Transitional fossils: From the ancestor of modern whales to baleen whales

Finishing off these transitional whale fossils, I will now discuss the second major lineage of modern whales, the baleen whales. Baleen whales are characterized by having sheets of keratin (baleen) used for filter feeding instead of teeth.


Though some of these whales are relatively small, many of them are among the largest animals of all time, including the enormous blue whale.


Let’s refer to McGowen et al’s (1) phylogeny (evolutionary tree) one more time


Janjucetus 28.4-23.03 million years ago* Janjucetus_Melb_Museum_email

Mammalodon 25.2-23.03 million years ago


The first thing you should notice is that these are both found in rocks that are dated younger than the most recent predecessor to modern whales (that I’ve discussed), Basilosaurus (40.4-33.9 million years ago). The next thing you might notice is that they both have teeth. Janjucetus and Mammalodon are unique baleen whales in that they actually have no evidence of having possessed baleen. It might cause one to wonder why paleontologists have suggested that these are somehow transitional baleen whales. One feature that they share in common with other baleen whales is a broadened rostrum, the bones of which meet the braincase in a way that is particular to baleen whales.

Aetiocetus 33.9-23.03 million years ago


Aetiocetus is an even more convincing transitional baleen whale because it not only has evidence of baleen (arrows on right point to blood vessels that nourished baleen), but it had baleen side-by-side with teeth! Whether or not Aetiocetus fed with both teeth and baleen is a matter of speculation, but it’s an intriguing hypothesis nonetheless.

Eomysticetus 28.4-23.03 million years ago


Eomysticetus then dealt away with teeth altogether and probably fed via filter feeding exclusively. It differs from modern baleen whales in that modern species have bowed mandibles and a telescoped skull.

Summary and questions for creationists

I have highlighted 16 putatively transitional fossils in my last three posts, documenting a lineage of land mammals shifting from a terrestrial habitat, to semiaquatic forms, to an obligately aquatic habit and thereafter transitioning into modern toothed and baleen whales respectively. The fossils that are still tied to land are found in rocks that are dated older (55.8-37.2 million years ago) than the rocks in which primitive obligately aquatic whales are found. These rocks are still older than those in which the whales that resemble more modern toothed (33.9-25.2 million years ago) and baleen whales (33.9-23.03 million years ago) are found. Each fossil shows traits that are a mix of primitive characters, uncharacteristic of modern whales, and some that are similar to modern whales. It’s important to ask yourself: is this all a coincidence? Where are all of these primitive whales today? Shouldn’t those that are aquatic still be around since they could have survived the Flood? Why would God have created a whale with both baleen and teeth, but all modern whales have baleen or teeth? Are truly none of these fossils convincingly transitional?

*all fossil ranges based on the paleobiology database


1. McGowen, M. R., Gatesy, J., & Wildman, D. E. (2014). Molecular evolution tracks macroevolutionary transitions in Cetacea. Trends in ecology & evolution


2 thoughts on “Transitional fossils: From the ancestor of modern whales to baleen whales

  1. Pingback: Pseudogenes: Whales have remnants of tooth genes | Evolution For Skeptics

  2. Pingback: Ontogeny recapitulates phylogeny: Baby baleen whales have teeth (before they lose them) | Evolution For Skeptics

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