Cretaceous–Paleogene extinction event

They went extinct during the mid Cretaceous correct? I know they lived more in the open ocean and early Mosasaurs in the mid Cretaceous were relatively basal and lived in coastal waters for the most part so they wouldn't be the culprit like some believe. I read somewhere that global warming was having a large effect on the oceans around that time but who knows until more fossils are discovered. More on reddit.com

Two things. Firstly, it’s important to remember that the Mesozoic Era, the ‘Age of Dinosaurs’ lasted 190 million years. The Cenozoic, or the ‘Age of Mammals’ has only lasted 65 million years. During the Mesozoic many different groups of plants and animals waxed and waned, and they did not all exist at once. Secondly, none of the marine reptiles during the Mesozoic were Dinosaurs; instead they belonged to six main groups: Sauropterygi (which includes the Plesiosauria) Thalattosaurs Ichthyosaurs Squamata (includes modern lizards and snakes, but also the Cretaceous Mosasaurs and Aigialosaurs) Crocodylomorphs Chelonia (Turtles) The latter three groups are still around, and all three groups contain marine species such as sea snakes, sea turtles, marine iguanas and salt water crocodiles. In saying that, aside from the Sea turtles, all the modern marine groups are more recently descended from terrestrial organisms. I’m also going to ignore the Thalattosaurs, because they died out at the end of the Triassic and weren’t around for most of the Mesozoic. The first major group of marine reptiles during the Mesozoic was the Ichthyosaurs. The Ichthyosaurs evolved really early on, at the beginning of the Triassic, and survived a major extinction that happened at the end of the Triassic. The Ichthyosaurs looked remarkably like dolphins, with highly streamlined bodies and gave birth to live young. During the Triassic and early Jurassic they were extremely successful. During the late Jurassic however, they went into decline, and they went extinct during the mid-Cretaceous, some 25 million years before the K/T extinction event. It is hypothesized that the rise of the ‘ray-finned’ teleost fishes led to the decline of the Ichthyosaurs; this group includes the modern pelagic fishes that outcompeted the ichthyosaurs preferred prey belemnites. Predation by larger marine reptiles, such as the pliosaurs and mosasaurs may have also lead to the extinction of the ichthyosaurs. A third hypothesis is that a major anoxic event in the world’s oceans around 91 mya knocked them out. The Plesiosaurians were the second major group of Mesozoic marine reptiles. They became successful following a mass extinction event at the end of the Triassic, which wiped out many earlier groups of marine reptiles (with the exception of the Ichthyosaurs). While there were many types of Plesiosaurians that flourished early on, two main groups became established, and stuck around for the rest of the Mesozoic; the pliosaurs and plesiosaurs. Loosely speaking, the plesiosaurs were the ‘long-necked’ ones such as elasmosaurus, while the pliosaurs were the ‘short-necked’ ones such as liopleurodon (which starred in Walking with Dinosaurs). These two groups thrived during the Jurassic and became increasingly less common during the Cretaceous. Some of the pliosaurs grew to be quite massive, and probably occupied an ecological niche similar to that of the modern orca. Despite their successes, the pliosaurs were wiped out around the same time as the Ichthyosaurs, possibly due to the same anoxic event around 91mya. The pleisosaurs were probably slow swimmers, perhaps ambush predators and lasted until the K/T mass extinction. The third main group of marine reptiles during the Mesozoic was the Mosasaurs. The Mosasaurs were descended from lizards (think monitor lizards), and were very much late comers, entering the marine environment only 20 million years before the K/T event. The mosasaurs took advantage of the vacant ecological niche left by the then extinct pliosaurs and ichthyosaurs. Despite their short period of success, they grew to massive sizes- up to 15m long, and were apex predators of the time. So by the time the asteroid strike that wiped out the last of the dinosaurs came, there were only the pleisosaurs and the mosasaurs left, in addition to the crocodilians and the sea turtles. And when the K/T event actually happened, neither of these groups were doing particularly well, because by the end of the Cretaceous the world’s sea levels had massively regressed, drying up much of the shallow continental shelves which they would have inhabited. So it’s likely that these groups were doing poorly prior to the asteroid impact, and the asteroid impact was the final nail on the coffin for these groups. Selected sources: Ancient Marine Reptiles Oceans of Kansas Book / Website Benson, R.B.J., Butler, R.J., Lindgren, J., Smith, A.S. Mesozoic marine tetrapod diversity: Mass extinctions and temporal heterogeneity in geological megabiases affecting vertebrates (2010) Proceedings of the Royal Society B: Biological Sciences, 277 (1683), pp. 829-834. More on reddit.com

