Sphenophyllum sp. and Alethopteris grandini

Sphenophyllum is a genre of equiseto de porte herbáceo formado por un rizoma o tallo subterráneo que crece horizontalmente y del cual surgen brotes herbáceos erectos con nudos y entrenudos. Las hojas de Sphenophyllum They develop from the nodes in whorls and have a cuneiform to linear blade with parallel venation. The reproductive structures are narrow and long strobili that arise in a terminal position or from the nodes of the stem and are called Bowmanites and how Sphenophyllostachys. These strobili are formed by a central axis with several whorls of bracts that fuse at their base. Numerous sporangiophores bearing sporangia appear on the abaxial surface of these bracts.

Alethopteris es un género de plantas prehistóricas de pteridospermatofitas (helechos con semillas) fósiles. Las pteridospermatofitas o pteridospermas comenzaron su declive principal al final de la era Paleozoica, pero algunos grupos sobrevivieron como vestigios hasta el Eoceno, extinguiéndose por completo mucho después de los dinosaurios.

The Llewellyn Formation is a Pennsylvanian geological unit (about 300 to 308 million years ago) located in Pennsylvania, famous for hosting anthracite coal deposits and exceptional plant fossils. It features repetitive sequences of gray sandstone, siltstone, shale, conglomerate and large veins of anthracite coal. It contains the thickest anthracite coal deposit in the world, the Mammoth vein.