how did they become extinct?
By catastrophic events such as the massive asteroid impact that caused the Chicxulub crater.
Late Cretaceous
Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater, in combination with increased volcanic activity, such as that recorded in the Deccan Traps, both of which have been firmly dated to the time of the extinction event. 
who was alexander cameron rutherford? Canadian lawyer and politician where was he born? On a  dairy farm near Ormond, Canada West what was his connection with alberta? He was elected university's Chancellor in 1927. was he involved in any ontroversies? Yes, in a Railway scandal. whom did he marry? Mattie Birkett where was he elected a premier? Alberta where is this place located? Canada are fossils found in this place of canada? Yes, fossils of Late Cretaceous dinosaur. where were they found? UNANSWERABLE
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Late Cretaceous [SEP] Cretaceous–Paleogene mass extinction
Mosasaurs, plesiosaurs, pterosaurs and many species of plants and invertebrates also became extinct. Mammalian and bird clades passed through the boundary with few extinctions, and evolutionary radiation from those Maastrichtian clades occurred well past the boundary. Rates of extinction and radiation varied across different clades of organisms. Many scientists hypothesize that the Cretaceous–Paleogene extinctions were caused by catastrophic events such as the massive asteroid impact that caused the Chicxulub crater, in combination with increased volcanic activity, such as that recorded in the Deccan Traps, both of which have been firmly dated to the time of the extinction event. In theory, these events reduced sunlight and hindered photosynthesis, leading to a massive disruption in Earth's ecology.