Have you seen the Caloris Basin on Mercury? It is a crater the size of Texas and it fills about one-fourth of an entire hemisphere on Mercury.
4 billion years ago, a 100 kilometer-wide asteroid struck Mercury creating an impact crater that is 1300 kilometers wide. The Caloris Basin, as the crater is called, could hold the entire state of Texas!
The Caloris Basin on Mercury
Indeed, there are many examples of large impact craters. But as you can see from your images of Caloris Basin, this happened a very long time ago, as evidenced by the number of more recent (and much smaller) craters marring the outline of Caloris Basin.
And here is where I become very hesitant to accept the idea of a large bolide impacting and causing the K/T extinction event: by the time the Sinclair dinosaur lumbered across land, most of the large remnants of solar system formation had been swept up by the still-forming planets.
No, I do not discount the possibility that some rogue chunk of matter was still roaming about, however I think the chances of this happening were very, very small. Until more evidence is presented, I will remain quite puzzled.
