What happened to the dinosaurs? For over a century, paleontologists have been puzzling over the fate of our favorite prehistoric oddities. The non-avian dinosaurs dominated the planet for an inconceivably long period of time, and their evolutionary success only heightens the mystery of their downfall.



Our understanding of dinosaurian demise has changed a great deal since 19th-century naturalists started studying the long lost animals. Today, paleontologists have discerned that most dinosaur lineages disappeared by about 66 million years ago after intense volcanic activity, climate change and a catastrophic asteroid impact triggered one of the worst mass extinctions in our planet’s history. Many forms of life disappeared. Among our favorite prehistoric celebrities, only the avian dinosaurs— birds— were left to carry on the legacy of Velociraptor and kin.



But before our current view came together, the extinction of the non-avian dinosaurs was an open-ended question. Here is a list of some of the stranger—now discarded—theories explaining the loss of our dear departed dinosaurs:



Egg-eating

George Wieland, an early 20th-century paleontologist, argued that the dinosaurs ate themselves into extinction. The ancestors of the fearsome Tyrannosaurus, he said, probably “got their first impulse toward gigantism on a diet of sauropod eggs.” Even the most caring of dinosaur mothers couldn’t stop the near-constant depredations of egg-hungry carnivores. Wieland conceded that monitor lizards and snakes may have consumed their share of embryonic dinosaurs, too, but the Yale researcher ultimately concluded that, “The potent feeders on dinosaur eggs and young must be sought for amongst the dinosaurians themselves.” In the years since Wieland’s 1925 hypothesis, fossil evidence has confirmed that dinosaurs, snakes and even mammals preyed on dinosaur eggs and infants, but never at a rate that could have caused mass extinction.



Pathological Shells

Invertebrate fossil expert H.K. Erben and colleagues thought that eggs led to the dinosaurian downfall in a different way. In a 1979 paper, the researchers reported that fossilized dinosaur eggshell fragments found in southern France and the Spanish Pyrenees showed two sorts of disorders —some had multiple shell layers, while others were pathologically thin. Either situation was lethal. Multi-layered eggs could have suffocated developing dinosaurs, while thin eggs easily broke or dehydrated the embryos. Some sort of climate change spurred hormonal changes in dinosaur mothers, the researchers suggested. But this explanation didn’t fit for other dinosaurs around the globe at the time. The deformed eggshells seem to have been a local phenomenon.

Overactive Glands

Baron Franz Nopcsa von Felső-Szilvás, a Hungarian-born aristocrat and a spy, was one of the most peculiar characters in the field of paleontology—and his extinction theories were just as unusual. Early in the 20th century, Nopsca suggested that a shortage of food, a “low power of resistance” and even diminished sex drive contributed to the demise of the dinosaurs. His favorite theory, though, was death by overactive glands. He believed that dinosaurs grew to their tremendous size thanks to secretions from their pituitary gland. Eventually, he argued, the gland drove the growth of dinosaurs to such excess that the animals became pathologically huge and grotesque. Nopsca tried to tie human pathologies to the conundrum of dinosaur extinction, but there’s no indication that the pituitary had anything to do with immense dinosaur sizes or their disappearance.



Evolutionary self-destruct



In a slight to some of the most wonderful creatures of all time, “Going the way of the dinosaur” means falling into obsolescence by becoming too sluggish, stupid or oversized to survive. For a time, that’s what paleontologists believed happened to the dinosaurs. During the early 1900s— when Darwin’s theory of natural selection was still not entirely accepted within the scientific community— many paleontologists believed that organisms evolved along confined pathways. According to this thoroughly debunked notion, dinosaurs possessed a kind of evolutionary inertia that caused them to keep getting bigger and weirder. Some researchers even proposed that dinosaurs were dumb (compared to mammals) because they invested too much of their internal energies in growing huge and fierce. Yet, as even fossil experts of the time realized, this notion couldn’t explain why some of the biggest and strangest specimens —such as Stegosaurus and Brachiosaurus—thrived throughout the dinosaurs’ reign on Earth.

