Of Whale and Feather Evolution: <i>Nature</i>'s Two Macroevolutionary Lumps of Coal - Evolution News & Views

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Of Whale and Feather Evolution: Nature's Two Macroevolutionary Lumps of Coal

Links to our 9-Part Series Responding to Nature's Evolution Evangelism Packet:
• Part 1: Evaluating Nature's 2009 "15 Evolutionary Gems" Darwin-Evangelism Kit
• Part 2: Microevolutionary Gems: Lizards, Fish, Snakes, and Clams
• Part 3: Microevolutionary Gems: Bird-Sized Evolutionary Change
• Part 4: Microevolutionary Gems: Flea and Guppy-Sized Evolutionary Change
• Part 5: Microevolution Meets Microevolution
• Part 6: Evolutionary "Gems" or "Narrative Gloss"?
• Part 7: Muscling Past Homology Problems in Nature's Vertebrate Skeleton "Evolutionary Gem"
• Part 8: Of Whale and Feather Evolution: Two Macroevolutionary Lumps of Coal
• Part 9: Evolutionary Biologists Are Unaware of Their Own Arguments: Reappraising Nature's Prized "Gem," Tiktaalik
Having now addressed all of the microevolutionary or even non-evolutionary "gems" from Nature's evolution-evangelism packet, I turn my attention in this series of posts to the few examples that actually led off their packet. Arguably, 12 of the 15 evolutionary gems had nothing to do with "macroevolution." But the very first "gem" was whale evolution, where the packet claims there are "numerous fossils from the first ten million years or so of whale evolution." This is odd since Phillip Gingerich has admitted that these are merely "fossils illustrating three or four steps that bridge the precursor of whales to today's mammals." The Nature packet recites the standard fossils, which are nearly always given as alleged evidence of transitional forms between land mammals and whales. Something very important is missing from their analysis. But we must not miss their comment about "the first ten million years" of whale evolution.

These "ten million years" are mentioned again in the main article cited in the packet, which opens with a retroactive admission of ignorance, stating, "Although the first ten million years of whale evolution are documented by a remarkable series of fossil skeletons, the link to the ancestor of cetaceans has been missing." According to the paper, the land-mammal ancestor of modern whales was very much like:

Indohyus ... a small, stocky artiodactyl, roughly the size of the raccoon Procyon lotor. It was not an adept swimmer; instead it waded in shallow water, with its heavy bones providing ballast to keep its feet anchored. Indohyus may have fed on land, although a specialized aquatic diet is also possible. The modern artiodactyl morphologically most similar to Indohyus is probably the African mousedeer...

(J. G. M. Thewissen, Lisa Noelle Cooper, Mark T. Clementz, Sunil Bajpai & B. N. Tiwari, "Whales originated from aquatic artiodactyls in the Eocene epoch of India," Nature, Vol. 450:1190-1194 (December 20/27, 2007).)

The inference of ancestry is made based upon just a few similar features--namely, tooth and ear morphology, limb-bone density, and δ18O values (reflective of habitat and diet). On this basis, Nature's first gem article suggests that raoellids (an artiodactyl group which includes Indohyus) were in fact the "ancestors" of whales: "Our working hypothesis for the origin of whales is that raoellid ancestors, although herbivores or omnivores on land, took to fresh water in times of danger."

Inferring ancestry based upon a couple similar features, like we see here, is kind of like reading tea leaves. Even if there are morphological or behavioral similarities between certain raoellids and whales, ancestry is difficult to unequivocally support. As Nature editor Henry Gee commented with regards to studying the much more recent relationships among hominids, "To take a line of fossils and claim that they represent a lineage is not a scientific hypothesis that can be tested, but an assertion that carries the same validity as a bedtime story--amusing, perhaps even instructive, but not scientific." (Henry Gee, In Search of Deep Time, 1999.) With that in mind, how seriously should we take Nature's packet when it confidently asserts that raoellids like Indohyus were "the land-living creatures from which whales eventually evolved"?

