Dinosaur extinction

Yes. And it wasn’t just the non-avian dinosaurs that died out 65M years ago. For example, Pterosaurs. Most people probably think they are dinosaurs, but they’re not.

Yes. Other large Mesozoic reptiles that were not dinosaurs include the ichthyosaurs, plesiosaurs, and mosasaurs (the latter actually being giant aquatic lizards). Even earlier, the finbacks like Dimetrodon were actually more closely related to ancestral mammals.
The closest living relatives to birds are crocodilians. Crocodiles are more closely related to hummingbirds than they are to lizards.

Oedipus means “swollen-foot.” His feet were tied when he was abandoned at birth, hence the name.

I know that “ichthyosaur” means “fish lizard”, but are they accurately called aquatic lizards as opposed to aquatic reptiles?

Ichthyosaurs and plesiosaurs (including elasmosaurs and pliosaurs), along with a couple of earlier forms, are in the group called Euryapsida, which is likely a lump-together pseudo-taxon within the diapsids. They were not “lizards” in any sense except the use of “-saur” in the nomenclature. The Mosasauridae, on the other hand, were actually lizards, allies of the monitors (Varanidae) in the strict sense, and in fact part of the monitors (Varanoidea) in the broader sense.

Possibly as brief as one day.

Indeed. While scientists have not established whether the “dinosaurs” all died out immediately after the Chicxulub impact or whether the following impact winter did them in…and how long that took…it’s possible the dinos were all killed on Judgment Day. The event was that violent – the earth’s atmosphere was set on fire worldwide; molten rock was thrown completely around the earth; a huge cloud of acid spread out from the impact; it sent mega-tsunamis miles inland in North and South America; it possibly spawned “Hypercanes” that sucked the ozone layer away while ravaging the land with 500-mile-an-hour winds; some sources have estimated the shockwave was heard by every living animal on earth. That the sun was blotted out for years certainly would have finished the job, but it’s possible the impact itself did it. These things are bad for one’s health.

I was just referring to the mosasaurs when I said they were lizards, as Polycarp has explained.

:smack: I mixed up the meaning of “latter” with “former”.

One theory I’ve heard is that at the time of the K-Pg extinction (the Tertiary is out as an official period), neornithines tended to occupy mainly seashore habitats. Like modern seagulls, they were probably very adaptable generalists willing to eat anything they could. Other coelurosaurian lineages like the enantiornithines and deinonychosaurs had more specific dietary requirements. So neornithines were more likely to survive a mass extinction.

The other thing people tend to ignore is that dinosaur diversity was already at something of an all-time low. This might be due to some faunas not becoming fossilized, but I can think of only a handful of spots in the world where we can demonstrate dinosaurs still existed in force, and even there, not with the kind of species diversity you saw during the rest of the Mesozoic. The major hotspots for dinosaurs at the K-Pg were Western North America (Hell Creek Formation and equivalent strata) and the Maevarano formation of Madagascar. That’s pretty much it for latest Maastrichtian dinosaurs. All the dinosaurs present were either large to quite large, with a handful of small “raptors” and some birds. Even there, discoveries are threatening diversity. The Hell Creek wiki page lists 5 species of pachycephalosaur, but at least two of those are probably juvenile forms of Pachycephalosaurus. Of the ornithopods, one of those Edmontosaur species is reliably known only from older strata and Anatotitan is almost certainly a synonym of the other, leaving only one duck-bill present. Torosaurus has recently been shown to be a growth stage of Triceratops. Nanotyrannus is almost certainly a juvenile T. rex. That leaves you with two big herbivores, one big carnivore, several mid-sized herbivores and carnivores, and a bunch of birds. And this is the most diverse dinosaur assemblage that we know of at the K-Pg boundary.

Long story short, it looks like non-avian dinosaurs were already restricted to somewhat relict populations by the time the asteroid finished them off. Relict in the sense of modern marsupials where they’re totally dominating one small continent-sized land mass, but still not the worldwide, specious phenomenon of the late Jurassic and early Cretaceous.

