Araucaria mirabilis

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. 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. It has previously been assigned to the section Bunya of Araucaria, which contains the living Australian bunya-bunya (Araucaria bidwillii). 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. Araucaria mirabilis cones The cones are spherical, ovoid to ellipsoidal in shape, with a wide axis. They average in length. The seed integument has three layers of tissues – the sarcotesta, the thickened sclerotesta, and endotesta. It is fused to the nucellus (central portion of the ovule) only at the base. The size of the cones did not indicate maturity as small cones around in diameter can be found with fully formed embryos. Most of the cones have been preserved before their seeds could be dispersed. Some cones, however, do not contain embryos and the naked axes of cones have also been recovered (described by Wieland as a separate species – Proaraucaria patagonica). It is believed that A. mirabilis shed only its seeds but not the scales at maturity. Nevertheless, no separate petrified seeds or bracts have been recovered. ==Paleobiology and paleoecology==

A. mirabilis exhibits two characteristics shared only by A. bidwillii among extant Araucaria species. First is the separate origins of the vascular bundles of the bract and fertile scales; second is the highly vascularized "ligule". P. patagonica is also known from cones. It has no living descendants and its closest living relatives appear to be members of the modern family Cupressaceae (cypresses). A. sanctaecrucis fossils consist of foliage and branches. It is believed that the long necks of sauropod dinosaurs may have evolved specifically for browsing the foliage of the typically very tall A. mirabilis and other Araucaria trees. The energy-rich Araucaria leaves required long digestion times and were low in protein. This and the global distribution of vast forests of Araucaria makes it likely that they were the primary food sources for adult sauropods during the Jurassic. Juveniles, however, which lacked the bulk of the adults and required larger amounts of proteins for growth, probably subsisted on other plants. A. mirabilis fossils have been found with damage resulting from beetle larvae. These beetles are believed to be the ancestors of the most ancient lineage of bark beetles in the weevil family (Curculionidae) - the members of the tribe Tomicini, which are still serious pests of conifers today. They were probably host-specific to members of the genus Araucaria since the Mesozoic. Modern A. bidwillii are also hosts to primitive weevils from the family Megalopodidae and leaf beetles from the family Nemonychidae. ==Distribution and geologic time range==

Araucaria forests were distributed globally and formed a major part of the woody flora of the Mesozoic era. == See also ==