Were Dinosaurs Doomed Before the Asteroid?

By Eric Betz | April 18, 2016 3:21 pm

Sauropod species, including large plant-eaters like Brontosaurus and Alamosaurus, shown here, may have started dying off more than 100 million years before the Chicxulub asteroid impact. Yet Alamosaurus fossils are found just below the worldwide layer of impact debris, indicating they were among the last surviving dinosaur species. (Credit: rDiBgd/Wikimedia Commons)

The age of the dinosaurs was growing stale long before that infamous impact.

A new study claims that dinosaurs were doomed to extinction before a city-sized space rock abruptly ended their reign some 66 million years ago. The analysis, published online Monday in Proceedings of the National Academy of Sciences, shows many species had already been dwindling for tens of millions of years.

Fading Away

The team’s analysis shows some of these shriveling branches on the dinosaur tree of life extend back more than 100 million years before final the extinction. And, starting around 40 million years before the impact, as existing species disappeared, fewer new species sprung up to replace them.

With diversity in decline, the overall dinosaur population was primed for a mass extinction event, the authors say. So when the asteroid hit, there were fewer species to adapt to the new conditions.

The team used a phylogenetic approach — you can think of it as an evolutionary tree containing hundreds of dinosaur species. This allowed them to examine the statistics of speciation events, which happen when certain dinosaur species appear or go extinct. It’s the first time researchers have taken such an approach. The authors do concede that sampling bias might have skewed their results. However, logic would imply that the fossil record should have fewer older specimens; instead, they found significantly fewer younger specimens exist.

Widespread Die-Offs

The die-offs weren’t isolated to one part of the world either.

“We looked at trends across dinosaurs as a whole, in terms of their whole evolutionary history and across the entire globe,” says the study’s lead author Manabu Sakamoto of the University of Reading in the United Kingdom. “We did run a version of the analysis separating the data according to different parts of the world, but this did not have a major effect on the outcomes, meaning that the long-term demise was global.”

Sauropods, a long-lived family of massive herbivores that includes Brontosaurus, struggled disproportionately. The number of sauropod species dying off exceeded new species evolving as far back as 114 million years ago.

But in a surprise finding, their analysis shows that populations of ceratopsids like triceratops and hadrosaurs — an extremely common kind of duck-billed dinosaur — actually increased as other species disappeared.

“These two groups acquired specialized jaw structures that allowed them to process food efficiently” says Sakamoto. “They were also numerous yet very similar to their close relatives — slight variations on the same theme — and their ability to differentiate amongst themselves rather than having a single cosmopolitan species resulted in numerous new species arising.”

The Rise of the Mammal

Another surprise benefactor: mammals. Dinosaurs dominated the day, but as more and more Mesozoic megafauna disappeared, our ancestors were able to flourish in these ecological niches. Until recently, paleontologists didn’t recognize this explosion of mammals happened at the feet of the dinosaurs. It was more commonly thought that small mammals were simply the eventual benefactors of the asteroid impact.

But what could have caused this earlier die off? The researchers’ statistical method doesn’t point to a cause, but the team highlights a collection of possible calamities that would make an Egyptian pharaoh blush.

Supercontinents broke up and limiting free movement. Intense volcanism persisted for millions of years. The climate changed and sea levels rose.

Despite these factors, the team says the asteroid still delivered the coup de grâce

“The asteroid impact did indeed wipe out the dinosaurs (except birds), and while there are other alternative causal explanations, for instance, prolonged volcanism, it is not clear whether these would have triggered the mass extinction event 66 million years ago had the asteroid not impacted,” says Sakamoto.

CATEGORIZED UNDER: Living World, top posts
MORE ABOUT: dinosaurs
  • EquusMtn

    It has always puzzled me to consider which species survived the asteroid impact and which didn’t. It seems to me there were basically only 2 ways to survive: underwater and underground. Underwater seems pretty obvious. Surviving underground means eating roots (probably some pretty unsavory dead ones toward the end) for the years until the surface returned to some semblance of normal. So crocodilians, turtles, and burrowing mammals made it. Are we assuming there were no burrowing dinosaurs, except for birds? (There are some burrowing birds now.) Is this a good explanation for who the survivors were and weren’t?

