''Araucarioxylon arizonicum'' is an extinct species of

conifer Conifers are a group of conifer cone, cone-bearing Spermatophyte, seed plants, a subset of gymnosperms. Scientifically, they make up the phylum, division Pinophyta (), also known as Coniferophyta () or Coniferae. The division contains a single ...

that is the

state fossil Most American states have made a state fossil designation, in many cases during the 1980s. It is common to designate one species in which fossilization has occurred, rather than a single specimen, or a category of fossils not limited to a single ...

Arizona Arizona ( ; nv, Hoozdo Hahoodzo ; ood, Alĭ ṣonak ) is a state in the Southwestern United States. It is the 6th largest and the 14th most populous of the 50 states. Its capital and largest city is Phoenix. Arizona is part of the Fou ...

. The species is known from massive

tree trunks In botany, the trunk (or bole) is the stem and main wooden axis of a tree, which is an important feature in tree identification, and which often differs markedly from the bottom of the trunk to the top, depending on the species. The trunk is the ...

that weather out of the

Chinle Formation The Chinle Formation is an Upper Triassic continental geological formation of fluvial, lacustrine, and palustrine to eolian deposits spread across the U.S. states of Nevada, Utah, northern Arizona, western New Mexico, and western Colorado. In Ne ...

in desert

badland Badlands are a type of dry terrain where softer sedimentary rocks and clay-rich soils have been extensively eroded."Badlands" in ''Chambers's Encyclopædia''. London: George Newnes, 1961, Vol. 2, p. 47. They are characterized by steep slopes, mi ...

s of northern Arizona and adjacent New Mexico and

Chemnitz petrified forest The Chemnitz petrified forest is a petrified forest in Chemnitz, Germany. Most of the trunks are exhibited in the Museum of Natural History in Chemnitz inside of Kulturkaufhaus Tietz , including slices of trunks with polished edges. A small colle ...

Chemnitz Chemnitz (; from 1953 to 1990: Karl-Marx-Stadt , ) is the third-largest city in the German state of Saxony after Leipzig and Dresden. It is the 28th largest city of Germany as well as the fourth largest city in the area of former East Germany a ...

Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...

, most notably in the

Petrified Forest National Park Petrified Forest National Park is an American national park in Navajo County, Arizona, Navajo and Apache County, Arizona, Apache counties in northeastern Arizona. Named for its large deposits of petrified wood, the park covers about , encompassin ...

. There, these trunks are locally so abundant that they have been used as building materials.

Description

The

petrified wood Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of ''fossilized wood'', the fossilized remains of terrestrial vegetation. ''P ...

of this tree is frequently referred to as "Rainbow wood" because of the large variety of colors some

specimen Specimen may refer to: Science and technology * Sample (material), a limited quantity of something which is intended to be similar to and represent a larger amount * Biological specimen or biospecimen, an organic specimen held by a biorepository ...

s exhibit. The red and yellow are produced by large particulate forms of

iron oxide Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whic ...

, the yellow being

limonite Limonite () is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·H2O, although this is not entirely accurate as the ratio of oxide to hydroxid ...

and the red being

hematite Hematite (), also spelled as haematite, is a common iron oxide compound with the formula, Fe2O3 and is widely found in rocks and soils. Hematite crystals belong to the rhombohedral lattice system which is designated the alpha polymorph of . ...

. The purple hue comes from extremely fine spherules of hematite distributed throughout the

quartz Quartz is a hard, crystalline mineral composed of silica (silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical form ...

matrix, and not from

manganese Manganese is a chemical element with the symbol Mn and atomic number 25. It is a hard, brittle, silvery metal, often found in minerals in combination with iron. Manganese is a transition metal with a multifaceted array of industrial alloy use ...

, as has sometimes been suggested. The trunks were large and slender, tapering slightly towards their apex. The largest known trunk in Petrified Forest was 'Old Faithful', from the Rainbow Forest sandstone beds of the Sonsela Member. This trunk had a diameter of 2.9 meters (9.5 feet) at its base, and a maximum estimated height of 59 meters (194 feet) based on modern conifer proportions. Branches are broken off in most fossils, but their bases leave scars indicating that the branches were slender and bent upwards at around 30-40 degrees above the horizontal. The branches are regularly and widely spaced around nearly the entire trunk. Some fragments from the upper part of the trunk have thin branches arranged in small clusters. Preserved bark is rare, but known bark fossils show that it is thin and "rippled", with low ridges and longitudinal furrows similar to some modern

pines A pine is any conifer tree or shrub in the genus ''Pinus'' () of the family Pinaceae. ''Pinus'' is the sole genus in the subfamily Pinoideae. The World Flora Online created by the Royal Botanic Gardens, Kew and Missouri Botanical Garden accep ...

. The roots, when preserved, are significantly different from modern conifers: There is a massive central

taproot A taproot is a large, central, and dominant root from which other roots sprout laterally. Typically a taproot is somewhat straight and very thick, is tapering in shape, and grows directly downward. In some plants, such as the carrot, the taproo ...

, up to 5 meters (16.4 feet) long, ringed by four to six thick lateral roots. Modern conifers, on the other hand, typically bear a circular cluster of relatively small, narrow roots. No known conifer foliage is directly associated with the trunks, but common conifer leaves such as ''

Pagiophyllum ''Pagiophyllum'' is a form genus of fossil coniferous plant foliage. Plants of the genus have been variously assigned to several different conifer groups including Araucariaceae and Cheirolepidiaceae. They were found around the globe during the ...

