Araucarioxylon arizonicum
Encyclopedia
Araucarioxylon arizonicum is an extinct species of conifer that is the state fossil
of Arizona
. The species is known from massive tree trunks
that weather out of the Chinle Formation
in desert badlands of northern Arizona and adjacent New Mexico, most notably in the 378.51 square kilometres (93,531.8 acre) Petrified Forest National Park
. There, these trunks are locally so abundant that they have been used as building materials.
of this tree is frequently referred to as "Rainbow wood" because of the large variety of colors some specimen
s exhibit. The red and yellow are produced by large particulate forms of iron oxide
, the yellow being limonite
and the red being hematite
. The purple hue comes from extremely fine spherules of hematite distributed throughout the quartz
matrix, and not from manganese
, as has sometimes been suggested.
period (around ), Arizona was a flat tropical expanse in the northwest corner of the supercontinent
Pangaea
. There, a forest grew in which A. arizonicum towered as high as 60 metres (196.9 ft) and measured more than 60 centimetres (2 ft) in diameter. Fossils frequently show boreholes of insect
larva
e, possibly beetle
s similar to members of the modern family Anobiidae
.
Araucariaceae
. They were first described in 1889 by the American paleobotanist Frank Hall Knowlton.
The validity of the name Araucarioxylon arizonicum has been questioned. A. arizonicum may actually be composed of several different genera
and species
. A 2007 study on the syntype
s used by Knowlton in describing the species has revealed that they belonged to three species. They were tentatively reclassifed as Pullisilvaxylon arizonicum, Pullisilvaxylon daughertii, and Chinleoxylon knowltonii. The genus Araucarioxylon may thus be superfluous and illegitimate
; and the petrified logs of Petrified Forest National Park may be composed of a greater diversity than initially believed.
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 species....
of Arizona
Arizona
Arizona ; is a state located in the southwestern region of the United States. It is also part of the western United States and the mountain west. The capital and largest city is Phoenix...
. The species is known from massive tree trunks
Trunk (botany)
In botany, trunk refers to the main wooden axis of a tree that supports the branches and is supported by and directly attached to the roots. The trunk is covered by the bark, which is an important diagnostic feature in tree identification, and which often differs markedly from the bottom of the...
that weather out of the Chinle Formation
Chinle Formation
The Chinle is a geologic formation that is spread across the U.S. states of northern Arizona, Nevada, Utah, western New Mexico, and western Colorado. The Chinle is controversially considered to be synonymous to the Dockum Group in eastern Colorado, eastern New Mexico, southwestern Kansas, the...
in desert badlands of northern Arizona and adjacent New Mexico, most notably in the 378.51 square kilometres (93,531.8 acre) Petrified Forest National Park
Petrified Forest National Park
Petrified Forest National Park is a United States national park in Navajo and Apache counties in northeastern Arizona. The park's headquarters are about east of Holbrook along Interstate 40 , which parallels a railroad line, the Puerco River, and historic U.S. Route 66, all crossing the park...
. There, these trunks are locally so abundant that they have been used as building materials.
Description
The petrified woodPetrified 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...
of this tree is frequently referred to as "Rainbow wood" because of the large variety of colors some specimen
Specimen
A specimen is a portion/quantity of material for use in testing, examination, or study.BiologyA laboratory specimen is an individual animal, part of an animal, a plant, part of a plant, or a microorganism, used as a representative to study the properties of the whole population of that species or...
s exhibit. The red and yellow are produced by large particulate forms of iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...
, the yellow being limonite
Limonite
Limonite is an ore consisting in a mixture of hydrated iron oxide-hydroxide of varying composition. The generic formula is frequently written as FeO·nH2O, although this is not entirely accurate as limonite often contains a varying amount of oxide compared to hydroxide.Together with hematite, it has...
and the red being hematite
Hematite
Hematite, also spelled as haematite, is the mineral form of iron oxide , one of several iron oxides. Hematite crystallizes in the rhombohedral system, and it has the same crystal structure as ilmenite and corundum...
. The purple hue comes from extremely fine spherules of hematite distributed throughout the quartz
Quartz
Quartz is the second-most-abundant mineral in the Earth's continental crust, after feldspar. It is made up of a continuous framework of SiO4 silicon–oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall formula SiO2. There are many different varieties of quartz,...
matrix, and not from manganese
Manganese
Manganese is a chemical element, designated by the symbol Mn. It has the atomic number 25. It is found as a free element in nature , and in many minerals...
