When it comes to hypothetical questions, "What if a giant asteroid (or whatever) hadn't killed off all the dinosaurs?" is one of my favorites, mostly because I imagine living in Bedrock and driving a brontosaurus for a living.But this week researchers led by the American Museum of Natural History released a report stating that some species of dinosaurs were already on the decline before the mass extinction. While "dinosaur" is a broad enough category that it resists any easy generalizations, the report states that "large bodied, 'bulk-feeding' herbivores were declining during the last 12 million years of the Cretaceous." So if you were imagining a non-asteroid world where you could commute to work on a Triceratops, you better fantasize a little harder, because it looks like the dinosaurs were already on the way out.Researchers from Columbia University, the AMNH and two German institutions are looking at the fossil record and trying to piece together what the world was like at the end of the age of the dinosaurs.Rather than looking at the number of taxonomical differences among dinosaurs as a whole, this study divides them up into seven groups based on wide-ranging characteristics including intricate skeletal structure. This more nuanced approach to the fossil record may produce a more accurate picture of which dinosaurs were evolving, which were in decline, and how the world looked before the massive extinction which would ultimately make all those dinosaurs working their asses off to evolve look mighty foolish."Dinosaurs were hugely diverse. There were hundreds of species living in the Late Cretaceous, and these differed enormously in diet, shape, and size," said Richard Butler from Ludwig Maximilian University of Munich, who worked on the study. "Different groups were probably evolving in different ways and the results of our study show that very clearly."Some of the dinosaur groups showed great diversity within the groups, a sign that they were evolving and looking for that "ecological edge." As the Cretaceous drew to a close, carnivores, small herbivores and the massive sauropods were holding steady, or even growing in diversity. However, the duck-billed herbivore hadrosaurs and the frilled and often-horned ceratopsids were experiencing a decline in biodiversity.This doesn't necessarily mean those species were on the decline. “Even if the disparity of some dinosaur clades or regional faunas were in decline, this does not automatically mean that dinosaurs were doomed to extinction,” said Mark Norell of the AMNH (and friend of Motherboard). “Dinosaur diversity fluctuated throughout the Mesozoic, and small increases or decreases between two or three time intervals may not be noteworthy within the context of the entire 150-million-year history of the group.”The study focused mainly on North America, which is replete with good, diverse fossil samples, but may or may not have been representative of the rest of the world 77-65 million years ago. Things like the fluctuation of the Western Interior Seaway, a body of water that split North America where the Rocky Mountains now run, impacted biodiversity as well.It’s hard to come up with a hard and fast takeaway from the study, thanks to the fact that, while it does suggest that some dinos were in decline, it’s not yet clear why or how that happened. However it is a reminder that, as the lead author Steve Brusatte, a Columbia University graduate student, put it, "the Late Cretaceous wasn’t a static ‘lost world’ that was violently interrupted by an asteroid impact. Some dinosaurs were undergoing dramatic changes during this time." Dramatic being relative, of course, in light of the destructive events to come.
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