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Animal Arrival
Animal Arrival
The ‘land’ then consisted mainly of bare rock, but also lots of weathered debris accumulating, loess, estuarine and overbank sediments. The creatures were mainly marine and part of the great explosion that occurred during the Cambrian age.
However there were some that played roles in early soil formation. Most of those are still confined to mosses and other early plants, implying they were part of the plot all those years ago.
There were all sorts of creatures – crawlers, walkers, wrigglers and jumpers - that have given rise to just about all the creatures alive in the world today. There were a lot of changes along the way. But there were no insects nor earthworms.
We can find early examples of the main groups, like onychophorans and springtails which foretold Annelids and Arthropods, as they provide the basic body structures that dominate our world today.
Wet & Dry
Wet & Dry
They were all connected with water often in films, but beginning to withstand dry conditions. This 2-way adaptation could not have occurred overnight and requires a stable environment to develop the adaptations to cope with whatever the climate throws at them. If not stable, any new adaptations would have been washed, blown away or crushed. This wet/dry property persists to this day for all soil dwellers.
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Tardigrades
Tardigrades
Tardigrades (meaning ‘slow walkers’) have probably been around for 600 million years. On the surface of the soil, we often find moss, which grows in wet conditions. Living in that moss are these very unusual – miniscule - creatures, called 'water bears' or 'moss piglets'.
They live in moss, to this day But it does not seem they gave a great helping hand to soil development – other than providing food for those who were to do that. They can survive long periods of drought – useful in developing living soils. They would have been in at the beginning of living soils evolving.
Tardigrades are covered in a tough cuticle, similar to the exoskeletons of grasshoppers, praying mantises, and other insects and like them, they have to shed their cuticles in order to grow.
Tardigrades as possible stem-group arthropods (Budd 2001) or sister group of arthropods (Nelson 2002)
They can be found in all sorts of environments all over the world. Looking like a bag with legs, they eat anything – plants, alga and fungi. They suck the juices from algae, lichens and moss. Some species are carnivores and even cannibals — they can prey on other tardigrades . Some eat tiny animals called nematodes (below) and rotifers that also live in moss. They have stylets to eat their prey or food. A sucking pharyngeal bulb enables them to then ingest the internal contents of their food items.
Indestructible
Indestructible
They defy the definition between life and death (see Quantum Entanglement). They were first found accidentally by the man – Leeuwenhoek - who wanted to show off microscopes in the early 1700s. From ‘dead’ moss in guttering, he found that these minute 'dead' creatures just appeared – as if they had come to life. He found that within an hour many small "animalcules" became active, and began swimming and crawling around. They were tardigrades. He wasn’t to realise it then, that they can go years without water, and survive temperatures near absolute zero.
They have been found recently to be virtually indestructible, withstanding temperatures down to – 272C – nearly absolute zero and they can be heated up to 143C. They are the stuff of science function with powers beyond belief, as they can also go without water for over a year. They defy our definition between life and death. Much less than a millimetre long, the tardigrade is tough - really tough! This is due to two main features, anhydrobiosis and trehalose.
Quantum Entanglement
Quantum Entanglement
Tardigrades may also be the first ‘quantum entangled’ creatures. " Researchers have exposed tardigrades to the coldest temperatures and highest pressures that moss piglets have ever survived — not just to test the critters' biological limits, but also to see whether a frozen tardigrade could be incorporated into two quantum entangled electric circuits, then later revived to its normal active state. The results, reported in a new paper published to the preprint database arXiv, suggest that, yes — scientists may be able to add "temporary quantum entanglement" to the tardigrade's growing list of accomplishments. However, early responses to the paper have taken issue with this finding."
