Archaeopteris
Encyclopedia
Archaeopteris is an extinct genus
of tree-like plants with fern
-like leaves. A useful index fossil
, this tree is found in strata
dating from the Upper Devonian
to Lower Carboniferous
, and has a global distribution.
Until the 2007 discovery of Wattieza
, many scientists considered Archaeopteris to be the earliest known tree. Bearing buds, reinforced branch joints, and branched trunks similar to today's timber
, it is more reminiscent of modern seed-bearing trees than other spore bearing taxa; It combines characteristics of woody trees and herb
aceous ferns, and belongs to a group of extinct plants sometimes called the progymnosperms, plants with gymnosperm-like wood but that produce spores rather than seeds.
s were thickly set with fan-shaped leaflets on stems that inclined sharply upward. They typically grew to 10 m in height. Some species are large, with trunks that exceeded 1.5 m in diameter. The veining branches diverged dichotomously. There was also intermediate feathering at each frond node or axes.
Leafy shoots occurred in opposite arrangement in a single plane. The leaflets, or pinnules, overlapped one another and were subcircular to wedge-shaped. On fertile branches, the leaves were replaced by spore capsules.
foliage or like trees in the cypress family Cupressaceae
.
The plant had nodal zones that would have been important sites for the subsequent development of lateral roots and branches. Some branches were latent and adventitious, similar to those produced by living trees that eventually develop into roots. Before this time, shallow, rhizomatous
roots had been the norm, but with Archaeopteris, deeper root systems were being developed that could support ever higher growth.
s, growing close to river
systems and in flood plain woodlands. It would have formed a significant part of the canopy vegetation of early forests. Speaking of the first appearance of Archaeopteris on the world-scene, Stephen Scheckler, a professor of biology and geological sciences at Virginia Polytechnic Institute, says, "When [Archaeopteris] appears, it very quickly became the dominant tree all over the Earth. On all of the land areas that were habitable, they all had this tree".
Scheckler believes that Archaeopteris had a major role in transforming its environment. "Its litter fed the streams and was a major factor in the evolution of freshwater fishes, whose numbers and varieties exploded in that time, and influenced the evolution of other marine ecosystems. It was the first plant to produce an extensive root system, so had a profound impact on soil chemistry. And once these ecosystem changes happened, they were changed for all time. It was a one-time thing."
Looking roughly like a top-heavy Christmas tree
, Archaeopteris may have played a part in the transformation of Earth’s climate
during the Devonian before becoming extinct within a short period of time at the beginning of the Carboniferous period.
n paleontologist Mikhail Dimitrievich Zalessky described a new type of petrified wood
from the Donetz Basin in Russia
. He called the wood Callixylon, though he did not find any structures other than the trunk. The similarity to conifer wood was recognized. It was also noted that ferns of the genus Archaeopteris were often found associated with fossil
s of Callixylon.
In the 1960s, paleontologist Charles B. Beck was able to demonstrate that the fossil wood known as Callixylon and the leaves known as Archaeopteris were actually part of the same plant. It was a plant with a mixture of characteristics not seen in any living plant, a link between true gymnosperm
s and ferns.
The genus Archaeopteris is placed in the order Archaeopteridales and family Archaeopteridaceae. The name is similar to that of the first known feathered bird, Archaeopteryx
, but in this case refers to the feather-like nature of the plant's fronds.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of tree-like plants with fern
Fern
A fern is any one of a group of about 12,000 species of plants belonging to the botanical group known as Pteridophyta. Unlike mosses, they have xylem and phloem . They have stems, leaves, and roots like other vascular plants...
-like leaves. A useful index fossil
Index fossil
Index fossils are fossils used to define and identify geologic periods . They work on the premise that, although different sediments may look different depending on the conditions under which they were laid down, they may include the remains of the same species of fossil...
