First off – the dinosaurs went extinct around 65.5 million years ago (not billions) at the boundary between the Cretaceous and Tertiary periods (almost certainly) after the impact of a massive meteor at what is now Chixulub in South America (you can see the impact crater from the air – pretty cool!).
One of the results of this impact would probably have been global darkness as a result of impact dust being fired into the atmosphere, which could have lasted anywhere from 3-4 months to around 2 years, depending on who you ask. Along with this there is various evidence for large chemical changes in the oceans, such as a rapid increase in acidity. Basically, the lack of light and other big changes in the oceans would have disrupted phytoplankton communities. Phytoplankton are effectively the plants of the sea and are at the base of the marine food-chain, so if these tiny organisms start to die off, larger organisms also die off. Larger animals require more food, so only the smaller ones would survive. Larger animals (like the water dinos) would also be more susceptible to the massive shock waves caused by the meteor.
So basically, those that weren't killed by the immediate shock of the impact would probably have died of starvation in the recovery period after the impact. For earth systems to recover from such a massive disturbance probably took several tens of thousands of years, at the end of which large, vulnerable animals like the dinosaurs had died out, leaving only smaller, better suited animals behind. Basically, being large is only a benefit in times of plenty, otherwise smaller is better!
Hope that helps. References : Biology degree – I did my dissertation on changes in the ocean over the Cretacious-Tertiary boundary.
From what I know, it is possible that the dinosaurs in the oceans could have evolved to form the animals of the sea we know today. Whales and dolphins may be some of them and so because they still retain some of their characteristics as dinosaurs, they have to come to the surface to blow out water through their blow holes. References :
June 27th, 2009 | 
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What happened to the dinosaurs in the deep ocean?
I know that dinosaurs get extinct billions of years ago but what happened to the other water dinos?
Global cooling and growing earth theory.
The world ran out of higher levels of oxygen and carbon dioxide.
http://www.youtube.com/watch?v=oJfBSc6e7QQ
References :
First off – the dinosaurs went extinct around 65.5 million years ago (not billions) at the boundary between the Cretaceous and Tertiary periods (almost certainly) after the impact of a massive meteor at what is now Chixulub in South America (you can see the impact crater from the air – pretty cool!).
One of the results of this impact would probably have been global darkness as a result of impact dust being fired into the atmosphere, which could have lasted anywhere from 3-4 months to around 2 years, depending on who you ask. Along with this there is various evidence for large chemical changes in the oceans, such as a rapid increase in acidity. Basically, the lack of light and other big changes in the oceans would have disrupted phytoplankton communities. Phytoplankton are effectively the plants of the sea and are at the base of the marine food-chain, so if these tiny organisms start to die off, larger organisms also die off. Larger animals require more food, so only the smaller ones would survive. Larger animals (like the water dinos) would also be more susceptible to the massive shock waves caused by the meteor.
So basically, those that weren't killed by the immediate shock of the impact would probably have died of starvation in the recovery period after the impact. For earth systems to recover from such a massive disturbance probably took several tens of thousands of years, at the end of which large, vulnerable animals like the dinosaurs had died out, leaving only smaller, better suited animals behind. Basically, being large is only a benefit in times of plenty, otherwise smaller is better!
Hope that helps.
References :
Biology degree – I did my dissertation on changes in the ocean over the Cretacious-Tertiary boundary.
From what I know, it is possible that the dinosaurs in the oceans could have evolved to form the animals of the sea we know today. Whales and dolphins may be some of them and so because they still retain some of their characteristics as dinosaurs, they have to come to the surface to blow out water through their blow holes.
References :