Morphometric analysis of fossil conifer cones collected from a high-elevation, Late Pleistocene, deposit near Snowmass Village, Colorado

Background/Question/Methods:

Morphometric analysis of fossil conifer cones collected from a high-elevation, Late Pleistocene, deposit near Snowmass Village, Colorado

Miller, Dane M.¹, Jackson, Stephen T. ¹, and Miller, Ian M ²

¹Department of Botany, University of Wyoming, Laramie, WY 82071 (dmille65@uwyo.edu); ²Denver Museum of Nature & Science, 2001 Colorado Blvd, Denver, CO 80205

In fall 2010 construction of a reservoir near Snowmass Village, CO revealed bones of mammoth and other extinct species. Subsequent excavation coordinated by the Denver Museum of Nature and Science recovered a rich assemblage of vertebrate, plant, and other fossils.  The site sits at 2705 m elevation on a ridge between the Brush Creek and Snowmass Creek drainages. The 120,000 m² basin originated as a moraine-dammed lake formed approximately 130,000 years ago during the Bull Lake glaciation. The basin was filled with ~30 meters of windblown silt and clay, local gravity and debris flow deposits, and shallow-water peats between ~130,000 and 45,000 years ago.  An interdisciplinary team of Quaternary scientists is studying the geology, paleontology, and sedimentology of the site. Our research focuses on the rich assemblages of conifer macrofossils from the site, applying cone morphometrics and needle anatomy to identify species and better understand the ecological and biogeographic history of the site from the last interglacial to the start of the most recent glacial period.

Approximately, 150 fossil conifer cones have been recovered from the site.  We are conducting studies of the fossils together with cones of extant species (Abies concolor, Abies lasiocarpa, Picea engelmannii, Picea glauca, Picea pungens, Pseudotsuga menziesii, Tsuga heterophylla, Tsuga mertensiana) from the Rocky Mountain and adjacent regions.

Results/Conclusions:

 Initial results indicate that many of the cones are assignable to Pseudotsuga menziesii. These cones show eroded bracts on the bases of cone scales and distinct seed morphology characteristic of modern P. menziesii. Existing populations of P. menziesii near the site are restricted to regions of permanent moisture, north facing slopes, and considerable shade. Abundance of P. menziesii macrofossils suggests a wetter and warmer climate. Further taxonomic and morphometric analysis of the rest of the fossil cones assemblage is needed to distinguish other conifer taxa. Many cones from post-interglacial assemblages resemble Picea glauca, and we are pursuing studies to confirm that identification.  P. glauca does not grow in the region today, although extant populations are widespread in northern Wyoming, and P. glauca X engelmannii hybrids occur along the Wyoming/Colorado border.