Archaeomarasmius
Encyclopedia
Archaeomarasmius is an extinct genus
of gilled fungus
in the Agaricales
family Tricholomataceae
, containing the single species
Archaeomarasmius leggetti. It is known from two fruit bodies
recovered from amber
, one consisting of a complete cap
with a broken stem
, the other consisting of a fragment of a cap. The cap has a diameter ranging from 3.2 to 6 mm (0.125984251968504 to 0.236220472440945 in), while the stem is 0.5 mm (0.0196850393700787 in) thick. Spore
s were also recovered from the amber, and are broadly ellipsoid to egg-shaped, measuring roughly 7.3 by 4.7 μm
. The species, which resembles the extant genera Marasmius
and Marasmiellus
, is inferred to have been saprobic on plant litter
or other forest debris
.
The genus is solely known from the New Jersey amber deposits along the Atlantic coastal plain
in New Jersey
, United States, which date from the Turonian
stage (about 90–94 Mya) of the Upper Cretaceous. Archaeomarasmius is one of only five known agaric fungus species known in the fossil record, and the only one to be described from New Jersey amber.
fossils, a fruit body
(or mushroom
) and a fragment of a mushroom, both currently residing in the American Museum of Natural History
. The specimens, collected in November 1994 from the area of East Brunswick, New Jersey, by G.R. Case, P.D. Borodin, and J.J. Leggett, were found as a single clear yellow amber nodule 6 cm (2.4 in) in diameter. The specimen was found above the South Amboy Fire Clay, part of the Raritan Formation
, suggesting that it is Turonian
in age (Upper Cretaceous, about 90 to 94 million years ago). Due to weathering, the amber specimen AMNH NJ-90 fractured into a number of chips along fractures and flow lines. The chips with the holotype specimens, AMNH NJ-90Y and AMNH NJ-90Z, were first studied by a group of researchers consisting of David Hibbett
and Michael Donoghue from Harvard University
with David Grimaldi
of the AMNH. Hibbett and colleagues published their 1997 type description
in the American Journal of Botany
. The generic epithet Archaeomarasmius is a combination of the Greek
archaeo- meaning "ancient" and "Marasmius
", a modern genus which it resembles. The specific epithet "leggetti" was coined by the authors in honor of J.J. Leggett and company, who first discovered the amber nodule and donated it to the AMNH.
When first reported, Archaeomarasmius leggetti was the second extinct species of agaric fungus to be described, and it is the only species to be known from the New Jersey amber. Three species, Aureofungus yaniguaensis
, Coprinites dominicana and Protomycena electra
, have been described from the Miocene
Dominican amber
found in the Dominican Republic. The extinct Agaricomycetes
species Quatsinoporites cranhamii
, found in marine calcareous concretion
s on Vancouver Island
, Canada, and dating to about 130–125 Mya, is probably in the Hymenochaetales
or the Polyporales
. In 2007, another agaric was reported, Palaeoagaracites antiquus
, found in Early Cretaceous Burmese amber (about 100 Mya).
s. Specimen AMNH NJ-90Y is a nearly complete mushroom, broken off near the base of the stipe
(stem). The pileus
(cap) is up to 6 mm (0.236220472440945 in) in diameter and has a convex shape sporting an umbo
(a broad raised central region). The mushroom is a medium-dark brown color with thin, minutely textured flesh
and an incurved margin. The lamellae or gills are distantly spaced, with 12 gills extending fully from the cap edge to the stipe, and lack lamellulae (short gills which do not reach the stipe from the edge of the pileus). The pileus is centered on the stipe, which is 0.5 by long and is broken off above the base. The stipe lacks a veil
and is smooth and cylindrical. The top of the pileus is exposed on a fracture plain
, and to prevent oxidation
, the area was coated in a fine layer of synthetic resin
, which also resulted in slightly improved visibility of the mushroom.
