A close second look at a fossil has revealed a previously unknown breeding ground for an extinct whale, and potentially sheds light on how species respond to changing climatic conditions.

In a paper published in the journal PeerJ, Cheng-Hsiu Tsai of the National Museum of Nature and Science, in Tsukuba, Japan, reports on a careful re-examination of several fossils of an extinct baleen whale, Parietobalaena yamaokai, that existed around 15 million years ago.

The fossils had hall been collected over the past century from around Hiroshima, and were held in that city’s Hiwa Museum for Natural History.

Examining one of the exhibits, part of a skull, Tsai noticed that two of the bones had not knitted together fully, indicating that the animal must have been under six months old when it died.

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The discovery, Tsai writes, indicates “a previously hidden and unknown breeding ground for the extinct baleen whale”.

She goes on to suggest that the breeding ground is the earliest ever identified in the northern memisphere, and that uncovering further evidence could shed light on ancient baleen whale behaviour.

“Identifying a possible Miocene breeding site for baleen whales in the northern

hemisphere also raises some interesting questions,” she concludes. “When, where, and which species of baleen whales initiated the annual, long migration between feeding and calving grounds?”

The answers to these questions could help to provide clues about the breeding grounds of modern day baleen whales – the locations of which are largely unknown.

This, in turn, will have direct application for conservation strategies.