Plant hypothesis - Restaurant l'Iroise

Once these features had evolved, there was a substantial diversification of land plants during the Devonian period (408 - 362 million years ago). These included lycophytes (the clubmosses are the best-known modern members of this group:), horsetails (e.g. Equisetum), and progymnosperms, intermediate between seedless vascular plants and the seed plants. While the early forms were small & lacked woody tissue, the first tree-like plants (including progymnosperms and tree-sized lycophytes) had appeared by the mid-Devonian. The first real trees (e.g. Archaeopteris) had developed by the late Devonian, and the seed-bearing had evolved from the progymnosperms by the end of this geological period. The appearance of trees had a significant effect on the environment, because their advanced root systems influenced soil production and led to increased weathering.

plant radiation: an ecological hypothesis

One of the more interesting of these is the "Devonian Plant Hypothesis"

What is the Devonian Plant Hypothesis?

As scientists know with mammals, although , it comes with a great energetic cost. As with plants, an animal can spend its on consumption (metabolism) or investment (growth). An intriguing hypothesis is that growing large was part of an energy strategy, as the benefits of size (reduced risk of predation, ease of conserving body heat and consequently less need for a high metabolism, ability to access new food sources, such as foliage high above the ground) outweighed their costs (energy devoted to growth instead of metabolism, the need to constantly feed). Their size and the warm climate meant that large dinosaurs did not need as intense internal energy generation as mammals do, for instance, and dinosaurs may have been , with internal energy regulation greater than , but not as great as (mammals and birds).

The Devonian: The Plant World and the Animal World

Conifer forests, which , first . Devonian forests were 10 meters tall, Carboniferous rainforests were 30 meters tall, and Mesozoic conifers reached 60 meters tall and even sequoias appeared. Conifers were one of the early seed plants and used pollen to fertilize their seeds; that method that did not need the water that spores did. As conifers appeared during an ice age, they are well-adapted to cold climates, which is why conifer forests are so prevalent today. As , conifers were later displaced by , which engaged in an unprecedented symbiosis with animals, and conifers were pushed to Earth’s cold margins. declined after the Carboniferous, but still exist today.

A severe loss in biodiversity and a ‘floral crisis’ in land plants were triggered by the Late Devonian mass extinction.
Both low-temperature stress (hypothermia) and oxygen deprivation (hypoxia) are implicated in the Late Devonian mass extinction.

Devonian Times - Mass Extinction

From a biomass perspective, the Devonian’s primary change was the proliferation of land plants. Below is an artist's conception of a Devonian forest. (Source: Wikimedia Commons)

glacation/climate change asteroid impact global marine anoxia* volcanism Devonian plant hypothesis

14/07/2015 · Abstract

The Famennian plant locality of Barraba, in north-eastern New South Wales, is one of the rare Devonian sites of Australia to have yielded permineralized plants. In addition, a large number of vegetative axes of are preserved as adpressions. Two permineralized specimens of lycopsids have been collected in this locality (Chambers and Regan, 1986). One is the large cone reported in the present paper, the second a lycopsid stem that Chambers and Regan referred to as and that we are currently investigating. The Barraba cone is the single lycopsid fructification yet published from any Late Devonian plant locality in Australia. Because of the rarity of this type of remains, we have chosen to use X-Ray Synchrotron microtomography to investigate its three-dimensional structure and to discard, as far as possible, any of the destructive methods (i.e., peel-sections, thin-sections) classically employed to study anatomically preserved specimens. This cone represents a new taxon whose affinities are discussed.

One of the more interesting of these is the Devonian Plant Hypothesis.

the period is associated with the development of plant rooting ..

The climate was warm and seasonally dry, in at least some parts of the world, during the early and middle parts of the Devonian, and it was at this time that the land first came to be dominated by large plants. Bushy, shrublike forms and small treelike statures, which included primitive fernlike types, primitive ancestral types of the conifers and horsetails of the present, were achieved by several groups of plants in the Middle Devonian. Treelike morphologies were attained by lycopsids and progymnosperms, such as , the latter growing up to 18 m tall, for the first time. It is suggested that a significant canopy layer would have been formed by these trees which would have provided shade and shelter for the early terrestrial animals. The island of Santiago (San Salvador) in the Galapagos Islands of the present the habitat was dominated by ferns and lycopsids, miniature representatives of the sort of landscape that would have existed in the Middle Devonian.