Specimen AMNH NJ-90Z is a small wedge-shaped fragment of pileus which was accidentally fractured during preparation for study, splitting it in half. Though the researchers had not intended to perform destructive analysis on the sample, this fracturing warranted the sacrifice of some parts of the specimen for structural and molecular study. Small pieces of the specimen were mounted directly on scanning electron microscopy (SEM) stubs and sputter coated
with a gold
/palladium
alloy. The resulting images showed that little intact tissue remained, and only fragmented and crushed basidiospores were seen. Another sample of the specimen was mounted in spurr's resin (an embedding medium used in electron microscopy) and sectioned with a diamond knife; the resulting sections were examined with transmission electron microscopy
(TEM). The lack of discernible biological material from the mushroom seen in the SEM study was confirmed in the TEM analysis. A final section of the fossil was selected to attempt DNA
sequencing. A small sample of the fossil was extracted at the AMNH and sent to the Peabody Museum of Archaeology and Ethnology
for DNA amplification. None of the three selected extracts showed any results after the amplification was attempted. It is possible that the fractures and flowlines which split AMNH NJ-90Z during initial preparation had already penetrated into the fossil and destroyed the hermetic seal
which would have been needed for preserving the organic matter of the mushroom.
The basidiospores recovered with the fruiting body were examined during the SEM study. The spores showed considerable damage from both the fossilization process and the subsequent weathering and specimen collection. They also displayed distinct halos in the amber, possibly from gas or liquid leaching out, or a reaction in the spores that prevented the resin from turning to amber. Even so, enough remained to make some observations about spore morphology
. The basidiospores are broadly elliptic to oval, measuring approximately 7.3 by 4.7 μm
, and each shows a distinct hilar appendage.
The combined characters of Archaeomarasmius indicate a relation to the modern family Tricholomataceae
, with a close similarity to the genera Marasmius
and Marasmiellus
. Both genera are noted for marcescence
, toughening and drying, rather than putrifying
. This property would increase the chances of a mushroom becoming entombed in amber. However, a number of other species are also possible close relatives of Archaeomarasmius, mostly in Tricholomataceae, although some species in the family Strophariaceae
are also marasmioid. The authors suggest it may also be appropriate to classify Archaeomarasmius more conservatively as incertae sedis
(of uncertain placement) within the Tricholomatoceae, Agaricales, or Homobasidiomycetes.
and Chironomidae
, together with caddisflies of the order Trichoptera
, suggest that the mushroom was growing near fresh water. Beetles from the family Elateridae, a termite
and a pseudoscorpion
, in addition to the mushroom, are indicators of rotting wood, probably from a tree in the Cupressaceae
family. Modern Marasmiaceae
members are saprobic—obtaining nutrients by breaking down organic matter—and specimens included with Archaeomarasmius indicate a similar habit for the mushroom.
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 gilled fungus
Fungus
A fungus is a member of a large group of eukaryotic organisms that includes microorganisms such as yeasts and molds , as well as the more familiar mushrooms. These organisms are classified as a kingdom, Fungi, which is separate from plants, animals, and bacteria...
in the Agaricales
Agaricales
The fungal order Agaricales, also known as gilled mushrooms , or euagarics, contains some of the most familiar types of mushrooms. The order has 33 extant families, 413 genera, and over 13000 described species, along with five extinct genera known only from the fossil record...
family Tricholomataceae
Tricholomataceae
The Tricholomataceae are a large family of mushrooms within the Agaricales. A classic "wastebasket taxon", the Tricholomataceae is inclusive of any white-, yellow-, or pink-spored genera in the Agaricales not already classified as belonging to the Amanitaceae, Lepiotaceae, Hygrophoraceae,...
, containing the single species
Species
In biology, a species is one of the basic units of biological classification and a taxonomic rank. A species is often defined as a group of organisms capable of interbreeding and producing fertile offspring. While in many cases this definition is adequate, more precise or differing measures are...
Archaeomarasmius leggetti. It is known from two fruit bodies
Basidiocarp
In fungi, a basidiocarp, basidiome or basidioma , is the sporocarp of a basidiomycete, the multicellular structure on which the spore-producing hymenium is borne. Basidiocarps are characteristic of the hymenomycetes; rusts and smuts do not produce such structures...
recovered from amber
Amber
Amber is fossilized tree resin , which has been appreciated for its color and natural beauty since Neolithic times. Amber is used as an ingredient in perfumes, as a healing agent in folk medicine, and as jewelry. There are five classes of amber, defined on the basis of their chemical constituents...
