Soil Animals

66-0mya Cenozoic

Soil Survival Plants Grass Impacts Soil animals Ground beetles

This is the era when there were three main soil biomes - conifer and broad-leaved forests, and now grasslands.

In a big Slovenian study “The analyses of mesoarthropods show that mites (Acarina) account for 75%, springtails (Collembola) for 22%, and other mesoarthropods for a mere 3% of the whole fauna. … The highest density is found in the pine forest, with 115,720 subjects/m2 . In the other two forest stands it is lower, in the hornbeam forest it is 78,689 and in the oak and in the oak forest 65,237, and the lowest density is in two grassland soils with 52,263 and 44,517 subjects/m2 . (Lozej & Urbancic 1998) This broadly fits with the finding of the UK's Countryside Survey (Chap 8) (NERC)

This is also the era when the sight of birds eating soil animals came into being. The birds had not been there before, as they are descended from theropods, a group of bipedal, meat-eating dinosaurs that also includes Tyrannosaurus rex. They also had a new environment to explore, full off juicy creatures, that were also increasing in number eating the tender plant remains.

Earthworms

"There would have b two major earthworm clades, each of which consists of a Northern Hemisphere subclade and a Southern Hemisphere subclade. Divergence time analysis results are concordant with the hypothesis that these north-south splits are the result of the breakup of the supercontinent Pangaea". (Anderson et al 2017).

2 clades

Northern Hemisphere clade comprising Lutodrilus (North America) and Lumbricoidea (Criodrilidae, Hormogastridae, Lumbricidae) (Europa and Asia) and a primarily

Southern Hemisphere clade comprising representatives of Almidae, Acanthodrilidae, Eudrilidae, Glossoscolecidae, Megascolecidae, Microchaetidae and Ocnerodrilidae (Africa, Australia, New Zealand and South America).

The surviving relatives of dinosaurs, birds ,lived on what was living on or in the soil. These are the early birds with new food source'.

This divergence continued with more adaptation after the Indian-Eurasian collision (Yuan et al 2018) which "led from the “greenhouse” state of the Late Eocene to the “icehouse” conditions of the Oligocene 34–33.5 Mya" (Hren et al 2013)

Divergence in Cenozoic

"Dispersal of Megascolecidae (Southern Clade) from outside of the Hengduan mountains (HMs) to this region (in China) coincides with Indian-Eurasian collision between Eocene and Oligocene. The reconstruction of ancestral-area reveals the clades in Megascolecidae (Group 2–8) may have experienced different evolutionary histories following their divergence time during Cenozoic, which suggests that paleogeographical events might promote the dispersal and diversification of earthworm in the HMs". (Yuan et al 2019)

Earthworms in Grassland

The least numbers are found in coniferous forests - as their ecosystem predates earthworm evolutions. The next would be broadleaved woodlands as they have a nice leaf litter, and that is when we first saw them - 200- 145mya (Jurassic)
By this era, we have seen two new forms - distinct clades - of earthworm emerge, as Pangea split. But what would happen under grass, this newer environment.

Preferences

“Earthworms prefer a soil habitat that is low in acidity, cool, moist, and well-aerated. They are generally found in the upper layer where there is plentiful litter and an abundance of organic matter available. Calcium abundance in a soil is an important factor as it is a critical component of their mucigel secretion. In coniferous forest environments, soil tends to have a lower pH as the needles they drop are more acidic and resistant to decomposition, but any calcium may have leached. “We expect to find the least amount of earthworms under coniferous soils. Contrarily, fallen leaves of deciduous trees are decomposed more easily and contain stored calcium This will lead to more suitable soil conditions for earthworms and as a result we expect to find more of them in these soils. In regard to grasslands, they have thicker A horizons that distributes organic matter deeper into the soil profile , so we expect to find a higher earthworm density in grassland compared to the coniferous forests”

"To date, our data appears to indicate that there are in fact more earthworms found in the deciduous forest than the coniferous in the Morgan Arboretum. The grassland has far greater abundance than coniferous as well, however significantly less than the deciduous habitat. A study in India also found that deciduous forest soil had much more earthworm density (Naik et al 2024)

The role between grass and 'early' worms is probably as important as that between grass & herbivore mammals and their associated dung beetles.

