Oliver Langan, of Dunedin, asks :-

I have often read or heard that the cause of the demise of the Dinosaur species, was due to a very large asteroid crashing into the earth somewhere in the Mexican region. Assuming these large animals were present throughout the planet alongside many species of animals, birds and insects,when the impact occurred, how is it then that every living thing didn't get wiped out as well as the dinosaurs? I ask because on radio recently, an item discussing New Zealand's giant weta,the speaker mentioned how these insects have been around before and after the dinosaur age.

Daphne Lee, a zoologist at the University of Otago, responded.

The major global extinction at the end of the Cretaceous, about 66 million years ago, caused the selective extinction of many groups of organisms, but by no means all. All creatures alive today are descended from organisms that survived the K-T extinction event (K-T from Cretaceous-Tertiary). Note that this major event in Earth history is now often labelled the K-Pg boundary (from Cretaceous-Paleogene).

In the oceans, two major groups of molluscs, the ammonites and belemnites disappeared, together with some types of bivalves. More than half of all species of tiny floating single-celled marine organisms called coccoliths and planktic foraminifera vanished, causing major perturbations to the food chains in the oceans. But, many groups of marine organisms survived, including benthic foraminifera, sponges, corals, nautiloid molluscs and some fish.

On land, the major groups to suffer the effects of the huge asteroid/comet impact at Chicxulub on the coast of Yucatan, Mexico and its accompanying forest fires, acid rain, tsunamis and "impact winter" included most groups of animals larger than 25 kg including dinosaurs and pterosaurs on land, and the giant marine reptiles (mosasaurs and plesiosaurs) in the oceans. And, even then, avian dinosaurs (the first birds) survived and are still around today. Groups of frogs, snakes, crocodilians, turtles, lizards and some small mammals escaped the devastation. Animal survivors on land may have lived in burrows, or were partly aquatic, and/or had a varied diet from many food sources.

Many land plants appear to have survived. Some could regrow from seeds or underground root structures when conditions improved. And, possibly some areas of the planet such as New Zealand and Australia were shielded from the effects of an impact in the Northern Hemisphere.

The question mentions that weta in New Zealand are said to have been around before and after the dinosaur age. This is something that we have no direct fossil evidence for. Until very recently, there were almost no pre-Quaternary (more than 2 million-year-old) insect fossils known from New Zealand. Our research team has increased the number from about 5 to 500 in the past 5 years, but as yet we have found no evidence of fossil wetas in New Zealand, although some distantly related forms are known from Australia fossil deposits that pre-date the K-Pg extinction event.

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