, one consisting of a complete cap
Pileus (mycology)
The pileus is the technical name for the cap, or cap-like part, of a basidiocarp or ascocarp that supports a spore-bearing surface, the hymenium. The hymenium may consist of lamellae, tubes, or teeth, on the underside of the pileus...
with a broken stem
Stipe (mycology)
thumb|150px|right|Diagram of a [[basidiomycete]] stipe with an [[annulus |annulus]] and [[volva |volva]]In mycology a stipe refers to the stem or stalk-like feature supporting the cap of a mushroom. Like all tissues of the mushroom other than the hymenium, the stipe is composed of sterile hyphal...
, the other consisting of a fragment of a cap. The cap has a diameter ranging from 3.2 to 6 mm (0.125984251968504 to 0.236220472440945 in), while the stem is 0.5 mm (0.0196850393700787 in) thick. 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 were also recovered from the amber, and are broadly ellipsoid to egg-shaped, measuring roughly 7.3 by 4.7 μm
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...
. The species, which resembles the extant genera Marasmius
Marasmius
Marasmius is a genus of mushrooms, in the family Marasmiaceae. It contains about 500 species of agarics, of which a few, such as Marasmius oreades, are edible. However, most members of this genus are small, unimpressive brown mushrooms...
and Marasmiellus
Marasmiellus
Marasmiellus is a genus of fungus in the Marasmiaceae family of mushrooms. The widespread genus, circumscribed by American mycologist William Murrill in 1915, contains about 250 species.The name comes from the Greek marasmus meaning wasting....
, is inferred to have been saprobic on plant litter
Plant litter
Plant litter, leaf litter or tree litter is dead plant material, such as leaves, bark, needles, and twigs, that has fallen to the ground. Litter provides habitat for small animals, fungi, and plants, and the material may be used to construct nests. As litter decomposes, nutrients are released to...
or other forest debris
Forest floor
The forest floor, also called detritus, duff and the O horizon, is one of the most distinctive features of a forest ecosystem. It mainly consists of shed vegetative parts, such as leaves, branches, bark, and stems, existing in various stages of decomposition above the soil surface...
.
The genus is solely known from the New Jersey amber deposits along the Atlantic coastal plain
Atlantic Coastal Plain
The Atlantic coastal plain has both low elevation and low relief, but it is also a relatively flat landform extending from the New York Bight southward to a Georgia/Florida section of the Eastern Continental Divide, which demarcates the plain from the ACF River Basin in the Gulf Coastal Plain to...
in New Jersey
New Jersey
New Jersey is a state in the Northeastern and Middle Atlantic regions of the United States. , its population was 8,791,894. It is bordered on the north and east by the state of New York, on the southeast and south by the Atlantic Ocean, on the west by Pennsylvania and on the southwest by Delaware...
, United States, which date from the Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
stage (about 90–94 Mya) of the Upper Cretaceous. Archaeomarasmius is one of only five known agaric fungus species known in the fossil record, and the only one to be described from New Jersey amber.
History and classification
The genus is known only from the two holotypeHolotype
A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
fossils, a fruit body
Basidiocarp
In fungi, a basidiocarp, basidiome or basidioma , is the sporocarp of a basidiomycete, the multicellular structure on which the spore-producing hymenium is borne. Basidiocarps are characteristic of the hymenomycetes; rusts and smuts do not produce such structures...
(or mushroom
Mushroom
A mushroom is the fleshy, spore-bearing fruiting body of a fungus, typically produced above ground on soil or on its food source. The standard for the name "mushroom" is the cultivated white button mushroom, Agaricus bisporus; hence the word "mushroom" is most often applied to those fungi that...
) and a fragment of a mushroom, both currently residing in the American Museum of Natural History
American Museum of Natural History
The American Museum of Natural History , located on the Upper West Side of Manhattan in New York City, United States, is one of the largest and most celebrated museums in the world...
