In The Blink Of An Eye

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Authors: Andrew Parker

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Table of Contents

Chapter 1 - Evolution's Big Bang

Life as we know it

Understanding the variety of life

The Cambrian explosion in brief

âThe History of Life' from the very beginning

The Burgess quarries today

A century of research

Palaeontological gold

The $64 million question

The answers proposed

Preview

Chapter 2 - The Virtual Life of Fossils

The youngest fossils

Old bones, new science

The active Earth

Reconstructing ancient environments

Palaeontology - the first forensic science

Trace fossils

Adding further flesh to the bones

Palaeontology meets modern engineering

Taking our tools to the Cambrian

Chapter 3 - The Infusion of Light

Before the Victorians

Another Victorian curiosity

Pigments

Evolutionary interlude

The purpose of pigments

The officer's hat, or the relevance of size and shape

Structural colours

Chapter 4 - When Darkness Descends

Night-time on land

The deep sea

Caves

Chapter 5 - Light, Time and Evolution

Living fossils

Diffraction gratings - a subject of physics

A sudden flash of green light

Bioluminescent seed-shrimps

The global view - evolution of all notched seed-shrimps

Natural diffraction gratings

Australia's upside-down flies

From sound to light

The list continues

Chapter 6 - Colour in the Cambrian?

Ammonites - multilayer reflectors and modifications

The Messel beetles - original multilayer reflectors

Fossils of the Burgess Shale - diffraction gratings

Chapter 7 - The Making of a Sense

Not to see

To see

Ancestral eyes

Chapter 8 - The Killer Instinct

Another thing about eyes

Swords, shields and scars

In the original line of fire

Chapter 9 - The Solution

Should we consider predation too?

Armaments are ornaments

The âLight Switch' theory

Life as we know it

Why vision and not other senses?

Near-final thoughts

Chapter 10 - End of Story?

A final word

Index

Table of Figures

Figure 1.1
The division of life into categories of different levels, using the woodlouse Porcellio scaber as an example. There are thirty-eight phyla of multicelled animals.

Figure 1.2
The geological timescale and epochs.

Figure 1.3
An amoeba - a cell with a nucleus and organelles.

Figure 1.4
Sections through representative bodies of different phyla showing simplified examples of internal body plans.

Figure 1.5
The Ediacaran animals Tribrachidium, Mawsonites and Parvancorina.

Figure 1.6
The Ediacaran animal Dickinsonia costata.

Figure 1.7
Marrella from the Burgess Shale - fossil and three-dimensional reconstruction.

Figure 1.8
Tow versions of the history of the animal phyla. From the first soft-bodied form, evolutionary branching is equivalent in both models. (A) indicates that both internal body plans and external parts diversified throughout this branching, and most theories on the cause of the Cambrian explosion have been based on this model. (B) is the correct model and properly identifies the Cambrian explosion - that it was the simultaneous evolution of external forms in all phyla.

Figure 2.1
Butterworth's 1920s illustration of Diplodocus walking, crocodile-style.

Figure 2.2
Diagrammatic cross-section of a living nautilus (eye not shown) and photograph of a fossil ammonite (part of tube preserved near centre of shell).

Figure 2.3
The footprints discovered in Greenland, made in both firm ground and sloppy mud.

Figure 2.4
Palaeo-map of the world, at the time of the Burgess dynasty, showing the original location of the Burgess reef.

Figure 3.1
Newton's own drawing of his experimentum crucis. Unfortunately he lacked the artistic genius of Leonardo.

Figure 3.2
Light rays affected by a thin film, such as a fly's wing, in air. The film is shown in cross-section; the light-ray paths and wave profiles are illustrated as solid lines (incoming light) and dashed lines (reflected light).

Figure 3.3
A cross-section through a liquid crystal (left), showing individual helical molecules, and its approximation as a stack of thin layers and effect on light (right). Reflected light rays are in phase when the layers are approximately a quarter of their wavelength in thickness.

Figure 4.1
A twelfth-century fishing trap recovered from the River Thames.

Figure 4.2
A typical scavenging isopod, amphipod and ostracod (seed-shrimp).

Figure 4.3
Simplified schematic section through two of Earth's plates, showing the submarine landscape between, including their line of separation.

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.

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

Figure 5.3
Scanning electron micrograph of a diffraction grating of the âbaked bean' (Azygocypridina lowryi). Spacing between grooves is 0.6 microns. (Plate 15 in the colour section shows the iridescent effect of this structure.)

Figure 5.4
Frame from a video recording of a pair of the notched seed-shrimp Skogsbergia species mating. The iridescent flash of the male is arrowed.

Figure 5.5
Electron micrograph of a hair from Lobochesis longiseta, a bristle worm. The ridges are spaced about one micron apart, forming a diffraction grating that causes a spectral effect.

Figure 6.1
Micrographs of the Burgess bristle worm Canadia at increasing magnification - from x10 to x1,500. The top picture shows the front half of the animal, the middle pictures show details of bristles. The bottom picture shows the surface of a bristle as removed from the rock matrix, revealing the remnants of a diffraction grating with a ridge spacing of 0.9 microns.

