A possible Cretaceous polar scene with Pachyrhinosaurus and changing fall colored foliage
While things are heating up and days are lengthening in the southern hemisphere, in the northern latitudes daylight hours are waning and the leaves of deciduous trees are turning to a riot of reds and gold hues. For only several weeks this vivid palette of the deciduous (non-evergreen) northern forests will delight the populations of America, Europe and Asia.
Then the leaves will fall, as the trees prepare to hibernate through the scant light and mighty chill of winter.
Although a magnificent spectacle to experience, today we take this annual ritual for granted. But it begs the question: did dinosaurs experience a similar annual rite of nature? Did prehistoric creatures witness foliage changing colors and shedding leaves?
Many modern plant species got their evolutionary start during the Mesozoic Era. Species of magnolia, laurel, sycamore, and redwood trees are known from the Cretaceous Period. And the gingko tree hails from before the first appearance of dinosaurs, with fossil species found in Permian deposits.
However, Permian and Mesozoic climates were warmer than today, with less variation between the equator and polar regions. Polar environments were not frozen. And the fossil record indicates that the prehistoric ancestors of modern trees were evergreen. Even trees that today are deciduous (annually shed their leaves) had not yet evolved the leaf-shedding process during the age of the dinosaurs, as exemplified by the sycamore family, which today is largely deciduous, but had evergreen dinosaur-era ancestors.
But wait a minute! Although earth's climate was much more mild when dinosaurs roamed, the earth had the same tilt relative to the sun as it has today. The tilt of the earth is the cause of the seasons, and as a result, the dinosaurs' realm did experience seasonal changes. During dinosaur seasons, temperature changes were less than experienced today, but the changes in the amount of daylight - the changing length of days - was virtually identical to today's daylight.
Trees didn't evolve forms that shed their leaves due to changes in temperature, but in response to seasonal changes in the amount of daylight available for leaves to conduct photosynthesis: deciduous (leaf shedding) trees evolved to accommodate the 3 months of reduced daylight during winter months. During the Mesozoic, the tree species that evolved to drop leaves and live a "modern" deciduous lifestyle evolved at the most northern and southern latitudes as a response to extended seasonal lack of sunlight.
Unlike today, where deciduous species are dominant throughout the "temperate" latitudes of the the United States, Canada, Europe, South America and asia; during the Age of Dinosaurs deciduous species only occurred at the most extreme latitudes - areas that experience total darkness several weeks of the year. This includes regions represented today by northern most Alaska, Scandinavia, Siberia; and Antarctica in the south.
Contrary to "old school" theories, we now know that dinosaurs lived in the polar regions. Polar zones were not frozen barrens during the Mesozoic, but were more similar to the cool, moist environments of modern coastal British Columbia and northwestern Washington State. Discoveries of "polar dinosaurs" that inhabited the extreme latitudes now suggest that, in fact, many dinosaurs DID witness seasonal color displays, as polar deciduous trees evolved to drop their leaves in the company of dinosaurs sharing the polar environment during dark winter months. In fact, the changing of colors may have helped signal the advent of winter to dinosaurs - who are thought to have mostly possessed excellent color vision - to prepare for the approaching dark months: either gather your herd and migrate to more sunlit climates, or get into hibernation mode.
Prehistoric ancestors of the modern deciduous forms of the sycamore tree were widely distributed throughout the polar regions of the Cretaceous Period. In fact, the prehistoric sycamore may have evolved a deciduous lifestyle as a direct response to occupying environments with extreme seasonal variations in sunlight. And, accompanied by an unknown visual symphony of additional plant species, the sycamore may have been just one among many prehistoric tree forms that did regale dinosaurs with an annual visual feast of seasonal changes.....
However, due to a relatively uniform global warmth, the polar regions may have been the only areas that experienced such seasonal fluctuations: everywhere beyond the polar zones - that is, most of the Mesozoic realm, would have been dominated by a dizzying variety of evergreen foliage that never seasonally changed color or dropped leaves. Fortunately, we do have good modern relatives of many plant forms that evolved in the Mesozoic, and can therefore determine the likely lifestyles and appearances of the extinct versions.