. The specimens, collected in November 1994 from the area of East Brunswick, New Jersey, by G.R. Case, P.D. Borodin, and J.J. Leggett, were found as a single clear yellow amber nodule 6 cm (2.4 in) in diameter. The specimen was found above the South Amboy Fire Clay, part of the Raritan Formation
Raritan Formation
The Raritan Formation is a Mesozoic geologic formation. Dinosaur remains are among the fossils that have been recovered from the formation, although none have yet been referred to a specific genus.-See also:* List of dinosaur-bearing rock formations...
, suggesting that it is Turonian
Turonian
The Turonian is, in the ICS' geologic timescale, the second age in the Late Cretaceous epoch, or a stage in the Upper Cretaceous series. It spans the time between 93.5 ± 0.8 Ma and 89.3 ± 1 Ma...
in age (Upper Cretaceous, about 90 to 94 million years ago). Due to weathering, the amber specimen AMNH NJ-90 fractured into a number of chips along fractures and flow lines. The chips with the holotype specimens, AMNH NJ-90Y and AMNH NJ-90Z, were first studied by a group of researchers consisting of David Hibbett
David S. Hibbett
David Hibbett is an associate professor in biology at Clark University. He is considered one of today's leading researchers "in the analysis of fungal relationships through DNA analysis." At Clark he concentrates his lab work in evolutionary biology and ecology of Fungi.He spent 1991 as a Science...
and Michael Donoghue from Harvard University
Harvard University
Harvard University is a private Ivy League university located in Cambridge, Massachusetts, United States, established in 1636 by the Massachusetts legislature. Harvard is the oldest institution of higher learning in the United States and the first corporation chartered in the country...
with David Grimaldi
David Grimaldi
David A. Grimaldi is an entomologist and Curator of Invertebrate Zoology at the American Museum of Natural History in New York. He received his graduate training at Cornell University, where he earned his doctorate in Entomology in 1986. Dr. Grimaldi is an authority in many fields of insect...
of the AMNH. Hibbett and colleagues published their 1997 type description
Species description
A species description or type description is a formal description of a newly discovered species, usually in the form of a scientific paper. Its purpose is to give a clear description of a new species of organism and explain how it differs from species which have been described previously, or are...
in the American Journal of Botany
American Journal of Botany
The American Journal of Botany is a peer-reviewed scientific journal which includes research papers on all aspects of plant biology. It is published by the Botanical Society of America on a monthly basis since 1914....
. The generic epithet Archaeomarasmius is a combination of the Greek
Greek language
Greek is an independent branch of the Indo-European family of languages. Native to the southern Balkans, it has the longest documented history of any Indo-European language, spanning 34 centuries of written records. Its writing system has been the Greek alphabet for the majority of its history;...
archaeo- meaning "ancient" and "Marasmius
Marasmius
Marasmius is a genus of mushrooms, in the family Marasmiaceae. It contains about 500 species of agarics, of which a few, such as Marasmius oreades, are edible. However, most members of this genus are small, unimpressive brown mushrooms...
", a modern genus which it resembles. The specific epithet "leggetti" was coined by the authors in honor of J.J. Leggett and company, who first discovered the amber nodule and donated it to the AMNH.
When first reported, Archaeomarasmius leggetti was the second extinct species of agaric fungus to be described, and it is the only species to be known from the New Jersey amber. Three species, Aureofungus yaniguaensis
Aureofungus
Aureofungus is an extinct monotypic genus of gilled fungus in the order Agaricales. At present it contains the single species Aureofungus yaniguaensis....
, Coprinites dominicana and Protomycena electra
Protomycena
Protomycena is an extinct monotypic genus of gilled fungus in the Mycenaceae family, of order Agaricales. At present it contains the single species Protomycena electra, known from a single specimen collected in an amber mine in the Cordillera Septentrional area of the Dominican Republic...
, have been described from the Miocene
Miocene
The Miocene is a geological epoch of the Neogene Period and extends from about . The Miocene was named by Sir Charles Lyell. Its name comes from the Greek words and and means "less recent" because it has 18% fewer modern sea invertebrates than the Pliocene. The Miocene follows the Oligocene...