Did earthworms move across to grass?

'Early' worms

The most likely early worms in grassland soils are
Ancestral Members of the Lumbricidae Family: The Lumbricidae family, which includes the common earthworms we know today, is believed to have had ancestors that were present during the Eocene. These earthworms are well-suited for living in temperate environments, including grasslands, and their ancestors likely had similar adaptations. Lumbricids are known for their ability to process large amounts of organic material and contribute significantly to soil aeration and nutrient cycling, both important traits for early grassland ecosystems.

Early Megascolecidae Family Members: Another family that could have been among the first earthworms to inhabit grasslands is the Megascolecidae. This family is diverse and includes species adapted to a wide range of habitats, from forests to grasslands. Some early ancestors of this group likely adapted to grassland conditions as these environments became more widespread. They are part of the Southern Hemisphere clade and would have contributed to soil formation and structure in ancient grassland ecosystems.

Acanthodrilidae and Moniligastridae Families: Other earthworm families, such as Acanthodrilidae and Moniligastridae, might also have included species that were early grassland occupiers. These families are found in various parts of the world and include species that live in different soil types, suggesting a high degree of adaptability. While not as dominant in grasslands today as Lumbricidae or Megascolecidae, they might have played roles in the early stages of grassland development.

Nematodes

Nematodes, are a predominant component of soil communities, and by far the most abundant animals on Earth, so very likely played a critical role in determining the developmental direction of grasslands. We know they can adapt to changing conditions swiftly, so would likely to be early builders of grassland soil.

"Nematodes in grassland soils increase plant available nutrients, move beneficial microbes through the rhizosphere and control insect and mollusc herbivores....Nematodes have profound effects on the soil nitrogen status, with up to 27% of plant available nitrogen being attributed to nematode excretion...nematologists are starting to appreciate that the vast abundance and diversity of nematodes in agricultural soils provide several beneficial ecosystem services... and for use as bioindicators" (Wilson 2013)

It is likely that the families such as Tylenchidae, Pratylenchidae, Criconematidae, Cephalobidae, Rhabditidae, and Dorylaimidae were among those that adapted to the grassland environments as these ecosystems emerged and expanded during the Paleogene (66-23mya). These families would have found new ecological opportunities in the roots, soil environments, and microbial communities associated with grasses.

Nematode Families likely to have occupied grasslands

Tylenchidae: As plant-parasitic nematodes, the Tylenchidae likely found the roots of grasses a new and abundant food source as grasslands began to expand. Members of this family, such as species within the genus Tylenchus, feed on plant roots, including monocots (which include grasses). The emergence of widespread grasslands would have offered a large, continuous habitat for these root feeders to exploit.
Pratylenchidae: This family also includes plant-parasitic nematodes, such as those in the genus Pratylenchus (lesion nematodes), which are well adapted to feeding on the roots of grasses. Given their preference for the roots of monocotyledonous plants, it is likely that Pratylenchidae members were among the first to exploit the new grassland niches.
Criconematidae: Members of this family, including species in the genus Criconemoides, are sedentary ectoparasites that feed on plant roots. They tend to thrive in environments with lower moisture, which is characteristic of many grassland soils. The development of grasslands likely provided suitable conditions for these nematodes, especially in more open, drier, and well-drained soils.
Cephalobidae: These free-living, bacterivorous nematodes would have thrived in the new grassland environments due to the abundance of organic matter and microbial activity in the soil. As grasses grew and died, they contributed to soil organic content, fostering the bacterial populations that Cephalobidae feed on. These nematodes are known for their adaptability to different soil conditions, making them likely early colonizers of grasslands.
Rhabditidae: This family includes many free-living nematodes that feed on bacteria, fungi, and other soil microorganisms. As grasslands emerged and developed rich microbial ecosystems in their soils, the Rhabditidae would have found new opportunities to thrive, particularly in decomposing organic matter and in the rhizosphere (the region of soil influenced by plant roots).
Dorylaimidae: Predatory nematodes, such as those in the Dorylaimidae family, could have invaded grasslands by feeding on the diverse communities of other nematodes and small soil organisms that populated the newly formed habitats. As new prey species adapted to grasslands, predatory nematodes would have followed, maintaining their role in the food web.

