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Many of us associate 'Jurassic' with dinosaurs. But the next time you look up to one of these creatures, also think about the earth beneath their feet. It is now strong enough to take their weight, but also provide the structure and nutrients to help grow those foodstuffs for them to eat. Think worms, mites and podzols - soil with distinct horizons.
There must have been a lot of soil to cope with the dinosaur tread., as well as thier dung and carcasses. Their food, mainly plants, would provide deposits to help build up compost material. Then there are the birds and flying reptiles in the air, which would also have left their remains on the soil surface.. Many would be feeding on the insects now flying about, many with their larvae grubbing around in the soil, and providing a new food source for rove beetles and other predators.
This was the period when soils got darker, thanks to widespread humification and deeper, thanks to Ectomycorrhiza, It was when 'terrestrialisation' proper started with many more plants and animals moving to live in and build soil structures. They came from the air, water and other land. The plethora of creatures', like earthworms and higher oribatids, chewed, pooed, and glued and so contributed to the 3rd wave of decomposition and macroaggregation as well as better recycling of nutrients like nitrates and phosphates.
"The end-Triassic mass extinction (ETE) (c. 201.6 Ma) was one of the five largest mass-extinction events in the history of animal life. It was also associated with a dramatic, long-lasting change in sedimentation style along the margins of the Tethys Ocean, from generally organic-matter-poor sediments during the Triassic to generally organic-matter-rich black shales during the Jurassic." (Schootbrugge et al 2013). Organic geochemistry confirms that it is mostly marine, although there are some exceptions: jet and other terrestrial debris would have been discharged from river estuaries during flood events.
ETE
ETE
The end-Triassic extinction (ETE) occurred around 200 Mya and is one of the “Big Five” biotic crises of the last five hundred million years. There was a transition from a marine ecosystem to a less saline, shallow-water, microbial-mat environment and a mass extinction that occurred slightly later, caused by abrupt injection of volcanogenic CO2. (Fox et al., 2020)
Earthworms appear in soil. The holometabolous insects, like various beetles laid their eggs in soil for their larvae to grow there. They arrived to occupy the new deeper darker soil niche and their branches evolving differently as the new continents split apart.
The early soil characters, the springtails, nematodes and mites have been pretty well dug in for a long time, diversify in various ways, not least of which the oribatids turn brown and curl up as 'higher' oribatids - the ones we call 'armadillo' mites.
Generally support Ghilarov's hypothesis
Generally support Ghilarov's hypothesis
"Generally support Ghilarov‘s hypothesis. Many soil invertebrates have their evolutionary ancestors in a freshwater environment. So, soil can indeed be considered as an evolutionary transition zone between water and air. However, the situation is more complex than envisaged by Ghilarov, as there are different scenarios for the pathway. First of all, root herbivores must be seen as an exception, as all of them are secondarily adapted to soil conditions; their ancestors are aboveground, not in the water.
Another qualification of Ghilarov’s hypothesis is that there are major and minor terrestrializations. The major events have occurred only once in a lineage, happened a long time ago (early in the Paleozoic) and came with new body plans and significant adaptive radiation on land. Examples are the terrestrializations of hexapods, myriapods and chelicerates. The “minor” terrestrializations happened several times in the same clade, are more recent (in the Mesozoic or Cenozoic) and did not change the body plan much. Examples are the terrestrializations of potworms, land snails and amphipods. The major terrestrializations are also more successful in the sense that the changes in body plan were more profound and gave rise to entirely new classes or new orders of animals, while in the minor events a worm stayed a worm and an isopod remained isopod." (Straleen 2021)
There is also indication that the soil provided more space to live, as the pores got bigger, due to macroaggregation. These emerging structures, using new glues, also enabled soils to support greater weight of soil above them, as they proved a resilience not there previously. There is also something about size. The beetle larvae, immensely bigger than existing soil animals like springtails and oribatid mites, now exist in soil. Worms, whether blackworms (from water) or potworms (from bogs), evolved into the much bigger earthworms. The worms were leaving bigger burrows behind, again due to the new resilience, meaning more air could get down deeper. It is of course the same period that another group of creatures above ground were getting much larger. Is there anything we can learn, about soil sizes, from dinosaurs' gigantism?
Tracks
Tracks
Many of us know this Period - Jurassic - as the age of the dinosaurs. However, whenever you see a dinosaur from now on, please think ‘worms’. Those great dinosaur feet must have trodden a lot of soil and so squashed a few earthworms which were transforming the soil. The evolution of earthworms in this period was as significant as the dinosaurs – except that worms survived. These soil creatures evolved towards the end of Pangea, as it broke apart. Their presence across the world now reflects that early evolution.
I was originally disappointed not to find any dinosaurs tracks made in ‘soil’, in order to see if they could give us some clues about the soil. Were they only in mudflats or shorelines, because there have to be the exact conditions to make a fossil, and that didnt happen in soil. Soils tend to be in dynamic equilibrium (see entropy) verging towards erosion. We see all that silt in rivers during floods. Thus, soils are rarely preserved in the geological record - mud flats and shorelines are often sinking and thus become buried thus preserving footprints. Paleosols are rare,while non-marine mudstones and sandstones much much more common.
To survive until the present, several specific steps (geddit?) had to happen. The sediment the dinosaurs walked through needed to be just the right texture -- not too soft and not too hard. Prints in very wet soil would collapse on themselves, and walking in hard soil made less impression, because - as we are seeing - these emerging soils are more resilient to pressure.
Does the lack of dinosuar tracks demonstrate soil resilience?
Surely the dinosaurs walked on soil in order to get to eat their leaves? It was quite possible that the feet did not sink into soil, as it was resilient enough to withstand the weight - about the same as the big UK tractors and trailers today- so leave no track. Elephants and rhinos dont always leave footprints in the soil either. Let's find out more about dinosaur tread in the next period
Pangea was beginning to separate into several continents. The two largest, Laurasia, represent the Northern hemisphere and Gondwana the Southern.
Does Jurassic soil make good wine?
Frederick Marc Burrier, 17 years President of the growers’ union (Union des Producteurs de Pouilly-Fuissé) explained that to become primary cru, the technical criteria included soil, aspect, inclination, and altitude. “The soil has to originate from the Jurassic period"
Other evidence indicates later grapes <60mya Herrera 2024
The soil became much more like we know it today, as it became inhabited with a lot more familiar plants and creatures.
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