THIS was our first look at the realm of the invisible. In 1665, Robert Hooke’s Micrographia brought microscopic observations out of his laboratory to a wider world.

Hooke believed that, through the lens of a microscope, nothing could be “so small as to escape our inquiry”. The 38 copper engravings from his book, now republished by The Folio Society, detail many objects smaller than a grain of sand, in the manner of the diaries of travelling contemporaries who sketched rare exotic specimens on their travels around the New World.

Hooke chose subjects he thought looked attractive for his idealised and ordered catalogue of the microworld, including poppy seeds (above), an insect larva (below the poppy seeds), and a louse clinging to a human hair (below). Before drawing the head of a fly (top), Hooke first detached it so he could observe the organs inside the animal’s abdomen.

But he showed more tenderness to a tiny ant (bottom). Fearing that killing the insect would squash its miniature parts and destroy their beauty, he instead submerged it in alcohol so it would revive after the study was over “as if it had been awaken out of a drunken sleep”.

Micrographia by Robert Hooke is available from

This article appeared in print under the headline “Drawing the invisible”

How did the largest creatures ever to live on Earth evolve to feed on minuscule ones? A fossil skull belonging to a whale that could both filter feed and catch large prey reveals the first step in this process.

Baleen whales like the blue whale suck in enormous mouthfuls of water and then force it out through the baleen filter hanging from their upper jaw, retaining prey such as krill and small fish. But early whales had big, sharp teeth for catching large prey, so how one branch of the family evolved into filter feeders with baleen “sieves” made out of keratin – the same stuff as fingernails – has been a mystery.

The current idea is that the ancestors of baleen whales lost their normal teeth and only later evolved a “sieve”. But the skull of a previously unknown species of whale suggests instead that they started filter feeding by adapting teeth to act as sieves.

The 30-million-year-old skull was found on the bottom of South Carolina’s Wando river by a scuba diver about a decade ago. It has now been analysed and described by a team led by Jonathan Geisler of the New York Institute of Technology.

Filter feeding

This early whale, dubbed Coronodon havensteini by the team, had sharp, pointed front teeth that it used to catch large prey, like other early whales. But it also had unusual saw-like back teeth.

“The wear indicates they were not used for shearing food or for biting off chunks of prey,” says Geisler. “It took us some time to come to the realisation that these large teeth were framing narrow slots for filter feeding.”

The whale probably couldn’t suck in big mouthfuls of water like today’s baleen whales, though. Instead, the team think it was a ram feeder, opening its mouth and charging at shoals of small prey.

Modern leopard seals have evolved similar feeding habits: they can filter feed on krill as well as catching larger prey like penguins. In fact, before it was actually observed.

The skull doesn’t reveal how baleen evolved, however. This is hard to study because baleen doesn’t fossilise as well as bone. But the boom in fossil finds may yet reveal more about how it happened, just as recent discoveries have given us a nearly complete picture of how whales evolved from cat-sized hoofed land mammals.

“This study, if upheld by more evidence – which people will now be looking for – would nicely illuminate one of the previously more mysterious parts of the transition from some dog-like creature paddling by the shore 50 million years ago or so, to the blue whale,” says palaeobiologist Jan Zalasiewicz of the University of Leicester, UK.