Considerations for the occupation of Grasslands

The occupation of grasslands by nematodes around 50 million years ago likely involved several factors:

Adaptation to Plant Hosts: As grasses diversified, certain nematodes that could feed on the roots of grasses or other monocots would have found new opportunities. For example, nematodes that specialized in feeding on roots may have followed grasses as they spread.
Soil Environment: Grasslands often have well-drained, aerated soils with varying levels of organic matter. Nematode families that could adapt to these conditions, including both plant-parasitic and free-living species, would have been well-positioned to thrive.
Climate Adaptation: Grasslands are often associated with semi-arid to temperate climates. Nematodes that could tolerate or even prefer drier conditions, such as some Criconematidae species, would have been more successful in colonizing these environments.

Potential Evolutionary Adaptations

Grasslands would have selected for nematode species that:

Specialized in Grass Hosts: Adaptation to grasses and other monocot plants, particularly with adaptations to resist plant defenses or effectively feed on the unique root structures of grasses.
Drought and Temperature Tolerance: Ability to withstand drier conditions and temperature extremes typical of grasslands, leading to traits like anhydrobiosis (a state of suspended animation in response to desiccation).
Soil Microhabitat Preferences: Adaptation to specific soil conditions (e.g., organic matter content, pH, aeration), which are characteristic of grassland soils.

Would you like to explore specific species within these families, or delve further into the ecological roles these nematodes play in grasslands?

Myriapods

Those creatures with lots of legs (myriapods) include - centipedes (chilopods, 1 pr/leg/segment), hundreds and millipedes (diplopods 2 leg/segment) have been joined by a group called pauropods. Myriapods play an important role in the breakdown of dead vegetable material, although some, like centipedes are primarily carnivorous. Myriapods are most abundant and diverse in tropical and temperate forests, although some species of diplopods and an even greater number of chilopods thrive in grassland or semiarid habitats, and others live in desert conditions.

Pauropods

We seeing that many existing organisms moved into the new grass ecosystem. The only exception to that may be Pauropods, as we have no evidence of them existing until this period. Pauropods are soft, cylindrical animals with bodies 0.5 to 2 mm long. The first instar has three pairs of legs, but that number increases with each moult so that adult species may have nine to eleven pairs of legs. They feed chiefly on fungi , decaying organic matter and root hairs . They have neither eyes nor hearts, although they do have sensory organs which can detect light.

Pauropods can be found in a variety of soils worldwide, but they are common in forest soils with high organic content and moisture are generally more common in broad-leaved forest soils than in coniferous forest soils. This difference in abundance is primarily due to the variations in soil characteristics and the amount and type of organic matter present in these two types of forests. While they are present in grasslands, they are often less abundant there compared to forested areas due to the lower levels of organic material on the soil surface. Their distribution is highly dependent on soil moisture, organic content, and the presence of decomposing material.

No fossil pauropods have been found from before the time of the Baltic amber, about 40mya, but that may be because they are so fragile. Or nobody has looked. They are difficult to see, and of no agricultural importance.

It is unlikely that they would have survived as fossils from all that time ago. But a negative does not prove a positive. They have been hard to see – they are translucent and very boring looking. I remember having difficulty finding any – the one I sent off the British Museum for identification, was only the third time that species had ever been found in UK.

