“If history repeats itself, I am so getting a dinosaur.” – Anonymous
The fact that you are sitting there playing fantasy football or tweeting about last night’s disastrous date over Ramen noodles has very little to do with your evolutionary fitness. Don’t take it personally. You, my friend, are a mammal (well, most of you at any rate), and the evolutionary success of mammals is a fluke, a role of the dice, a spin of the wheel, and a great cosmic joke where the punchline is a series of mass extinction events that wiped dinosaurs off the face of the earth and made room for our furry little ancestors. Until then, dinosaurs pretty much ruled the roost and it looked like they would inherit the earth. If a big, freaking space rock hadn’t unceremoniously ruined their afternoon by crashing into the planet and killing them all, odds are the intelligent species on the planet would now be dinosauroid (the dominant terrestrial vertebrates from about 231 million years ago until the Cretaceous-Paleogene extinction event 66 million years ago that killed 75% of life on Earth) or archosauroid (dinosaur like creatures that lived from 200-250 million years ago and were similarly wiped out by the Triassic-Jurassic extinction event roughly 200 million years ago, making room for dinosaurs to take over). It’s a matter of precedence. Dinosaurs were here first and in the words of University of Alberta paleontologist Phil Currie, “They were the superlatives; they were the biggest, the heaviest, the meanest, the longest. You name it, dinosaurs were it.” Basically, mammals wouldn’t have stood a chance in a world where terrible lizards trod the boards. If it weren’t for the grand astronomical smackdown of the Cretaceous-Paleogene extinction event, there wouldn’t have been an ecological niche for any mammal much larger or more sophisticated than a rat or a boy band. Given there might be silicon-based monstrosities lurking out there in the universe, but they’ll be more interested in talking to your breast implants than to you. Thus, you can bet your bottom dollar that the first carbon-based extraterrestrials we meet will be lizards, and will be shocked to discover that you are not, since most every other alien they know is probably a lizard too.
Although imagining all manner of exotic non-carbon life forms is a fun exercise, the simple fact is that carbon is where it’s at when it comes to biochemistry, and it is not unreasonable to assume that this generally holds true elsewhere in the universe. Nobel Prize-winning biologist George Wald observed that extraterrestrial life “would mean something very like the life we know. Not the same creatures. We did not have the same creatures on Earth during its past as live here now. But life anywhere in the universe, I have been convinced for years, must be made of the same elements that principally constitute it here—carbon, hydrogen, nitrogen, and oxygen. Those four elements constitute about 99 percent of living material on the Earth, and I think are likely to come out that way wherever life exists, because I believe it to be literally true that no other elements in the Periodic System have the properties that will do that job. So I tell my students: learn your biochemistry here and you will be able to pass examinations on Arcturus” (Berendzen, 1973, p15-16). Primitive life evolved on Earth about 3.5 billion years ago in the oceans, but it wasn’t until about 360 million years ago that the first funky fishes started exploring what life was like on the shore, and only by 300 million years ago were amphibious vertebrates making the first forays into a semi-dry lifestyle. These brave amphibians eventually gave rise to all the vertebrate land animals, both alive and extinct, including our pals the archosaurs and dinosaurs. While being a vertebrate seems to be fairly important to developing complex intelligence, being a mammal is not really a prerequisite. The genus Homo showed up to the party late at around 2.5 million years ago, and what we would regard as behavioral modernity only appears about 50,000 years ago. Luckily we haven’t been hit by another sizable asteroid in that period of time or else some other fortunate vertebrate would be having this conversation. If we go with the Drake Equation’s guesstimate of roughly 40 million civilizations in the Milky Way Galaxy (all of course, being suspiciously quiet so as not to attract attention to themselves), it would be unreasonable and impolite to assume that global-level extinction events are a routine occurrence or standard operating procedure, unless of course existence is truly run by a set of cruel desert gods that amuse themselves by destroying worlds and wiping out species (which according to most of our religious texts is precisely what they get off on; then again we only have 50,000 years of experience with modernity, so what do we know).
Given that chemistry works pretty much the same out there in the great beyond as it does here, and given that dinosaurs seem to have an evolutionary leg up, so to speak, if they can manage not to get flattened by the flotsam and jetsam that’s hurtling through space, odds are that most aliens out there are going to be some variation on a smart dinosaur, rather than something more or less furry like us. We like to invent all sorts of reasons why only a bipedal mammal could have developed what we regard as higher intelligence, but really all it seems to take is reasonably big brains and opposable thumbs. Not long after, you get a space program, and that’s all she wrote, except for the crop circles and anal probes. Here’s a rule of thumb. If you happen to encounter something that looks mammalian, he’s probably just a mundane terrestrial monster. If you run into a bipedal lizard with a sense of fashion, experimental inclinations, and a sweet ride, you’re probably looking at an alien. Dinosaurs were cool. Dinosaurs were hip. And dinosaurs were here before us. This is probably true on countless other planets, and it’s just luck of the draw that they got walloped by a gigantic asteroid in this insignificant corner of the galaxy, although, as a descendant of the mammals that took advantage of this stroke of misfortune, let me just say “thanks, Universe”. We, of course, see everything in terms of being awesomely hominid, since our reference point only dates from about 2.5 million years ago and we are terribly enamored of our own species. As Robert T. Bakker said in his book The Dinosaur Heresies, “The public image of dinosaurs is tainted by extinction. It’s hard to accept dinosaurs as a success when they are all dead. But the fact of ultimate extinction should not make us overlook the absolutely unsurpassed role dinosaurs played in the history of life.” Unfortunately, among our hypothetical dinosaur aliens, a mammal probably amounts to little more than super-sized snack food. This does not bode well for first contact. Better keep some raw meat handy.
Berendzen, Richard, Boston University, and United States. National Aeronautics and Space Administration. Life Beyond Earth & the Mind of Man: a Symposium. Washington: National Aeronautics and Space Administration, Scientific and Technical Information Office, 1973.
What makes you think that Earthly biological groups will be found at least in similar form on other planets? Ultimately it boils down to luck that the dinosaurs succeeded in the first place, their success was built on the success of those organisms that came before. Change one thing and you get a butterfly effect. If you’ve got a completely different planet with different atmospheric, tectonic, solar, tidal, etc. conditions then it is deeply naive to assume that the same sorts of creatures will succeed.
What about a world where reptiles or reptile equivalents never arose in the first place? Maybe the forms of life on Earth are just one possible set of varieties and on alien planets there are forms of life as different to mammals and reptiles as birds are to arthropods. Think bigger, don’t just assume Earth life is representative of all life.
Thank you for your observations. They are interesting and well reasoned. Just not as funny : )