The extinction event that wiped out the dinosaurs and many other species 65 million years ago is known as the Cretaceous-Paleogene extinction event. Various factors are believed to have contributed to this mass extinction, including:

a) Chicxulub Impact: An asteroid impact in the present-day Gulf of Mexico created the Chicxulub crater, releasing vast amounts of debris and dust into the atmosphere. The impact also triggered massive wildfires and tsunamis.

b) Climate Changes: The impact caused significant changes in the Earth's climate, including global cooling, reduced sunlight due to dust and debris, and changes in ocean temperatures and circulation patterns.

c) Habitat Destruction: The impact and the subsequent environmental changes led to widespread destruction of habitats, both on land and in the oceans. Many fish species may have lost their specific ecological niches due to these disruptions.

d) Food Chain Disruptions: The extinctions of various plant and animal species, including marine phytoplankton and zooplankton, disrupted the food chain and affected the availability of resources for many fish species.

e) Oceanic Acidification: The impact and the aftermath caused significant changes in the Earth's chemistry, including ocean acidification. Acidic waters can be harmful to marine organisms, especially calcifying species like some fish species.

The combined effects of these factors created a catastrophic scenario for many fish species, resulting in their extinction. While there is still ongoing research on the specific impacts on different fish groups, the Cretaceous-Paleogene extinction event had profound consequences for marine ecosystems. Certain fish taxa, such as the bony fishes (teleosts), survived and radiated after the event to become the diverse group of fishes we see today.