Figure 7.1
Marginal sense organs of the jellyfish Paraphyllina intermedia and Aurelia aurita, showing different levels of complexity (particularly in their light detectors).

Figure 7.2
The three types of simple eye - pinhole, mirror and camera-type - and their effect on light rays. Light receptors (retinas) are shaded. The mirror eye has an underlying mirror (dashed region) and the camera-type eye has a lens, both of which focus light to form clear images.

Figure 7.3
Focusing of light rays (solid lines) by a graded lens (only three grades of material are shown). The dashed lines represent the paths induced by a standard lens of uniform material - the steeper angles of contact cause light to be bent more at the periphery. The core material of the graded lens, however, causes light to bend more than the material of the periphery layer, and so counteracts this angular discrepancy.

Figure 7.4
Scanning electron micrograph of the head of a fly, showing compound eyes.

Figure 7.5
Focusing mechanisms in the compound eyes of a) bees (apposition-type eye); b) moths and c) lobsters (superposition-type eyes). Graded material in b) and mirrors in c) (shown from the side and from above) achieve focusing. (Modified from Land, 1981.)

Figure 7.6
Anomalocaris and Waptia from the Burgess Shale. At around 7.5cm, Waptia is several times smaller than Anomalocaris.

Figure 7.7
Micrographs of the heads of a living âmysid' crustacean and Waptia from the Burgess Shale. Eyes show comparable internal architectures. Scale bars represent 2mm (top picture) and 0.5mm (bottom picture).

Figure 7.8
Yohoia, Perspicaris, Nectocaris and Sarotrocercus - examples of Burgess animals with eyes.

Figure 7.9
The tiny Cambrian arthropod Cambropachycope, with a single compound eye.

Figure 7.10
The Cambrian arthropods Canadaspis laevigata and Fortiforceps foliosa from Chengjiang, China.

Figure 7.11
The evolutionary tree of animals at the level of phyla (all those with representatives alive today are included; note that Choanoflagellata is not a true multicelled group). Asterisks mark the phyla with eyes (which are also numbered 1 to 6 as they appear in the text). Modified from a paper by Rouse and Fauchald.

Figure 7.12
Haikouella lanceolata from Chengjiang - the earliest known chordate.

Figure 7.13
Photographs of holochroal (above) and schizochroal (below) trilobite eyes.

Figure 7.14
The intralensar bowl design in the lenses of some trilobites; light rays striking all parts of the lens are focused in the same plane. An identically shaped lens without the intralensar bowl is shown for comparison.

Figure 7.15
Time ranges of genera within the seven families of trilobite, showing the occurrence of different kinds of eye (after Euan Clarkson, 1973). Note that the very first trilobites, living at the base of the Cambrian, bore (holochroal) eyes.

Figure 7.16
Nilsson and Pelger's predicted evolution of a camera-type eye, like that of a fish. The sequence begins with a flat patch of light-sensitive cells sandwiched between a transparent protective layer and a layer of dark pigment. A graded-index lens appears at stage 6. Reproduced from a 1994 paper by Nilsson and Pelger with permission from the authors.

Figure 8.1
One of the original stereograms of 1838. Blur the picture to produce a fused image in the centre. The inner ring will appear nearer than the outer ring.

Figure 8.2
The early Cambrian trilobite Fallotaspis typica showing eyes (shaded) positioned at the side of the head, although its sight is directed slightly forward.

Figure 8.3
Odaraia and Sidneyia from the Burgess Shale.

Figure 8.4
Naraoia, a Naraoid from the Burgess Shale.

Figure 8.5
Photograph of a trilobite when rolled up - âhead' spines can be seen projecting from the body. When the trilobite is flat, as we usually view trilobites, these spines lie flush with the body.

Figure 8.6
Pirania, Micromitra and Haplophrentis from the Burgess Shale.

Figure 8.7
A soft-bodied âtrilobite' from the Precambrian (about 565 million years old). Shaded regions in the head could be the precursor to compound eyes.

Figure 9.1
(overleaf) This is how all Precambrian animals would have pictured their neighbours using light as a stimulus.

Figure 9.2
Soft-bodied multicelled animals living at the end of the Precambrian. This is how the most sophisticated light receptors of the time - eyes - would have pictured the Very Late Precambrian or Early Cambrian world, around 543 million years ago.

Figure 9.3
Graph showing the very approximate evolution of receptors for different stimuli throughout geological time. Vision is the only sense that can divide geological time into two distinct phases.

Figure 10.1
Face-on view of our galaxy. Counterclockwise from the Sun (cross at top) are the Sagittarius-Carina arm, Scutum-Crux arm, Norma arm and Perseus arm. Triangles mark the times of the major post-Cambrian extinctions (modified from a paper by Erik Leitch and Gautam Vasisht). Some researchers believe the movement of our solar system into the spiral arms had an effect on these extinctions (such as a consequential encounter with giant meteors). The effect of unwinding is indicated by the dot-dashed lines defining the centroids of the arms for an unwinding of 1Â°, 4Â° and 8Â° for the first three arms, respectively.

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