A pioneering investigation has unveiled the earliest known instance of leaf mining by insects within a 312-million-year-old fossil, pushing back the estimated emergence of this behavior by a staggering 70 million years. This remarkable find offers fresh perspectives on the evolution and behaviors of ancient insects, providing an unprecedented window into their world.
Prehistoric insects, with their fragile and soft bodies, pose significant challenges when it comes to fossilization. While wings tend to be more commonly preserved, the bodies of these insects are frequently fragmented or incomplete, complicating scientific analysis. Paleontologists often turn to trace fossils as their primary source of information about these ancient insects, which are predominantly found as imprints on fossilized plants.
According to Richard J. Knecht, a Ph.D. candidate in the Department of Organismic and Evolutionary Biology at Harvard, “We have a rich fossil record of plants. However, further back in time, it is the trace fossils that provide crucial insights into the evolution and behavior of insects because they endure exceptionally well on plants. Unlike body fossils, traces remain fixed in their original locations and do not shift over time.”
In a significant breakthrough, a recent study, published in New Phytologist and led by Knecht and his team, unveils an endophytic trace fossil discovered on a Carboniferous seed-fern leaf. This fossil represents the earliest evidence of internal feeding within a leaf, commonly referred to as leaf mining. The discovery challenges previously held beliefs by demonstrating that this behavior was occurring around 70 million years earlier than previously thought.
Co-author Conrad C. Labandeira, Senior Research Geologist and Curator of Fossil Arthropods at the Smithsonian National Museum of Natural History, expressed, “Among the various ways insects feed internally within plants, such as mining the insides of leaves, inducing tumor-like galls, creating borings and galleries in wood, and invading seeds for nourishing embryonic tissues, leaf mining has remained the most enigmatic. The earliest instances of leaf mining are recorded from the Early Triassic, shortly after the devastating end-Permian extinction event, while other forms of feeding extend even further back into the Paleozoic. The delay in the emergence of leaf mining has long puzzled us, and I believe we now have an answer.”
Internal feeding on plants is a common behavior among holometabolous insects, which undergo complete metamorphosis. This group includes Lepidoptera (moths), Coleoptera (beetles), Diptera (flies), and Hymenopterans (wasps and sawflies). Larvae bore into leaves, feeding on the internal tissues and leaving distinctive trails in their wake. As the larva grows, it undergoes multiple molting stages and deposits its excrement, known as frass, within the leaf. The larva continues to create a trail within the leaf until it pupates, eventually emerging and departing from the leaf.
Knecht explains, “The presence of frass is a key indicator of internal feeding, and different characteristics of frass can aid in identifying the responsible insect species. The larva diligently carves a path within the leaf, avoiding its edges and major veins. This behavior is exclusively associated with holometabolous insects, which include their modern counterparts.”
This significant discovery was made in the Carboniferous Rhode Island Formation, an ancient swampy environment characterized by waterlogged conditions. These conditions, termed a Lagerstätte, are ideal for preserving plant fossils with remarkable fidelity. As Knecht notes, “Larvae are notoriously delicate and small, making them difficult to fossilize. Therefore, finding a trace fossil like this one is exceptionally informative, shedding light on larval behavior during the late Paleozoic period, about which we have very limited knowledge.”
The exceptional preservation of the Rhode Island Formation allowed researchers to discern the endophytic trace clearly, showcasing patterns consistent with leaf mining. These distinctive patterns, including meandering trails and the larva’s avoidance of leaf edges and major veins, are characteristics known to be associated with holometabolous insects, some of which still exist today.
Knecht concludes, “This discovery not only pushes back the emergence of leaf mining by 70 million years but also offers valuable insights into larval behavior, a facet rarely preserved in the fossil record. Moreover, it indicates that the evolution of full metamorphosis, holometabolism, was already underway during this ancient era.”
The fossil is currently housed at the Museum of Comparative Zoology at Harvard, alongside other fossils that Knecht and his team continue to investigate.
Reference: “Endophytic ancestors of modern leaf miners may have evolved in the Late Carboniferous” by Richard J. Knecht, Anshuman Swain, Jacob S. Benner, Steve L. Emma, Naomi E. Pierce and Conrad C. Labandeira, 05 October 2023, New Phytologist. DOI: 10.1111/nph.19266
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Frequently Asked Questions (FAQs) about Fossilized Leaf Mining Insect
What is the significance of the 312-million-year-old fossil discovery?
The discovery of this 312-million-year-old fossil is highly significant because it sheds light on the ancient behavior of leaf mining by insects, pushing back the estimated origin of this behavior by 70 million years. It provides valuable insights into the evolution and behaviors of early insects.
Why are prehistoric insects challenging to study through fossils?
Prehistoric insects, with their delicate bodies, are challenging to preserve as fossils. Their soft tissues often do not fossilize well, and their bodies are frequently fragmented or incomplete, making scientific study difficult. This is why paleontologists often rely on trace fossils for insights into ancient insect behaviors.
What is an endophytic trace fossil, and why is it important?
An endophytic trace fossil is evidence of internal feeding within a leaf, a behavior known as leaf mining. In this context, it’s crucial because it represents the earliest indication of such behavior, pushing back its emergence by 70 million years. It offers a glimpse into how insects fed internally within leaves in ancient times.
Which types of insects exhibit internal feeding behaviors like leaf mining?
Internal feeding behaviors, including leaf mining, are common among holometabolous insects, such as Lepidoptera (moths), Coleoptera (beetles), Diptera (flies), and Hymenopterans (wasps and sawflies). These insects bore into leaves, feeding on internal tissues, and leave characteristic trails behind.
Why is the Rhode Island Formation significant in this discovery?
The Rhode Island Formation is important because it provided exceptional preservation conditions, akin to a Lagerstätte. These conditions allowed for the remarkable fossilization of the 312-million-year-old leaf mining trace, which is a rare find as larvae, being delicate, typically do not fossilize well.
What insights does this discovery offer about the evolution of insects?
This discovery not only pushes back the emergence of leaf mining by 70 million years but also suggests that the evolution of full metamorphosis, known as holometabolism, was already underway during this ancient era. It provides valuable information about the evolutionary history of insects.
Where is the fossil currently housed?
The fossil is housed in the Museum of Comparative Zoology at Harvard, where it is available for further study and research by scientists and paleontologists.
3 comments
Fossils r so cool, they show us old insect life wow!
amazin discovery of old bug fossils!! intresting stuff!
gr8 job on explaining, vry cool find, mre fossils pls!