April 11, 2012
Somewhere, out in the interstellar void, there may be a planet inhabited by hyper-advanced dinosaurs. At least, that’s what a new paper by Columbia University chemist Ronald Breslow says.
This morning, friend and fellow science writer David Dobbs forwarded me an American Chemical Society press release titled “Could ‘advanced’ dinosaurs rule other planets?” Since I was still a little bleary-eyed at the early hour, I thought I had read that wrong. But I saw it right the first time. “New scientific research raises the possibility that advanced versions of T. rex and other dinosaurs—monstrous creatures with the intelligence and cunning of humans—may be the life forms that evolved on other planets in the universe,” the item explained.
I couldn’t help but wonder if the pronouncement was inspired Planet of Dinosaurs—the awful 1978 film about a futuristic space crew stranded on a planet stuck in the dinosaurian heyday of the Mesozoic. But the paper itself suggests a different origin for what is ultimately a fossil-based non sequitur.
Breslow’s paper is primarily concerned with why the biochemical signature of life on earth is so consistent. Molecules such as amino acids, sugars, DNA and RNA exist in one of two possible orientations, left-handed or right-handed. Instead of showing a mixture of both forms, biomolecules typically come in only one form: Most sugars have a right-handed orientation, while most amino acids exhibit a left-handed orientation. Why life on earth should exhibit these particular arrangements and not the other possible orientations is a mystery that goes back to the origin of life itself.
One idea, favored by Breslow, is that meteorites carried specific types of amino acids and other organic flotsam to earth around 4 billion years ago. This is an extension of the idea that life here was “seeded” by comets, asteroids or meteorites. The origin and subsequent evolution of our planet’s flora and fauna would be constrained by the characteristics of the biomolecules that gave life a jump-start.
None of this has anything to do with dinosaurs. (The first dinosaurs, as far as we know, originated a scant 230 million years ago.) Yet, in closing, Breslow briefly speculates on what alien creatures might look like—perhaps possessing the opposite biochemical orientations of life on earth. “Such life forms could well be advanced versions of dinosaurs,” Breslow writes, “if mammals did not have the good fortune to have the dinosaurs wiped out by an asteroidal collision.” Whatever such space dinosaurs might look like, though, “We would be better off not meeting them,” Breslow warns.
As much as I’m charmed by the idea of alien dinosaurs, Breslow’s conjecture makes my brain ache. Our planet’s fossil record has intricately detailed the fact that evolution is not a linear march of progress from one predestined waypoint to another. Dinosaurs were never destined to be. The history of life on earth has been greatly influenced by chance and contingency, and dinosaurs are a perfect example of this fact.
Prior to 250 million years ago, the synapsids—our ancestors and relatives—were the dominant creatures on land. But the apocalyptic extinction at the end of the Permian Period eliminated most synapsid lineages, in addition to many other forms of life. This clearing of the ecological slate is what allowed a different group of creatures to proliferate. Early archosaurs, or “ruling reptiles,” included the archaic forerunners of crocodiles, pterosaurs and dinosaurs, in addition to various groups now extinct, and these creatures dominated the Triassic.
Despite what has been traditionally told, though, the dinosaurian branch of the greater archosaur family tree didn’t immediately out-compete its neighbors. Eoraptor and Herrerasaurus were not the Triassic terrors they were cast as during the mid-1990s. For the most part, Triassic dinosaurs were small, rare, marginal parts of the ecosystems they inhabited. It was only after another mass extinction at the end of the Triassic, around 200 million years ago, that the competitors of early dinosaurs were removed and the reign of the dinosaurs truly began. “[T]here was nothing predestined or superior about dinosaurs when they first arose,” paleontologist Stephen Brusatte and colleagues wrote in a massive review of dinosaur origins, “and without the contingency of various earth-history events during the early Mesozoic, the Age of Dinosaurs might have never happened.”
Even if we ignore all the major evolutionary events prior to 250 million years ago, the fossil record demonstrates that the origin and rise of the dinosaurs were heavily influenced by two catastrophic extinction events. Had the Permian or Triassic extinctions not happened, there is no indication that dinosaurs would have evolved or come to rule the world—unforeseen events drastically shaped evolutionary history. Why on earth would we expect such patterns to be played out in just the right sequence on another planet? To say that there are dinosaurs on alien worlds presupposes that there is an irresistible direction that all life follows, and that dinosaurs are an inevitable actors in the drawn-out drama. There is no evidence that this is so.
The strange thing is that Breslow acknowledges the role of mass extinctions in evolutionary history. His speculative space dinosaurs are supposedly “advanced” creatures which were spared from oblivion. Other writers have toyed with this concept before, the most famous example being Dougal Dixon’s The New Dinosaurs. Sadly, though, Breslow did not include any illustrations or offer specific details about the sort of uber-dinosaurs he has in mind.
Yet, what we know of the history of life on earth dispenses with the need to imagine such fantastic, alien creatures. Dinosaurs still exist—birds are a surviving dinosaur lineage that has exploded into a beautifully array of disparate forms. And some birds, such as ravens, are quite intelligent, so we don’t have to wonder about what an especially smart dinosaur would have looked like. The reign of the dinosaurs may have ended 66 million years ago, but their 230-million-year-old legacy continues to this day. A simple shift in our understanding of dinosaur evolution has rescued the beloved creatures from extinction. I deeply doubt that there are dinosaurs in space, but I am glad that at least one variety of feathered dinosaur remains with us here.
Breslow, R. (2012). Evidence for the Likely Origin of Homochirality in Amino Acids, Sugars, and Nucleosides on Prebiotic Earth Journal of the American Chemical Society DOI: 10.1021/ja3012897
Brusatte, S., Nesbitt, S., Irmis, R., Butler, R., Benton, M., & Norell, M. (2010). The origin and early radiation of dinosaurs Earth-Science Reviews, 101 (1-2), 68-100 DOI: 10.1016/j.earscirev.2010.04.001