Araucaria mirabilis is an extinct species of coniferous tree from Patagonia, Argentina. It belongs to the genus Araucaria.
A. mirabilis are known from large amounts of very well preserved silicified wood and cones from the Cerro Cuadrado Petrified Forest, including tree trunks that reached in height in life. The site was buried by a volcanic eruption during the Middle Jurassic, approximately 160 million years ago.
Discovery
Fossils of Araucaria mirabilis are found in great abundance in the Cerro Cuadrado Petrified Forest of Patagonia, Argentina. They were the dominant species of a forest buried by a volcanic eruption about 160 million years ago.
The petrified forests of A. mirabilis were first discovered in 1919 by the German-Argentinean botanist Anselmo Windhausen. Noting that petrified cones were being kept as souvenirs by local farmers in the area, he explored the region and discovered the site of the petrified forests in 1923. He sent the specimens he collected to the German botanist Walther Gothan in Berlin in 1924. Gothan named them Araucaria windhauseni in honor of Windhausen in 1925.
However, the Italian-Argentinean botanist Carlo Luigi Spegazzini had also acquired specimens from the petrified forest from various sources. He tentatively identified the specimens as Araucarites mirabilis in 1924.
An American paleontological expedition led by Elmer S. Riggs (1923–1924) of the Field Museum of Natural History also discovered the petrified forests. The numerous specimens Riggs collected (who identified them as Araucaria) were later described by the American paleontologist and paleobotanist George Reber Wieland as Proaraucaria elongata (1929), Proaraucaria mirabilis (1935), and Proaraucaria patagonica (1935). Wieland and Gothan interpreted the absence of separate petrified seeds as evidence that the cones did not shed their scales at the final growth year. This was originally stated by Wieland as a justification for its classification under a new genus Proaraucaria.
An amended description was published by the Scottish paleobotanist Mary Gordon Calder in 1953. Calder questioned the conclusions of Wieland and Gothan. She also discarded the earlier classification of Spegazzini of Araucarites. The latter is a form genus, usually used for incomplete plant fossil specimens that resemble Araucaria but lack enough preserved details for more accurate classifications. Citing striking similarities with the extant Araucaria bidwillii, Calder reclassified the specimens as Araucaria mirabilis.
Taxonomy and nomenclature
Araucaria mirabilis belongs to the genus Araucaria. It is classified under the family Araucariaceae of the order Pinales. Its has previously been assigned to the section Bunya of Araucaria, which contains the living Australian bunya-bunya (Araucaria bidwillii). However, this has subsequently been questioned, with other studies finding it to have a basal position within Araucaria.
The genus name Araucaria is derived from the Spanish exonym Araucanos ("from Arauco"), referring to the Mapuche people of Chile and Argentina. The specific name mirabilis is from Latin for "wondrous" or "amazing".
Description
A large number of petrified tree trunks of A. mirabilis are found still standing in the Cerro Cuadrado Petrified Forest. Preserved in volcanic ash, some of the specimens measure in diameter and were at least in height when alive. The trees were preserved just as the cones had finished maturing.
The cones are spherical, ovoid to ellipsoidal in shape, with a wide axis. They average in length. The largest specimens are nearly in diameter. The center of the cones consist of a parenchymatous pith surrounded by fused vascular bundles (two for each bract-scale complex, with each vascular bundle containing resin canals).
The bracts have thick and wide woody wings tapering towards the base. They are around long and wide, including the wings. They are overlain by fertile scales containing one seed each, embedded on the upper surface. They are arranged helically. The "ligules" (the free tip of the fertile scale characteristic of Araucaria) are wide, high, and long.