Suppose you are looking at dinosaurs…
What do you mean you have not seen any dinosaurs recently? Do you not have any children, grandchildren, nieces, nephews, or little neighbors, or do you not know someone else who has children, grandchildren, nieces, nephews or little neighbors? Surely, you know someone who has access to a young person, and it is summertime, therefore, you can take them to a science museum or natural history museum or for heaven’s sake a Toys-R-Us to look at some dinosaurs.
As I was saying…
The collection you are looking at is probably not all, in fact, dinosaurs. As a general rule, dinosaurs in the Mesozoic age, aka the “Age of the Dinosaurs,” did not swim or fly. Those giant things in the water that looked like a turtle crossed with a giraffe? Or had teeth and flippers bigger than your head? Not dinosaurs. The thing with the membrane stretched across one finger, depicted gliding across the hundred foot fern trees? Not dinosaurs. This is true, even though most museum exhibits and reference books will include pterosaurs, plesiosaurs, and mososaurs. They might as well have included crocodiles or gekkos while they were at it.
Nothing Like a Good Ol’ Antorbital Fenestra
When I was back in college studying a little paleontology… (to give myself a break from calculating the internal rate of return on bond coupons and discussing the finer points of Edmund Spenser’s poem The Faerie Queen…UGH! just typing that makes me itch to think about something more interesting like what defines dinosaurs)… back then, dinosaurs were defined by two bone characteristics.
First, they had an extra hole in their head not used for eyes, nostrils or ears, which was called the antorbital fenestra. I just like to say that, and to coax a six year old into repeating it. Fenestra is such a good Latin word; it means window. One of my favorite words is defenestration. It means throwing something/someone out of a window. James Bond is good at defenestration.
Dinosaurs, as I was taught, had this antorbital fenestra between eye and nostril; you can point it out if there is a dinosaur skeleton handy. Scientists think it was to hold all the extra jaw muscles necessary to bite down on big things, like other reptiles. They also had hip bone structures that allowed their hind limbs to descend straight down, which allowed them to be able to walk upright. That distinguished them from prehistoric crocodiles and other reptiles that slithered.
However – and here is a shocking truth about dinosaurs and paleontology and science in general – the information about dinosaurs has changed in the thirty years since I first took Paleontology 2A. We know more, and the facts in my brain are no longer perfectly correct.
Classification Back in the Day
As information about the fossil records and about how DNA works has advanced dramatically since 1980, the classification system has changed to accommodate increasing levels of sophistication. I was taught the Linnean system – Kingdom, Phylum, Class, Order, Family, Genus, Species. There was even a mnemonic to remember it: King Philip Came Over From Great Spain. Humans, for example, were classified as Animals> Vertebrates> Mammals> Primates> Man> Homo> Sapiens.
Since the 1990s, though, classification structures have changed to develop trees with a lot more branches, which are now called clades. Wikipedia says clade is defined as “a group of organisms believed to have evolved from a common ancestor, according to the principles of cladistics…” which seems to me a bit self-referential. Except it makes sense; a clade is a description of the branch of the tree where the branches have common features. That allows the branches have branches – Suborders, SuperFamilies, SubFamilies, Tribes, and on and on.
It used to be Animals>Vertebrates> Reptiles> Dinosauria> Saurischia> Tyrannosaurus Rex. It’s now much longer: Animals> Vertebrates> …hold on to your hats for this… Sauropsids (which includes all Reptiles)> Eureptilia> Romeriida> Diapsid> Archosauromorpha> Archosauriforms> Archosauria> Avemetatarsalia> Dinosauromopha> Dinosauriforms> Dinosauria> Saurischia> Theropods> Tyrannosauridae> and then Tyrannosaurus Rex.
Don’t you just want to hear Julie Andrews sing that?
What kind of mnemonic would you need for that? We never would have survived memorizing all the categories. However, because we now have computers and have unpacked many of the mysteries of DNA, we can allow tree branches of classification to expand vastly in order to be clearer about the distinction between one group and the next.
The other thing we have a lot more of, thirty years later, is bones to look at. This is the other defining feature of paleontology. What you know is based on what you find. In 1842, when Sir Richard Owen coined the term dinosaur, there weren’t as many skeletons around. With so many more bones available now – and even discovered in the last few decades particularly in China and other previously off-limits locations – there are a lot more conclusions that can be drawn from the evidence. (Another fabulous example is the story of Luis and Walter Alvarez discovering that a meteor killed off the dinosaurs; I’ll save that for a future blog.)
Now if you look up what defines dinosaurs, there’s a list of eight separate unique skeletal characteristics with Latin names that are not as fun to coax a six year old into saying, so I will refrain from listing them all. The key one, to my mind, is still that they were able to walk upright. Owen’s term “Dinosaur” means “terrible lizard,” but dinosaurs are not lizards because lizards are not bipedal (in addition to the many other characteristics).
The Really Shocking Truth About Dinosaurs
Which brings me to the jaw-dropping notion that I can now reveal. Birds are a branch of the dinosaur clade. For years, scientists have theorized birds evolved from dinosaurs. But the science has gone further now that so many more dinosaur and dinosaur/bird skeletons have been discovered. Birds are not just related to or evolved from or share characteristics with….
Birds ARE Dinosaurs.
Since the mid 1980s, they have been regrouped, and are now classified under the clades Avemetatarsalia and Saurischia, which means they sit on the same branch of evolution as Tyrannosaurs. And, more to the point, they are no longer their own Class. When I think of the main groups of animals that I learned way back when – Fish, Reptiles, Amphibians, Mammals, Birds – Birds are no longer their own group. (And, oh wow, Fish aren’t their own group either as I just discovered, which … let’s not even go down that rabbit hole).
Birds are a sub-sub-sub-sub to the umpteenth group of Reptiles. When you look up Dinosaurs today, they are described as either non-avian dinosaurs, which are all extinct, or avian dinosaurs, which are still living. Squawking in your backyard. Soaring over the rooftops. No wonder snake tastes just like chicken.
Maybe today is a good day to have roast dinosaur for dinner. That’s what you should tell the nearest six year old.