, this tree is found in strata
Stratum
In geology and related fields, a stratum is a layer of sedimentary rock or soil with internally consistent characteristics that distinguish it from other layers...
dating from the Upper Devonian
Devonian
The Devonian is a geologic period and system of the Paleozoic Era spanning from the end of the Silurian Period, about 416.0 ± 2.8 Mya , to the beginning of the Carboniferous Period, about 359.2 ± 2.5 Mya...
to Lower Carboniferous
Carboniferous
The Carboniferous is a geologic period and system that extends from the end of the Devonian Period, about 359.2 ± 2.5 Mya , to the beginning of the Permian Period, about 299.0 ± 0.8 Mya . The name is derived from the Latin word for coal, carbo. Carboniferous means "coal-bearing"...
, and has a global distribution.
Until the 2007 discovery of Wattieza
Wattieza
Wattieza was a genus of prehistoric trees that existed in the mid-Devonian that belong to the cladoxylopsids, close relatives of the modern ferns and horsetails...
, many scientists considered Archaeopteris to be the earliest known tree. Bearing buds, reinforced branch joints, and branched trunks similar to today's timber
Timber
Timber may refer to:* Timber, a term common in the United Kingdom and Australia for wood materials * Timber, Oregon, an unincorporated community in the U.S...
, it is more reminiscent of modern seed-bearing trees than other spore bearing taxa; It combines characteristics of woody trees and herb
Herb
Except in botanical usage, an herb is "any plant with leaves, seeds, or flowers used for flavoring, food, medicine, or perfume" or "a part of such a plant as used in cooking"...
aceous ferns, and belongs to a group of extinct plants sometimes called the progymnosperms, plants with gymnosperm-like wood but that produce spores rather than seeds.
Anatomy
The trees of this genus were small to medium in size with leafy foliage reminiscent of some conifers. The large frondFrond
The term frond refers to a large, divided leaf. In both common usage and botanical nomenclature, the leaves of ferns are referred to as fronds and some botanists restrict the term to this group...
s were thickly set with fan-shaped leaflets on stems that inclined sharply upward. They typically grew to 10 m in height. Some species are large, with trunks that exceeded 1.5 m in diameter. The veining branches diverged dichotomously. There was also intermediate feathering at each frond node or axes.
Leafy shoots occurred in opposite arrangement in a single plane. The leaflets, or pinnules, overlapped one another and were subcircular to wedge-shaped. On fertile branches, the leaves were replaced by spore capsules.
Other modern adaptations
Aside from its woody trunk, Archaeopteris possessed other modern adaptations to light interception and perhaps to seasonality as well. The large umbrella of fronds seems to have been quite optimized for light interception at the canopy level. In some species, the pinnules were shaped and oriented to avoid shading one another. There is evidence that whole fronds were shed together as single units, perhaps seasonally like modern deciduousDeciduous
Deciduous means "falling off at maturity" or "tending to fall off", and is typically used in reference to trees or shrubs that lose their leaves seasonally, and to the shedding of other plant structures such as petals after flowering or fruit when ripe...
foliage or like trees in the cypress family Cupressaceae
Cupressaceae
The Cupressaceae or cypress family is a conifer family with worldwide distribution. The family includes 27 to 30 genera , which include the junipers and redwoods, with about 130-140 species in total. They are monoecious, subdioecious or dioecious trees and shrubs from 1-116 m tall...
.
The plant had nodal zones that would have been important sites for the subsequent development of lateral roots and branches. Some branches were latent and adventitious, similar to those produced by living trees that eventually develop into roots. Before this time, shallow, rhizomatous
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
roots had been the norm, but with Archaeopteris, deeper root systems were being developed that could support ever higher growth.
