What Scientists Blamed for Dinosaur Extinction: Rickets, Poison, Constipation
What Scientists Blamed for Dinosaur Extinction: Rickets, Poison, Constipation
This whole piece started with a deliberately silly question: what if pollen allergies took out the dinosaurs?
The deeper I dug, the more dinosaur extinction theories I found that were strange by modern scientific standards, yet were proposed in earnest by real researchers. Knowing those long-abandoned ideas sat right alongside genuine evidence-based research makes the story of how dinosaurs disappeared feel less like one clean answer and more like an overstuffed drawer nobody's ever fully sorted.
Scientists and dinosaurs surrounded by bizarre extinction theories including giant caterpillars, pollen clouds, fungi, volcanoes, and fragile dinosaur eggs in a realistic prehistoric museum-style scene.
What Actually Killed the Dinosaurs: Where the Certainty Stops
Ask most people what killed the dinosaurs and you'll get the same one-word answer: an asteroid. That's a fair summary. Geologist Walter Alvarez and his physicist father, Luis, proposed in 1980 that unusually high iridium at the Cretaceous-Paleogene boundary pointed to an impact from space. The case strengthened once researchers matched the timing to the Chicxulub crater off Mexico's Yucatán Peninsula, where non-avian dinosaurs went extinct around 66 million years ago. Today, the Chicxulub impact is the leading, best-supported trigger of the extinction. The debate is over how much of the dying had already started before it hit.
Before that debate took its current shape, though, I found that dinosaur extinction theories went through a much stranger phase first — one that had nothing to do with space rocks at all.
Early twentieth-century paleontologists debating unusual dinosaur extinction theories in a vintage laboratory surrounded by fossils, poisonous plants, thin eggshells, snow, and Triceratops illustrations.
When Paleontologists Diagnosed the Dinosaurs Like Patients
For a good stretch of the twentieth century, the leading dinosaur extinction theories read less like geology and more like a chart at a doctor's office, each specialist reaching for the ailment they knew best.
In 1928, University of Virginia pathologist Harry T. Marshall proposed that volcanic dust clouds had blocked enough sunlight to give dinosaurs a case of rickets, the same vitamin D deficiency that softens human bones. Science News-Letter covered the idea at the time, and Marshall argued the plants dinosaurs relied on would have lost their nutritional value too, starved of the same ultraviolet light.
The vitamin D angle didn't entirely die with Marshall. In 2019, a University of Sydney researcher revived it in the peer-reviewed Journal of Nutritional Science, with a twist: not adult rickets, but vitamin D3 deficiency killing embryos inside their eggs before they ever hatched. That a 1928 hunch could resurface as a peer-reviewed hypothesis nearly a century later is the kind of detail that kept pulling me deeper into this research.
Two other researchers reached for a different chart. In 1965, Royal Ontario Museum paleontologist Loris Russell argued dinosaurs were warm-blooded but had no fur or feathers to hold that heat in, leaving them vulnerable to cold winters. Two years later, paleontologist John Cys proposed that their sheer bulk left them unable to find shelter to hibernate, unlike the smaller reptiles that survived.
In 1982, British ophthalmologist L. R. Croft went further still, in his book The Last Dinosaurs. He linked the extinction to cataract blindness associated with rising global temperatures, and suggested that structures like a Triceratops's horned frill had evolved to shield the eyes from solar radiation. New Scientist, reviewing the idea at the time, reportedly called it "illuminating." The theory has an obvious hole, though: it does nothing to explain why so many other species, from marine reptiles to ammonites, disappeared at the very same moment as the dinosaurs.
Between a vitamin deficiency, a clouded pair of eyes, and a bad case of the chills, the twentieth century diagnosed dinosaurs with nearly every ailment except the one now blamed for it.
Primitive mammals raiding dinosaur nests while fungal spores spread across a burned Cretaceous forest after an asteroid impact in a scientifically accurate prehistoric landscape.
The Poison, the Caterpillars, and the Diet That Doomed Giants
Other researchers looked past disease and blamed the dinner table instead, sometimes one link of the food chain at a time.
In 1967, Seil Koch of the U.S. Geological Survey published a paper suggesting that selenium released from volcanic lava worked its way into the soil and then into plants. Herbivorous dinosaurs ate the toxic vegetation, Koch argued, and predators higher up the chain absorbed the poison in turn. The proposal even speculated that mammals avoided the worst of it because they were sharp enough to steer clear of toxic plants, the way cattle today avoid seleniferous vegetation.