Anhydrobiosis
Anhydrobiosis
When tardigrades dry out, they retract their legs and heads, transitioning into a form called a "tun." They can shut their metabolism down to 0.01 rate of its normal state, and stay like that for decades. It is called Anhydrobiosis. When rehydrated, it ‘comes back to life’.” Live tardigrades have been regenerated from dried moss kept in a museum for over 100 years. Once the moss was moistened, they successfully recovered from their tuns.Parasitic protozoa and fungi often infect tardigrade populations (Nelson, 2002)
Johann Goeze was the first to observe and describe a “Kleiner Wasser Bär” (little water bear) in 1773.Tardigrades may have been round for half a billion years, and be virtually indestructible, but they probably didn’t play a major role in soil formation. This is because today they are only found in those lumps of moss that fall from building - just as Leeuwenhoek found them. This implies that they can survive but they are not a major part of soil communities. They must have been in at the start, but perhaps they provided too good a food source for nematodes, amoeba and – even other tardigrades.
Tardigrades along with onychophorans are being considered the ancestors (along with their descendants ie ‘stem group’ of the immensely successful arthropods, the largest animal phylum on the planet. (Budd, 2001)Increasingly they are being called a ‘lobopod’, the collective name for the two phyla of animals Tardigrades and Onychophorans.
and
Trehalose
Trehalose
Research found that tardigrades use a sugar, trehalose, to replace water during its tun. These extraordinary survival abilities may hold the key to helping us extend the shelf life of both blood and vaccines. This could extend the distances organs can be transported. Blood platelets are vital to save lives but they are hard to keep. We can’t freeze them as vital cells are damaged. If we could use this trehalose to replace water in the cells, then we could ‘freeze’ the platelets without damaging them. Their transport potential becomes enormous. Imagine helping transfer body parts using this sort of freezing. It could extend the shelf life of platelets, and also vaccines, from days to months and we could get it all over the world, not just down the road. It could transform medicine across the world!. Trehalose is manufactured (Cai et al., 2019) for the food industry, but may find this use in the future. Trehalose coudl also be prevenatative treatment for SARS (Martinon 2020)
Springtails (Collembola)
Springtails (Collembola)
Springtails are one of the most ubiquitous animals on the planet, as we'll find as we go along. Springtails were around by the end of this phase as they have been found in the Rhynie chert. They probably fed on nematodes in the moss (Hodge, 2014).
They have two very discerning features. One is the 'furcula' (or furca ), which is the 'springing organ' giving these creatures their English name, springtail. They also have sticky protuberance or collophore giving them their Latin name Collembola.
When I was a lad, Collembola were classed as insects as they had the 'same' overall body shape. But in the 1990's the taxonomists separated them from insects and gave them their own 'Class' because it was considered that these two features were sufficiently distinct from anything insects have, and their mouthparts were internal rather than external.
It was pretty much agreed that the springing organ gave the creatures protection against predators. It always struck me that they needed a lot of space to escape, otherwise, they would bang their heads when living in the litter layers.
The function of the collophore was never really understood and was generally said to have something to do with water balance. I postulate - later - that they accidentally pick up spores, but clearly, that is accidental.
Being anthropomorphic, this spring translates to a human springing over the Eiffel Tower
They may well have jumped when they picked up the 'earth smell' telling them there was bacteria about - meaning food!
"Semiaquatic springtails can indeed control all three phases of jumping by adjusting their body posture and taking advantage of their appendages. They adjust the body angle and actuation speed of their leaping organ during takeoff, change their body posture in midair, and exploit the hydrophilic property of their ventral adhesive tube. The combination of these strategies allows springtails to achieve locomotion control, stability, and maneuverability, which can inform the design of small bio-inspired robots with controlled landing." (Ortega-Jimenez et al., 2022) Click video to see
M., V., Challita, E. J., Kim, B., Ko, H., Gwon, M., Koh, J., & Bhamla, M. S. (2022). Takeoff, aerial righting, and landing.
Proceedings of the National Academy of Sciences, 119,
One small spring for collembola
One giant leap for life on earth
Could the two dominant organs of springtails, their furcula and collephore, explain how these creatures came out of water - by following water films - on to land? Are we looking at one of the great steps/springs in evolution,?
