Australasian Science: Australia's authority on science since 1938

The Big Bang of Bird Evolution

The evolutionary tree of modern birds

The evolutionary tree of modern birds estimated from genomic data. Art by Jon Fjeldså.

By Simon Ho

Genome studies have revealed whether the extinction of dinosaurs coincided with the rapid diversification of birds.

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Studying the fossil record has allowed us to work out the timing of key events in evolution, such as when animals originated, when plants colonised land, and when we shared ancestors with our primate cousins. By dating fossils using geological methods, we can gain an estimate of the timescale of life.

But what if we are interested in the history of organisms whose fossil record is incomplete? If these organisms have left modern descendants, we can use molecular clocks to estimate their evolutionary timescales.

Molecular clocks are statistical models that describe evolutionary processes at the genomic level. They allow us to fill in some of the details of life’s evolutionary history that we cannot extract from the patchy fossil record.

I recently used molecular clocks as part of the largest-ever genetic study of bird evolution. Not only did this international study confirm that the major groups of modern birds diversified immediately after the demise of the dinosaurs, we also found that several bird lineages have been around for a lot longer and that the most diverse group, the passerines or perching birds, only rose to dominance in the past 40 million years.

To use molecular clocks, we need to collect information from the genomes of modern organisms. Genomes are essentially long strings of DNA made up of four building blocks called nucleotides...

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