A 170-year-old fossil puzzle is close to solution: the monster spires that loomed over early Earth were not fungi, plants or animals, but a lost biological kingdom that rewires our view of evolution.
Four hundred million years ago, before trees existed, Earth’s low-lying greenery was overshadowed by spires taller than a two-story house. These structures left behind cigar-sized fossils catalogued in 1843 and later christened Prototaxites—“early yew.” For a century and a half, every attempt to place them on the tree of life has ended in a shrug. A study released in Science Advances now argues the shrug was justified: the organism belonged to an entirely separate kingdom.
Why the mystery endured
Early paleobotanists saw woody tubes and assumed a conifer relative. Once microscope work ruled out tree ancestry, mycologists championed a fungal identity. Neither camp could explain the chaotic branching of its internal filaments or the absence of chitin, the chemical signature of every known fungus living or extinct. “It feels like it doesn’t fit comfortably anywhere,” says Matthew Nelsen of the Field Museum, who has tracked the debate for a decade.
New evidence, new kingdom
University of Edinburgh doctoral researcher Laura Cooper compared Rhynie chert fossils of undisputed fungi with contemporaneous Prototaxites slices. Key differences:
- Fungal hyphae grow in predictable, ladder-like grids; Prototaxites filaments tangle like a bird’s nest.
- Electron-microscopy scans found no chitin in the giant’s cell walls, while neighboring fungal fossils glowed with the polymer.
- Isotope profiles match decay-eaters, not photosynthesizers, confirming the towers were heterotrophs scavenging a plant-sparse planet.
The simplest explanation, the authors conclude, is that Prototaxites stands outside the six kingdoms currently recognized—an extinct, high-rise lineage that independently evolved multicellularity.
What this means for biology textbooks
If peer consensus follows, educators will redraw the standard six-kingdom chart. More importantly, the finding collapses the assumption that complex life on land followed a straight path from algae to plants and fungi. Instead, evolution experimented with at least one additional blueprint for building a 25-foot organism—then scrapped it.
Unanswered energy riddle
Even with taxonomic clarity, Prototaxites presents a logistical paradox. In a landscape of moss-height vegetation, how did a decomposer gather enough carbon to fuel skyscraper growth? Stanford paleobotanist Kevin Boyce calculates that a single tower would have required the litter of an area far larger than any contemporaneous ecosystem could supply. Cooper concedes, “The energy budget is still a complete mystery,” inviting fresh models of Devonian food webs.
Developer takeaway: evolution as algorithm
For AI researchers and synthetic-biologists, the saga is a reminder that optimization landscapes contain viable peaks never revisited. Extinct kingdoms like Prototaxites are real-world examples of alternative design solutions—useful inspiration for generative models searching beyond conventional biomimicry.
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