Australasian Science: Australia's authority on science since 1938

The Placoderm Renaissance

By John Long

Placoderm fish were once thought to be an evolutionary dead end, but new evidence is rewriting their importance to the ancestry of all jawed animals – including humans.

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Back in the 1960s, most of us had little interest in dinosaurs. They were thought to be a “dead end” lineage with no direct relationship to anything. Bob Bakker, a student at the time, said they were seen as “symbols of obsolescence and hulking inefficiency”. They were often depicted on the silver screen by using close-ups of living lizards bearing sails on their backs or with horns attached to their heads.

All this changed with just one man, Dr John Ostrom from Yale University. His discovery of the fleet-footed little predator Deinonychus, kin to the now infamous Velociraptor in Jurassic Park. His 1969 landmark paper on Deinonychus heralded what Bakker called the beginning of the Dinosaur Renaissance.

By comparing Deinonychus with the earliest known bird, Archaeopteryx, Ostrom pointed out some 20 anatomical similarities between living birds and dinosaurs. He proposed that birds evolved from dinosaurs and thus dinosaurs should no longer be seen as an evolutionary dead-end. Instead they gave insights into the origins and early adaptations of birds. It meant we could reinterpret dinosaurs in the light of bird behaviour.

Evidence emerged in many forms to support this theory. Dinosaurs were found brooding their young in nests, and caring for young before they could walk. The most convincing evidence comes from the recent discoveries of many fine...

The full text of this article can be purchased from Informit.