Was the Jurassic World a Dinosaur's World?

Our perception of the past is coloured by phrases like “the age of the dinosaurs”, but the history of life on Earth refuses such simplistic constraints. In fact, mammals have a far richer evolutionary story than these evocative sound-bites suggest.

In 2012, researchers at the University of Helsinki published a study showing that a group of mammals known as multituberculates diversified millions of years before the dinosaurs went extinct. The team used cartographic software to analyse high resolution scans of the teeth of over 40 multituberculates, offering insight into what these mammals were eating.

Their analysis revealed that early multituberculates were probably carnivorous or omnivores with an animal-rich diet, such as a combination of insects and fruit. The 20 million year period before the extinction of the dinosaurs saw a shift to herbivory coupled with increased variability. The diversity peaked around 66-62 million years ago, roughly at the time of the K-T extinction, and then decreased before multituberculates eventually went extinct.

One factor driving the early diversification of mammals may have been the radiation of flowering plants across ancient ecosystems. Researchers at Indiana University tested this idea in a recent study. They measured the jaw morphology of a wider range of mammal fossils to reconstruct their morphological and dietary diversity. While multituberculates shifted to a herbivorous diet, other groups of mammals were diversifying to prey on the insects that accompanied the spread of flowering plants.

Regardless of the precise details of the evolutionary story, it seems clear that mammals were already a diverse, vibrant group during the “age of the dinosaurs”. Some might argue that dinosaurs (or perhaps reptiles more generally) deserve the nominative honour by virtue of being ecologically dominant. If so, surely the true honour belongs to bacteria, or at least to plants, both of which are perennially dominant forces in planetary ecology. Dinosaurs may capture our imagination, but that doesn't mean they ever dominated the planet in a meaningful sense.

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Refs

Grossnickle, DM and Polly, PD. Mammal disparity decreases during the Cretaceous angiosperm radiation. Proceedings of the Royal Society B 280(1771): 20132110. (2013) doi: 10.1098/rspb.2013.2110

Wilson, G., Evans, A., Corfe, I., et al. Adaptive radiation of multituberculate mammals before the extinction of dinosaurs. Nature, 483 (7390), 457-460. (2012) doi: 10.1038/nature10880

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Image credits

The Deinonychus antirrhopus depicition is by Nobu Tamura and is distributed under a CC-BY license via Wikimedia Commons.

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