What is a dinosaur?
A child could answer that question. It’s a huge animal that died out millions of years ago. As a child I could have named brontosaurus, triceratops, stegasaurus and, of course, Tyrannosaurus Rex, just as I could name nine planets in order. I would have included pteranodon. Then I read the “very basic concept” that “pterosaurs are not dinosaurs”, but birds are, so decided to look up a more scientific answer. Much of this comes from Wikipedia, which I will call Wrong.
I did not understand the first sentence, Dinosaurs are a diverse group of reptiles of the clade Dinosauria, because I did not know what a “clade” was. A clade is a common ancestor and all its descendants. The ancestor can be an individual, a population, a species, a genus, etc, as recent as you like: mammals, placental mammals, primates and great apes are all clades.
Because dinosaurs, properly and scientifically speaking, are a clade, birds are dinosaurs. To me as a child, the idea that a chirpy little thrush was a dinosaur would have made no sense at all, and as I write now I am wondering whether to still assert that common sense notion. (“Common sense” is what everyone knows, or almost everyone, even if it is wrong.) It makes sense to me to imagine a group of organisms sharing a set of characteristics, and one of those characteristics was Died Out at the end of the Cretaceous period or Mesozoic era. As a child I would have known the names of a few periods or eras, but not like my autistic friend the names of all eras and periods in order. And not the Hadean: the usage was only coined in 1972, and even now the International Commission on Stratigraphy calls it “informal”.
Still, the end of the dinosaurs, definitely the end of the Cretaceous, was the end of Interesting prehuman life for me, when I was a child. Eohippus, or even a sabre-toothed tiger, was not a patch on Tyrannosaurus Rex. I am unsure how widespread such a feeling is. I am interested in everything, but some things more than others. You can easily buy model tyrannosaurs for wee bairns to play with, and the bairns play enthusiastically, going
as loudly as they can. (“Easily buy”- I meant, in shops! How old-fashioned my thinking is!) I only recently learned that Stegosaurs were long extinct before Tyrannosaurs arose, as that fact would not have interested me. As a child they were both creatures of fantasy, and that fantasy continues in adulthood though it is less important to most adults than to children.
When I was a child the theory that the Chicxulub impact had ended the dinosaurs (even excluding birds) had not become widely accepted, and now I understand it is scientific consensus with some sceptics still challenging the evidence and the reasoning. That too, an asteroid almost destroying life on Earth, is a powerful image, widely known outside the scientific community as it speaks to people, a dreadful horror beyond all others.
Are Pterosaurs dinosaurs? If I had had a rubber toy pterosaur it would have flown in my hand over the tyrannosaur attacking the stegosaur, and I would have conceived of them as one class of animal- big, extinct. Pterosaurs were an order existing from 228-66mya. (Million years ago, but you knew that.) Dinosaurs were named by Richard Owen in 1842, after evolution, the changing of species through strata, had been observed, but before Darwin had published the theory explaining evolution by natural selection. I don’t know if Owen was aware of pterosaurs, or whether he would have called them dinosaurs, but now dinosaurs are Ornithischia and Saurischia, not including Ichthyosaurs either.
So, I use the word “dinosaur” much as I would in my childhood, from a vague understanding of time, ending 66mya, starting, I dunno, maybe 200mya. Scientists are researching the exact origin now, of the clade. Clades are clearly more important to them than to me. I find the idea of a “Kingdom” useful: plants, animals and fungi are Kingdoms. There is another Kingdom, Protists, being eukaryotes not fitting in the other three, and Wikipedia tells me Some recent classifications based on modern cladistics have explicitly abandoned the term “kingdom”. I wrongly but belligerently include ichthyosaurs and pterosaurs as dinosaurs, and find “Protist” a useful new word even if it does not describe a clade. I might even (shock!) treat “pterosaur” and “pteranodon” as interchangeable.
Classifications change as people find out more, and the research continues. If Richard Owen returned to life now, I imagine he might support the cladistic definition of dinosaur, to include birds not pterosaurs, after it had been explained to him. Common sense goes from imprecise understandings and old ideas which are now discounted. I am happy with the idea of a dinosaur as a potent myth of a terrible lizard, because I do not systematically follow the latest research. I am delighted with occasional striking ideas, such as scientists examining fossils under the microscope and postulating what colours dinosaurs were.
I take a middle position between common sense and “modern cladistics”, myth and imagery and precise classification. Both are useful at different times. A tomato is a fruit and a vegetable. I see the point of asserting that birds are dinosaurs, but I will stick with the common idea of dinosaurs as Jurassic or Cretaceous reptiles, including pterosaurs, for most purposes.
I am writing about this partly because people were worried when I did not post for four days. I had not posted because I felt a bit down: less interested in posting, and not wanting to write too many “Oh god life is awful” posts like my recent My Life, and Trans Politics, posts seemed to me. I am interested in it. I have now formed a view, that a precise scientific understanding and an imprecise general misunderstanding of the concept “dinosaur” both have value.
I wanted a cheerful Gericault to contrast with yesterday’s picture, but see Gericault was not the most cheerful painter. I notice the wikimedia file looks much better when the screen is too bright for my eyes, so I have brightened it.