insect biomass in the fossil record with much precision. It would be possible to track the relative abundances of different higher insect taxa throughout deep time, but the scientific study of fossil insects has primarily focused on describing new genera and species rather than quantifying the ecological prevalence of clades. The contrasting methods used for the study of insects in modern versus ancient ecosystems results in a mismatch that makes it difficult to compare past extinction events with the current biodiversity crisis.

insect fossil record vs. ecological record

The scientific study of fossil insects has primarily focused on describing new genera and species rather than quantifying the ecological prevalence of clades. The contrasting methods used for the study of insects in modern versus ancient ecosystems results in a mismatch that makes it difficult to compare past extinction events with the current biodiversity crisis. (Image originally published in Schachat and Labandeira 2021, Annals of the Entomological Society of America. All icons are from PhyloPic.org. Mantoida nitida Newman, public domain. Trachypachus gibbsii Leconte by T. Michael Keesey and Yves Bousquet; Somatochlora tenebrosa Say by Gareth Monger; and Eristalis tenax (L.) by Gareth Monger, CC BY 3.0. Hyalophora cecropia (L.) by Mali’o Kodis and Jim Vargo, CC BY-NC-SA 3.0.)

We already have enough fossil material to begin evaluating the changing abundance of many of the dominant insect clades in deep time. This would be a great direction for future research.

Conclusion: There’s so much left to learn.

If the current biodiversity crisis continues unabated, we may witness an insect extinction event far more massive than anything known in the fossil record. But the good news is that there’s a lot we can do. We can take steps to halt the current extinction event and save the species that share this planet with us, and we can also collect data from the fossil record that are easier to compare with the data we have from modern ecosystems.

Want to learn more?

If you enjoyed this summary, we encourage you to take a look at our article, which provides in-depth explanations of the illustrations you’ve seen here. We discuss what we know and don’t know about how insects fared during the “Big Five” mass extinctions in deep time. We also compare the fossil record of insects to plants and vertebrates, and we also provide a broad overview of how to recognize a mass extinction event in the fossil record. More generally, we explain general features of the fossil record, such as the difference between “stem” and “crown” groups and unique aspects of the fossil record of insects. We hope that our article will provide entomologists with the context they need to evaluate future fossil discoveries.

Sandra R. Schachat is a Ph.D. candidate in geology at Stanford University and is a member of the ESA Student Affairs Committee and the ESA Committee on Diversity and Inclusion. Email: schachat@stanford.edu. Conrad C. Labandeira, Ph.D., is senior research geologist and curator of fossil arthropods at the Smithsonian National Museum of Natural History in Washington, DC. Email: labandec@si.edu.

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