Paleodictyon nodosum
Encyclopedia
The Paleodictyon nodosum is the creature which is thought to produce a certain form of Paleodictyon
burrows. They are found around mid ocean ridge systems in both the Pacific and Atlantic Oceans. Although scientists have collected many of the burrows of the Paleodictyon nodosum, they have never seen a live one. What a live specimen would look like is widely debated, with the debate being split into two main sides.
Adolf Seilacher
who discovered the original fossil
s of the Paleodictyon nodosum hypothesizes that the creature is a worm like species that burrows into the sediment around hydrothermal vents and deflects water flow through the burrows to catch food or farm its own food.
Peter A. Rona, discoverer of the modern burrows, suggests that the Paleodictyon nodosum may actually be a large protist
. There are other known examples of protists reaching the sizes that the Paleodictyon nodosum reaches, and they are known to be infaunal
.
Scientists ran various tests on the burrows of the Paleodictyon nodosum and were unable to reach a single conclusion as to the form of the Paleodictyon nodosum. The one thing that they can agree upon is that there are many markers that suggest that these forms are caused by a creature, and not by geological forces.
between 2400-3700m depth. Later, Seilacher and Rona used the deep-water submersible DSV Alvin
to recover samples of the same form near the Mid-Atlantic Ridge
. These samples were collected between 3430m and 3575m depth, around 26°N and 45°W. These burrows were found in very similar conditions as the ones found along the Galapagos Rift
. The biggest similarity between the habitats of all Paleodictyon nodosum is that they are all found along convergent plate boundaries
at both active and extinct hydrothermal vents.
The Top of the form is shaped like a shield, with the center raised, and a lip around the outside. The center is raised approximately 5mm above the low points. Each horizontal section consists of 3 equidistant rows of tiny holes (approximately 1mm in diameter) that connect at 120° angles. Each of these horizontal sections are connected by vertical shafts (approximately 2-3mm in diameter).
When actively being inhabited, the surface of the burrow is made of red metalliferous sediment. When it becomes inactive, this becomes covered with a light gray Lutite
and the top flattens out. The red sediment is only found under the surface sediment in this environment, so its presence at the surface hints at a biotic factor which brings up the sediment.
The number of rows and the spacing of these rows increases in correlation with the size of the overall form. This indicates that these burrows are a result of organic growth.
The raised parts of the burrow force water to flow through the burrow. As a result of this, scientists found large numbers of foraminifera
tests
within the burrows. These were trapped in certain areas suggesting that the burrows were engineered to catch food as prey. However the microbial counts didn’t change from the inside of the burrows to the area surrounding it.
These burrows could be one of the earliest examples of complex structures being built by animals.
Body Structure
.
Another animal that creates burrows and cultivates food within its burrows is the leafcutter ant
. This suggests that the idea of an animal cultivating its own food isn’t unreasonable, and the fact that the environment is so low in nutrition it seems like a logical evolutionary step to have been taken.
such as a xenophyophore left the structures as a cast of its body. Through testing of collected burrow samples, this theory gained a lot of evidence both for and against it.
One test that was run was watching how water flowed over the burrows. The forced water flow exhibited by these specimen was similar to the forced water flow in several sponges. Another reason that this hypothesis seems likely is that best estimates of the size of the worm suggest that it would have to travel unreasonably long distances (compared to its body length) to fully navigate its burrows (10^3-10^4).
However there are several problems with this hypothesis as well. If this was the remains of the body of a creature, you would expect to find organic matter from that creature throughout the burrow. However when the burrows were tested for DNA, scientists found DNA
from different types of large protists between different burrows. This suggests that the DNA found is just there because it was transported there by currents. However one encouraging fact is that one of the types of DNA found in a burrow was of the Vanhoeffenella, which creates hexagonal burrows similar to those of the Paleodictyon nodosum.
The barium
content in the sediment making up the burrows had no significant difference from the barium
content in the surrounding sediment. This is inconsistent with the burrows of other xenophyophores. Also the complexity and evenness of the burrows is not consistent with the forms that xenophyophores generally create.
and in Wales
. They are generally found in flysch
deposits from the Eocene
period, which began with the arrival of mammals.
