November 29, 2010 | David F. Coppedge

Mammals Partied When Dinosaurs Left

A research team headed by a biology professor at the University of New Mexico are claiming that mammals had a field day when the dinosaurs went extinct.  They got bigger and more diverse, filling in the ecological wasteland left by the missing giant reptiles.  Their analysis was published in Science.1
    In addition, they think the mammals waxed and waned with the temperature.  According to lead author Felicia Smith [U of NM], quoted in Science Daily, “Global temperature and terrestrial land area set constraints on the upper limit of mammal body size,” Smith said, “with larger mammals evolving when the earth was cooler and the terrestrial land area greater.”  But isn’t there more to evolutionary theory than changing times?
    A look at how they used the term evolution in their paper shows a rather cavalier assumption that evolution just happened.  As to how animals could evolve, they tried a random model, like Brownian motion on a large scale, and a saturation model, with evolution reaching to fill all available space somehow: “as maximum body size evolves, the evolutionary possibilities for increasing size are progressively exhausted.”
    Other than that, the authors treated evolution as a category of stuff happens,  speaking of “the evolution of” this or that.  They even invoked the convergence notion (01/26/2010): “the patterns suggest that large mammals convergently evolved to fill similar ecological roles.”  As for the atmospheric and geographic influences on evolution, they were gracious enough to warn, “However, some caution should be used in the interpretation of our results.”  There’s a lot of uncertainty, after all, about how oxygen levels and other environmental factors could influence evolution.  “Nevertheless, the potential role of abiotic factors in the overall trajectory of mammalian evolution cannot be ignored, and the available data suggest interesting and important trends, which should be explored further.”  Their last paragraph summed up their ideas:

Our analysis implies that the increase in the maximum mass of mammals over the Cenozoic was neither a statistical inevitability driven by increasing species richness nor a random evolutionary walk from a small initial size, but rather reflected processes operating consistently across trophic and taxonomic groups, and independent of the physiographic history of each continent.  We find no support for other hypotheses for the evolution of maximum body mass, including the expected increase in variance due to random divergence from a common ancestor or to increasing species richness; nor do terrestrial mammals ever approach sizes that might invoke biomechanical constraints.  The K/Pg extinction provided the ecological opportunity for mammals to become larger.  Terrestrial mammals did so in an exponentially decreasing fashion, reaching a more or less maximal size by 40 Ma as evolutionary possibilities for increasing body size were progressively exhausted and abiotic factors began constraining the upper limit.

The authors did not speculate about the cause of the dinosaur extinction.  In the abstract, their hypothesis was summed up in the statement, “the primary driver for the evolution of giant mammals was diversification to fill ecological niches, [but] environmental temperature and land area may have ultimately constrained the maximum size achieved.”
    Reporters leapt onto this idea, saying “Dino Demise Led to Evolutionary Explosion of Huge Mammals” (Live Science), “Giants among us: Paper explores evolution of the world’s largest mammals” (PhysOrg) and “Size of mammals exploded after dinosaur extinction” (PhysOrg again), New Scientist confidently explained “Why mammals grew big and then stopped,” while the BBC News teased, Dinosaur demise allowed mammals to ’go nuts.’”  The quotes refer to a statement by lead author Felissa Smith, who pretty much summed up her idea in a colloquial way: “But we had a giant Earth with nothing big on it anymore; and so I think that ecological opportunity allowed mammals to just go nuts.”  For the benefit of any culturally deprived readers, the BBC hastened to explain, “‘Going nuts’ meant land mammals diverging in shape and size.

1.  Felissa Smith, “The Evolution of Maximum Body Size of Terrestrial Mammals,” Science, 26 November 2010: Vol. 330 no. 6008 pp. 1216-1219, DOI: 10.1126/science.1194830.

Has a more vacuous scientific explanation ever been submitted in a serious scientific journal?  This is nothing more than the “If you build it, they will come” theory of evolution.  Simply provide the opportunity, and Darwin will send in his army of Tinker Bell helpers to zap the leftover animals with their mutation wands, and presto: giant mammals will emerge.  It’s like a land grant or homesteading act advertised to pioneers: “Go forth and build your towns, your factories, your civilizations!  Give me mammals to match my mountains!” The only caveat is that intelligent design is not allowed; everything must be undirected, purposeless, mindless, and random.
    Notice, further, that Smith and her co-conspirators ruled out all the other vacuous evolutionary explanations before coming up with their vacuous evolutionary explanation.  Can’t say it was “statistically inevitable.”  Can’t say it was a “random walk” in the evolutionary park.  Can’t say it was biomechanical constraints, nor “expected increase in variance due to random divergence from a common ancestor” nor due to “increasing species richness.”  No; all those vacuous, circular, question-begging Darwinian explanations are not vacuous enough.  We need a really vacuous explanation: “we had a giant Earth with nothing big on it anymore; and so I think that ecological opportunity allowed mammals to just go nuts.
    Any wonder why long ago we instituted a Stupid Evolution Quote of the Week award?
    For more nonsense about mammal evolution, see:

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