One small spring for collembolans, but a giant leap for soil evolution.
One small spring for collembolans, but a giant leap for soil evolution.
It may well have been one small spring for collembolans, but it was a giant leap to land evolution. Remember we said that it is not so much conquering the land as expanding the water films. These organs would not work in water, but together work ON the water. Now, quite recently, both these features have been found to be involved in the springs; the furcula provides the power and the collophore controls direction. Researchers discovered "that semiaquatic springtails, Isotomurus retardatus, can perform directional jumps, rapid aerial righting, and near-perfect landing on the water surface." (Ortega-Jimenez et al., 2022)
Look at the video and you can see how they can move great distances following any water left behind after in the rising and falling of waters. And if they do land on dry ground, they can leap again, with any luck back to moist film. They may also land on a lump of moist moss and make that their home.
These appendages would seem to be to keep the animals where they need to be - in moist conditions. The collophore helps them stick to water. They could get from moss ball to moss ball. They could travel much further than any of the worms, to get from the moss to any newly emerging roots, as we will see in the next phase
Water is crucial the element. Springtails could move from where rivers overflowed, as well as flood plains, buried springs, bogs and marshes. Springtails can live in intertidal zones, where they can be washed up and spring about their millions.
Where did springtails spring from?
Where did springtails spring from?
The idea that springtails may have evolved in caves prior to inhabiting moss needs exploring. Remember the two distinct features- the springtail and the collophore, plus eyes- present in early springtails - the endomobryomorphs. I am picking these characteristics out as being key to development - rather than -say - their 6-leggedness. Later springtail/collembolans lose them as we will see when they go underground.. These two distinct features have never been replicated in evolutionary history.
We are well aware of the earliest fossil springtail - Rhyniella from the Rhynie chert 407mya. Possibly the most recent review of Collembola systematics "strongly supports that the Collembola origin is quite older (than Rhynie) , and at least some of its main lineages, such as extant orders, superfamilies and families, were already established during the Early Devonian (420-393mya) (Bellini, Weiner, and Winck, 2023). ie this period we are in now.
But A review of arthropods in the Cambrian explosion does not give any possible precursors when looking for these two distinctive characteristics, despite Gould's famous Burgess shale explorations.
Most recent predictions of early springtails, involving many mitogenome studies and you will find talk of 'monophyly "Our main phylogeny recovered the four Collembola orders as monophyletic taxa, with the following topology: Neelipleona + (Symphypleona + (Entomobryomorpha + Poduromorpha)) (Bellini et al., 2023) "Though this study presents one of the most taxonomically and genetically comprehensive springtail phylogenies to date, " But there is no proposed monophyly for the group as a whole. At this date it seems, despite all the research that has gone on in this area for years, there is no proposed predecessor.
Furcula
Furcula
Their spring takes them away from unfavourable areas fast. They can both explore, but are also able to return to safety. if too dry, a useful trait. Different creatures have different ways of dealing with dryness – this would seem to be to escape, whereas others roll up in a ball till conditions improve. This is the jumping organ, furcula, that most people say it is their key characteristic - giving springtails their name The furcula requires a great commitment from its body, taking up a lot of structure and energy, so must gave given important advantage at this period. Getting ahead of the game, and getting back again in times of stress would seem to be a massive advantage.
