A new study (that included Nicholas Pyenson from the Smithsonian and an Affiliate Curator Burke Museum) looked at the origin of baleen and how modern toothless baleen whales evolved from early toothed forms without baleen. Baleen filter plates in whale jaws are unique among mammals, but are made of keratin similar to horns and hoofs. The researchers reviewed the fossil evidence and looked at four possible evolutionary scenarios in which whales had both teeth and baleen at the same time or lost their teeth before they evolved baleen. Other studies have suggested that suction feeding by toothed ancestors may have led to the development of baleen. The new study proposes that a toothless suction feeding stage may have come before baleen developed. Unfortunately, the embryonic development of tooth buds and baleen in modern whales is still not well understood.
Carlos Mauricio Peredo, Nicholas D. Pyenson and Alexandra T. Boersma (2017) Decoupling Tooth Loss from the Evolution of Baleen in Whales. Frontiers of Marine Science 4: Article 67 https://doi.org/10.3389/fmars.2017.00067
http://journal.frontiersin.org/article/10.3389/fmars.2017.00067/full