In The Blink Of An Eye (24 page)

The seed-shrimps that happened to like frozen pilchards and wandered into the traps were the lightweights, the group that had left little
behind in the fossil record. And in particular it was just one family of lightweights - Cypridinidae, seed-shrimps that generally have a small but well-defined notch at the front of their shells. I will refer to the Cypridinidae as the ‘notched' group. Notched seed-shrimps are usually the size and shape of tomato seeds, and typically spend much of their time buried in the sand on the sea floor. The tomato seed lookalikes occurred in the traps set in shallower waters. They were common also in traps set in deeper waters, but at depths of 200 and 300 metres they were occasionally accompanied by an oddball among notched seed-shrimps - the ‘baked bean'.

Figure 5.1
A notched lightweight seed-shrimp with one half of its shell removed to reveal its body and limbs inside (from Cannon, 1933,
Discovery Reports
). The arrow points to the halophores of the left first antenna.

The very first trap set in a depth of 200 metres off the coast of Sydney was hauled up and opened on board the fishing vessel hired for the job. The sight was as amusing as it was unnatural - the trap was full of what appeared to be baked beans. ‘Baked bean' is the official nickname given by local fishermen to ‘giant' orange/red seed-shrimps called
Azygocypridina
. Sometimes they are brought up in the catches of fishermen, who have no idea what they are dealing with, merely that they ‘don't make good eating'. Baked beans appear to be confined to the edges of the continental shelf. Like real baked beans, these seed-shrimps are about a centimetre long, oval and slightly flattened from side to side. They are orange/red because at a depth of 200 metres and beyond sunlight is almost exclusively blue. You can be sure, at least, that at such depths orange and red will be absent from the sun's spectrum. And with nothing left to light up the baked beans, they appear to be invisible. In a totally dark room, for instance, an orange cannot be found with a blue torch. But there is a difference in the appearance of the deep-water seed-shrimps and baked beans - the seed-shrimps possess their characteristic notch at one end. And so did the Scottish fossils.

Every once in a while a ‘living fossil' is discovered somewhere on Earth. Living fossils are species alive today that closely resemble forms otherwise found only as fossils, species that lived during ancient times. The nautilus could be considered a living fossil because it shares its looks, behaviour and, more importantly, its place in the evolutionary tree with the extinct nautiloids and ammonoids. But the nautilus lives on.

One of the most recent living fossils to emerge is the Wollemi pine. Fossils of this type of conifer were once known only from rocks containing dinosaur bones, and it was thought to have been extinct for millions of years. It was an important subject in palaeontology. Then all the hard work put into extracting and extrapolating the fine details of its anatomy to bring it to virtual life was undone by a single event - the discovery of a living specimen. Virtual life was suddenly replaced by real life - an occupational hazard for palaeo-artists (although a rare one).

In a remote part of New South Wales, Australia, forty adult Wollemi pines were found very much alive in a deep, sheltered gorge. The gorge supported a warm, temperate rainforest. It may seem amazing that the massive pines had not been discovered before, but much of inland Australia is actually unknown to science. There is considerable biology to be done in Australia. Spiders, for instance, are among the more populous animals on Earth, yet around two-thirds of Australia's spider species probably remain undiscovered and unnamed. So it is not so surprising that if a new species of tree is discovered today, it will turn up in Australia. Of course, as the world's rarest tree, the Wollemi pine must be closely monitored and protected, so much so that its precise location has been kept a secret. Even cultured specimens growing in Australian botanical gardens are kept under lock and key, and beyond the reach of the horticultural black market.

There is an obvious link between the Wollemi pine and the SEAS project. In the deeper localities, hagfish were caught in the large scavenger traps. Protected within a scabbard of slime, hagfish appear like eels. They have primitive mouthparts, and indeed are today's representatives of a primitive form of fish. Their mouthparts are quite an issue because hagfish have a strong fossil record, dating back some 500 million years, but the fossils show no sign of jaws. And the living hagfish confirm this - they really are jawless. The jaw is a feature of more derived forms of fishes - sharks and bony fish. But hagfish are scavengers, and can really get by without a jaw in certain environments, those in which they are preserved today. The relevance of the Wollemi pine and hagfish to this chapter is that the baked bean is a living fossil too. Although less apparent to begin with, morphometric analyses were employed to expose this truth.

Baked beans showed similarities in form to the 350-million-year-old, oval fossils discovered by David Siveter, who by this time had classified them as lightweight seed-shrimps. Morphometrics can give mathematical values to shapes. A morphometric value, in the form of relative coordinates on a grid, was given to the Siveter fossils, and it seemed appropriate to put the baked beans to a similar test. The match was perfect. David Siveter was right - he
had
found lightweight seed-shrimps that lived 350 million years ago. To be more specific, these
fossils belonged to the notched group of lightweight seed-shrimps. Before long, David Siveter and his team discovered further fossil lightweight seed-shrimps, now that they knew what to look for.

