Agathoxylon, the Wood Morphogenus Previously Known as Araucarioxylon

We've known for a couple of years now that the name Araucarioxylon, used for the majority of the petrified wood from the Chinle Formation is illigitimate. Savidge (2007) reexamined the type specimens of Araucarioxylon arizonicum, and assigned it to a new genus, Pullisilvaxylon arizonicum. Problematic is that the type specimen is from the Black Forest Bed, which is much younger than the main log bearing horizon in Petrified Forest National Park where thousands of colorful logs have been referred to A. arizonicum for over a century.

Complicating this problem is that the majority of this wood has been almost completely agatized, obliterating the cellular structures used to make taxonomic assignments.  Furthermore, Savidge (2007) found that there are actually several wood taxa at this horizon, in fact almost every specimen sampled turns out to be new.  Thus, park staff are at a loss when asked what the name the main type of fossil wood in the park is, and most just simply still continue to use the invalid name Araucarioxylon.

Philippe, in this new paper, suggests that a better name for the morphogenus is Agathoxylon.  However, I would be hesitant to refer the large amounts of currently unnamed wood to this genus as he also suggests that eventually it should be restricted to a single species.  Furthermore, because of the restriction of the type of P. arizonicum, the majority of Chinle wood lacks a direct assignment to a species-group name.  This is a mess that probably will never be resolved because of the poor preservation of the wood structures, thus the majority of Chinle wood will simply be referrable to Araucariaceae indeterminate (or maybe even a more inclusive clade or rank?).

Philippe, M., in press. How many species of Araucarioxylon? C. R. Palevol (2011), doi:10.1016/j.crpv.2010.10.010

Abstract - Fossil wood, similar to that of modern Araucariaceae, has been known for a long time, and is usually called Araucarioxylon. More than 400 morphospecies have been described, whereas this wood type displays few characteristic features. This taxonomical profusion is compounded by nomenclatural problems, Araucarioxylon being an illegitimate name. The status of the wood morphogenus, the infrageneric structure and the names that apply to the taxa designated for fossil woods of the Araucarioxylon-type are discussed. A database with 428 morphospecies designated for Araucarioxylon-type of wood is analyzed. The name Agathoxylon Hartig seems to be the most appropriate for the corresponding morphogenus. Albeit theoretically several hundred morphospecies could be recognized within this group, it is at least as probable that only one should be retained.

REFERENCES

Savidge, R.A. 2006. Xylotomic evidence for two new conifers and a ginkgo within the Late Triassic Chinle Formation of Petrified Forest National Park, Arizona, USA, 147–149. In Parker, W.G., Ash, S.R. & Irmis, R.B. (eds) A century of research at Petrified Forest National Park: geology and paleontology. Museum of Northern Arizona Bulletin 62.

Savidge, R. A. 2007. Wood anatomy of Late Triassic trees in Petrified Forest National Park, Arizona, USA, in relation to Araucarioxylon arizonicum Knowlton, 1889. Bulletin of Geosciences 82:301–328.

Savidge, R.A. & Ash, S.R. 2006. Arboramosa semicircumtrachea, an unusual Late Triassic tree in Petrified Forest National Park, Arizona, USA, 65–81. In Parker, W.G., Ash, S.R. & Irmis, R.B. (eds) A century of research at Petrified Forest National Park: geology and paleontology. Museum of Northern Arizona Bulletin 62.