'', ''

Brachyphyllum ''Brachyphyllum'' (meaning "short leaf") is a form genus of fossil coniferous plant foliage. Plants of the genus have been variously assigned to several different conifer groups including Araucariaceae and Cheirolepidiaceae. They are known from ...

'', and ''

Podozamites ''Podozamites'' is an extinct genus of fossil conifer leaves. In its broader sense, it has been used as a morphogenus (Form classification, form taxon) to refer to any broad leaved multi-veined conifer leaves. Modern broad-leaved conifers with a ...

'' are also known from the Chinle Formation. In life, ''Araucarioxylon arizonicum'' may have looked similar to a medium-sized ''

Sequoiadendron giganteum ''Sequoiadendron giganteum'' (giant sequoia; also known as giant redwood, Sierra redwood, Sierran redwood, California big tree, Wellingtonia or simply big treea nickname also used by John Muir) is the sole living species in the genus ''Sequoiade ...

'' (giant sequoia).

Paleoecology

In the

Triassic The Triassic ( ) is a geologic period and system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago ( Mya), to the beginning of the Jurassic Period 201.36 Mya. The Triassic is the first and shortest period ...

period (around ), Arizona was a flat tropical expanse in the northwest corner of the

supercontinent In geology, a supercontinent is the assembly of most or all of Earth's continent, continental blocks or cratons to form a single large landmass. However, some geologists use a different definition, "a grouping of formerly dispersed continents", ...

Pangaea Pangaea or Pangea () was a supercontinent that existed during the late Paleozoic and early Mesozoic eras. It assembled from the earlier continental units of Gondwana, Euramerica and Siberia during the Carboniferous approximately 335 million y ...

. There, a forest grew in which ''A. arizonicum'' towered as high as and measured more than in diameter. Fossils frequently show boreholes of

insect Insects (from Latin ') are pancrustacean hexapod invertebrates of the class Insecta. They are the largest group within the arthropod phylum. Insects have a chitinous exoskeleton, a three-part body ( head, thorax and abdomen), three pairs ...

larva A larva (; plural larvae ) is a distinct juvenile form many animals undergo before metamorphosis into adults. Animals with indirect development such as insects, amphibians, or cnidarians typically have a larval phase of their life cycle. The ...

e, possibly

beetle Beetles are insects that form the order Coleoptera (), in the superorder Endopterygota. Their front pair of wings are hardened into wing-cases, elytra, distinguishing them from most other insects. The Coleoptera, with about 400,000 describ ...

s similar to members of the modern family

Ptinidae Ptinidae is a family of beetles in the superfamily Bostrichoidea. There are at least 220 genera and 2,200 described species in Ptinidae worldwide. The family includes spider beetles and deathwatch beetles. The Ptinidae family species are hard ...

Taxonomy

''Araucarioxylon arizonicum'' is classified under

family Family (from la, familia) is a Social group, group of people related either by consanguinity (by recognized birth) or Affinity (law), affinity (by marriage or other relationship). The purpose of the family is to maintain the well-being of its ...

Araucariaceae Araucariaceae – also known as araucarians – is an extremely ancient family of coniferous trees. The family achieved its maximum diversity during the Jurassic and Cretaceous periods and the early Cenozoic, when it was distributed almost worldw ...

. They were first described in 1889 by the

American American(s) may refer to: * American, something of, from, or related to the United States of America, commonly known as the "United States" or "America" ** Americans, citizens and nationals of the United States of America ** American ancestry, pe ...

paleobotanist Paleobotany, which is also spelled as palaeobotany, is the branch of botany dealing with the recovery and identification of plant remains from geological contexts, and their use for the biological reconstruction of past environments (paleogeogr ...

Frank Hall Knowlton Frank Hall Knowlton (September 2, 1860 - November 22, 1926) was an American botanist, ornithologist and naturalist. Born in Vermont, he joined the Geological Survey and took an interest in fossil plants in the local lignite, later becoming a sp ...

. The validity of the name ''Araucarioxylon arizonicum'' has been questioned. ''A. arizonicum'' may actually be composed of several different

genera Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nomenclat ...

and

species In biology, a species is the basic unit of classification and a taxonomic rank of an organism, as well as a unit of biodiversity. A species is often defined as the largest group of organisms in which any two individuals of the appropriate s ...

. A 2007 study on the

syntype In biological nomenclature, a syntype is any one of two or more biological types that is listed in a description of a taxon where no holotype was designated. Precise definitions of this and related terms for types have been established as part of ...

s used by Knowlton in describing the species has revealed that they belonged to three species. They were tentatively reclassified as '' Pullisilvaxylon arizonicum'', '' Pullisilvaxylon daughertii'', and '' Chinleoxylon knowltonii''. The genus ''Araucarioxylon'' may thus be superfluous and

illegitimate Legitimacy, in traditional Western common law, is the status of a child born to parents who are legally married to each other, and of a child conceived before the parents obtain a legal divorce. Conversely, ''illegitimacy'', also known as ''b ...

; and the petrified logs of Petrified Forest National Park may be composed of a greater diversity than initially believed.

References

{{Taxonbar, from=Q135480 Triassic plants Flora of Arizona Flora of New Mexico Fossils of the United States Natural history of Arizona Triassic Arizona Triassic life of North America Araucariaceae Mesozoic trees Prehistoric plants of North America

Description

Paleoecology

Taxonomy

See also

References