Different forms of lightweight seed-shrimps were uncovered from older rocks, but here the baked bean forms were absent. The lightweight group as a whole could be dated back 500 million years to just after the Cambrian. But it seemed that the baked bean form, and the notched seed-shrimps in general, evolved about 350 million years ago. Now, for the first time, we were beginning to trace the geological history of the much forgotten lightweight seed-shrimps. But it was useful, also, to have a date on the evolution of baked beans for another reason.

The study of structural colours in animals has a long and distinguished history. Robert Hooke possibly pioneered the subject in the seventeenth century with his interpretation of the metallic appearance of silverfish insects, just pipping Newton to the post. And ever since, this subject has been famously represented, up until the work of Sir Andrew Huxley, Sir Eric Denton, Michael Land and Peter Herring in the latter half of the twentieth century. Consequently, animal forms of multilayer reflectors and structures that cause the scattering of sunlight, with all their variations, had been well documented and interpreted by biologists. But these were also subjects of optical physics. Physicists have been experimenting with optical materials for centuries, and had converged on the same structures that occurred in nature. Yet the two fields of biology and optical physics never seriously crossed paths.

Despite numerous studies on animals known to show metallic-like reflections, such as many beetles, butterflies, fishes and hummingbirds, there remained physical, optical structures that were known to physicists but not to biologists. Prisms, for instance, had never been found as light reflectors in animals. Perhaps their precise shapes or copious volumes made prisms an evolutionary impracticality. ‘Prisms' can be found occurring naturally, nonetheless, in raindrops that refract and reflect sunlight to create a rainbow.

In 1818, another type of physical structure with reflective properties was invented in a physics laboratory - the diffraction grating. Fine copper wire was wound tightly around a screw, and the acutely grooved surface created by the wire caused sunlight to be split into its component colours: a spectrum was reflected. A different colour could be seen from different directions. Diffraction gratings could be considered as tiny corrugated sheets, where the spacing of the grooves are fairly constant and approximate to the wavelength of light. At their most efficient they are microscopic. Diffraction gratings became major players in the scientific and commercial worlds of optics, and have become refined and varied to produce an array of optical effects. They are responsible for the metallic-like, coloured holograms found on credit cards or foil-type wrapping paper, and now they are also being used on stamps and bank-notes since they are difficult to forge. But they were unknown in nature and the subject of animal structural colours until 1993.

Figure 5.2
A diffraction grating splitting white light into a spectrum.

My role in the SEAS project was to describe the new species of seed-shrimps collected. Sixty unknown species of notched seed-shrimps emerged from an area where only a couple of species were thought to exist in total. But it was not simply their diversity that made the notched seed-shrimps such important scavengers; it was their abundance. A single trap, basically a foot-long section of drainpipe baited with a couple of dead pilchards, would attract up to 150,000 individuals. Considering the short distances seed-shrimps are prepared to travel for food, the SEAS findings indicated that notched seed-shrimps were probably the commonest multicelled animals on the Australian continental shelf. Yet until then they were virtually unknown. This typifies how little we know of the smaller, but probably more common, life forms on Earth. But thanks to the SEAS project, the secret of the notched seed-shrimps had been revealed. Well, at least the secret of their Australian affluence. A further secret lay waiting to be discovered, one that could only be revealed using microscopes.

To examine the body parts of preserved seed-shrimps, their shells must be removed. This operation involves manipulating a specimen under a microscope and attempting to sever the muscles that hold the shell closed. The tiny size of most seed-shrimps makes this job difficult, and often several attempts are needed. The seed-shrimps tend to roll around and fall in exactly the positions that are not required of them. One exceptionally long day in the Australian Museum I had been battling with seed-shrimps for this very reason. It was time to go home but I was delayed. Then something happened that would change the course of my research -
I saw a flash of light
.

As one preserved seed-shrimp rolled over in the glass dish under my microscope, it caught the microscope's light and sent an extremely brief blaze of green light towards my eyes. Unsure of what it was, or indeed if I was seeing things, I rolled the specimen over again, in an attempt to repeat the performance. Once again it shimmered with green light. Holding it in the appropriate position, the green reflection shone continuously. The shell of the animal appeared rather dull and its background was decidedly black, but the green light was blazing like a
neon sign in the night. I asked my nearest companions, the amphipod specialists Jim Lowry and Helen Stoddart, to double-check that this was really happening. It was, but it shouldn't have been. There was a big literature on seed-shrimps, and green flashes were not part of it.

The green part of the seed-shrimp belonged to its first pair of antennae. These antennae are equipped with long hairs, and each long hair is the bearer of smaller hairs, called halophores. Halophores are flexible because they are made of minute rings, stacked side by side. They are held together by a thin, elastic outer skin. But like the fine wire wrapped around a screw, they cause tiny ridges and grooves to appear on the outside of the halophores. The light microscope indicated that the green flash came precisely from the halophores. The electron microscope revealed the spacing of the very regular grooves - it approximated the wavelength of light. The surface of a halophore was a diffraction grating. Again, it shouldn't have been. There was also a considerable literature on structural colours in animals, and diffraction gratings, like seed-shrimps themselves, were absent from it.