So… if we tell you HOW? … will you actually retain the information? … so it isn’t such a puzzling outstanding question for you? There’s not much point in maintain a discussion with you if you have a long-standing track record for not remembering anything anyone ever shares with you about your questions concerning Evolution.
The arrival of the Dino-killing asteroid appears to have struck most heavily on creatures larger than a certain size (by weight). Generally speaking, the Asteroid theory is supported by the fact that huge forests of evergreens (in North America particularly) were replaced with deciduous trees, which were not what the vegetarian dinosaurs of North America ate.
But let’s compare 3 different large extinctions:
LARGE ANIMAL-KILLING BY ASTEROID (Most Animals > 100 Pounds)
“Mammals and dinosaurs coexisted for approximately 140 million years, during which time dinosaurs dominated the majority of large terrestrial vertebrate niches. This extinction most likely was the result of a large meteor impact that eliminated over half of all species on the planet. Mammals survived that extinction event relatively well, probably because the majority of Mesozoic mammals were species with short generation times and large litters.” (“During the Tertiary period, mammals underwent a rapid adaptive radiation , filling niches similar to those vacated by dinosaurs.”)
GREAT COOLING OF THE EOCENE
“A second major extinction event occurred during the Eocene-Oligocene period, 30 to 35 million years ago. This extinction was the result of global cooling due to changes in ocean current patterns. Prior to this period modern families of mammals comprised only about 15 percent of the mammalian fauna; after cooling modern mammals made up more than 50 percent of the fauna at the family level.”
LARGE MAMMAL EXTINCTION BY HUNTERS (Greater than 100 Pounds)
“The third mass extinction event began around 15,000 years ago and is still ongoing. Large species (mammoths, ground sloths, horses, camels, and lions) were more adversely impacted by the most recent extinction event than other taxa. In the twenty-first century, there are only about a dozen species of large mammals (over 100 pounds) in North America. As recently as 11,000 years ago there may have been three times that number.”
This page treats the conundrum of bird survival during the KT event:
“The survival of birds is the strangest of all the K-T boundary events, if we are to accept the catastrophic scenarios. Smaller dinosaurs overlapped with larger birds in size and in ecological roles as terrestrial bipeds. How did birds survive while dinosaurs did not?”
"Birds seek food in the open, by sight; they are small and warm-blooded, with high metabolic rates and small energy stores. Even a sudden storm or a slightly severe winter can cause high mortality among bird populations. Yet an impact scenario, according to its enthusiasts, includes “a nightmare of environmental disasters, including storms, tsunamis, cold and darkness, greenhouse warming, acid rains and global fires.”
It should be remembered that this narrative is focusing on the niche where smaller dinosaurs, the same size as larger birds, died off while the birds did not. Above this niche, the answers are easier. Large vegetarians died when their forests died. Meat-eaters wouldn’t have perished until all the large plant eaters were gone.
Housekeeping: @T_aquaticus (and @Christy) - - I have been most dutiful about respecting the presumption that there was once placental creatures on Australia that went extinct before the Marsupials arrived. But based on the article above, it appears that any “placental-like” creature that might have gone extinct on Australia was a “precursor” rather than an official Placental mammal. Now I don’t have to step so gingerly on the Australia topic!
@Edgar, as for this question:
Knowing where Whales come from is part of the refutation to the assertion at the top of this thread!: The Fossil Record does not fit best with progressive creation - - precisely because of Whales in the world’s oceans and Marsupials in Australia!