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

In my previous post, I described McGowen et al.’s [1] summary of fossil evidence for a transition between a terrestrial mammal and the ancestor of modern whales. Here I will begin to discuss their review of the transition from that hypothetical ancestral whale to today’s modern whales.

Many people are probably unaware that there are two major lineages of whales: the toothed whales and the baleen whales. Toothed whales, as their name implies, have teeth whereas baleen whales have baleen, fibers of keratin used for filter feeding. Additional differences include one blowhole in toothed whales with two in baleen whales, and toothed whales have the ability to echolocate. Examples of toothed species include dolphins, porpoises, belugas, narwhals, beaked whales and sperm whales.

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Here’s the phylogeny (evolutionary tree) from McGowen et al. [1] again, showing the transitions.

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Let’s start with transitional fossils in the toothed whales.

Simocetus 33.9-28.4 million years ago*

Simocetus appears after Basilosaurus and Dorudon, the last fossils I described appearing before the ancestor of modern whales. Simocetus possessed an elongated skull, a feature characteristic of toothed whales. Though not shown in the figure in McGowen et al., it also appears to have had a melon, a feature found in toothed whales to direct their echolocating clicks.

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Waipatia 27.3-25.2 million year ago

Slightly younger than Simocetus, Waipatia has the same features, uniting the two of them with toothed whales.

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What both species lacked, however are asymmetrical skulls and homodont dentition. The former is a characteristic though to be advantageous for underwater hearing. The right side of the skull is always larger than the left side. You can see it clearly in the bottlenose dolphin diagram below:

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Homodonty (“same teeth”) is defined as having teeth that look approximately identical. This trait is found in many fish-eating vertebrates such as toothed-whales, sea lions, and gharials. Most other mammals have heterodonty (“different teeth”). Whereas we have incisors, canines, premolars and molars, dolphin teeth are extremely similar. Early whales had heterodonty, a trait still preserved, albeit slightly, in Simocetus and Waipatia.

Compare the teeth in this sperm whale:

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with those of the ancient whale Basilosaurus:

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In short, fossils appear to document a transition between early whales and modern toothed whales.

Question for Creationists

Why would God create whales with homodonty and heterodonty, but only those whales with homodonty have survived into the present? Shouldn’t both groups have been able to survive Noah’s flood?

*all fossil ranges based on the Paleobiology database

References

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

 

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