Scamper

“They have an unusual gait, more of a funny, joyful scamper than a walk. Even being so small, the way they move is so distinctive, that without a hand lens, they can easily be picked out in a line up from similar sized millipedes. They run for a couple of seconds before stopping dead. Then after a quick, inquisitive twirl of their antennae, they run off in another direction"

Relatives

They seem to be an old group. Needless to say there is a debate about their closest relatives, some saying they are more closely related with millipedes and centipedes, whereas others say more to Symphylans. All their relatives go back a few hundred million years and are considered to be ‘myriapods’ although the strict classification (Myriapoda) is not used anymore.

Morphology & Molecules

“ Morphology and development provide compelling support for Diplopoda (millipedes) and Pauropoda being closest relatives, and moderate support for Symphyla being more closely related to the diplopod-pauropod group than any of them are to Chilopoda (centipedes). In contrast, several molecular datasets have contradicted the Diplopoda–Pauropoda grouping (named Dignatha), often recovering a Symphyla–Pauropoda group (named Edafopoda)" (Fernandez et al 2018) Here again is an uncertainty between morphology and molecules.

Can sorting out their origins help explain why they have not been seen before. The cladogram gives the impression Pauropods were between Symphylans and Millipedes (Diploda). Yet they may be several hundred million years apart .Their head capsules show great similarities to millipedes: both have three pairs of mouthparts and Their reproductive organs open at the bases of the second legs. Moreover, both groups have a pupoid phase at the end of the embryonic development. The two groups probably have a common origin, morphologically speaking. The body segments have ventral tracheal/spiracular pouches, a bit like millipedes and Symphylans.. But…I cannot make up my mind. So lets look at the environment and their behaviours to see if we can get guidance.

Let’s rule out centipedes as they are carnivores and pauropods are herbivores and there are few examples of evolution that way round. It seems that the size and movement of pauropods allow them to go deeper than other myriapods. I think behaviourally it is less likely for surface dwelling millipedes to descend, whereas the symphylans are already moving in soil pores. As those pores get smaller so do the symphylans....

Pauropods are shy of light, and will attempt to distance themselves from light sources. They occasionally migrate upwards or downwards throughout the soil based on moisture levels.

Did this happen hundreds of millions of years ago and they survive the asteroid, as they were living quite deeply? Or did they evolve in this era by adapting to new emerging conditions? If so they seem to be the only soil creatures which did.

I am going for their origins being a few hundred million years earlier. Their fossils have not been found as they would not fossilise easily and are hard to see, even when looking - which few people have. I have to await somebody finding a fossil of them from 400-100mya, but may between 145-66mya according to their presence today in broad-leaved woodlands

Preening

"There is no other word for it, but pauropods ‘preen’. The antennae or legs are lifted out of the way before they start to delicately groom themselves" (Chaos of Delight)

I have seen this among collembolans and mesostigmatid mites – cleaning themselves for quite some time. At first we wonder: “Why bother cleaning up in this dirt?”, but it is clear that cleanliness is important to several soil animals. Why would that be?

Springtail cleaning itself 3.25 mins

Pauropods are generally more abundant in broad-leaved forest soils than in coniferous forest soils. The key factors contributing to this pattern are the higher organic matter content, more favorable pH, and faster decomposition rates

Studies on earthworm diversity with respect to soil properties in different land use systems in Koraput region of the Eastern Ghats, India | Biodiversity and Conservation (springer.com)

Prostigmatid mites, -soil suckers

Astigmata hitch rides

Mites

Did the mites move from forest soil to grass soil too?

Habitats with highest mite : springtail ratio were Bog, Dwarf Shrub Heath and Acid Grassland. Woodlands were intermediate, while values in Arable and Horticulture, Neutral Grassland and Improved Grassland soils were the lowest of the studied habitats CS Chap 8

For mites, the most abundant group, the subjects in samples were identified into groups Cryptostigmata, Mesostigmata, Prostigmata, and Astigmata, the dominance of families was determined. .. The average density for mites was 53,327 individuals /m2, the density for individual groups and by group

Cryptostigmata .... 36,192 ...Mesostigmata ... 5,006 ... Prostigmata ...11,452 ...Astigmata ........ 675 ..

