Thoughts about Pleistocene pecans.
The pecan tree is 1 of 17 species of hickory trees. Hickories are native to North America and Asia and formerly occurred in Europe, but Ice Ages, beginning about 2.5 million years ago, wiped them out there. European mountains have an east to west orientation, while American mountains are oriented north to south. Hickories prefer temperate climates, and the east-west mountains blocked their retreat in Europe during glacial expansions. This explains why hickories and so many other tree species survived Ice Ages in North America but not in Europe.
Evidence of fossil pollen grains suggests hickory trees grew alongside dinosaurs during the late Cretaceous, though the oldest fossil hickory nut dates to about 34 million years ago. Most early hickory species had thin shells, but they evolved thicker shells about 38 million years ago in response to the evolution of tree squirrels. Squirrels love the nutrient rich nuts, so hickories evolved…
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