Dominican amber
Dominican amber
Dominican amber is amber from the Dominican Republic. Resin from the extinct species Hymenaea protera is the source of Dominican amber and probably of most amber found in the tropics....
found in the Dominican Republic. The extinct Agaricomycetes
Agaricomycetes
Agaricomycetes is a class of fungi. The taxon is roughly identical to that defined for the Homobasidiomycetes by Hibbett & Thorn, with the inclusion of Auriculariales and Sebacinales. It includes not only mushrooms but also most species placed in the deprecated taxa Gasteromycetes and...
species Quatsinoporites cranhamii
Quatsinoporites
Quatsinoporites is an extinct monotypic genus of agaricomycet fungus in the Agaricomycetes family Hymenochaetaceae. At present it contains the single species Quatsinoporites cranhamii....
, found in marine calcareous concretion
Concretion
A concretion is a volume of sedimentary rock in which a mineral cement fills the porosity . Concretions are often ovoid or spherical in shape, although irregular shapes also occur. The word 'concretion' is derived from the Latin con meaning 'together' and crescere meaning 'to grow'...
s on Vancouver Island
Vancouver Island
Vancouver Island is a large island in British Columbia, Canada. It is one of several North American locations named after George Vancouver, the British Royal Navy officer who explored the Pacific Northwest coast of North America between 1791 and 1794...
, Canada, and dating to about 130–125 Mya, is probably in the Hymenochaetales
Hymenochaetales
The Hymenochaetales are an order of fungi in the class Agaricomycetes. The order in its current sense is based on molecular research and not on any unifying morphological characteristics. According to one 2008 estimate, the Hymenochaetales contain around 600 species worldwide, mostly corticioid...
or the Polyporales
Polyporales
The Polyporales are an order of fungi in the class Agaricomycetes. The order includes some polypores as well as many corticioid fungi and a few agarics . Species within the order are saprotrophic, most of them wood-rotters...
. In 2007, another agaric was reported, Palaeoagaracites antiquus
Palaeoagaracites
Palaeoagaracites is an extinct monotypic genus of gilled fungus in the order Agaricales. At present it contains the single species Palaeoagaracites antiquus....
, found in Early Cretaceous Burmese amber (about 100 Mya).
Description
The holotypes of Archaeomarasmius consist of mushrooms and associated basidiosporeBasidiospore
A basidiospore is a reproductive spore produced by Basidiomycete fungi. Basidiospores typically each contain one haploid nucleus that is the product of meiosis, and they are produced by specialized fungal cells called basidia. In grills under a cap of one common species in the phylum of...
s. Specimen AMNH NJ-90Y is a nearly complete mushroom, broken off near the base of the stipe
Stipe (mycology)
thumb|150px|right|Diagram of a [[basidiomycete]] stipe with an [[annulus |annulus]] and [[volva |volva]]In mycology a stipe refers to the stem or stalk-like feature supporting the cap of a mushroom. Like all tissues of the mushroom other than the hymenium, the stipe is composed of sterile hyphal...
(stem). The pileus
Pileus (mycology)
The pileus is the technical name for the cap, or cap-like part, of a basidiocarp or ascocarp that supports a spore-bearing surface, the hymenium. The hymenium may consist of lamellae, tubes, or teeth, on the underside of the pileus...
(cap) is up to 6 mm (0.236220472440945 in) in diameter and has a convex shape sporting an umbo
Umbo (mycology)
thumb|right|[[Cantharellula umbonata]] has an umbo.thumb|right|The cap of [[Psilocybe makarorae]] is acutely papillate.An umbo is a raised area in the center of a mushroom cap. Caps that possess this feature are called umbonate. Umbos that are sharply pointed are called acute, while those that are...
(a broad raised central region). The mushroom is a medium-dark brown color with thin, minutely textured flesh
Trama (mycology)
In mycology trama is a term for the inner, fleshy portion of a mushroom's basidiocarp, or fruit body. It is distinct from the outer layer of tissue, known as the pileipellis or cuticle, and from the spore-bearing tissue layer known as the hymenium....
and an incurved margin. The lamellae or gills are distantly spaced, with 12 gills extending fully from the cap edge to the stipe, and lack lamellulae (short gills which do not reach the stipe from the edge of the pileus). The pileus is centered on the stipe, which is 0.5 by long and is broken off above the base. The stipe lacks a veil
Universal veil
In mycology, a universal veil is a temporary membranous tissue that fully envelops immature fruiting bodies of certain gilled mushrooms. The developing Caesar's mushroom , for example, which may resemble a small white sphere at this point, is protected by this structure...
and is smooth and cylindrical. The top of the pileus is exposed on a fracture plain
Fracture (mineralogy)
In the field of mineralogy, fracture is a term used to describe the shape and texture of the surface formed when a mineral is fractured. Minerals often have a highly distinctive fracture, making it a principal feature used in their identification....
