The first exclusively terrestrial animals to appear in the fossil record are not any species of vertebrate but millipedes, which have been found in the Old Red Sandstone beds at Stonehaven, Aberdeenshire, dating back to the mid Silurian. ‘The first air-breathing animal was Scottish’ ran the proud headline of Scotland’s Sunday Herald when the find was announced. In fact (considerations of palaeogeography aside) the animal was probably English, since Ordovician trackways of what were probably millipedes have been found in the Lake District, even further back in time.

Whatever their nationality, these early arrivals do nothing to justify the Pravda-like gloss put on the fossil record by the Public Broadcasting Service – an alliance of 349 public television stations in the United States:

Fossil evidence shows that different groups including insects, millipedes and centipedes, spiders and scorpions – all came ashore on their own at different times.

As the authors of the paper which prompted the headline confirmed (Wilson & Anderson 2004), ‘The oldest known millipedes were fully terrestrial.’ They had the spiracles and tracheal system of air-breathers, and had many ‘derived characters’, that is, there were no signs of their having just evolved from any other kind of organism. They were not only advanced in morphology but highly diverse, as we know from the recent report of an entirely different order of millipede, also of mid-Silurian date (Wilson 2005).

Indeed, many marine creatures suggest the idea of imitation, or adaptation, of terrestrial forms rather than evolution, as if designed to subvert the idea that similarity of form implies common ancestry. Thus sea spiders look like land spiders, but on closer inspection exhibit too many differences to support an evolutionary relationship; the origins of sea and land spiders are each a mystery. The only group amongst the animals listed in the PBS article that may have emerged from the sea is the scorpions (the evidence being as yet indecisive).

The other groups were entirely terrestrial, and appeared on the scene within a remarkably brief span of time. Centipedes are known from the late Silurian, as are the extinct spider-like animals called trigonotarbids and an extinct millipede-like animal called Eoarthropleura. The oldest true spider dates to the early Devonian. The oldest harvestman, another spider-like animal unrelated to spiders also dates to the early Devonian. In the paper reporting this find the harvestman was said to suggest ‘an extraordinary degree of morphological stasis within the eupnoid line [harvestmen], with the Devonian forms differing little in gross morphology from their modern counterparts’.

Other land-dwelling invertebrates that first appeared in the Devonian include mites, springtails, bristletails, pseudoscorpions (tiny creatures that look like scorpions except that they have no tail – they are not therefore thought to be directly related to them) and a second order of arthropleurid known as Microdecemplex.

Although millipedes and arthropleurids looked quite similar, they are not thought to have been closely related. As with the trigonotarbids that looked like spiders and the pseudoscorpions that looked like scorpions, arthropleurids differed from their look-alikes in so many respects that it is not possible to argue that they evolved from a common ancestor. A third order, Arthropleura, appeared in the Carboniferous and was a much larger animal than the others, with some examples attaining a length of more than 2 metres. It lived in a different habitat, feeding on the rotten trunk wood of lycopsid trees amongst other things. The first two orders became extinct around the end of the Devonian, the third, early in the Permian.

In the Carboniferous all these unique kinds were joined by a host of other land-dwelling invertebrates: mayflies, dragonflies, cockroaches, crickets, as well as numerous extinct groups. Around 17 orders of insects are known from this period, and every one of them seems to have evolved ex nihilo. This is the situation also with the other invertebrate groups. Without exception millipedes, scorpions, spiders and so on lack fossil forebears that might credibly link them into a single ‘tree of life’.

After their first appearance, it only adds to the problem that most of them spectacularly increase in diversity. However many new species arise, they still somehow retain their essential identity. The latest cockroaches are still cockroaches, the latest mayflies still mayflies.

What we see is evolution on an amazing scale, but it is not Darwinian evolution. Consider the scorpions, which with around 1,500 extant species are by no means one of the most diverse groups. If species lasted on average around 3 million years in radioisotope time, and if (as has been suggested) they were once more diverse than they are today, that would mean that the total number of species that ever lived would be hundreds of thousands. Is it really plausible that each of the character differences that marked each one as a new species arose as a result of conferring some advantage, rendering it fitter than other competitors in the struggle for existence? The sheer number of species is actually an argument against the theory of evolution.

Invading the land – from the air, not the sea

The fossil evidence shows that millipedes, centipedes, spiders and insects did not originate from the sea, nor from simpler terrestrial precursors. It contradicts what, on the basis of Darwinism, we would expect the record to show. So what alternative explanation might do justice to the evidence? As was seen after the Mt St Helens disaster, insects, spiders and other such creatures invade empty territory by falling out of the sky – swept up by winds and borne along in the air over hundreds of miles. After a catastrophe these animals are generally the first to recolonise the land. Correspondingly, wind-transport would have been the way in which tiny invertebrates reached new land after the cataclysm terminating the Hadean. They were transported over the world involuntarily, like plant spores. Animals that were heavier, reproduced less prolifically and had neither the ability nor the incentive to migrate as quickly would have arrived – depending on the distance travelled – considerably later, on foot.

The creatures that occur early in the terrestrial record are all very small (most less than 2 cm) and invariably sparse. They become more common as time goes on, as if globally stocks are now recovering. Undoubtedly part of the reason for their extreme rarity is that the fossilisation of their delicate structures required exceptional conditions (not just high rates of sedimentation), but it also seems to be the case that initially populations were few and far between. This is anomalous in a scenario where innovations become fixed in populations because more of the offspring inheriting the innovations survive, and where over tens of thousands of years, spanning a tiny fraction of a geological period, invertebrates competing with each other might be expected to overrun the earth. In that scenario the various terrestrial invertebrates ought to be as abundant at the beginning as at any other time in the fossil record. The same point applies to plants.

Sparse though they are, the fossils do not generally occur in contexts which suggest that the animals were the very first generation of pioneers, isolated, without sustenance and perishing where they dropped. Invertebrates tend to be found in association with other invertebrates unrelated to themselves, and close to plant material, indicating that what was fossilised was the remains of a comparatively mature ecosystem. The most spectacular of such localities – such as the Ludford Lane Bonebed or the Rhynie Chert (both in the UK) – are known as Lagerstätten. Evidently the plants were there before the animals, and the animals were living either off the plants or off each other. The insects used their mandibles to nibble on the spores, and the spiders preyed on the insects. With the exception of the arthropleurids, the invertebrates appearing in the Devonian are all components of modern leaf-litter faunas. The simultaneous appearance of diverse groups of organisms, unrelated ancestrally but related ecologically, is of course of the essence of recolonisation.

However, we have not yet looked at the story of how vertebrates conquered the land. Although invertebrates fail to substantiate the Darwinian narrative – for even the aquatic scorpions were still scorpions after the transition – certain fish might present a more convincing case. Did they evolve limbs, air-breathing apparatus and a great array of other apparently miraculous changes, until they abandoned the water and became reptiles? Anything is possible in the natural world. A tadpole can sprout legs and evolve into a frog in a single generation. Did fish manage to do the same in the course of twenty million years?