Too many males

Within the past decade, infertility specialist Sherman Silber has repeatedly asserted that dinosaurs perished because they couldn’t find mates. Silber has speculated that—much like present-day alligators and crocodiles—changes in external temperature could determine the sex of dinosaur embryos developing in their eggs. In this case, he has argued, climate change caused by volcanic activity and asteroid impact could have skewed the global thermostat so that only one sex was produced. But beyond the fact that we really don’t know whether dinosaur sexes were determined by temperature or genetics alone, the idea doesn’t explain why reptiles that probably did have temperature-determined sexes, such as crocodylians, survived while non-avian dinosaurs died out. Silber’s proposal contradicts itself.



Caterpillars



In a fight, a caterpillar would hardly seem to be a match for a Triceratops. But in a 1962 paper based on his observations of the devastation caterpillars could cause among crops, entomologist Stanley Flanders proposed that the larvae of the first moths and butterflies would have quickly and totally denuded the Cretaceous landscape of vegetation. Herbivorous dinosaurs would have starved, Stanley argued, and predatory dinosaurs would soon be left with nothing to eat but each other. But not only did butterflies and moths coexist with dinosaurs for millions of years, there is no sign of such a disastrous caterpillar spike in the fossil record.



Cataracts

Explanations for dinosaur extinctions often reflected the expertise and perspective of the people who proposed them. No surprise, then, that in 1982 ophthalmologist L.R. Croft suggested that bad eyesight undid the dinosaurs. Since exposure to heat can make cataracts form more quickly, Croft surmised that dinosaurs with weird horns or crests developed these bizarre ornaments to shield their eyes from the relentless Mesozoic sun. In the world warmed by harsh sunlight, though, Croft expected that even these attempts to shade dinosaur eyes failed and that the creatures started to go blind before they hit sexual maturity. Croft’s idea, however, totally fails to explain the mass extinction of species other than the non-avian dinosaurs, 66 million years ago.

Supernova



Before the asteroid impact hypothesis gained widespread credibility, in 1971 physicist Wallace Tucker and paleontologist Dale Russell suggested another kind of death from above. Although the researchers lacked any direct evidence for their idea, they proposed that a nearby supernova could have had catastrophic consequences for life at the end of the Cretaceous. The explosion of a neighboring star, Tucker and Russell proposed, would bombard the upper atmosphere with X-rays and other forms of radiation that would quickly alter the climate, causing temperatures on Earth to plummet. No evidence of such a nearby event 66 million years ago has ever been uncovered.



Aliens

A display at Utah State University’s Prehistoric Museum points out that aliens could not have wiped out the dinosaurs, not least of all because, “There is no evidence of aliens or their garbage in the fossil record.” That hasn’t stopped some more imaginative folks from suggesting such sci-fi scenarios (most recently given a nod in the monster mash blockbuster Pacific Rim). Last year, the basic cable program “Ancient Aliens” devoted an entire episode to the idea, borrowing misunderstandings and outright fabrications from creationists to help make their case that extra-terrestrials eliminated the dinosaurs to make room for humanity. Apatosaurus only ever faced down aliens in comic books and movies.



Dinosaur Farts



Much like death by aliens, the idea that dinosaurs farted themselves into extinction was never a scientific hypothesis. The notion was a misconstrued conclusion drawn from some recent dinosaur research. Last year, paleontologist David Wilkinson and collaborators tried to calculate how much gas the long-necked, hefty sauropod dinosaurs could have produced. The researchers speculated that the dinosaurs’ annual output of methane gas would have been enough to influence the global climate, but the researchers said nothing about extinction. After all, a variety of sauropods existed for tens of millions of years without showing any sign of gassing themselves out of existence. Ignoring the actual research by Wilkinson and colleagues,, various news sites jumped on the study to suggest that dinosaurs gassed themselves into oblivion. Such sites were only blowing hot air.