In 1962, entomologist Stanley Flanders offered a much smaller villain: caterpillars. Writing in the Journal of Research on the Lepidoptera, he reasoned that without natural predators to hold their numbers down, swarms of the insects could reduce entire regions of vegetation to bare ground, leaving every plant-eater with nothing left to graze. Of everything I came across while researching this, the caterpillar hypothesis is the one that's stuck with me most — there's something almost endearing about an entomologist's total confidence that his own field held the answer.
One more theory looked at what the plants themselves became. As flowering plants and hardwood forests spread across the Cretaceous, crowding out ginkgoes, cycads, and conifers, some researchers suggested that herbivorous dinosaurs couldn't adjust to the new menu and starved. In its crudest retelling, the hypothesis blamed digestive trouble: the new diet, this version held, caused fatal constipation.
Set the poison, the pests, and the bad diet side by side, and a pattern starts to show: nearly every one of these theories pictured a food chain failing quietly at ground level, decades before anyone pictured a rock falling from space.
Modern paleontologists analyzing fossils, asteroid impact simulations, volcanic eruptions, and climate models inside an advanced dinosaur extinction research laboratory.
Cracked Eggs, Spreading Fungus, and the Mammals Waiting in the Wings
A third group of theories skipped illness and diet altogether and went straight for the nursery.
In the early 1970s, researchers in France and Germany reported dinosaur eggs with shells noticeably thinner than earlier specimens. They pointed to hormonal changes triggered by overcrowding, and theorized the shells had grown too fragile to protect a developing embryo. It was a tidy explanation with one problem: the thinning turned out to be a local pattern, not a global one. The American Museum of Natural History now lists it among the explanations that don't hold up, since plenty of dinosaurs had ordinary shells, and living relatives like birds and crocodiles do fine with thin ones. It's a pattern I kept running into while working through this material: a theory can be published, taken seriously, and still turn out wrong once more data comes in.
A weirder version of the same nursery-focused idea arrived in 2008, when three Chinese researchers examined fossilized dinosaur eggshells from a Late Cretaceous rock formation in central China and found microscopic fungal structures embedded directly in the shell material. The fungi, the theory goes, had penetrated the eggs and interfered with the embryos developing inside, keeping them from ever hatching.
In the early twentieth century, some researchers floated mammals as a new evolutionary competitor capable of displacing the dinosaurs outright: a story about being out-competed, not simply out-lived. Others believed mammals raided dinosaur nests and ate the eggs and hatchlings directly. The American Museum of Natural History notes that dinosaurs and mammals coexisted for more than 150 million years, which makes a sudden mammal-driven extinction hard to square with the timeline.
The strangest part of this batch may be how many of the theories never blamed the adult dinosaurs at all. The eggs and the nests took the fall instead.
The Theories Too Vague to Even Name a Single Culprit
Not every old theory came with a clean, checkable citation attached. Some got vaguer as the certainty ran out.
Early paleontologist Richard Swann Lull, writing before natural selection was widely accepted as the driving force behind extinction, argued that dinosaurs were driven by some internal urge to keep growing larger, trading brainpower for body size and armor as the eons passed. Stegosaurus, a favorite example, carried a brain researchers of the era compared to a walnut. Even Lull seemed uneasy with his own idea, noting that dinosaurs survived an oddly long time for animals supposedly doomed by their own excess.
The same era floated a related notion, that dinosaurs simply lost the drive to reproduce. Paleontologist Michael Benton has described this whole stretch of early-to-mid-twentieth-century thinking as the field's "Dilettante Phase," when any interested outsider could propose a pet theory for what ended the Mesozoic. I'll admit that phrase might be my favorite find from this whole research process — it captures in two words what took the field decades to work through.
Connect the rickets diagnosis to the cataracts diagnosis to a supposed loss of libido, and it starts to look like one thread runs through all of them: a falling asteroid is hard to picture, but a familiar ailment isn't.
Museum timeline illustrating more than one hundred years of dinosaur extinction theories from early paleontology to modern asteroid impact research.
