Claim: Gradual decline of dinosaurs before extinction

For your “Unverifiable Hypothesis” file.

The media release and abstract are below.

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Statistical analysis suggests that the mass extinction of dinosaurs thought to have been triggered by an asteroid impact was preceded by the animals’ gradual but inexorable decline over at least 40 million years, according to a study. The Chicxulub asteroid impact in Mexico is thought to have driven most dinosaurs to extinction around 66 million years ago, but whether dinosaurs experienced a gradual decline toward oblivion or thrived until the cataclysmic impact remains unclear. Using Bayesian phylogenetic analysis of three large dinosaur datasets, Chris Venditti and colleagues explored dinosaur speciation and extinction dynamics before the asteroid impact. The model revealed that extinction rates surpassed speciation rates beginning around 24 million years before the impact; when the three major dinosaur groups were separately considered, extinction rates exceeded speciation rates as early as 48-53 million years before impact. Modeling also found a minor but positive effect of sea level rise on dinosaur speciation, which rose by 0.2-0.25% per meter increase in sea level, lending support to a hypothesis that rising seas lead to habitat fragmentation, reproductive isolation, and speciation. The precise triggers of the speciation decline remain unknown, but Cretaceous phenomena such as the breakup of supercontinents, sustained volcanism, and ecological factors may have possibly influenced the downturn. According to the authors, dinosaurs gradually lost the ability to replace extinct species with new ones, thus likely favoring the rise of mammals that began to flourish in previously unavailable ecological niches.