Morphometric Analysis of Fossil Conifer Cones from a High Elevation Late Pleistocene Deposit Near Snowmass Village, Colorado

Résumé du livre

Late Pleistocene fossil conifer seed cones were recovered near Snowmass Village, Colorado, in 2010 and 2011. The site is known as the Ziegler Reservoir fossil site and is a 12 hectare basin that was formed by a glacier approximately 145 ka, during the Bull Lake glaciation. The elevation of the site is 2705 m. A total of 201 fossil conifer seed cones were recovered from the site, representing nearly 90 k during the late Pleistocene. Fossil conifer species were identified using morphometric analysis of the seed cones, cone scales, seeds, and bracts. The taxonomic placements of fossil conifer species were confirmed using specimens of extant conifer species from western North America. The same morphological characters were specifically studied, including distinctive morphological features of the bract apicula. Four fossil conifer species were identified. Abies concolor and Pseudotsuga menziesii fossils were recovered from stratigraphic units corresponding to interglacial periods of the site. In addition, Abies concolor fossils represent the first documented occurrence of the species from the late Pleistocene in Colorado. This has provided new hypotheses for Abies concolor biogeographic history. Picea engelmannii fossils were recovered from stratigraphic units corresponding to glacial periods of the site. Picea sp. indet, an unknown conifer species, showed some morphological similarities with extant Picea pungens. However, the taxonomic placement remains uncertain. Picea sp. indet fossils were recovered from stratigraphic units representing both interglacial and glacial periods.