Collembola would have helped spread mosses at this time. “These animals are thought to contribute to the dispersal of microflora in addition to purely trophic relationships. This promising field of research is rarely considered so far. Interestingly, Collembola are involved in plant dispersal as well, since living soil algae are readily found in faecal pellets) and Collembola specifically ‘pollinate’ mosses. Through their effects on assembly processes in microbial communities, Collembola may exert an indirect effect on ecosystem functioning, however it is not easy to quantify their effect. A better understanding of these interactions would be possible with more data on how Collembola move and select their food” (Potapov et al., 2020)
Roundworm (Nematodes)
Roundworm (Nematodes)
It seems there would have been what we call roundworms, or nematodes 1/2 b ya. (Global Map)
All nematodes have similar simple bodies and can exist in the meniscus of the water covering all sorts of surfaces. For each human, there are 60 billion nematodes living in the soil[60], There are 4.4 x 1020 nematodes present in the Earth’s topsoil. They are by far the most abundant soil animals, accounting for about four-fifths of all animals on Earth. Just one single gram of soil can house up to several hundreds of these tiny worms.
Nematodes live in pores, much as they may have done in freshwater (Straalen 2021)
Niches
Niches
Nematode evolutionary history is particularly interesting because of the diversity of niches they occupy – ranging from the blood and tissues of vertebrate and invertebrate animals, unicellular eukaryotes, all parts of plants, virtually every terrestrial habitat, and all aquatic environments including deep-sea hydrothermal vent communities – is unrivaled in Metazoa.
Food
Food
Over the millions of years their mouthparts became more adapted to particular food sources – whether the roots, fungi, bacteria, or themselves. There are 7-8 different sorts. The first soil nematodes were likely bacterial feeders (Soil Invertebrates p39). Later they developed plant and animal parasites.
About 90% of nematodes live in the top 15 cm (6") of soil. Nematodes do not decompose organic matter, but, instead, are parasitic and free-living organisms that feed on living material like bacteria and fungal spores. Nematodes can effectively regulate bacterial population and community composition—they may eat up to 5,000 bacteria per minute. Also, nematodes can play an important role in the nitrogen cycle by way of nitrogen mineralization. Nematodes are also known to excrete enzymes that help break down complex organic molecules which helps release nutrients that can be taken up by other organisms.
1st plant eaters
1st plant eaters
Poinar says: "The oldest known nematodes are from about 400 million years ago, but could date back to around 1 billion years". He found them in the Rhynie Chert, along with many other early animals. It may well have been that the nematodes had lived in freshwater environments. but this is likely to be the first inside a plant, so perhaps first example of plants and animals living together. The species, now extinct, was Palaeonema phyticum described from the stomatal chambers of the early land plant Aglaophyton majus "Suggested ecological relationships of the terrestrial Rhynie animals (407mya) recorded to date suggest the only potential example of true herbivory, i.e. the consumption of living plant tissue, is the nematode. (Dunlop and Garwood, 2017)
Family Tree
Family Tree
Morphologial analyses have been taken over by molecular mapping which recognise three major lineages of nematodes: Dorylaimia (Clade I), Enoplia (Clade II), and Chromadoria, which consists of Spirurina (Clade III), Tylenchina (Clade IV), Rhabditina(Clade V). Dorylaimia includes many free-living soil nematodes. Enoplia primarily consists of free-living aquatic nematodes, but also several lineages of soil nematodes (Smythe 2019)
Nematodes have traditionally been assumed to have evolved in the marine environment. However, it has been estimated that 'no less than 30 independent transitions between marine and limnoterrestrial habitats have occurred during nematode evolution (Holterman, Schratzberger, and Helder, 2019). Basically the thin water surfaces in soil would be similar to many marine and groundwater environments.
The marine habits of Enoplia, along with ancestral features, makes them candidates for the earliest-branching nematode lineage (Ahmed et al., 2022). De Ley and Blaxter (1998) suggested the possibility of a terrestrial origin of nematodes with Dorylaimia. Ribosomal DNA-based studies have been unable to resolve the branching order among these deepest branches within Nematoda, suggesting that additional molecular markers are needed to resolve deep nematode family tree (phylogeny).
There is general agreement they first appeared in seas, but did they wriggle onto land, inhabit pores opening up soils, or were they parasites in creatures coming into the soils?
