Nice article ! Here is the abstract for it:
Abstract
Reconstructing the evolution of baleen whales (Mysticeti) has been problematic because morphological and genetic analyses have produced different scenarios. This might be caused by genomic admixture that may have taken place among some rorquals. We present the genomes of six whales, including the blue whale (Balaenoptera musculus), to reconstruct a species tree of baleen whales and to identify phylogenetic conflicts.
Evolutionary multilocus analyses of 34,192 genome fragments reveal a fast radiation of rorquals at 10.5 to 7.5 million years ago coinciding with oceanic circulation shifts. The evolutionarily enigmatic gray whale (Eschrichtius robustus) is placed among rorquals, and the blue whale genome shows a high degree of heterozygosity. The nearly equal frequency of conflicting gene trees suggests that speciation of rorqual evolution occurred under gene flow, which is best depicted by evolutionary networks. Especially in marine environments, sympatric speciation might be common; our results raise questions about how genetic divergence can be established."
The sentence I put a bold emphasis on, regarding fast radiation, once again demonstrates that the pace of Evolution has a lot to do with an life form’s population being able to respond to a propitious wave of environmental changes … - - “catching the wave” of changes that are most likely to lead to changes in form and structure.
If there hadn’t have been suitable areas where strong-finned walking fish could move up onto land easily, as well as having something to eat up on the land, evolution from fish to tetrapod could have been delayed for millions of years more.
If the planet-killing asteroid had not wiped out the giant marine reptiles, there might not have been as much of a reason for a land mammal to start foraging for food in the ocean margins - - fish populations appear to have become quite large in the absence of constant reptile predation. But, further, if carnivorous terrestrial dinosaurs were still roaming the continents, no land mammal could have become big enough to survive hunting for fish in coastal waters . . . there are no “tiny otters” in the world’s inventory of marine mammals.