During the Late Triassic period, a lush, humid forest flourished where the arid deserts of Arizona and New Mexico now lie. Among the giants of this ancient ecosystem was Pullisilvaxylon, a remarkable gymnosperm whose massive trunks eventually petrified into stunning stone monuments.
Most of the colossal fossilized logs found in the Petrified Forest National Park were once assigned to other taxa before meticulous anatomical studies revealed their true identity. These ancient trunks were transported by prehistoric river systems before being buried and mineralized over millions of years.
Since the only surviving remains of Pullisilvaxylon are fluvially transported trunk sections, scientific description is limited to its fossilized wood anatomy. The trunks exhibit pycnoxylic secondary xylem characterized by a complete or near-total absence of parenchymatous tissue.
Under magnification, the vascular cylinder reveals large tracheids measuring up to 70 micrometers in diameter in longitudinal sections and 40 micrometers in transverse sections. The secondary tissue contains cells about 10 micrometers in diameter with wide intercellular spaces and scattered axial parenchyma.
Intercellular communication is facilitated by circular, uniseriate pits visible in transverse sections. These cupressoid or taxoid pit structures measure 18 micrometers in diameter with a 5-micrometer lumen.
The generic name Pullisilvaxylon translates literally from Latin to mean "wood of the Black Forest," referencing the specific area in Arizona where the fossils were first excavated. This region remains one of the world's most significant fossil sites.
For decades, these massive logs were classified under the famous species Araucarioxylon arizonicum. Detailed microscopic examination of the wood structure eventually justified their relocation to this distinct genus.
The fossilized wood of Pullisilvaxylon dates back to the Late Triassic period, approximately 208 to 230 million years ago. This placing makes these specimens witnesses to the dawn of the dinosaur era.
External Databases: GBIF
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