Protosalvinia
Encyclopedia
Protosalvinia is a prehistoric plant
found commonly in shale
from shoreline habitat
s of the Upper Devonian
period. The name Protosalvinia is a misnomer
. The name literally means early Salvinia, and was given in the erroneous belief that the fossils were an earlier form of the living aquatic fern
Salvinia
. It is no longer believed that the fossils come from a fern, but deciding exactly what the fossil
s represent is still a matter of debate. This is surprising when one considers how much is known about the fossils.
The most likely interpretation of Protosalvinia is that it represents either a fossil liverwort
or brown alga, although no definitive brown algae have been identified from before the Tertiary period, and examination of the spore structure shows no features in common with living groups of brown algae. The living plant
was a thallus with short dichotomous branching. The branches in the largest species were as much as one centimeter across. In some fossils, the branching lobes lie flat, but in others the tips of the branches are curled up over the fossil, giving it a round outline. Embedded in the tissues of the thallus are chambers in which spore
s (200 micrometre
diameter) were produced by meiosis
.
Because Protosalvinia is usually preserved as a compression fossil
, it can be difficult to determine whether its anatomy
is more like a plant or an alga. Some biochemical evidence favors interpretation as an alga. Lignin and cutin have been found in the thalli, and sporopollenin
in the spore walls. The grouping of the spores found in the thallus favors interpretation as a plant. The absence of any stomata on the surface is inconclusive, as all bryophyte
s lack stomata on the main body of the plant.
However, the tips of Protosalvinia branches show evidence of conceptacle
-like dips.
Protosalvinia is found in association with conodont
elements.
For the present, the relationships of Protosalvinia remain uncertain.
Paleobotany
Paleobotany, also spelled as palaeobotany , is the branch of paleontology or paleobiology dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments , and both the evolutionary history of plants, with a...
found commonly in shale
Shale
Shale is a fine-grained, clastic sedimentary rock composed of mud that is a mix of flakes of clay minerals and tiny fragments of other minerals, especially quartz and calcite. The ratio of clay to other minerals is variable. Shale is characterized by breaks along thin laminae or parallel layering...
from shoreline habitat
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
s of 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...
period. The name Protosalvinia is a misnomer
Misnomer
A misnomer is a term which suggests an interpretation that is known to be untrue. Such incorrect terms sometimes derive their names because of the form, action, or origin of the subject becoming named popularly or widely referenced—long before their true natures were known.- Sources of misnomers...
. The name literally means early Salvinia, and was given in the erroneous belief that the fossils were an earlier form of the living aquatic 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...
Salvinia
Salvinia
Salvinia, a genus in the family Salviniaceae, is a floating fern named in honor of Antonio Maria Salvini, a 17th Century Italian scientist. The genus was published by Séguier, in Pl. Veron. 3: 52. 1754. About ten species exist....
. It is no longer believed that the fossils come from a fern, but deciding exactly what the fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s represent is still a matter of debate. This is surprising when one considers how much is known about the fossils.
The most likely interpretation of Protosalvinia is that it represents either a fossil liverwort
Marchantiophyta
The Marchantiophyta are a division of bryophyte plants commonly referred to as hepatics or liverworts. Like other bryophytes, they have a gametophyte-dominant life cycle, in which cells of the plant carry only a single set of genetic information....
or brown alga, although no definitive brown algae have been identified from before the Tertiary period, and examination of the spore structure shows no features in common with living groups of brown algae. The living plant
Plant
Plants are living organisms belonging to the kingdom Plantae. Precise definitions of the kingdom vary, but as the term is used here, plants include familiar organisms such as trees, flowers, herbs, bushes, grasses, vines, ferns, mosses, and green algae. The group is also called green plants or...
was a thallus with short dichotomous branching. The branches in the largest species were as much as one centimeter across. In some fossils, the branching lobes lie flat, but in others the tips of the branches are curled up over the fossil, giving it a round outline. Embedded in the tissues of the thallus are chambers in which spore
Spore
In biology, a spore is a reproductive structure that is adapted for dispersal and surviving for extended periods of time in unfavorable conditions. Spores form part of the life cycles of many bacteria, plants, algae, fungi and some protozoa. According to scientist Dr...
s (200 micrometre
Micrometre
A micrometer , is by definition 1×10-6 of a meter .In plain English, it means one-millionth of a meter . Its unit symbol in the International System of Units is μm...
diameter) were produced by meiosis
Meiosis
Meiosis is a special type of cell division necessary for sexual reproduction. The cells produced by meiosis are gametes or spores. The animals' gametes are called sperm and egg cells....
.
Compression fossil
A compression fossil is a fossil preserved in sedimentary rock that has undergone physical compression. While it is uncommon to find animals preserved as good compression fossils, it is very common to find plants preserved this way...
, it can be difficult to determine whether its anatomy
Anatomy
Anatomy is a branch of biology and medicine that is the consideration of the structure of living things. It is a general term that includes human anatomy, animal anatomy , and plant anatomy...
is more like a plant or an alga. Some biochemical evidence favors interpretation as an alga. Lignin and cutin have been found in the thalli, and sporopollenin
Sporopollenin
thumb|right|270px|[[Scanning electron microscope|SEM]] image of pollen grainsSporopollenin is a major component of the tough outer walls of spores and pollen grains. It is chemically very stable and is usually well preserved in soils and sediments...
in the spore walls. The grouping of the spores found in the thallus favors interpretation as a plant. The absence of any stomata on the surface is inconclusive, as all bryophyte
Bryophyte
Bryophyte is a traditional name used to refer to all embryophytes that do not have true vascular tissue and are therefore called 'non-vascular plants'. Some bryophytes do have specialized tissues for the transport of water; however since these do not contain lignin, they are not considered to be...
s lack stomata on the main body of the plant.
However, the tips of Protosalvinia branches show evidence of conceptacle
Conceptacle
Conceptacles are specialised cavities of marine and freshwater algae that contain the reproductive organs. They are situated in the receptacle and open by a small ostiole. Conceptacles are present in Corallinaceae, and Hildenbrandiales, as well as the brown Fucales. In the Fucales there is no...
-like dips.
Protosalvinia is found in association with conodont
Conodont
Conodonts are extinct chordates resembling eels, classified in the class Conodonta. For many years, they were known only from tooth-like microfossils now called conodont elements, found in isolation. Knowledge about soft tissues remains relatively sparse to this day...
elements.
For the present, the relationships of Protosalvinia remain uncertain.
Further reading
- Kenrick, Paul & Crane, Peter R. (1997). The Origin and Early Diversification of Land Plants: A Cladistic Study. Washington, D. C.: Smithsonian Institution Press. ISBN 1-56098-730-8.
- Stewart, Wilson N. & Rothwell, Gar W. (1993). Paleobotany and the Evolution of Plants (2nd ed.). Cambridge: Cambridge University PressCambridge University PressCambridge University Press is the publishing business of the University of Cambridge. Granted letters patent by Henry VIII in 1534, it is the world's oldest publishing house, and the second largest university press in the world...
. ISBN 0-521-38294-7. - Taylor, Thomas N. & Taylor, Edith L. (1993). The Biology and Evolution of Fossil Plants. Englewood Cliffs, NJ: Prentice Hall. ISBN 0-13-651589-4.