The first published name for this fossil "fig" was Aesculus antiquus because the original author J.W. Dawson thought it resembled an ancient species of Aesculus (horsechesnut or buckeye) in 1875. See the horsechestnut fruit (left) photographed in Montana. Apparently most of the fossils don't have the spiny fruit wall. With an outer spiny pericarp, this fossil simply cannot be a fig syconium (Ficus). Knowlton did not cite Dawson in his 1911 paper where he describes Ficus ceratops. He was apparently unaware of the spiny outer wall on this fruit. Since Dawson's name predates Knowlton's Ficus ceratops, Dawson becomes the parenthetical author and Elizabeth McIver becomes the new author: Spinifructus antiquus (Dawson) McIver.

Another major goal on this trip was to photograph the K-T (Cretaceous-Tertiary) boundary. This is a dark, narrow band of sediments and carbonized plant material (coal) that separates the Cretaceous and Tertiary periods about 65 million years ago. In Makoshika Stae Park the tan strata above the K-T band is called the Fort Union Formation. It is younger than 65 million years and does not contain dinosaur fossils. The term Paleocene ("early-recent") refers to a time period when dinosaurs were replaced by smaller mammals, long before modern mammalian orders emerged. Below the K-T band is the older brownish-gray Hell Creek Formation that is rich in dinosaur fossils, including Tyrannosaurus rex, Triceratops and the amazing duck-billed Hadrosaurus. The best explanation (scientific theory) for the mass extinction of non-avian dinosaurs is an enormous 10 km (6 mile) diameter asteroid that collided with the earth about 65 (65.5) million years ago causing a global dust cloud that blotted out the sun for many months. Estimates as high as 85 percent of all species disappeared from the face of the earth at this time. This catastrophic event forever changed the direction of the evolution of life on earth.

The impact crater from this giant asteroid is buried beneath the Yucatan Peninsula. It was named Chicxulub (CHEEK-she-loob) after the nearby town of Chicxulub, Mexico. It has been estimated that he energy released from this astronomical collision is equivalent to 100 trillion tons of TNT. This is more than one billion times the power of the atom bombs that destroyed Hiroshima and Nagasaki. By comparison, the explosive force of meteor crater, Arizona was about 20 million tons of TNT: 1/5000000 or one five-millionth the blast force of Chicxulub!

In 1980, a team of researchers consisting of Nobel prize-winning physicist Luis Alvarez, his son, geologist Walter Alvarez, and chemists Frank Asaro and Helen Michels discovered that sedimentary layers found all over the world at the K-T boundary contain a concentration of iridium many times greater than normal. Iridium is a rare earth element that is abundant in most asteroids and comets. It is the second densest element after osmium and the most corrosion-resistant metal. The Alvarez team suggested that an asteroid struck the earth at the time of the K-T boundary.