May 11 2018

The Evolution of Baleen Whales

A recent survey finds that knowledge of evolution correlates with acceptance of evolution. This was widely reported as suggesting that educating the public about evolution could lead to higher rates of acceptance. Sure, but to be clear the survey does not actually show this. We can also interpret the same data to suggest that acceptance of evolution leads to greater knowledge of it.

This latter interpretation makes sense in light of the fact that there is a tremendous amount of misinformation about evolution from creationist sources. If you are anti-evolution for ideological reasons, you are likely to be highly misinformed about the science because your rely on secondary hostile creationist sources for your information. If you accept the scientific consensus on evolution, you may be more likely to avail yourself of legitimate scientific sources of information.

But probably both factors are at play, and we certainly should strive to improve public education about evolutionary science. It is a complex and subtle science that is poorly understood by the public. The survey also found that 68% of those surveyed failed to demonstrate a basic knowledge of evolutionary theory. And it is certainly easier to spread misinformation about a science the public generally does not understand. In this case knowledge would be a good defense against propaganda.

It is also true that the evidence for the basic fact that life on Earth is the result of evolutionary processes is a scientific home run. It is a phenomenally well-established fact, with no viable competing theory. This often creates the naive belief among those with a solid understanding of evolution and the evidence for it that if they could only explain that evidence to a typical creationist, they will win them over with the massive force of that evidence. That does sometimes happen, but more often evidence is no match for motivated reasoning.

With all that said, I am still going to write about the evidence for evolution in the hopes of nudging public acceptance even a little.

Baleen Whales

One of the best sources of fossil evidence for an evolutionary history to life on Earth are those times when a population of creatures undergoes a radical change in their lifestyle, usually by adapting to a new environment or basic survival strategy. When small feathered theropod dinosaurs took to the wing, flying imposed a host of new adaptive stresses on them, resulting in a suite of anatomical changes. For this reason the evolution of non-avian dinosaurs to birds, now that we have discovered a treasure trove of fossils, is on of the most dramatic examples of evolutionary change.

Other similar examples occur whenever a species migrates from the sea to the land (like Tiktaalik), or from the land to the sea. Whales are a great example of the latter – their ancestors started out as terrestrial quadrapedal mammals. Modern whales are completely adapted to a full-time aquatic life. This creates a great opportunity for evolutionary theory to make a testable prediction. Since whales are clearly mammals, and mammals evolved on land, whale likely have a terrestrial ancestor. So it was predicted, long before the first whale ancestor fossils were discovered, that if evolution is true we should find fossils representing a reasonable sequence of whale ancestors progressively more adapted to the sea.

This sequence is perhaps best represented by Ambulocetus, because this genus is close to being right in the middle of the transition. It is the proverbial half-land mammal, half-whale. As the name implies, it is the walking whale, retaining stubby legs. We also see over time increases in body size, the movement of the nostril to the top of the head, the development of the fins, and the streamlining of the body design for hydrodynamics.

One groups of whales, called baleen whales (technical term Mysticeti) also lost their teeth and replaced them with comb-like tissue that hangs down from the top of their mouths. Modern baleen whales take large amounts of water containing many small creatures they eat for food into their mouths, then then squeeze the water out through their baleen, which filters and retains the creatures to then be swallowed. This type of feeding is called suction feeding.

That is a pretty big transition from teeth to baleen. Unfortunately, baleen is all soft tissue, and it doesn’t fossilize. But, scientists can infer the presence and location of baleen by looking at the underlying bone, which should contain spaces for the blood vessels that feed the baleen.

Llanocetus denticrenatus

All this background brings us to a new study examining the complete skull of a very early whale ancestor, Llanocetus. The specimen is 34 million years old, making it the second-oldest Mysticeti specimen known. Specimens from the very early days of an evolutionary clade are especially useful, because they can tell us about the path that diverging groups took. What features were present at the beginning, and which ones evolved later?

Also by determining what came first, we can infer what features or behaviors drove which evolutionary changes. For example, did baleen develop first, or did whales develop their large size first? Did they lose their teeth entirely prior to developing baleen?

Llanocetus can potentially answer these questions. We already knew that Llanocetus was huge – 8 meters in length. This is still small for a modern whale, but within the range of the smallest whales. The new analysis confirms that Llanocetus had teeth. The structures in the skull also suggest that he did not have baleen.

So the earliest ancestors of the baleen whale clade were large toothed predators. Llanocetus likely engaged in what scientists call “raptorial” feeding. The scientists conclude that baleen whales evolved through a stage they call suction-assisted raptorial feeding. Then eventually to pure suction feeding, with increasing amounts of baleen to make the process more efficient.

This is another common feature we find when we have a good sequence of fossils in an evolutionary clade – when a new significant life strategy is undertaken, at first it is very primitive and inefficient. The first land animals were clumsy walkers, the first birds were inefficient fliers, and the first suction-feeding whales were also inefficient. We then see the later occurrence of specific anatomical adaptions that increase efficiency. The first birds did not have a keeled sternum, for example, but later ones did.

Evolutionary theory does not depend upon any particular sequence of events being true. Whales or birds or whatever may have taken many twisting paths to their current forms. What evolutionary theory does require, and therefore predict, is that there is some path.

For many major groups, now, we have found enough fossil specimens to have a good idea of the evolutionary paths taken during dramatic transitions. If evolution were not true, and whales were just another created “kind,” then there would be no reason for Llanocetus or Ambulocetus or any of the other transitional whales to exist. Evolution requires that something like them do exist, however.

Creationists often incorrectly say that evolution makes no testable predictions, but they are clearly wrong. They are making a category mistake, either out of ignorance or motivated reasoning. Evolutionary theory does not predict the details of the path taken, but it does predict that we will find evidence of some path.

With whales, we clearly have. Creationists used to point to the absence of fossils for whale ancestors. They still do:

The lack of transitional forms in the fossil record was realized by evolutionary whale experts like the late E.J. Slijper: ‘We do not possess a single fossil of the transitional forms between the aforementioned land animals [i.e., carnivores and ungulates] and the whales.’

The reference is to a book from 1962 – before all the transitional fossils were discovered. Quoting a scientist from over 50 years ago is standard procedure for creationists. What follows is a discussion of some of the whale fossils, with silly reasons given for dismissing their implications, in conspiratorial tones. But the writer, Jonathan Sarfati, misses the big picture – the existence of the fossils at all. Yes, 50 years ago they did not exist, and creationists harped on this giant “gap” in the fossil record. Now the gap has largely been filled in, with a beautiful sequence of morphological transitions. Creationists now harp on the smaller and smaller gaps, or the missing bones.

I do have to wonder if they believe their own nonsense, or if somewhere deep they know in their guts that these fossils are devastating to their denial. Probably not, but they should.

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