Over time the fossils gain a much more uniform shape. The oldest fossils show much less uniformly hexagonal burrows, but as time goes on their burrows become much more consistent and precise.
describes the search for the Paleodictyon nodosum, using the deep-water submersible DSV Alvin
near volcanic vents that lie 3500 meters (12,000 feet) underwater in the Mid-Atlantic Ridge. Samples were taken from several honeycomb burrows, however no creatures were found in any of them. They theorized that the burrows were being used for bacterial farming by whichever creature created them.
Many of these ideas are fairly vague, and while the general principles hold true, how we define each part of this set of rules has been challenged by the Paleodictyon nodosum.
It was once assumed that the only source of energy that supported life was the sun. However the discovery of chemosynthetic bacteria
in Giant Tube Worms introduced a new source of energy, chemicals from within the earth. However this discovery led people to believe that creatures could only survive in these environments when the vents were active. However the Paleodictyon nodosum can survive even after the extinction of these vents. This challenges our ideas of what a suitable environment truly means. The fact that a creature can survive in an area where there is extreme pressure and almost no biomass gives us a new appreciation of the adaptations that animals will develop in order to survive in even the most inhospitable locations on the planet.
Paleodictyon
Paleodictyon is a pattern, usually interpreted to be a burrow, which appears in the geologic record beginning in the Cambrian and in modern ocean environments. Both irregular and regular nets are known throughout the stratigraphic range of Paleodictyon, but it is the striking regular honeycomb...
burrows. They are found around mid ocean ridge systems in both the Pacific and Atlantic Oceans. Although scientists have collected many of the burrows of the Paleodictyon nodosum, they have never seen a live one. What a live specimen would look like is widely debated, with the debate being split into two main sides.
Adolf Seilacher
Adolf Seilacher
Adolf "Dolf" Seilacher is a German palaeontologist who has made major contributions to evolutionary and ecological palaeobiology in a career stretching over 60 years. He won the Crafoord Prize in 1992, the Paleontological Society Medal in 1994 and the Palaeontological Association's Lapworth Medal...
who discovered the original fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
s of the Paleodictyon nodosum hypothesizes that the creature is a worm like species that burrows into the sediment around hydrothermal vents and deflects water flow through the burrows to catch food or farm its own food.
Peter A. Rona, discoverer of the modern burrows, suggests that the Paleodictyon nodosum may actually be a large protist
Protist
Protists are a diverse group of eukaryotic microorganisms. Historically, protists were treated as the kingdom Protista, which includes mostly unicellular organisms that do not fit into the other kingdoms, but this group is contested in modern taxonomy...
. There are other known examples of protists reaching the sizes that the Paleodictyon nodosum reaches, and they are known to be infaunal
Fauna
Fauna or faunæ is all of the animal life of any particular region or time. The corresponding term for plants is flora.Zoologists and paleontologists use fauna to refer to a typical collection of animals found in a specific time or place, e.g. the "Sonoran Desert fauna" or the "Burgess shale fauna"...
.
Scientists ran various tests on the burrows of the Paleodictyon nodosum and were unable to reach a single conclusion as to the form of the Paleodictyon nodosum. The one thing that they can agree upon is that there are many markers that suggest that these forms are caused by a creature, and not by geological forces.
Distribution/Discovery
They were originally photographed in 1976 on the Galapagos RiftGalápagos hotspot
The Galápagos hotspot is a volcanic hotspot in the East Pacific Ocean responsible for the creation of the Galapagos Islands as well as three major aseismic ridge systems, Carnegie, Cocos and Malpelso which are on two tectonic plates. The hotspot is located near the Equator on the Nazca Plate not...
between 2400-3700m depth. Later, Seilacher and Rona used the deep-water submersible DSV Alvin
DSV Alvin
Alvin is a manned deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts. The vehicle was built by General Mills' Electronics Group in the same factory used to manufacture breakfast cereal-producing...
to recover samples of the same form near the Mid-Atlantic Ridge
Mid-Atlantic Ridge
The Mid-Atlantic Ridge is a mid-ocean ridge, a divergent tectonic plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. It separates the Eurasian Plate and North American Plate in the North Atlantic, and the African Plate from the South...
. These samples were collected between 3430m and 3575m depth, around 26°N and 45°W. These burrows were found in very similar conditions as the ones found along the Galapagos Rift
Galápagos hotspot
The Galápagos hotspot is a volcanic hotspot in the East Pacific Ocean responsible for the creation of the Galapagos Islands as well as three major aseismic ridge systems, Carnegie, Cocos and Malpelso which are on two tectonic plates. The hotspot is located near the Equator on the Nazca Plate not...