Even in this case there are questions about which direction the data is pointing. As regards teeth similarities, the authors note that "all of these characters are found in some mammals unrelated to cetaceans." As regards ear morphology, Figure 3 (x-axis) shows that by at least one measurement, other artiodactyls are more similar to whales than Indohyus. As regards δ18O values, they claim it shows Indohyus had a semi-aquatic lifestyle, but δ13C values of Indohyus "are most similar to the δ13C values in enamel for terrestrial mammals from early and middle Eocene deposits in India and Pakistan." Something tells me they really want Indohyus to have a semi-aquatic lifestyle, as they make the odd conclusion that "although" Indohyus had a semi-aquatic lifestyle "it did not necessarily have an aquatic diet (as suggested by carbon isotopes)." If Indohyus does represent the ancestors of cetaceans, the argument is hardly a clean case.

But let's return to the comments from Nature's evolution-evangelism packet that there are "numerous fossils from the first ten million years or so of whale evolution," also mentioned in the opening line of the paper. Why are the ten million years so important? It's because the fossil record shows that there are less than ten million years available for the transition from a full-fledged land mammal to a fully aquatic whale. So let's grant, for the sake of argument, that these fossils have some characteristics that appear intermediate between the features of land-mammals and whales. Have Darwinian paleontologists made their case?

The fossil record requires that evolution of whales from small land mammals supposedly took place in less than 10 million years. Think about that for a moment. According to this paper, whales, with all of their complex adaptations for aquatic life, supposedly evolved from something like Indohyus, a mouse-deer like animal, into a full-fledged whale in less than ten million years. Whales have a long generation time, meaning that there were perhaps only a few million generations at best to allow for the change to add up. If they had a generation time as short as 5 years, Haldane's dilemma predicts that only a few thousand mutations could become fixed into an evolving population during that time period. (See Walter ReMine, The Biotic Message.) In other words, the fossil record permits dramatically insufficient time to convert a land mammal into a whale.

Feathered Dinosaurs or Feathered Birds?
Nature gives only praise for the whale series, showing no appreciation for the mathematical difficulties of evolving a whale in so few generations. But the packet really starts to evangelize for evolution when it gets into the evolution of feathers. Discussing "feathered dinosaurs," it states:

The discovery of feathered dinosaurs not only vindicated the idea of transitional forms, but also showed that evolution has a way of coming up with a dazzling variety of solutions when we had no idea that there were even problems. Flight could have been no more than an additional opportunity that presented itself to creatures already clothed in feathers.

The main example given by the packet, Epidexipteryx, highlights the problem with many of these claimed "feathered dinosaurs." Unmentioned by Nature's packet is the fact that the original paper contains language directly hinting that Epidexipteryx could also be "interpreted as secondarily flightless." (See Fucheng Zhang, Zhonghe Zhou, Xing Xu, Xiaolin Wang & Corwin Sullivan, "A bizarre Jurassic maniraptoran from China with elongate ribbon-like feathers," Nature, Vol. 455:1105-1108 (October 23, 2008).) In other words, this fossil could actually be a bird that lost its ability to fly.

Various authorities support such interpretations of these classes of fossils. Bird evolution expert Alan Feduccia believes that "Caudipteryx and Protoarchaeopteryx, in fact, are replete with features of secondarily flightless Mesozoic sauriurine birds..." (The Origin and Evolution of Birds, pg. 396, Yale University Press, 1999.) Feduccia further writes:

Given the now substantial evidence that certain taxa once thought to be dinosaurs (e.g. Caudipteryx, Protarchaeopteryx, and the Oviraptosauria; Maryanska et al. 2002) are most likely secondarily flightless birds, and the new hypothesis that certain dinosaurs were secondarily flightless descendants of Mesozoic birds (Paul 2002), we must now carefully consider the possibility that there may have been a number of radiations of secondarily flightless Mesozoic birds that evolved morphologies quite similar to theropod dinosaurs.

Likewise a 2000 Nature paper suggested that "Caudipteryx was a secondarily flightless, post-Archaeopteryx, cursorial bird" because "it [is] a striking coincidence that the only unambiguously feathered theropod was also the only known theropod likely to have utilized locomotory mechanisms identical to those of cursorial birds." (See Terry D. Jones et al.,"Cursoriality in bipedal archosaurs," Nature, Vol. 406:716-718 (August 17 2000).)

Somehow that 2000 Nature paper didn't make it into Nature's evolution-evangelism packet. After all, "secondarily flightless" birds are a lot less impressive than "feathered dinosaurs," so there's no mention of this dissenting viewpoint in the Nature packet.

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