Habitat
Evidence indicates that Archaeopteris preferred wet soilSoil
Soil is a natural body consisting of layers of mineral constituents of variable thicknesses, which differ from the parent materials in their morphological, physical, chemical, and mineralogical characteristics...
s, growing close to river
River
A river is a natural watercourse, usually freshwater, flowing towards an ocean, a lake, a sea, or another river. In a few cases, a river simply flows into the ground or dries up completely before reaching another body of water. Small rivers may also be called by several other names, including...
systems and in flood plain woodlands. It would have formed a significant part of the canopy vegetation of early forests. Speaking of the first appearance of Archaeopteris on the world-scene, Stephen Scheckler, a professor of biology and geological sciences at Virginia Polytechnic Institute, says, "When [Archaeopteris] appears, it very quickly became the dominant tree all over the Earth. On all of the land areas that were habitable, they all had this tree".
Scheckler believes that Archaeopteris had a major role in transforming its environment. "Its litter fed the streams and was a major factor in the evolution of freshwater fishes, whose numbers and varieties exploded in that time, and influenced the evolution of other marine ecosystems. It was the first plant to produce an extensive root system, so had a profound impact on soil chemistry. And once these ecosystem changes happened, they were changed for all time. It was a one-time thing."
Looking roughly like a top-heavy Christmas tree
Christmas tree
The Christmas tree is a decorated evergreen coniferous tree, real or artificial, and a tradition associated with the celebration of Christmas. The tradition of decorating an evergreen tree at Christmas started in Livonia and Germany in the 16th century...
, Archaeopteris may have played a part in the transformation of Earth’s climate
Climate
Climate encompasses the statistics of temperature, humidity, atmospheric pressure, wind, rainfall, atmospheric particle count and other meteorological elemental measurements in a given region over long periods...
during the Devonian before becoming extinct within a short period of time at the beginning of the Carboniferous period.
Relationship to conifers
Because Archaeopteris reproduced by releasing spores rather than by producing seeds, paleobotanists suspect that modern trees come from a sibling line of plants they call the "progymnosperms". Archaeopteris is more like an ancient cousin than a direct ancestor.Discovery and classification
Archaeopteris was originally classified as a fern, and it remained classified so for over 100 years. In 1911, RussiaRussia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
n paleontologist Mikhail Dimitrievich Zalessky described a new type of petrified wood
Petrified wood
Petrified wood is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree having turned completely into stone by the process of permineralization...
from the Donetz Basin in Russia
Russia
Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...
. He called the wood Callixylon, though he did not find any structures other than the trunk. The similarity to conifer wood was recognized. It was also noted that ferns of the genus Archaeopteris were often found associated with fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s of Callixylon.
In the 1960s, paleontologist Charles B. Beck was able to demonstrate that the fossil wood known as Callixylon and the leaves known as Archaeopteris were actually part of the same plant. It was a plant with a mixture of characteristics not seen in any living plant, a link between true gymnosperm
Gymnosperm
The gymnosperms are a group of seed-bearing plants that includes conifers, cycads, Ginkgo, and Gnetales. The term "gymnosperm" comes from the Greek word gymnospermos , meaning "naked seeds", after the unenclosed condition of their seeds...
s and ferns.
The genus Archaeopteris is placed in the order Archaeopteridales and family Archaeopteridaceae. The name is similar to that of the first known feathered bird, Archaeopteryx
Archaeopteryx
Archaeopteryx , sometimes referred to by its German name Urvogel , is a genus of theropod dinosaur that is closely related to birds. The name derives from the Ancient Greek meaning "ancient", and , meaning "feather" or "wing"...
, but in this case refers to the feather-like nature of the plant's fronds.
External links
- History of Paleozoic Forests: the Early Forests and the Progymnosperms
- Consequences of Rapid Expansion of Late Devonian Forests, by Stephen E. Scheckler
- Walker, Cyril and David Ward. Fossils. Smithsonian Handbooks. Dorling Kindersley, Inc. New York, NY (2002).
- Mayr, Helmut. A Guide to Fossils. Princeton University Press, Princeton, NJ (1992).
- Introduction to the Progymnosperms
- Davis, Paul and Kenrick, Paul; Fossil Plants. Smithsonian Books (in association with the Natural History Museum of London), Washington, D.C. (2004). ISBN 1-58834-156-9