Talk about humble beginnings. Most of our notions about our mammal ancestors portray them as shrewlike critters barely eking out an existence in the shadow of dinosaurs for millions of years. When the hulking giants got felled in the aftermath of environmental changes from a giant meteor impact, the pathetic warm-blooded runts finally got to make their move, eventually blossoming into the wide diversity of successful species we see today, including humans.

Not so fast. As paleontologists Stephen Brusatte and Zhe-Xi Luo write in this issue's cover story, “Ascent of the Mammals,” a series of spectacular recent fossil discoveries reveal surprising twists on the old tales you learned in your schoolbooks. Millions of years before it was ever thought possible, evolution began to lay the groundwork for mammals to become the world's dominant vertebrate species.

The tiny animals developed an array of specializations and evolutionary innovations, making them adept at taking advantage of a variety of ecosystem niches. Their tooth shapes enabled the processing of new foods, and their growth patterns enhanced survival of their young. Early mammals came to climb, to glide, to swim. Ultimately, as we know, they crawled all over this blue planet. 

Delve Deeper

The process of science has many admirable traits, and one of them is how it builds on prior knowledge—which is ideally freely shared. For that reason, a little over a year ago Scientific American's parent company began an experiment of its own: through the use of software from ReadCube, supported by the company Digital Science, it enabled readers of this magazine and about 100 other mass-market publications free access to view original research papers published in close to 50 journals, including Nature. Readers who clicked on links placed in articles at ScientificAmerican.com and elsewhere could follow their curiosity, delving deeper into the methods and results of published findings. Each paper received an average of 200 more views during the 15-month trial.

Now I'm delighted to report that such content sharing is extended to the entire Springer Nature portfolio, covering more than 2,700 journals and 300,000 new articles a year. That means there's a whole new world of science freely available, just for you.