. The biggest similarity between the habitats of all Paleodictyon nodosum is that they are all found along convergent plate boundaries
Convergent boundary
In plate tectonics, a convergent boundary, also known as a destructive plate boundary , is an actively deforming region where two tectonic plates or fragments of lithosphere move toward one another and collide...
at both active and extinct hydrothermal vents.
Burrows
The burrows of the Paleodictyon nodosum are one of the few things about them that scientists are actually able to study, and so this is possibly the area of which we know the most about the Paleodictyon nodosum.The Top of the form is shaped like a shield, with the center raised, and a lip around the outside. The center is raised approximately 5mm above the low points. Each horizontal section consists of 3 equidistant rows of tiny holes (approximately 1mm in diameter) that connect at 120° angles. Each of these horizontal sections are connected by vertical shafts (approximately 2-3mm in diameter).
When actively being inhabited, the surface of the burrow is made of red metalliferous sediment. When it becomes inactive, this becomes covered with a light gray Lutite
Lutite
Lutite is old terminology, which is currently not widely used, by Earth scientists in field descriptions for fine-grained, sedimentary rocks, which are composed of silt-size sediment, clay-size sediment, or a mixture of both. When mixed with water lutites often disintegrate into mud...
and the top flattens out. The red sediment is only found under the surface sediment in this environment, so its presence at the surface hints at a biotic factor which brings up the sediment.
The number of rows and the spacing of these rows increases in correlation with the size of the overall form. This indicates that these burrows are a result of organic growth.
The raised parts of the burrow force water to flow through the burrow. As a result of this, scientists found large numbers of foraminifera
Foraminifera
The Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...
tests
Test (biology)
A test is a term used to refer to the shell of sea urchins, and also the shell of certain microorganisms, such as testate foraminifera and testate amoebae....
within the burrows. These were trapped in certain areas suggesting that the burrows were engineered to catch food as prey. However the microbial counts didn’t change from the inside of the burrows to the area surrounding it.
These burrows could be one of the earliest examples of complex structures being built by animals.
Body Structure
Theory 1 - trace fossil
The theory that Seilacher supports, that the burrows we find are trace fossils of a worm like animal, is supported by several features of the burrows, and is also not an unheard of concept in the animal kingdom. The shape of the burrows is consistent with other graphoglyptids. The burrows also had several exits, which is inconsistent with the idea of a megalith foraminiferaForaminifera
The Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...
.
Another animal that creates burrows and cultivates food within its burrows is the leafcutter ant
Leafcutter ant
Leafcutter ants, a non-generic name, are any of 47 species of leaf-chewing ants belonging to the two genera Atta and Acromyrmex.These species of tropical, fungus-growing ants are all endemic to South, Central America, Mexico and parts of the southern United States.The Acromyrmex and Atta ants have...
. This suggests that the idea of an animal cultivating its own food isn’t unreasonable, and the fact that the environment is so low in nutrition it seems like a logical evolutionary step to have been taken.
Theory 2 - sponge/xenophyophore
The second hypothesis, supported by Rona, is that a sponge or megalith foraminiferaForaminifera
The Foraminifera , or forams for short, are a large group of amoeboid protists which are among the commonest plankton species. They have reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net...
such as a xenophyophore left the structures as a cast of its body. Through testing of collected burrow samples, this theory gained a lot of evidence both for and against it.
One test that was run was watching how water flowed over the burrows. The forced water flow exhibited by these specimen was similar to the forced water flow in several sponges. Another reason that this hypothesis seems likely is that best estimates of the size of the worm suggest that it would have to travel unreasonably long distances (compared to its body length) to fully navigate its burrows (10^3-10^4).
However there are several problems with this hypothesis as well. If this was the remains of the body of a creature, you would expect to find organic matter from that creature throughout the burrow. However when the burrows were tested for DNA, scientists found DNA
DNA
Deoxyribonucleic acid is a nucleic acid that contains the genetic instructions used in the development and functioning of all known living organisms . The DNA segments that carry this genetic information are called genes, but other DNA sequences have structural purposes, or are involved in...
from different types of large protists between different burrows. This suggests that the DNA found is just there because it was transported there by currents. However one encouraging fact is that one of the types of DNA found in a burrow was of the Vanhoeffenella, which creates hexagonal burrows similar to those of the Paleodictyon nodosum.
The barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
content in the sediment making up the burrows had no significant difference from the barium
Barium
Barium is a chemical element with the symbol Ba and atomic number 56. It is the fifth element in Group 2, a soft silvery metallic alkaline earth metal. Barium is never found in nature in its pure form due to its reactivity with air. Its oxide is historically known as baryta but it reacts with...
content in the surrounding sediment. This is inconsistent with the burrows of other xenophyophores. Also the complexity and evenness of the burrows is not consistent with the forms that xenophyophores generally create.
Fossil Record
The fossils of the Paleodictyon nodosum were first found in the cliffs of Spain in the 1950’s. Since then, they have been discovered all over EuropeEurope
Europe is, by convention, one of the world's seven continents. Comprising the westernmost peninsula of Eurasia, Europe is generally 'divided' from Asia to its east by the watershed divides of the Ural and Caucasus Mountains, the Ural River, the Caspian and Black Seas, and the waterways connecting...
and in Wales
Wales
Wales is a country that is part of the United Kingdom and the island of Great Britain, bordered by England to its east and the Atlantic Ocean and Irish Sea to its west. It has a population of three million, and a total area of 20,779 km²...
. They are generally found in flysch
Flysch
Flysch is a sequence of sedimentary rocks that is deposited in a deep marine facies in the foreland basin of a developing orogen. Flysch is typically deposited during an early stage of the orogenesis. When the orogen evolves the foreland basin becomes shallower and molasse is deposited on top of...
deposits from the Eocene
Eocene
The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...
period, which began with the arrival of mammals.
Over time the fossils gain a much more uniform shape. The oldest fossils show much less uniformly hexagonal burrows, but as time goes on their burrows become much more consistent and precise.
Popular Exposure
The IMAX film Volcanoes of the Deep SeaVolcanoes of the Deep Sea
Volcanoes of the Deep Sea is a 2003 documentary film directed by Stephen Low in the IMAX format about undersea volcanoes.-Production:Richard Lutz served as Principal Investigator and Lutz and Peter Rona served as Science Directors of the film, which was funded by the National Science Foundation and...
describes the search for the Paleodictyon nodosum, using the deep-water submersible DSV Alvin
DSV Alvin
Alvin is a manned deep-ocean research submersible owned by the United States Navy and operated by the Woods Hole Oceanographic Institution in Woods Hole, Massachusetts. The vehicle was built by General Mills' Electronics Group in the same factory used to manufacture breakfast cereal-producing...
near volcanic vents that lie 3500 meters (12,000 feet) underwater in the Mid-Atlantic Ridge. Samples were taken from several honeycomb burrows, however no creatures were found in any of them. They theorized that the burrows were being used for bacterial farming by whichever creature created them.
Implications on Necessities for Life
George Wald presented the idea that the 4 necessities of life were:- the presence of liquid water
- Elements for metabolismMetabolismMetabolism is the set of chemical reactions that happen in the cells of living organisms to sustain life. These processes allow organisms to grow and reproduce, maintain their structures, and respond to their environments. Metabolism is usually divided into two categories...
and reproduction - A source of energy
- suitable environmental conditions
Many of these ideas are fairly vague, and while the general principles hold true, how we define each part of this set of rules has been challenged by the Paleodictyon nodosum.
It was once assumed that the only source of energy that supported life was the sun. However the discovery of chemosynthetic bacteria
Chemosynthesis
In biochemistry, chemosynthesis is the biological conversion of one or more carbon molecules and nutrients into organic matter using the oxidation of inorganic molecules or methane as a source of energy, rather than sunlight, as in photosynthesis...
in Giant Tube Worms introduced a new source of energy, chemicals from within the earth. However this discovery led people to believe that creatures could only survive in these environments when the vents were active. However the Paleodictyon nodosum can survive even after the extinction of these vents. This challenges our ideas of what a suitable environment truly means. The fact that a creature can survive in an area where there is extreme pressure and almost no biomass gives us a new appreciation of the adaptations that animals will develop in order to survive in even the most inhospitable locations on the planet.