National Geographic

How many types of dinosaurs were there?

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Few creatures, living or dead, can capture our imaginations like dinosaurs. But those of us who were mesmerised by these creatures as children may find today’s cast strange and unfamiliar. Our well-known mainstays like Tyrannosaurus have been joined by Hollywood-sponsored favourites like Velociraptor, while new names are cropping up at great pace. Clearly, many new species are waiting to join the ranks. The question is: how many?

According to a study from 2006, we have only scratched the surface of dinosaur diversity. With over 1300 new groups left to discover, fossil-hunters should be kept busy for decades to come.

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There are many problems with estimating dinosaur numbers. For a start, the fossil record is incomplete and many species are known only from small fragments. The best information we have comes from the Dinosauria ­­- the dinosaur enthusiast’s bible – which put the number of known genera at 285 in its 1990 edition. ‘Genera’ is a term referring to groups of closely related species. For dinosaurs, it is a good an indicator of diversity as any, as most genera have only one representative.

Since 1990, palaeontologists have been busy. Countries like China and Argentina have proven to be particularly rich digging grounds and the number of new groups being unearthed has accelerated at a tremendous rate. About 15 new genera are discovered every year, and the total has almost doubled to 527, excluding those based on isolated teeth or single fragments. The newcomers have included several record-breakers, including the massive Argentinosaurus, the tyrannosaur-trumping Giganotosaurus, and the minute Microraptor.

Now, Steve Wang and Peter Dodson from the University of Pennsylvania have plugged the data from the Dinosauria into an established mathematical model to work out how many genera are still undiscovered. By their reckoning, we have only begun to scratch the surface of dinosaur diversity. We have found less than a third of all possible groups, and a further 1300 or so are still hidden beneath our feet.

The study also provides some tantalising hints as to what killed off the dinosaurs – a topic that is still hotly contested today. Wang and Dodson looked at the change in dinosaur diversity towards the end of the Cretaceous period and found that it remained fairly constant. While the analysis is not accurate enough to provide concrete answers, it weighs against the idea that the dinosaur dynasty was already in decline towards the end of their reign. Instead, their doom most likely came suddenly crashing down from the heavens in asteroid form.

Obviously, the method is not perfectly accurate, but if anything, the total estimate of about 1850 genera is most likely to be too low. For a start, Wang and Dodson have deliberately ignored the dinosaurs’ biggest triumphs – the birds, evolutionary descendants of dinosaurs and technically part of their group. The statistics also cannot account for the large number of genera that will never be discovered because by chance, they left no fossils.

For those genera that did fossilise, the researchers believe that they will not stay hidden for long. According to their study, will we have discovered about 75-90% of the remaining groups by the turn of the century. But this will only happen if we can sustain the current golden age of discovery. With China and Argentina rapidly yielding their secrets, new veins of fossils will need to be found and tapped. Even since this article was originally written at the end of 2006, palaeontologists have unearthed Mahakala, Eotriceratops, Albertaceratops, Suzhousaurus, Eocursor, Glacialisaurus, Gigantoraptor, Kryptops, Eocarcharia, Velafrons, Sahaliyania,Wulagasaurus, Futalognkosaurus and Xenoposeidon, to name just a few.

These statistics should act as a clarion call to budding palaeontologists looking to make an impact. Go grab your shovel, here be dragons.

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Reference:Wang, S.C., Dodson, P. (2006). Estimating the diversity of dinosaurs. Proceedings of the National Academy of Sciences, 103(37), 13601-13605. DOI: 10.1073/pnas.0606028103

There are 3 Comments. Add Yours.

  1. Amiya Sarkar
    June 7, 2008

    I just don’t understand why scientists are propounding one hypothesis after another to explain the extinction of dinosaurs. Shouldn’t we also keep this in mind that one ‘generalized’ cause of extinction, would also wipe away the entire ‘flora and fauna’ from the face of the world, and evolution would have to begin afresh?

  2. Laelaps
    June 8, 2008

    Amiya; There has been a boom in the number of extinction hypotheses lately, but the end-Cretaceous extinction is a big question. Why, for instance, did non-avian dinosaurs become extinct but their avian descendants made it through? Many other groups of animals became extinct, too, (like mosasaurs, the last of the ammonites, etc.) so the question of why some groups survived and others did not is something that can keep a paleontologist up at night. The focus on dinosaurs has partly been because of their popularity, but also because if we can understand why they became extinct during a time when they were still diverse perhaps the extinction of other groups will become clearer.
    Extinctions are difficult to study; even though they are clearly seen in the fossil record their causes may have roots that go far back. As David Raup pondered in his slim (but well-written) book Extinction, is extinction caused by “bad genes” or “bad luck”? In many cases it seems to be a case of bad luck, a number of historical contingencies putting some species in a particularly bad place, and survival is accidental (there’s no way to prepare for or evolve resistance to a meteor strike, for instance).
    Anyway, there are a lot of hypotheses out there, but the question is a big one and I am glad that extinction is getting so much attention.

  3. Jim Thomerson
    June 12, 2008

    I like to know more about the statistics. Are they using a species area curve? If so, we are clearly on the ascending arm of the curve and thus have no idea when the rise an numbers will slow down. I really don’t see how a final number can be predicted when new finds are coming in at a high rate. Never-the-less, their guess sounds reasonable. I think I read of a much lower guess, which I did not think reasonable, something over 500 as I recall.

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