Our ancestors at the time were small shrew-like creatures. The extinction event occurred in several phases. The immediate impact directly devastated the local region and created a mega-tsunami that spread yet more destruction. It also kicked up a huge amount of debris which then re-entered Earth's atmosphere around the world over the course of the next roughly hour or so. This would have heated most of the atmosphere to the temperature of an oven, sparking massive wildfires and killing off most land animals. The ash and other crud injected into the stratosphere (such as sulfur dioxide) would have stuck around for several years and reduced the effective insolation at the Earth's surface substantially, causing massive die-off of plants and a contraction of primary productivity (biomass creation) across the globe (effectively a "great depression" in the food web).
Many aquatic animals would have been able to survive the initial effects but would have been put in quite a pinch by the reduction in food that set in after. As mentioned, large land animals on the surface would have been mostly wiped out pretty quick, many of the rest would have starved as the one two punch of massive fires and reduced sunlight (and possibly global cooling) would have produced. Small animals that lived or took refuge underground (or perhaps were aquatic or semi-aquatic) could have survived the initial effects in large numbers and though they would have diminished in population in the hard times afterward could have eked through.
Scrappy little omnivores and/or scavengers would have been well suited to ride the waves of chaotic changes following the mass extinction.
> Finally, he showed me a photograph of a fossil jawbone; it belonged to the mammal he’d found in the burrow. “This is the jaw of Dougie,” he said. The bone was big for a Cretaceous mammal—three inches long—and almost complete, with a tooth
The mammal mentioned in the article was a marsupial, so not in our ancestral line. Marsupials have split from the eutherians (to which we belong) long before the C-T boundary. At C-T there were already early primates, which is our closer family.
A fascinating story about this is in Baxter's "Evolution" book which starts with a little primate at the CT boundary and traces the history of the family to modern humans.
Many aquatic animals would have been able to survive the initial effects but would have been put in quite a pinch by the reduction in food that set in after. As mentioned, large land animals on the surface would have been mostly wiped out pretty quick, many of the rest would have starved as the one two punch of massive fires and reduced sunlight (and possibly global cooling) would have produced. Small animals that lived or took refuge underground (or perhaps were aquatic or semi-aquatic) could have survived the initial effects in large numbers and though they would have diminished in population in the hard times afterward could have eked through.
Scrappy little omnivores and/or scavengers would have been well suited to ride the waves of chaotic changes following the mass extinction.