, as has sometimes been suggested.
Paleoecology
In the TriassicTriassic
The Triassic is a geologic period and system that extends from about 250 to 200 Mya . As the first period of the Mesozoic Era, the Triassic follows the Permian and is followed by the Jurassic. Both the start and end of the Triassic are marked by major extinction events...
period (around ), Arizona was a flat tropical expanse in the northwest corner of the supercontinent
Supercontinent
In geology, a supercontinent is a landmass comprising more than one continental core, or craton. The assembly of cratons and accreted terranes that form Eurasia qualifies as a supercontinent today.-History:...
Pangaea
Pangaea
Pangaea, Pangæa, or Pangea is hypothesized as a supercontinent that existed during the Paleozoic and Mesozoic eras about 250 million years ago, before the component continents were separated into their current configuration....
. There, a forest grew in which A. arizonicum towered as high as 60 metres (196.9 ft) and measured more than 60 centimetres (2 ft) in diameter. Fossils frequently show boreholes of insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
larva
Larva
A larva 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...
e, possibly beetle
Beetle
Coleoptera is an order of insects commonly called beetles. The word "coleoptera" is from the Greek , koleos, "sheath"; and , pteron, "wing", thus "sheathed wing". Coleoptera contains more species than any other order, constituting almost 25% of all known life-forms...
s similar to members of the modern family Anobiidae
Anobiidae
Anobiidae is a family of beetles. The larvae of a number of species tend to bore into wood, earning them the name "woodworm" or "wood borer". A few species are pests, causing damage to wooden furniture and house structures, notably the death watch beetle, Xestobium rufovillosum, and the common...
.
Taxonomy
Araucarioxylon arizonicum is classified under familyFamily (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Araucariaceae
Araucariaceae
Araucariaceae, commonly referred to as araucarians, is a very ancient family of coniferous trees. It achieved its maximum diversity in the Jurassic and Cretaceous periods, when it was distributed almost worldwide...
. They were first described in 1889 by the American paleobotanist Frank Hall Knowlton.
The validity of the name Araucarioxylon arizonicum has been questioned. A. arizonicum may actually be composed of several different genera
Genera
Genera is a commercial operating system and development environment for Lisp machines developed by Symbolics. It is essentially a fork of an earlier operating system originating on the MIT AI Lab's Lisp machines which Symbolics had used in common with LMI and Texas Instruments...
and 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...
. A 2007 study on the syntype
Syntype
In biological nomenclature, a syntype is a term used to indicate a specimen with a special status.In zoological nomenclature, a syntype is defined as "Each specimen of a type series from which neither a holotype nor a lectotype has been designated [Arts. 72.1.2, 73.2, 74]. The syntypes...
s used by Knowlton in describing the species has revealed that they belonged to three species. They were tentatively reclassifed as Pullisilvaxylon arizonicum, Pullisilvaxylon daughertii, and Chinleoxylon knowltonii. The genus Araucarioxylon may thus be superfluous and illegitimate
Nomen illegitimum
A nomen illegitimum is a technical term, used mainly in botany. It is usually abbreviated as nom. illeg..-Definition:...
; and the petrified logs of Petrified Forest National Park may be composed of a greater diversity than initially believed.
See also
- List of extinct plants
- PaleobotanyPaleobotanyPaleobotany, 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...
- AraucariaAraucariaAraucaria is a genus of evergreen coniferous trees in the family Araucariaceae. There are 19 extant species in the genus, with a highly disjunct distribution in New Caledonia , Norfolk Island, eastern Australia, New Guinea, Argentina, Chile, and southern Brazil.-Description:Araucaria are mainly...
- Araucaria mirabilisAraucaria mirabilisAraucaria mirabilis is an extinct species of coniferous trees from Patagonia, Argentina. It belongs to the section Bunya of the genus Araucaria; the only living species of which is Araucaria bidwillii from Australia.A...
- Araucarites sanctaecrucisAraucarites sanctaecrucisAraucarites sanctaecrucis is an extinct coniferous tree from Patagonia, Argentina. Its exact affinities are unknown and it is currently assigned to the form genus Araucarites of the family Araucariaceae. A. sanctaecrucis are known from petrified fossils of branches, foliage, and cones from the...
- NothofagusNothofagusNothofagus, also known as the southern beeches, is a genus of 35 species of trees and shrubs native to the temperate oceanic to tropical Southern Hemisphere in southern South America and Australasia...