Prey
Prey
Nematodes provide food for a vast array of creatures. and organisms At that time, bacteria amobae and flagellates would have, and later springtails and mites. It is quite likely there were already fungi that fed on nematodes They are called nematophagous fungi and are specialised in trapping and digesting nematodes. Around 160 species exist, with both those that live inside the nematodes from the beginning and others that catch them, mostly with glue traps or in rings, which constrict on contact..
Hairy Back worms
Hairy Back worms
There’s a group of miniscule worms (<1mm) animals abundant in freshwater called Gastrotricha or ‘Hairy backs’. Terrestrial species live in the water films around grains of soil and they can be found frequently in submerged moss today (Strayer, 2014). This implies they may well have had a role in early soil creation.
Relations
Relations
Many gastrotrich species are found in vegetated areas or in surface sediment. They may be planktonic or benthic (bottom dwelling), and are found in marine and freshwater environments, including lakes, ponds, and wetlands. Some species are semi-terrestrial, living in water films on land. A recent, exclusively molecular phylogenetic study indicated their inclusion within the clade known as Spiralia, which includes Gnathostomulida, Platyhelminthes (flatworms), Syndermata (rotifers and spiny-headed worms), and Lophotrochozoa (nemerteans, phoronids, bryozoans, brachiopods, molluscs, and annelids). However, a study combining morphology, developmental characters, genetic data, and ecological characteristics indicated a possible relationship with Ecdysozoa (arthropods, nematodes, and assorted smaller phyla)". More recent work points to a closer relationship with platyhelminths (Saponi and Todaro, 2023)
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Poo
Poo
They feed on small particles and microorganisms in the water, and as such they are important components of the aquatic food web. But they also play a role in nutrient cycling and sediment turnover, as they consume organic matter and excrete it as fecal pellets that contribute to the sediment. As we will see throughout our soil evolution, poo is important in our forensic investigation. We can expect these minute worms would have been around in this period, but getting proof is hard work. Their small size and transparency of their bodies make gastrotrichs difficult to discover among bottom samples; moreover, their contractility and fragility make their handling and morphological survey of the specimens rather difficult. And the molecules are not much more help.
Velvet Worms
Velvet Worms
Onychophorans or ‘velvet worms’ , exist to this day. They and tardigrades are widely considered as the surviving descendants of Cambrian marine lobopodians, despite the great ecological gap. Resemblances between early lobopodians and living onychophorans are not just caterpillar-like gross morphology but distinctive features, such as unjointed ‘lobopodous’ limbs – or ‘stubby legs’ as they are called. Their name Onychophora means claw bearers, from Greek onyches "claws" and pherein "carry", as each stubby leg has a pair of claws.
Threads
Threads
They are carnivorous and entangle their prey in slimy threads. These threads are ejected from modified appendages behind their antennae called papillae, after which their jaws puncture the cuticle and the prey’s body injected with saliva for the velvet worms to suck up. Their prey nowadays includes beetles and crickets but then were perhaps millipedes…
They live predominantly in rotting logs and show a peculiar distribution, one group predominantly equatorial and tropical, while the others are all found south of the equator.
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It is the only animal phylum that is wholly endemic to terrestrial environments. There is an epic evolutionary battle about their evolutionary scenarios and 'phylogenetic' significance, as ancestors of annelids and arthropods. (Qiang 2020)
Oribatid Mites
Oribatid Mites
A very well-preserved oribatid mite - perhaps the most ubiquitous of all soil animals - has been found in Ordovician sediment in Sweden (right top). "Probably this mite was not fully terrestrial in habits, but lived among the rich organic substance (algae & fungi) on the coastline. Perhaps its life was not too much different from that of present-day ameronothrids" (Bernini et al., 2002)
Several of the mites, as well as the collembolans, are strong candidates for having been mycophages since their living relatives have been regularly reported feeding on fungi. " (Dunlop and Garwood, 2017)
Origins
Origins
The authors who found this old mite in Sweden believe this find challenges a common assumption that oribatids are not present till Jurassic times, citing other early traces like coprolites (=fossil poo) and tunnels in plants. They go on: "This specimen represents the oldest record of the arachnids"
These Swedish coastal mites could have given rise to the moss mites or 'lower' oriibatids 50- 100 million years later, that evolved into the higher oribatids - in Jurassic times. That may be what has lead to the belief that oribatids evolved in Jurassic times. Higher oribatids did evolve in Jurassic times, but that was a couple of hundred million years later than the lower oribatids. We will see more later.