Why "The Asteroid Did It" Still Isn't the Whole Answer
So which was it: the impact, the volcanic activity happening around the same time, or the climate both of those disrupted? For a long stretch, the field treated that as close to a settled question. It isn't, and chasing down the most recent papers on the subject made that clear fast.
A 2015 review in Biological Reviews, led by paleontologist Stephen Brusatte, found little support for a long-term, global decline in dinosaur diversity before the end of the Cretaceous. A 2021 study in Nature Communications, led by Fabien Condamine, disagreed: six major dinosaur families were already declining for roughly ten million years before the impact, likely pushed along by global cooling and duck-billed hadrosaurs outcompeting their herbivore rivals. Two peer-reviewed papers, six years apart, and still no agreement on whether the decline was real or the asteroid alone explains what happened.
The Deccan Traps, the enormous Indian volcanic eruptions from around the same era, raise a similar dispute, and the timing turns out to be stranger than a simple "volcanoes first, then asteroid" story. Princeton geologist Blair Schoene's team dated the main eruptive pulse to a start about 250,000 years before the extinction, running roughly 750,000 years in total. Most of that lava, by volume, erupted after the impact rather than before it. That timing has fed a different argument entirely: whether the volcanism helped trigger the extinction, or whether the impact itself intensified volcanic activity already underway. A separate, Yale-led team under Pincelli Hull traced the same volcanism through ocean sediment records instead, and found its climate effects had already faded out too early to have mattered, concluding the asteroid did the job on its own.
Put together, the last several years of research haven't really been arguing over whether an asteroid hit. The argument has shifted to something narrower: in what order, and at what intensity, the impact, the volcanism, and the climate that followed each did their share of the work. It's the same instinct that produced the rickets theory and the caterpillar theory, just dressed in better data: something happened, and everyone still wants to know exactly which part of it to blame.
A quick timeline of the old guesses, side by side:
| Year | Theory | Proposed By | Status Today |
|---|---|---|---|
| 1928 | Rickets from blocked sunlight | Harry T. Marshall | Considered untestable in the fossil record |
| 1962 | Caterpillar infestation | Stanley Flanders | A regional mechanism, not a global one |
| 1967 | Selenium poisoning up the food chain | Seil Koch, USGS | Superseded by the stronger asteroid evidence |
| 1982 | Cataracts from sun-damaged eyes | L. R. Croft | Doesn't explain why other species went extinct too |
Add it all up and dinosaurs have, at one point or another, been formally suspected of going blind, catching a chill, running short on vitamin D, poisoning themselves on the wrong plants, losing interest in mating, and simply outgrowing their own brains. Every one of those was somebody's serious, published best guess.
The theory most widely accepted today is that an asteroid struck Earth. The finer details, though, still aren't fully settled, so more than one interpretation survives, and probably will for a while yet. Dinosaurs ran this planet for a length of time that makes the whole of human history look brief by comparison. Set against that scale, it's the strange, half-right guesses about their extinction that catch my attention before the accepted answer does. Maybe the actual appeal of this story was never the one correct explanation. It's the pile of half-right ideas that got us there.
A massive asteroid descends toward Earth as dinosaurs roam the Late Cretaceous landscape with distant volcanic eruptions beneath a dramatic sunset sky.
Sources & References
- Gizmodo, Mark Strauss, "The Ten Most Bizarre Theories About Why the Dinosaurs Went Extinct" (2014)
- National Geographic, Riley Black, "The Most Famous Extinction" (2013)
- National Geographic, Victoria Jaggard, "Why Did the Dinosaurs Go Extinct?" (2019)
- Nature Communications, Condamine et al., "Dinosaur biodiversity declined well before the asteroid impact" (2021)
- Biological Reviews, Brusatte et al., "The extinction of the dinosaurs" (2015)
- Journal of Nutritional Science, Fraser, "Why did the dinosaurs become extinct? Could cholecalciferol (vitamin D3) deficiency be the answer?" (2019)
- Science (AAAS), "Did Volcanic Eruptions Help Kill Off the Dinosaurs?"
- ScienceDaily, "In Death of Dinosaurs, It Was All About the Asteroid — Not Volcanoes" (2020)
- Natural History Museum (UK), "How an Asteroid Ended the Age of the Dinosaurs"
- American Museum of Natural History, "Discarded Theories"
Comments
Post a Comment