Dinosaurs Doomed By Decline In Diversity?
April 27, 2016
In this illustration, a group of dinosaurs and flying reptiles flee a vast fire. Such an event, connected to the eruption of a volcano, could have caused the extinction of the dinosaurs at the end of the Cretaceous, some 65 million years ago. Credit: © Mark Garlick, Photo Researchers
Dinosaurs reigned supreme on Earth for tens of millions of years. Other animals, such as mammals, lived in the shadows, eking out an existence among giant plant-eaters and ferocious predators. Dinosaurs were so dominant that, if it hadn’t been for some extremely bad luck 65 million years ago in the form of a giant asteroid, they might still populate Earth today. Right? Maybe, maybe not.
A recent study published in the journal Proceedings of the National Academy of Sciences casts doubt on this picture of dinosaur supremacy. Paleontologists Manabu Sakamoto and Chris Venditti of the University of Reading and Michael Benton of the University of Bristol analyzed parts of the dinosaur family tree over time. They compared speciation (spee see AYE shun) events to extinction events. Speciation is when one species evolves from another—for example, human beings, chimpanzees, and gorillas evolved from a common ancestor that lived between 4 million and 10 million years ago. That split that occurred was a speciation event. Sakamoto, Venditti, and Benton made comparisons of speciation and extinction events within five groups of dinosaurs: meat-eating theropods, long-necked sauropods, horned ceratopsians, duck-billed hadrosaurs, and other plant-eating dinosaurs.
The scientists found that the rate of extinction began to exceed the rate of speciation for theropods, sauropods, and other plant-eating dinosaurs 50 million years before the asteroid hit. This means that dinosaur species in these groups were going extinct faster than new species evolved to take their place as much as 115 million years ago, in the middle of the Cretaceous Period.
Does this mean that dinosaurs were already on their way out, and a huge rock from space only hastened their demise? Absolutely not! While the dinosaurs may have been experiencing a downturn in diversity, this study does not indicate that they were at death’s door. Whether dinosaurs gradually declined before their extinction has been a hotly-debated topic in paleontology for many years. In fact, long before the Chicxulub impact crater (created by an asteroid that struck Earth 65 million years ago) was discovered, most paleontologists thought the dinosaurs had slowly died out and that there was no mass extinction. The question of dinosaur decline is very complicated and touches on such paleontology issues as the completeness of the fossil record. Because of many differences in the layers of Earth, some animals in some periods have nearly complete fossil records, while others from other periods may have few or no fossils. This study will not be the last word on the matter.
The study does, however, highlight a few important things about dinosaur diversity and extinction. First, the extinction of the dinosaurs was a complex event. The environment of the Late Cretaceous was challenging. Enormous volcanoes called the Deccan Traps raged in what is now India. The climate was getting colder. Drifting continents and changing sea levels were fragmenting land habitats, making it more difficult for land-dwelling dinosaurs to move from place to place. These factors may have affected the group’s species diversity.
Second, the study highlights how diverse dinosaurs were. There are about 600 named dinosaur species, and scientists estimate that another 600 or more remain to be discovered. Some of these species may have lived in regions where fossilization rarely occurs (such as mountain environments) and thus will never be found. Some paleontologists involved in assessing dinosaur diversity point out that the astonishing diversification that occurred in the Jurassic Period could never have lasted forever, particularly in the challenging environment of the Late Cretaceous.
Finally, the study holds great relevance for us today. If the results are borne out by future analyses, it would suggest that a modest loss of species diversity may have made the dinosaurs more susceptible to random cataclysmic events such as the Chicxulub asteroid. Today, many species are going extinct, and the planet is warming rapidly. The loss of diversity might make today’s ecosystems more susceptible to collapse from random events such as volcanic eruptions or asteroid impacts. Like the dinosaurs, humans might have built their global dominance on an unstable foundation. Unlike the dinosaurs, however, we have the ability to make changes to strengthen ecosystems and reduce global warming, giving us more of a fighting chance against extinction.
Other World Book articles
- Drilling for Answers (March 9, 2016) – Behind the Headlines article
- Geology (2007) – A Back in Time Article
- Global warming