(Lower oribatids Higher Oribatids)
'Lower' oribatidPalaeosomata
Millipedes
Millipedes
As well as fossils, we can now look for tracks of creatures. “Pin cushion” millipedes showed a stepping gait of trackway, consistent with them having been made around 450mya (Garwood and Edgecombe, 2011) Millipedes belong to a group called myriapods – creatures which many legs. Millipedes do not usually have a 1000 legs, more often 32 or 64, although one recently set the world record for the most legs.
They are well-down 'detrivores' eat dead plant matter. (Crawford 1990). While these creatures are full of armour with fearful weapons, were they the ones which went off and conquered the land? These creatures could not have lasted a couple of days.
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Oldest terrestrial invertebrate
Oldest terrestrial invertebrate
Millipedes (or Diploda = 2 legs/segment) fossils date back from around 430mya (Silurian).“The oldest recorded terrestrial invertebrates are various small Diplopods (millepedes) from the Lower Old Red Sandstone of Britain which were probably preserved preferentially due to their robust calcified exoskeleton" (Almond & Lawson 1985). It was a millipede named Pneumodesmus newmani....
Pneumodesmus newmani
Pneumodesmus newmani
One millipede Pneumodesmus newmani is important as the earliest known terrestrial animal. There are earlier fossils which resemble millipedes, but this counts as the first land animal, according to Guinness World Records, "The fossil of a 1-cm-long (0.39 in) centipede found near Stonehaven, Scotland, UK, by bus driver and amateur palaeontologist Mike Newman (UK) is thought to be 428 million years old and the earliest evidence of a creature living on land rather than in the sea.”The millipede was formally named Pneumodesmus newmani in 2004. This arthropod had spiracles - primitive air-breathing structures on the outside of its body - which acted as a gas exchange system, making it the oldest air-breathing creature yet discovered.
Newman made his find on the foreshore of Cowie Harbour in 2004 and placed the specimen in the charge of the National Museums of Scotland in Edinburgh. P. newmani would have been remarkably similar to today's millipedes. However, it did not belong to the same branch of myriapods as modern millipedes."These things are living fossils," said Dr Lyall Anderson, curator of invertebrate palaeontology at Scotland's National Museums. "Their morphology, shape and function really hasn't changed very much in all those 420 million years." We will revisit both myriapods and ‘living fossils’
Millipedes exhibit the first evidence of a chemical defence system. (Shear 2015) Against what? Those velvet worms? Millipedes overwinter in the soil. When the temperatures rise in the spring, they lay between 20 and 300 eggs in the soil, and after several weeks young millipedes emerge.
Growing up
Growing up
The young millipedes are small, and they have no more than seven segments and three pairs of legs. After each moult, they add segments and legs until sexual maturity is reached, which occurs between two and five years. Millipedes generally require moist places, so they are often found in mulch and organic debris outdoors. Towards winter, they migrate away from feeding areas but cannot survive dry conditions.
Poo
Poo
We can also look at poo from the period. One study found “larger, ovoid and cylindrical heterogeneous bodies composed of hyphal fragments which resemble the fecal pellets of mycophagous microarthropods.” (Sherwood-Pike and Gray, 1985) Nice job if you can get it. They did not identify further the poo of fungal-eating small invertebrate animals. It could be millipedes or springtails - which nibble fungi.
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