Araucarioxylon
Araucarioxylon is the outdated name of various species of extinct conifers in the Araucariaceae family . The individual species exist as fragments of trunks and branches and can only be distinguished under the microscope. In the Petrified Forest National Park , up to 90% of the fragments of petrified wood occurring there are referred to as Araucarioxylon arizonicum .
Under this name the fossils are the state fossil of Arizona . The petrified wood of these trees is known as "rainbow wood " because of the variety of colors that some specimens have.
Taxonomy
The genus Araucarioxylon was established by Gregor Kraus in 1870 , and Frank Hall Knowlton subsequently listed Araucarioxylon arizonicum as a new species in 1889 . All fragments of petrified wood with the "typical" appearance of Araucarioxylon found in the Petrified Forest and its surroundings were subsequently assigned to this species. In this way the image of a coniferous species was created that grew on a tropical plain in prehistoric Arizona, which at that time was located in the northwestern part of the supercontinent Pangea .
The affiliation of these fragments to a single species was questioned as early as the beginning of the 20th century. Later investigations showed that it is actually not a single species, but several species that can only be distinguished under a microscope. For example, the first description of Knowlton in 1889 was based on three logs from the Petrified Forest area. In 2007, Savidge considered Araucarioxylon to be an invalid name ( nomen superfluum ) because it was arbitrarily derived from other, already existing names. In addition, the species based on this name obviously comprised different species. For this reason, he assigned these syntypes to three different genres based on the differences in structure found during microscopic examinations .
So far, the following Morphotaxa have been newly described:
- Pullisilvaxylon daughertii
- Pullisilvaxylon arizonicum
- Chinleoxylon knowltonii
- Silicisilvaxylon imprimicrystallus
- Crystalloxylon imprimicrystallus
- Crystalloxylon secundacrystallus
- Arboramosa semicircumtrachea
- Protocupressin oxylon arizonica
- Ginkgoxylpropinquus hewardii
- Protopiceoxylon novum
description
The petrified trunks are usually long and up to three meters in diameter, so that tree heights of up to 60 m are assumed. At first glance, the trunk surfaces, which are similar at first glance, show knot scars that are not arranged as vertebrae, but are distributed irregularly over the trunk. Some of the specimens show remains of bark which does not resemble that of the modern Araucaria heterophylla . The branch and trunk fragments often have bores from insects and remains of sticks from ancient insects, which have been compared to modern bees .
The plant fossils exist as fragments of trunks and branches that have black, red to purple, yellow and rarely green colors. Black colors indicate a noticeable level of organic carbon . The red and yellow colors are caused by large iron oxide particles: the red by hematite and the yellow by limonite . The purple shimmer of some petrified pieces of wood is due to very small spheres of hematite that are distributed in the quartz matrix. The rarely occurring green colors are attributed to chrome .
The stems almost always appear in groups that are likely to be stranded together; only in a few cases do they appear to have been preserved in a normal growth position. Woodworthia arizonica , Dadoxylon chaneyi , Lyssoxylon grigsbyi , Charmorgia dijolli and Schilderia adamanica occur together with “ Araucarioxylon arizonicum ”, some of which can be distinguished from these with the naked eye.
distribution
The fossilized trunks previously ascribed to Araucarioxylon arizonicum occur in the Chinle Formation of the late Triassic , which spans the Carnic and Norian stages . Their rocks were deposited in rivers and lakes or come from flood plains. The fossils in the lower part ( Shinarump members ) of the Chinle Formation are often conspicuous, especially in southeastern Utah . They are also often in the Sonsela Member , which is open in the southern half of the Petrified Forest . Even more recent occurrences are in the uppermost part of the Chinle Formation , such as Wolverine Petrified Forest (southeastern Utah) and in the northern part of the Petrified Forest. Other deposits are in New Mexico .
literature
- FH Knowlton: New species of fossil wood ( Araucarioxylon arizonicum ) from Arizona and New Mexico . In: Proceedings of the United States National Museum . tape 11 (1888) , 1889, pp. 1-4 .
- RA Savidge: Wood anatomy of Late Triassic trees in Petrified Forest National Park, Arizona, USA, in relation to Araucarioxylon arizonicum Knowlton, 1889 . In: Czech Geological Service (Ed.): Bulletin of Geosciences . tape 82 , no. 4 , 2007, ISSN 1214-1119 , p. 301–328 ( geology.cz [PDF; 2.5 MB ]).
Individual evidence
- ^ A b Wayne P. Armstrong: A Taxonomic Problem With Araucarioxylon arizonicum. In: Wayne's Word. December 2008, accessed on July 12, 2020 .
- ↑ Sidney R. Ash & Rodney A. Savidge: The Bark of the late Triassic Araucarioxylon arizonicum tree from Petrified Forest National Park, Arizona . In: IAWA Journal . tape 25 , no. 3 , 2004, p. 349-368 .
- ^ Adele Conover: The Object at Hand. In: Smithsonian Magazine. Smithsonian Institute, June 1997, accessed December 15, 2009 .
- ↑ Araucarioxylon arizonicum Petrified Wood. Retrieved December 15, 2009 .