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Cones
Cones
No new major plant groups originated during this time, although Jurassic plant communities differed considerably from their predecessors. The seed-fern floras of Triassic times had died out.
“Naked-seed” plants (Gymonsperms) dominated the earth and consisted of three groups: cycads, conifers, and ginkgos. The cone-bearing plants (Conifers, like modern pine trees) made up a large part of Jurassic forests, with most modern conifers evolved by the end of the period. Many of their fossils have been assigned to modern families such as Araucariaceae, Pinaceae and Taxodiaceae. The fruit bearing ginkgo was fairly widespread, although only one species is alive today.
Distribution
Distribution
Plant diversity was lowest in drier equatorial regions, increasing to a maximum in midlatitudes and then decreasing toward the wetter poles. What is curious is "there is an obvious geographic mismatch between known dinosaur distributions and their primary food source." (Rees et al 2004) Perhaps their bodies fossilised better in the drier climes.
Lots of slow-growing evergreen trees and shrubs contributed the dinosaurs' herbivorous diets, including redwoods, yews, pines, the monkey puzzle tree, & cypress. We will find out how their poo helped the soil in the next period. The tree trunks would have fallen back to ground.
The secondary decomposition process - de-lignification was now there to help break down the hard lignin. There were thousands of fungi, flies, beetle larvae and springtails, to break the detritus down to feed back into the soil - completing the nutrient cycles we know today. The soil became both a rich source and substrate for many life forms. It was probably in a better state than it had ever been.
Holacanthella
We may get a glimpse of one of the springtails which could have existed in those fallen trees.
New Zealand has been cut off from the rest of the world since Jurassic times and is where we find giant springtails - like this one - up to 15mm (cf1mm normally). They seem to like the wettest coldest forest.
Ginko
Cycad
Conifers and ginkgoes exploded in diversity. Today only a small fragment of the species that existed back then remain. I planted Gingko biloba (or maidenhair tree) as its little, fan-shaped leaves turn a beautiful yellow in autumn that bring a lovely injection of colour to our gardens.
Cycads were one of the first plants to be pollinated by insects, with beetles transferring pollen from the slender male cones on one plant to the female cones on another plant
Roots
Roots
Conifers roots spread out widely - witness how they rip up tarmac - rather than go deep as a taproot. These roots developed a symbiosis with the newly emerging ectomycorrhiza, that cycled the nutrients better, and enabled the roots to penetrate further. They can go down two metres. Somehow the fungi could breath deeper down - presumably aided by the roots providing air and water channels and pores.
Fig Tree featured in the Jurassic Park movies - Allerton Botanical Garden, Kauai
"Three types of rooting systems are recognized from two fossiliferous beds Middle Jurassic, Beijing, China. Cladophlebis-dominated community is associated with Type-A & B rooting system, which consist of abundant in situ vertical rhizomes, fine shoot-borne roots and lateral roots, and are consistent with those of some extant ferns.. The Type-C rooting system shows a thick central taproot and at least three orders of lateral roots, an architecture typical of various gymnosperms. The in situ rooting systems, as well as sedimentary evidence, contribute to the recognition of stacked, reworked Entisols (recently formed, little horizon & 1/5 all soils today) in a dynamic waterlogged environment." (Liu et al 2018)
Redox Potential
Redox Potential
While predominantly aerobic, with 'new' ectomycorrhzal fungi turning plant compounds to food for springtails and other soil animals, soil could also switch to anaerobic. This is called the ‘redox potential’ – the potential to switch between Aerobic oxidising conditions and anaerobic reducing conditions..
The role of these roots, with their associated rhizosphere would have bought major changes to soil, enabling it to function much deeper. Their new mycorrhiza could take them where they had not gone before and provide pores and channels for many other creatures like oribatid mites, that could also now go further and deeper, thanks to thier stronger exoskelton. There they, along with newly arrived earthworms could make more humus which helped bind the mineral soil elements into macraggregates providing still more support for the roots - and hence the trees.
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