, and to prevent oxidation
Redox
Redox reactions describe all chemical reactions in which atoms have their oxidation state changed....
, the area was coated in a fine layer of synthetic resin
Resin
Resin in the most specific use of the term is a hydrocarbon secretion of many plants, particularly coniferous trees. Resins are valued for their chemical properties and associated uses, such as the production of varnishes, adhesives, and food glazing agents; as an important source of raw materials...
, which also resulted in slightly improved visibility of the mushroom.
Specimen AMNH NJ-90Z is a small wedge-shaped fragment of pileus which was accidentally fractured during preparation for study, splitting it in half. Though the researchers had not intended to perform destructive analysis on the sample, this fracturing warranted the sacrifice of some parts of the specimen for structural and molecular study. Small pieces of the specimen were mounted directly on scanning electron microscopy (SEM) stubs and sputter coated
Sputter coating
Sputter coating in scanning electron microscopy is a process of covering a specimen with a very thin layer of conducting material, typically a metal, such as a gold/palladium alloy. Conductive coating is needed to prevent charging of a specimen with an electron beam in conventional SEM mode...
with a gold
Gold
Gold is a chemical element with the symbol Au and an atomic number of 79. Gold is a dense, soft, shiny, malleable and ductile metal. Pure gold has a bright yellow color and luster traditionally considered attractive, which it maintains without oxidizing in air or water. Chemically, gold is a...
/palladium
Palladium
Palladium is a chemical element with the chemical symbol Pd and an atomic number of 46. It is a rare and lustrous silvery-white metal discovered in 1803 by William Hyde Wollaston. He named it after the asteroid Pallas, which was itself named after the epithet of the Greek goddess Athena, acquired...
alloy. The resulting images showed that little intact tissue remained, and only fragmented and crushed basidiospores were seen. Another sample of the specimen was mounted in spurr's resin (an embedding medium used in electron microscopy) and sectioned with a diamond knife; the resulting sections were examined with transmission electron microscopy
Transmission electron microscopy
Transmission electron microscopy is a microscopy technique whereby a beam of electrons is transmitted through an ultra thin specimen, interacting with the specimen as it passes through...
(TEM). The lack of discernible biological material from the mushroom seen in the SEM study was confirmed in the TEM analysis. A final section of the fossil was selected to attempt 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...
sequencing. A small sample of the fossil was extracted at the AMNH and sent to the Peabody Museum of Archaeology and Ethnology
Peabody Museum of Archaeology and Ethnology
The Peabody Museum of Archaeology and Ethnology is a museum affiliated with Harvard University in Cambridge, Massachusetts, USA.Founded in 1866, the Peabody Museum is one of the oldest and largest museums focusing on anthropological material, and is particularly strong in New World ethnography and...
for DNA amplification. None of the three selected extracts showed any results after the amplification was attempted. It is possible that the fractures and flowlines which split AMNH NJ-90Z during initial preparation had already penetrated into the fossil and destroyed the hermetic seal
Hermetic seal
A hermetic seal is the quality of being airtight. In common usage, the term often implies being impervious to air or gas. When used technically, it is stated in conjunction with a specific test method and conditions of usage.-Etymology :...
which would have been needed for preserving the organic matter of the mushroom.
The basidiospores recovered with the fruiting body were examined during the SEM study. The spores showed considerable damage from both the fossilization process and the subsequent weathering and specimen collection. They also displayed distinct halos in the amber, possibly from gas or liquid leaching out, or a reaction in the spores that prevented the resin from turning to amber. Even so, enough remained to make some observations about spore morphology
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
. The basidiospores are broadly elliptic to oval, measuring approximately 7.3 by 4.7 μm
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...
