Fred.
Or is that another yet to be discovered missing link?
Here's what the article is about:
In a paper appearing this week in the Online Early Edition of the Proceedings of the National Academy of Sciences, Boisserie and colleagues Michel Brunet and Fabrice Lihoreau fill in this gap by proposing that whales and hippos had a common water-loving ancestor 50 to 60 million years ago that evolved and split into two groups: the early cetaceans, which eventually spurned land altogether and became totally aquatic; and a large and diverse group of four-legged beasts called anthracotheres. The pig-like anthracotheres, which blossomed over a 40-million-year period into at least 37 distinct genera on all continents except Oceania and South America, died out less than 2 and a half million years ago, leaving only one descendent: the hippopotamus.It is basically about connecting hippos to anthracotheres, heretofore considered a weak link. This page, for instance, cites difficulties making the connection.
In many, perhaps most, phylogenies, this taxon includes the Hippopotamidae. Early anthracotheroids were small. See the image of Anthracobunodon below. Later anthracotheroids were indisputably large and generally hippo-like in aquatic habit and adaptations [PS02]. Traditionally, the story was also told that the decline of the anthracotheres was closely correlated with the rise of the hippos, who, in turn were marginalized by bovids of various sorts [C88]. However, in critical details, the last anthracotheres were not very similar to the first hippos, and the timing no longer seems suggestive. Indeed, the entire clade disappeared too soon to have produced the first known hippo, Kenyapotamus [PS02] [????]. ATW040724.The study cited in this article answers that. It shows previously unrecognized characters linking the hippo and anthracotheres clades. Arguing from gaps is always a lousy idea.
Anyway, connecting hippos to anthracotheres leaves hippos diverging from something like this thing.
Meanwhile, the earliest "whale" looks like this.
Illustration by Carl Buell, and taken from http://www.neoucom.edu/Depts/Anat/Thewissen/whale_origins/whales/Pakicetid.html.
(So one's a little livelier than the other, but less transparent.) So your answer is, "Where's the thing bridging the gap?"