Wolfe et al. (2009) propose that "conifers of the family Sciadopityaceae, closely allied to the sole extant representative, Sciadopitys verticillata, were involved in the genesis of Baltic amber." Their "conclusions challenge hypotheses advocating members of either of the families Araucariaceae or Pinaceae as the primary amber-producing trees and correlate favourably with the progressive demise of subtropical forest biomes from northern Europe as palaeotemperatures cooled following the Eocene climate optimum."