Among oribatids, Oppiidae occurred in all locations as the most eudominant (overwhelmingly dominant) family, from 24% in the abandoned pasture compared with 78% in the oak forest. Among mesostygmatic mites, the dominance of families varied in different locations. Among prostygmatic mites, Trombididae were always found to be eudominant, with between 70% and 90%.”[8]

Cryptostigmatid mites include oribatids

Mesostigmatid mites, mainly predators

Oribatids

The oribatids do not seem to dominate arthropod populations in pasture (ca 1/5) compared with forest (ca 4/5) According to the graphic new forms evolved with new feeding habits

Other mite groups - like Trombidiforms (including Prostigmata above), seem to have colonised equally. This is probably not surprising as oribatids do not seem as mobile as Trombidiforms. They rely on their cuticle and deep dwelling for protection. It is hard to see they would need ‘refugia’.

The evolution (right) indicates that there were a few evolutionary events but mainly round feeding habits.

Springtails

The are new cases of fossil inclusions of Symphypleona. They - like those mites in the previous period, like hitching a ride - its called 'phoretic behaviour' . They took advantage of the drastic increase of eusocial soil insects’ having an ecological impact over Cenozoic era. Winged castes of ants and termites may have been a mechanism for the worldwide dispersal of these springtails.

“Fossil springtails are reported from Cretaceous and Cenozoic amber deposits, in which they have occasionally been documented attached onto other invertebrates. Cases correspond to members of the order Symphypleona attached to harvestmen (Opiliones) and a false blister beetle (Oedemeridae) from the 55-35mya as well as a mayfly (Leptophlebiidae) 25-5 mya in Dominican amber. These springtails exhibit antennae either grasping arthropod limbs or pointing toward a potential surface of attachment, implying they were grasping onto these other arthropods while alive. This repeated fossil association has been argued to have no observed modern counterpar£ (Robin et al 2019)

Some consider part of the reason for hitching rides is that furcula motility is not now sufficient for dispersal. In the old days - 400+mya their big evolutionary advantage would have been used to move along water films. Now there is much more in the way so modern springtails are thought to disperse with soil particles as “aerial plankton” and by water for long-distance transportation (Dunger et al 2002).

We have already seen that ants dominate leaf litter in temperate grassland and termites in tropical grassland. The springtails have found a good way to be dispersed into the new territory where they can help build the mycorrhizal relationship between grasses and fungi.

One case study found “a ~ 16 Ma old fossil association: a winged termite and ant with 25 springtails attached or positioned close to the body. The collembola exhibit rare features for fossils, reflecting their courtship and phoretic (hitching a ride) behaviours. By observing (1) the positions and modes of attachment of springtails on different arthropods, (2) their sex representation and (3) ratios in springtail antennal anatomies in new and previously reported cases, we infer an attachment process for dispersal in symphypleonan springtails. By revealing hidden evidence of modern springtails associated with other invertebrates such as ants and termites, new cases of fossil inclusions of Symphypleona and termites, and pointing out the drastic increase of eusocial soil insects’ ecological impact over Cenozoic… we infer that association with winged castes of ants and termites may have been a mechanism for the worldwide dispersal of these springtails" (Robin et al 2019)

No wonder there are lots of Symphypleons in grass.

Springtails and feeding niches from sminths eating lichens to onchiurids more fungal..

Insects

The effects of the K-Pg event on plant–insect interactions have been examined extensively. These focus on the Western Interior of North America, Western Europe, and Patagonia, Argentina. In various, but there has been no indication that this significant global event had an effect at the level of mouthpart class diversity (Labandeira 2019)

Ants

Nobody would have predicted that the asteroid would have given rise to a new insect. While ants emerged in previous ages, there is an amazing new development within them, with the emergence of fungus-growing ants. They are called ‘attines’ and they tend the crop for their own delectation. Most use leaf litter, but some cut leaves. The fungi are predominantly basidiomycetes - higher fungi. The fungus provides nutrients for the ants, which may accumulate in specialized hyphal-tips known as "gongylidia". These growths are synthesized from plant substrates and are rich in lipids and carbohydrates.

