The Nicaraguan asteroid/comet impact 65 million years ago wiped out all the dinosaurs…
…and other species, I presume.
How did species like crocodilians and other reptiles survive?
Why didn’t plesiosaurs make it like other sea-going species?
They were air breathing aquatic reptiles, and very large predators . If they survived the extinction event at all they probably ran out of food. Sharks were probably the largest survivor of the extinction, they could breathe underwater and were smaller than plesiosaurs.
If you’re referring to the impact coincident with the Cretaceous–Paleogene (K-Pg or K-T) extinction event, it occurred in the northern part of what is now Yucatán Peninsula in southern Mexico, not Nicaragua, and closer to 66 million years ago. There are numerous books covering various speculations about how the extinctions were caused by the impact event but there is no broadly accepted agreement beyond that dust kicked up by the impact resulted in occlusion of sunlight for a period lasting from a few months to decades, and possibly exacerbated by vulcanism at the Deccan Traps injecting sulphur and ash into the atmosphere.
It is not the case that the event “wiped out all of the dinosaurs”, decedents which still exist today in materially similar planforms as Aves (birds), although certainly the large megafaunal species were extincted, either directly through loss of food and habitat, or in competition with the more adaptable smaller dinosaur species and mammalian upstarts in foraging for what nutrients were available. It is also possible that the large dinosaurs were already facing serious adaptive pressures as the fossil record indicates that a number of prominent species went extinct starting several million years before the K-Pg event. The event may have just been the inciting incident that caused massive changes in evolutionary pressures.
Plesiosaurs as a class were large active hunters, and while described as “reptiles” were likely homothermic (warm-blooded), filling essentially the same keystone role today as the various species of cetaceans which essentially replaced them. As apex predators, they would have been vulnerable to a collapse of the complex marine food chain and extinction is unsurprising.
Extant Crocodylia are not much changed from their antecedents of that era, and likely survived in the same way that alligators and crocodiles survive long winters today, by large reserves of fat, entering a hibernation state, and generally just being really accomplished predators and foragers. It should be noted, however, that earlier species of Crocodylia were incredibly diverse, essentially filling the evolutionary ‘role’ of primates in recent evolutionary history in adapting to every livable habitat and some species even possibly walking upright, and nearly all of that diversity disappeared in the K-Pg extinction.
There are many books on the topic of the extinction even but Steve Brusatte’s The Rise and Fall of the Dinosaurs: A New History of the Lost World is probably the most accessible and informed of recent books.
Stranger
Wow (bolding mine).
Can you say more about this ?
Sleestak
Hmmm, not what I had hoped, but… thanks.
I believe it’s documented here…
Wile they walked upright, they never developed big brains.
Just speculating here, but two things stand out in my mind. The first is that, “size mattered”. The second is that, if you were a totally land locked creature that was dependent on food that also lived totally on land, you were probably toast, also.
However, since a large part of the earth is made up of oceans, those creatures would be able to avoid the scorching heat and would continue to have their ocean based food supply. Reptiles that lived and fed in water, like crocodilians, would have a shot at surviving because they could access food that was able to survive in water.
One thing I recall reading was that anything over about 5 pounds weight, died. The conditions for survival - being in an environment that avoided being baked, finding food until things got going agian, sheer population numbers which would imply that the 1-in-1000 or whatever surviving would find mates and reproduce… all that favoured the smaller animals, and the ones that lived in burrows, in the ocean, in the mud… Presumably scavengers had it better, since there would be plenty of pre-cooked meals around. As mentione, large predators were at a real disadvantage.
IIRC we’ve found fossil evidence of many types of ancient crocodilians with some showing superficial resemblance to modern aquatic species but also forms that resemble many other ancient and modern reptiles. That would include forms more suitable to terrestrial life with longer legs and possibly bipedal. That was long, long before dinosaurs ruled the earth and crocodilians had considerably larger competition to deal with.
It didn’t wipe out all the dinosaurs. Some dinosaur species survived and are still with us, in a much-evolved form that we call “birds”.
Bipedal is probably more accurate than upright. Think modern T rex posture, not 50s movies tail dragging upright crocs.