, and each shows a distinct hilar appendage.
The combined characters of Archaeomarasmius indicate a relation to the modern family Tricholomataceae
Tricholomataceae
The Tricholomataceae are a large family of mushrooms within the Agaricales. A classic "wastebasket taxon", the Tricholomataceae is inclusive of any white-, yellow-, or pink-spored genera in the Agaricales not already classified as belonging to the Amanitaceae, Lepiotaceae, Hygrophoraceae,...
, with a close similarity to the genera Marasmius
Marasmius
Marasmius is a genus of mushrooms, in the family Marasmiaceae. It contains about 500 species of agarics, of which a few, such as Marasmius oreades, are edible. However, most members of this genus are small, unimpressive brown mushrooms...
and Marasmiellus
Marasmiellus
Marasmiellus is a genus of fungus in the Marasmiaceae family of mushrooms. The widespread genus, circumscribed by American mycologist William Murrill in 1915, contains about 250 species.The name comes from the Greek marasmus meaning wasting....
. Both genera are noted for marcescence
Marcescence
Marcescence is the retention of dead plant organs that normally are shed. It is most obvious in deciduous trees that retain leaves through the winter. Several trees normally have marcescent leaves such as oak , beech and hornbeam . Marcescent leaves of pin oak complete development of their...
, toughening and drying, rather than putrifying
Decomposition
Decomposition is the process by which organic material is broken down into simpler forms of matter. The process is essential for recycling the finite matter that occupies physical space in the biome. Bodies of living organisms begin to decompose shortly after death...
. This property would increase the chances of a mushroom becoming entombed in amber. However, a number of other species are also possible close relatives of Archaeomarasmius, mostly in Tricholomataceae, although some species in the family Strophariaceae
Strophariaceae
The Strophariaceae are a family of fungi in the order Agaricales. The family contains 18 genera and 1316 species. The species of Strophariaceae have a red-brown to dark brown spore print, while the spores themselves are smooth and have an apical germ pore. These agarics are also characterized by...
are also marasmioid. The authors suggest it may also be appropriate to classify Archaeomarasmius more conservatively as incertae sedis
Incertae sedis
, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
(of uncertain placement) within the Tricholomatoceae, Agaricales, or Homobasidiomycetes.
Associated inclusions
The amber specimen "AMNH NJ-90", which preserved the two holotypes, also preserved a number of other inclusions that give indications as to what the ecology of Archaeomarasmius may have been. Of the approximately forty insect inclusions present, flies in the families CeratopogonidaeCeratopogonidae
Ceratopogonidae, or biting midges , are a family of small flies in the order Diptera...
and Chironomidae
Chironomidae
Chironomidae are a family of nematoceran flies with a global distribution. They are closely related to the Ceratopogonidae, Simuliidae, and Thaumaleidae...
, together with caddisflies of the order Trichoptera
Trichoptera
The caddisflies are an order, Trichoptera, of insects with approximately 12,000 described species. Also called sedge-flies or rail-flies, they are small moth-like insects having two pairs of hairy membranous wings...
, suggest that the mushroom was growing near fresh water. Beetles from the family Elateridae, a termite
Termite
Termites are a group of eusocial insects that, until recently, were classified at the taxonomic rank of order Isoptera , but are now accepted as the epifamily Termitoidae, of the cockroach order Blattodea...
and a pseudoscorpion
Pseudoscorpion
A pseudoscorpion, , is an arachnid belonging to the order Pseudoscorpionida, also known as Pseudoscorpiones or Chelonethida....
, in addition to the mushroom, are indicators of rotting wood, probably from a tree in the 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...
family. Modern Marasmiaceae
Marasmiaceae
The Marasmiaceae are a family of basidiomycete fungi which have white spores. They mostly have a tough stem and the capability of shrivelling up during a dry period and later recovering. The widely consumed edible fungus Lentinula edodes, the Shiitake mushroom, is a member of this family...
members are saprobic—obtaining nutrients by breaking down organic matter—and specimens included with Archaeomarasmius indicate a similar habit for the mushroom.