In general, the idea that the object that made the Chicxulub crater is at least partially responsible for the K-Pg mass extinction is not really controversial. However, there has been some suggestion that the late Cretaceous was already a somewhat difficult time for many large vertebrates, and so this impact may have been the giant asteroid that broke the camel's back, so to speak. Arens and West 2008 suggest what they call a "press-pulse" model of extinction, wherein several of the worst extinction events throughout Earth's history are associated with the co-occurrence of both impact events and changing climates on Earth (mostly due to periods of volcanic activity). There is at least some appeal to this idea, since we know of a few other large asteroid impacts that took place in the past but which don't seem to be responsible for extinction events of anywhere close to the same magnitude as the K-Pg (e.g., the Manicougan crater in Québec, which at best is loosely associated with a minor extinction in the middle of the Triassic; source ). One finding that appears to support this idea somewhat is that many groups of dinosaurs were already experiencing negative net diversification rates (i.e., species were going extinct faster than new species evolved) by the late Cretaceous ( source ). But of course, dinosaurs are just one group of animals that suffered the effects of the K-Pg extinction, and the cause of this decline is not clear, so it doesn't necessarily imply any kind of strong extrinsic pressure. It might be the case that the asteroid impact was pretty much the sole culprit after all. On the other extreme, there is also still a minority of researchers who maintain that the K-Pg extinction was mostly or even entirely caused by volcanic effects, most notably Gerta Keller (see her 2008 paper for example). More on reddit.com

The current estimated size of the crater is 110 miles across and 12 miles deep (189 km & 20 km). How big of one do you want? This volume is roughly 66x the volume of Mt Everest. All vaporized and/or ejected in what amounts to happening in a single instant. The amount of energy required to do this is insane. The estimated energy needed is 72 teratons of tnt. An extremely high estimate (biggest nuke yield x number of total nukes) of the total yield of all nukes on the earth is 450 gigatons, or 0.45 teratons. This total amount of nukes is generally agreed to kill all life on the earth several times over. And the impact crater's energy is 160x that number. Again, happening in one instant. Also, geological effects can be seen 6000 miles away from the crater The number of fossils we find is such a miniscule percentage of the total flora & fauna that have lived, it is not surprising in the least that we haven't seen a "blast effect" pile of fossils. Assuming that such a thing exists, it won't be all that close to the epicenter. Everything within a large radius would have been vaporized, a wider radius would be burnt beyond recognition, then finally you might find what you are looking for. The extinctions are due to ecosystem collapses not as a direct result of the giant space rock hitting the earth. So yes, sea creatures can swim away, but with the greatly reduced light (all the dust in the air), the acidic rain (again, all the dust), the greenhouse effect (yup, dust, but also gases released from the explosion) it's amazing anything survived at all. To put this in a modern context, first the amount of plankton is greatly reduced due to reasons listed above. Then the krill and other things that eat the plankton start to die off because of lack of food. Then whatever eats the krill begin to starve, and so on up the entire food chain. What stands the best chance of living through all of this is whatever can eat the widest variety and widest state of food (omnivores & scavengers). Hebivores have a significantly better chance than dedicated carnivores. Also size plays into this as well, the smaller you are, the less food you need, the more of you that can survive on a now very scarce resource. Again, lets look at a modern context. After a forest fire, what happens? First plants need to reestablish themselves, then it is the inscects and small critters (mice etc) and finally the bigger critters. The added complication 66 mya is there was no safe place for the larger critters to wait out the regrowth. More on reddit.com