I have a dumb question, feel free to ignore. So documentaries about dinosaurs often say that non-avian dinosaurs went extinct, I was wondering which species of avian dinosaurs we know survived.
Hey! That’s not a dumb question at all - it’s a very smart one. After all, since birds are here now, and birds were around during the mesozoic, some birds had to have lived through the extinction and not died. So which ones were they?
Well…that’s not really an easy question to answer, unfortunately. The fossil record is incomplete. Really really incomplete. Really really really really incomplete. It’s as incomplete as this sentence: s ea c t . It’s that incomplete.
It’s incomplete because in order to get into the fossil record, something has to die in the right place to buried, and then it has to not get eaten or decomposed or smashed or eroded or stepped on or used as a home for little tiny mice before it gets buried, and then the stuff it gets buried in has to get turned into rocks, and then those rocks have to avoid getting shoved under a continent or melted by lava, and THEN those rocks have to come to the surface, and THEN some farmer has to notice the bones before they are eroded, and noticing bones really can be quite difficult to do when you’re on a horse going 30km/hr chasing a runaway piglet.
And it’s especially hard for birds to get into the fossil record, because they tend to be little, and have small fragile bones, and are easy to overlook when one is in hot pursuit of a bolting swine. When they are found, they tend to be really incomplete, because birds get smashed up pretty easily, a fact you know if you live in a house with large windows and have elected not to put little stickers up to make sure birds don’t smack into them and get smashed up. So when we do find bird fossils they kinda tend to be crappy.
In fact, we only have one really definite “birdy” bird fossil from the mesozoic - that is, a crown bird, or one that is descended from the common ancestor of all living birds.
(The alternative is being a “stem-bird”, which is all extinct species outside of this crown bird group, but who are closer relatives of birds than to anything else alive. T. rex, Triceratops, and Pteranodon are all stem-birds)
That one definite mesozoic bird is Vegavis iaai, a bird from Antarctica whose closest modern relatives are ducks and geese. We don’t have a skull of it, but it probably looked something like this:
(Image: An illustration of Vegavis. It looks, uh, kinda like a duck or goose. Image by Jack Wood @thewoodparable - give him a follow!)
Vegavis lived right around the end of the mesozoic era, around 66 million years ago. We don’t have evidence of it right after the K-Pg extinction, but it’s not impossible for it to have survived. Oh, and it’s worth noting that Antarctica was not all icy yet - that only really happened around 30 million years ago, when it became totally cut off from the rest of the world and the circum-polar current formed, making all the cold water circulate and just stay there instead of going elsewhere to warm up.
However, there are several other animals from around the same time that may be relatives of Vegavis. They include animals like Polarornis (also from the latest Cretaceous, and also from Antarctica) and Australornis, from New Zealand, along with a few other bits and scraps of things. What’s interesting about Australornis, however, is that it is known only from after the extinction. If it is indeed a relative of Vegavis, it would mean that this group survived the K-Pg extinction!
The placement of these genera is not certain, though, and there’s debate over whether they should be included together, or whether they are even really duck relatives. If they are, the evolutionary position of ducks would indicate that the ancestors of ratites (ostriches and friends), galliforms (chickens and friends), and neoavians (any other living bird you think of) would have had to also be around somewhere.
This would be in rough agreement with molecular clocks — which are another story - long story short, DNA evidence of modern species are used to find the differences between them, these are time-calibrated using fossils, and this lets us make an estimate of when groups diverged based on differences over time. There’s a lot more to it than that, but that’s what you need to know for now — but this would be in rough agreement with molecular clocks that give an estimate of the origin of modern birds around the Late Cretaceous.
There are some other bits and scraps of purported crown birds from the Mesozoic — a few things are claimed to be loons/divers, Graculavus has been claimed to be a shorebird/wader, Austinornis has been claimed to be a galliform, Lonchodytes has been claimed to be an albatross relative, Torotix has been claimed to be a pelican relative, and so on. I don’t find any of these especially convincing, but they are things that are out there. There’s more, too; I encourage you to check out the Theropod Database if you want to really dig into the world of Mesozoic crown-birds (or any theropods, really!).
To make a long story short - We don’t know, unfortunately, because the fossil record is really poor, and is especially poor for these animals. We have some hints as to what kinds of things might have survived, though!