I don’t see any reason to prefer that conclusion over that of dinosaurs remaining worldwide until their extinction. No one has reported a Maastrichtian terrestrial fauna that completely lacks dinosaurs, have they?

I’m not sure, but there is one where only one species of dinosaur has been found (Carnotaurus) compared to several mammals, the La Colonia Formation of Argentina.

What about the theory that dinosaurs survived in Antarctica long after the K-T event? How crackpot is it?

The interesting thing about the Cretaceous period is that the difference in temperatures between the equator and the poles was significantly less than it is today. If we had the same conditions today, you wouldn’t see folks from Canada heading south to Florida for the winter because the temperatures in Canada and Florida weren’t that much different. Antarctica wasn’t covered in ice. It was a forest.

The big question though is when did Antarctica get cold and icy.

I went poking around on the net, and according to a chart I found, Antarctica started to cool about 70 million years ago. The author of that chart had an arrow pointing to the first ice sheets in Antarctica as pre-dating the K-T event. These weren’t permanent ice sheets (according to the chart that only started 40 million years ago) but I doubt that dinosaurs would survive for long in an area that got even temporarily covered in ice.

This isn’t my area of expertise (I’ve just read a lot about it because it interests me), so I don’t know how much debate there is over exactly when Antarctica started to cool. If the cooling didn’t start until after the K-T event then it’s possible there were dino populations there for a short while at least. They have found late Cretaceous dinosaurs in Antarctica, so who knows.

I personally would say while there isn’t any evidence to support it yet, your theory isn’t really a crackpot theory at all.

I would say it’s spot-on.


It’s not my theory; I remember reading about it somewhere. Supposedly, various non-avian antarctican dinosaurs had already adapted to relatively cold and dark environments before the K-T event, improving their chances of surviving the resulting “nuclear winter”. These creatures survived there, isolated from the rest of the world, until the continent wandered south to the pole some 40 million years later, and the glaciers finished them off.

From what I understand, this seems to be based on a few fragments of dino fossils found somewhere they shouldn’t have been.

I’m not sure it’s surprising. Weren’t most avian lineages wiped out at the KT event also?

Most lineages of most species were wiped out during the K-T event. It wasn’t like some sort of neutron bomb, killing all the dinosurs while leaving mammals and birds standing. The vast majority of all living creatures on the planet died; those that survived were the rare exceptions.

I went looking for a table I remembered about the impact of the K-T event but couldn’t locate it. I do remember that marine protists (or at least the ones like diatoms and radiolarians that had fossilizable hard parts) were, um, decimated in the popular sense of the term – few species survived, though they radiated rapidly during the Paleocene. One number from the table I do recall is that 75% of marsupial families were wiped out – only the Didelphidae survived.

I do see your point, but that’s not quite true. The K-T extinction event picked on certain types of species much more than others. Some families managed to survive almost completely intact.

Everything big died. Period. Nothing over a few hundred pounds survived. This isn’t surprising, since when food gets scarce, the big guys that need the most food die first.

All non-avian dinosaurs died. All pterasaurs and plesiosaurs died. Some folks say the pterasaurs were already gone before K-T though.

50 to 60 percent of plant species died.

Frogs and amphibians however survived almost intact. A lot of lizards, turtles, and crocodilians survived.

80 percent of cartilage type fish survived. 90 percent of bony fish survived.

I haven’t been able to find a good cite for birds, but the best numbers I’ve seen so far indicate about 50 percent of their species survived. A lot of the surviving species of birds lived in wet marshlands and could dive under water for protection, or made burrows or nests of some sort that could protect them.

It is interesting, as was previously mentioned, that many bird species survived but many small dinosaur species did not. Maybe the little dinos didn’t hide in nests and such well enough. Who knows.

Molecular data suggest that quite a few avian lineages survived the KT event. That goes for mammalian lineages as well.