But yes, before the KT extinction, all three major groups of archosaurs (dinosaurs, crocodilians, and pterosaurs) were incredibly diverse. You know ahout dinosaurs and pterosaurs, I am sure, but there were endless varities of crocs too. They lived in freshwater habitats and estuaries, like modern freshwater and saltwater crocs, but there were also fully marine crocs with flippers and a tall tail for propulsion:
Fast running terrestrial crocs who hunted on land…
Some were herbivores…
And some, yes, were bipedal.
As noted, all of that diversity went away at the KT boundary.
So, the big issue wasn’t the asteroid itself. (Well, if you were close enough, that was your problem; but most of the world was not close enough).
The bigger issue was the massive cloud of debris and ash and soot that blocked out the sun and prevented photosynthesis after the asteroid strike.
On land, this was catastrophic, because plants couldn’t grow. So anything that relied on eating a lot of fresh plant matter - grazers who ate leaves and ferns for example (no grass yet) - would have died. Anything that ate those things for a living, like the big meat eating dinos, also died. The things that survived were small, and could eat things like seeds.
Incidentally, the seeds also helped land plants recover. As soon as the sun came back, seeds could grow back, even if every single adult plant of the species had died off during the extinction.
The oceans were hit just as hard. (Off hand I seem to recall that they were hit harder, but don’t quote me on that because I couldn’t confirm my memory with a quick search). Oceanic food chains all rely on phytoplankton at their base, and single celled organisms are fantastic at quickly (exponentially, even) reproducing to whatever level the available resources allow - and, when resource levels fall, just as quickly dying off to the newly sustainable levels.
Anyone who has accidentally left their fish tank light on overnight (or worse, over an out of town weekend) can tell you that light is one of those limiting resources. The asteroid did the same thing, but in reverse - and oceanic food webs crashed.
As noted, food couldn’t just survive in the ocean, because oceanic food webs rely on phytoplankton.
In fact it was freshwater ecosystems that did well. Organic material continued washing into rivers and streams, and then into lakes. Freshwater ecosystems appear ot have suffered fewer losses than either land or ocean ecosystems.
How long did that last? A few days, months, years?
I’d heard of the three major groups of archosaurs, but I had no idea how diverse crocodilians were. Fascinating.
Why wouldn’t organic material wash into oceans as well? There must have been massive tsumanis and, as the water receded, it should have drawn a lot of organic material with it. Also, rivers empty into ocean as well as into lakes. Honestly, I don’t know and am only speculating, but I wouldn’t just dismiss the oceans out of hand.
I don’t know that we know yet, precisely. We have evidence for a globally distributed ash layer, and obviously we have fossil evidence for the mass extinction that very neatly lines up with the KT boundary. We also have the Chicxulub crater whose date matches the KT boundary.
Based on these pieces of evidence, we’ve constructed a narrative that fits all available evidence; and as evidence changes, we tweak the narrative.
So we don’t necessarily know the answer to detailed questions like “exactly how long was the sun blocked for”.
Also, note that the sun doesn’t need to be completely blocked to disrupt photosynthesis enough to severely impact global ecosystems.
All that being said - I’ve seen figures for everything from a few months to a decade - the most common figure I see cited is around 2 years but that may not be correct.
We don’t know with a great deal of certainty, but it was certainly more than a few days. Probably on the order of years, maybe longer. With an explosion equivalent to millions of nuclear bombs, it’s going to take a while for the dust to settle, literally.
All this is true, but a river or even a giant lake is a drop compared to the massive bucket that is the ocean.
Certainly, life survived in the oceans. But major open water ecosystems - schools of large bodied fish, sharks and other predatory fish, and marine reptiles - these food webs are based on photosynthetic microorganisms, not on things that wash into the ocean.
Animals that live in estuaries, or who sift through ocean bottom muck, or who live on deep ocean vents - they probably survived, for similar reasons as freshwater ecosystems. But that’s a small fraction of oceanic life, especially by biomass.
Especially because some of the dust likely reached the very highest levels of the atmosphere, where it would have taken a very long time to fall back down.