Degraded Wood in the Upper Triassic Petrified Forest Formation (chinle Group), Northern Arizona: Differentiating Fungal Rot from Arthropod Boring

Permineralized wood from the middle of the Upper Triassic Petrified Forest Formation in Arizona, in strata correlative with the Sonsela Member, displays various forms of heartwood degradation. Pitting of the wood exhibits two primary morphologies. Elongated cavities are up to several mm long, parallel to the wood grain and may merge to form channels that extend longitudinally through the wood for lengths of several cm. Circular to elliptical cavities that cross-cut the wood grain are up to several mm wide. Both forms of degradation are interpreted as the result of pre-burial biotic activity. The pitting appears to be caused by pathogenic fungi (white rot and white pocket rot in particular) that degraded and removed tracheids in the secondary xylem. The size and shape of some of the features, such as the longitudinal channels, may be consistent with some forms of arthropod burrowing, but the weight of the evidence, in particular the lack of frass, suggests that these also resulted from