The Evidence That Shows Dinosaurs Were In Decline For 40 Million Years Before The Asteroid Hit

The end was nigh. Shutterstock

Kristy Hamilton 28 Feb 2017, 22:33

But did the dinosaurs really disappear with a bang? New evidence now suggests instead a very, very, long decline, perhaps as long as 40m years. Part of this comes from our application of a modelling technique to the data. The key here is to have an evolutionary tree, what is known as a “phylogeny”, which is dated accurately against geological time. Although the fossil record of dinosaurs is incomplete and patchy, we do have high quality phylogenies, tested over 30 years of research, that provide solid information on dinosaurian relationships.

Once you have a phylogeny, and date it against a geological time scale, you can read off a great deal of new information. It helps to joins the dots, linking isolated finds, and bridging gaps. It also provides a framework from which rich data on rates of evolution can be calculated.

We wanted to explore a hint of decline that had been noted in the first such comparative phylogenetic analysis.Our new work focused on exploring the diversity dynamics of dinosaurs through their entire evolution. We confirmed first that they did most of their evolving in the first half of their reign on Earth, during the late Triassic and early to middle Jurassic periods, some 230m to 150m years ago.

Decline and fall

Most importantly, we found clear evidence for a long-term decline from 40m years before the end of the Cretaceous period. We looked at all dinosaurs, and then each of the main subgroups. The only exceptions were the duck-billed dinosaurs (hadrosaurs) and the horned ceratopsians, both of which showed renewed bursts of evolving into new distinct species later on.

So after so much recent disagreement, can our new theory be believed? We believe so. It is based on the most detailed data ever assembled, a complete evolutionary tree of more than 600 species of dinosaurs, with better control on the time scale than ever before.

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