We often think that humans inventing agriculture, but..

“In a rain forest in South America millions of years ago, itty-bitty ants with brains no bigger than a pinpoint had already figured it out. They started farming fungus for food — probably not too long after the Chicxulub meteor impact caused the mass extinction event that obliterated up to three-quarters of the rest of Earth’s plants and animals."

Attines

Attines are exclusive to the Americas and appear to be part of the fallout of the K-Pg event, As hunting and gathering may have got harder they would have found looking after fungi easier. Their sister group, Dacetina became predators. The development ant-fungus mutualism was not straightforward, as they lost the ability to synthesize arginine, which created a dependency on their cultivars

There are 240 ants in the group attine that evolved more than 50 million years ago, capable of growing elaborate fungal gardens as a source of food within nests for their colonies. This mutualism is thought to have originated in the basin of the Amazon rainforest some 50–66 million years ago. Leaf-cutting ants, the dominant herbivores of the Neotropics, evolved remarkably recently, only 8–12 Ma (Schultz & Brady 2008).

We saw earlier that fungi appear to be the most vulnerable organisms when it comes to forest fires. Perhaps the ants did them favour in helping them recover. Neither the ants nor the fungal cultivars can survive outside of the symbiosis.

“Although all members of this tribe cultivate fungi, attine ants are surprisingly heterogeneous with regard to symbiont associations and agricultural system, colony size and social structure, nesting behavior, and mating system. This variation is a key reason that the Attini have become a model system for understanding the evolution of complex symbioses."(Mehdiabidi & Schultz)

What do attines do in soil?

“There is good evidence for environmental (from soil) recruitment of antibiotic-producing actinomycetes by attine ants and for the idea that actinomycete-produced antibiotics are important for helping the right bacteria to colonize and establish mutualism with attine ants. Recent studies have shown that the co-evolved Pseudonocardia mutualists are not phylogenetically very distinct from environmental isolates and that the antifungals produced by these bacteria have generalised activity rather than specifically targeting Escovopsis" (Bark et al 2011)

5 types of fungal farming

There are five main types of agriculture that fungus-growing ants practice: Lower agriculture commonly involves smaller nests and they use techniques besides cutting leaves to obtain plant material. Coral-fungus agriculture is practiced by 34 species by a single derived clade within the genus Apterostigma. Some grow yeast. “Higher agriculture is practiced by 63 species in two genera and refers to the condition of highly domesticated fungus. The fungi used in higher agriculture cannot survive without its agriculturalists to tend it and has phenotypic changes that allow for increased ease of ant harvesting" (Schultz & Brady 2008).

Termites

We have seen that termites appeared about 125-150mya, but they really dispersed in this Cenozoic period. They now dominate tropical grassland leaf litter. (Hedenic et al 2022).

“They have exceptional biomass and play important roles in decomposition of dead plant matter, in soil manipulation, and as the primary food for many animals, especially in the tropics. Higher termites are most diverse in rainforests, with estimated origins in the late Eocene (54 Ma), postdating the breakup of Pangaea and Gondwana when most continents became separated. Since termites are poor fliers, their origin and spread across the globe requires alternative explanation. Here, we show that higher termites originated 42-54 Mya in Africa and subsequently underwent at least 24 ‘dispersal events’ between the continents in two main periods"

We have seen in the Cretacous period, and above, that springtails hitched rides on ants and termites, and this is likely to have continued in the invasion of grassland in the tropics.

Flies

Bibionid flies also have their larval stage in soil under grass are. 2 Bibionid flies that are common to amenity turfgrass These flies are pollinators of fruit and other crops, while, their larvae can damage turf by feeding on the roots.

Starlings going mad for Bibionid larvae.Click image for video

Again we find the new generation of above ground animals, here birds, living off that below.

There are 3 'trophic levels' - birds eating bugs & beetles that eat tiny soil animals

Page updated

Google Sites

Report abuse