The extinction was characterized by the elimination of many lines of animals, including nearly all of the dinosaurs and many marine invertebrates.
The impact hypothesis was bolstered by the discovery of the 180-kilometer-wide Chicxulub crater in the Gulf of Mexico in the late 1970s which provided conclusive evidence that the K–Pg boundary clay represented debris from an asteroid impact. The fact that the extinctions occurred at the same time as the impact provides strong evidence that the K–Pg extinction was caused by the asteroid. However, some scientists maintain the extinction was caused or exacerbated by other factors, such as volcanic eruptions, climate change, and/or sea level change.
A wide range of species perished in the K–Pg extinction including the non-avian dinosaurs, mammals, pterosaurs, birds, lizards, insects, and plants. The K–Pg extinction devastated the giant marine, plesiosaurs, fish,sharks, mollusks and many species of plankton in the oceans. It is estimated that 75% or more of all species on Earth vanished.
The devastation caused by the extinction however provided evolutionary opportunities as many groups underwent remarkable adaptive radiations — a sudden and prolific divergence into new forms and species within the disrupted and emptied ecological niches resulting from the event. Mammals in particular diversified in the Paleogene, producing new forms such as horses, whales, bats, and primates.