Long before dinosaurs vanished, a shadowy fungus was already forging alliances with insects inside ancient trees. Now, a fossil from Jurassic China has pushed the history of that relationship 80 million years deeper into time.
Key Points at a Glance
- Oldest fossil evidence of blue-stain fungus found in Jurassic conifer wood
- Extends fungal evolutionary timeline by 80 million years
- Fossil reveals early insect-fungal ecological interactions
- Suggests fungal-insect symbiosis predates bark beetles
In a discovery that reshapes our understanding of fungal evolution and deep-time ecology, researchers have identified the oldest known fossil of blue-stain fungus—entombed in Jurassic conifer wood from northeastern China. The find, reported in the journal National Science Review, extends the evolutionary record of these wood-colonizing fungi by roughly 80 million years.
Blue-stain fungi are known today for their distinctive pigmented hyphae that discolor sapwood—especially in conifers—and their notorious partnerships with bark beetles. Though not fatal themselves, these fungi weaken trees and accelerate mortality when combined with insect damage. Until now, the earliest known fossil of this fungal group dated to the Late Cretaceous. This new find pushes their history back into the Jurassic, nearly 160 million years ago.
The fossil was discovered in silicified wood of the extinct conifer Xenoxylon phyllocladoides from the Tiaojishan Formation in western Liaoning Province. Inside the preserved wood, researchers observed dark, septate hyphae with hallmarks of blue-stain fungi—penetrating ray cells and tracheid walls via appressorium-like structures and hyphal pegs.
“These structures are almost identical to those seen in modern blue-stain fungi,” said lead author Ning Tian. “Their ability to mechanically penetrate cell walls, their colonization patterns, and even their pigment are all there.”
Unlike wood-rotting fungi that decompose lignocellulose, blue-stain fungi rely on mechanical entry into plant cells, often facilitated by insect partners. In this fossil, the wood shows insect boring holes—evidence that ancient beetles or arthropods may have acted as fungal vectors long before modern bark beetles evolved.
Intriguingly, the fossil reveals two distinct types of hyphae: one thick, pigmented type and another thinner, hyaline variety with chlamydospore-like structures—mirroring the diversity found in living blue-stain fungi. These details, preserved across radial and tangential sections of the wood, provide rare insight into fungal morphology from a period when such preservation is exceedingly rare.
The implications go beyond taxonomy. This fossil proves that complex insect-fungal ecological networks were already in play during the Jurassic. Although today’s blue-stain fungi are often associated with Scolytinae bark beetles—thought to have emerged no earlier than the Early Cretaceous—this fossil predates them. That suggests earlier, more primitive insects may have filled a similar ecological role.
“This rewrites the timeline for one of the most important symbiotic relationships in forest ecosystems,” said co-author Yongdong Wang. “The insect-fungus interaction likely began far earlier than we realized.”
Fossils of fungi are rare due to their delicate structures and rapid decomposition. That makes this exquisitely preserved example all the more significant—not just for fungal evolutionary history, but for understanding how ecosystems functioned in the age of dinosaurs.
As molecular phylogenetic studies have long suggested, the divergence of Sordariomycetes—the fungal class to which blue-stain fungi belong—occurred in the Late Paleozoic to early Mesozoic. This fossil now offers direct, tangible proof that blue-stain fungi were already active participants in Earth’s ecosystems by the Jurassic.
What other hidden players in Earth’s evolutionary drama have yet to be unearthed? One thing is clear: in the fossilized scars of ancient trees, the blue-stain fungi left their mark—not just in pigment, but in legacy.
Source: National Science Review
