Was Triceratops the last dinosaur?

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EDINBURGH: A new fossil discovery has suggested that dinosaurs were alive right up until the asteroid impact, and did not go extinct gradually due to climate change or changes in sea level, as previous theories have proposed.

Scientists have discovered a fossilised dinosaur horn very close to the K/T boundary in the Hell Creek Formation of South-Eastern Montana, U.S. They believe the horn likely belonged to Triceratops, or possibly Torosaurus.

The discovery of this horn disputes the hypothesis that a three-metre zone directly below the K/T boundary is devoid of vertebrate fossils, indicating that dinosaurs were extinct prior to the asteroid impact. It's the latest development in the 30-year-old war of words over the extinction of the dinosaurs.

"We collected rock samples above and below the horn to determine the exact placement of the K/T boundary, and were surprised to see that the horn was no more than 13 cm below it. This discovery indicates that at least some dinosaurs lived right up to the K/T boundary, and likely went extinct as a result of the asteroid impact off the Yucatan peninsula", said researcher Tyler Lyson, of Yale University.

The Impact Theory

The K-T boundary is a band of concentrated iridium in the sedimentary layers of the Earth. Iridium is rarely found in the Earth's crust but is present at greater concentrations in asteroids. At the boundary layer, the concentration of this chemical is many times greater than normal, leading researchers to suggest the asteroid impact theory.

The asteroid, which was around 15 km wide, is believed to have hit Earth with a force one billion times more powerful than the atomic bomb at Hiroshima and would have blasted material at high velocity into the atmosphere, triggering a chain of events that caused a global winter.

However some scientists argue that populations of dinosaurs began to decrease prior to the impact due to other factors (such as climate change or reductions in sea level).

This fossil discovery, to be published in the Journal of the Royal Society Biology Letters, suggests that at least some species of dinosaur were still roaming the Earth as the asteroid hit - and went out with a bang.

Revelations in the dirt

The 45 cm brown horn was identified to have belonged to a horned dinosaur, known as a Ceratopsidae. This family of dinosaurs were characterised by their elaborate horns and rows of frills.

The discovery of the horn adds further weight to the hypothesis that the impact event was the major factor leading to the extinction of the dinosaurs. Prior to this, no fossil examples of non-flying dinosaurs had been identified up to 3 m below the K-T Boundary.

"This putative barren zone, coined the 3 m gap, has been used by some to argue that dinosaurs were extinct prior to the asteroid impact. The discovery of this fossil is inconsistent with this hypothesis, rather dinosaurs lived right up to the K/T boundary," said Lyson.

Evidence for a mass extinction event

Although more field work is required to identify exactly how many dinosaurs actually survived up the K/T boundary, the research is an interesting find, unravelling the mysteries of how the Earth looked before the impact event.

"The paper demonstrates that field work is still the age-old best way to solve problems in palaeontology," said John Long, an Australian palaeontologist from the Natural History Museum of Los Angeles County in the U.S., who was not involved in the study.

"Finding this bone in the correct geological context near the boundary layer squashes the argument that dinosaurs might have gradually gone extinct, as we now have clear proof showing they were alive right before the big asteroid struck the planet at the end of the Cretaceous Period."