Whale family tree catalogued

Dr Felix Marx (left) and Prof Ewan Fordyce, of the University of Otago geology department, look at marine fossils used by Dr Marx in his wide-ranging study. Photo / Ewan Fordyce

New University of Otago research is providing the most comprehensive picture of the nearly 40million-year-long evolutionary history of baleen whales, which are the largest animals ever to live on Earth.

The study also reflected the importance of ancient marine mammal research being undertaken at the university, Prof Ewan Fordyce, of the Otago geology department, said.

The research also continued to highlight Otago's standing as a Pacific Rim ''hot spot'' for the discovery of marine mammal fossils.

In a paper appearing in the UK journal Royal Society Open Science, Otago geology graduate Dr Felix Marx and Prof Fordyce present a comprehensive family tree of living and extinct baleen whales.

Prof Fordyce said blue whales - the largest baleen whales - grew up to 30m long and weighed up to 100 tonnes.

Baleen whales were also unusual animals.

Most mammals ate plants or grabbed a single prey animal at a time, but baleen whales were well-known for their ''gigantic mouths'' and their ability to ''gulp and filter an enormous volume of water and food''.

The two researchers said similar family trees have been constructed before, but theirs was the largest and the first to be directly calibrated using many dated fossils.

The research also highlighted the evolutionary importance of the Southern Ocean in whale evolution.

With the opening up of that ocean about 25 million years ago, a forerunner of the present Antarctic Circumpolar Current delivered nutrient-rich water, which was used by small prey species such as phytoplankton and krill, Prof Fordyce said.

This was likely to have increased the competitive viability of the baleen whale feeding strategy, he said.

Through Dr Marx's PhD research, he had done a ''extremely satisfying'' job of advancing understanding of baleen whale lineage, Prof Fordyce said.

The two researchers had found that earliest baleen whales underwent a sudden ''evolutionary burst''.

Many of the early whales had well-developed teeth and hunted sizeable prey but such toothed ''baleen'' whales disappeared, leaving only their filter-feeding cousins.

Small baleen whale species disappeared about three million years ago, leaving only today's giants.