    • donl

      Well there’s always Nessie and Champ, but at that time there weren’t a lot of true mammals around, This article brings up a subject and belief of something not yet fully studied,still to early to discuss!…more of a ‘what if’

  • cthusar

    I have seen no discussion of food sources (and changes thereof) as a contributing factor. Would not have climate changes also affected food availability? Might the massive dinos have eaten themselves out of house and home?

  • The History Man

    If the human race had existed already for 100 million years and looked forward to another 40 million years or so, subject to no asteroid disaster, I rather think we wouldn’t think our species ‘doomed’.

    The alarming thing is that we are probably viewing the survival of our species in terms of a century or so, almost entirely due to our own activities.

    It really makes you wonder which was the smartest species.

    • MingTM

      Rise of intelligence may actually be a negative for species’ survival. Lack of “visible” sentient civilizations “out there” may be another sign of this.
      Adaptability is king. Size is hard to maintain with habitat destruction, natural or unnatural.

    • Don Huntington

      I’m quite sure that technology will save the human species, perhaps for millions of years into the future. But it is going to save a relatively small number of survivors. It won’t save billions of us.

      • reed1v

        Highly doubtful. If you look at technology related to health as one example, we are already almost asymptotic to the cost per live saved and also to the cost per longevity gained axis. Clean water saved most folks, then sewers, then antibiotics. Those big gains are over. Now its extremely expensive to advance further along the health spectrum. Same is occurring in other technologically driven fields.

        Diminishing marginal returns rule. Few will survive, none will reproduce. Millions of years? More like a thousand or so, if that. Given the events we know will happen, and given our increased technologically dependent globe, its an easily foreseeable train wreck not too far in the future.

        • Don Huntington

          I don’t think any of us can imagine what technology will look like in fifty years, or the controlled environments that might be created underground, within enormous geodesic domes, or inside an asteroid. Scientists are attacking the principles of terraforming other planets. In a century they should be able to figure out how to terraform ours.

          I can’t believe that a reproducing remnant of our species won’t survive for the long-run. Consider the amazing recoveries some wild species have made — the bald eagle, for example — back from the edges of extinction.

          Carl Sagan imagined our migration into space as ensuring the survival of the race for any imaginable length of time. (By his estimates, if we conquered interstellar travel, we could populate the galaxy in 30,000 years.)

          • reed1v

            Good old Dr. Carl. Took an intro class from him at Cornell back in the 60s. Was basically a sci-fi freak. Strange how the “future” envisioned back in the 50s, future being 50 years hence, has never occurred.

          • Don Huntington

            Well, technology actually produced some things that “Dr. Carl” could never have imagined back then. I believe 2001 A Space Odyssey could have happened except that nobody imagined NASA would be created and would syphon 90 percent of the Federal space budget into conducting experiments, building infrastructure, and financing a vast PR program that had nothing to do with manned spacecraft.

          • reed1v

            Much like the internet, space exploration will only progress when the private sector can make it a paying commercial venture. Remember well the intense debate over letting the private sector into the government’s internet system back in the 80s.

          • Luke101

            I agree with you. Who can say what the future of Bioengineering may bring us, both on our own DNA level and when directed at virulent enemies of Humanity.

        • Dale

          Ya what he said

        • Waden Kleinsasser

          good thinking i agree with you.

    • Luke101

      An unwarranted assumption.

  • Luke101

    Seems to me the ultimate questions are: Did the Yucatan Impact bring about the evolutionary rise of Mammals/Humans?
    Did that Unnatural event (?), change the evolutionary progress on Earth in ways that make this planet more unique than we imagine?

  • Arttai

    Can we deduce anything from these findings about the current state of evolution of mammals?

  • Hillary

    Organized religion may prove to be the asteroid that finishes off humanity.

  • Waden Kleinsasser

    I would say a asteroid killed all the dinausaurs


Discover's Newsletter

Sign up to get the latest science news delivered weekly right to your inbox!


See More

Collapse bottom bar